WO2020011922A1

WO2020011922A1 - Photoinitiator compounds

Info

Publication number: WO2020011922A1
Application number: PCT/EP2019/068682
Authority: WO
Inventors: Paolo Melchiorre; Bertrand Schweitzer-Chaput; Frank ARROYAVE
Original assignee: Fundació Institut Català D'investigació Química (Iciq); Institució Catalana De Recerca I Estudis Avançats (Icrea) (
Priority date: 2018-07-11
Filing date: 2019-07-11
Publication date: 2020-01-16

Abstract

The present invention relates to certain dithiocarbamate compounds of formula (I) comprising a nitrogen containing heterocyclic ring, and exhibiting strong absorption in the visible range of the light spectrum. The compounds of the invention are useful as photoinitiators, in particular in polymerization reactions.

Description

PHOTOINITIATOR COMPOUNDS

This application claims the benefit of the European Patent Application EP18382518 filed on July 11^th, 2018.

The present invention relates to certain dithiocarbamate compounds comprising a nitrogen containing heterocyclic ring useful as photoinitiators or photoiniferters in radical polymerization. The compounds of the invention exhibit strong absorption in the visible range of the light spectrum. The compounds of the invention are useful as photoinitiators, in particular in polymerization reaction and in RAFT polymerization triggered by visible light irradiation. The research leading to this invention has received funding from“la Caixa” Foundation.

BACKGROUND ART

[001] Free radical polymerization is commonly widely used at industrial level in the preparation of a broad range of polymers, in particular polyolefins. Such process typically goes through a three-step mechanism: (i) initiation; (ii) propagation and (iii) termination. During the initiation step, an initiator is used to generate under certain conditions a reactive free radical species having a slow recombination rate. The reactive species then reacts with a monomer during the propagation phase to generate a new free radical containing one moiety from the monomer. This new free radical successively reacts with monomer molecules to allow for the formation of the growing polymer chain, which still has a free reactive radical. The termination typically occurs when the free radical polymer chain combines with another free radical present in the reaction mixture. The major challenge of free radical polymerization processes is to find suitable reagents and mild conditions of reaction to reach (i) a high degree of polymerization or a high molecular weight, which is related to the efficiency of the initiator among other factors and (ii) full control of the reaction in terms of homogeneity of the length of the formed polymer chains (polydispersity) in combination with suitable kinetics of polymerization. Consequently, several strategies to initiate free radical polymerizations have been implemented.

[002] There exist different types of initiation mechanisms and classes of initiators. Thermal initiators typically generate free radical species upon heating and include several classes of compounds such as peroxides (e.g. dicumyl peroxide) or diazo compounds, which both suffer from being explosive or hazardous to handle and store. Alternative initiation mechanisms have been sought after, such as Redox initiation, which typically requires the use of a metal salt to generate the free radical by reduction of a peroxide (typically, hydrogen peroxide is used). Another commonly used redox couple consists of the combination of a peroxide with an amine compound such as toluidine. A more advantageous and developed approach consists in using light to trigger the dissociation of a photoinitiator compound, where light irradiation is used to cleave a bond homolytically in the photoinitiator compound. Such compounds typically absorb in a wavelength range from 200 to 400 nm (UV part of the spectrum) and generate free radicals able to attack a carbon-carbon double bond comprised in a monomer. Most commonly, photoinitiators are soluble in the medium of polymerization. Industry typically favours photoinitiators that do not generate toxic residues or by- products in the final product and do not confer any odour or colour to the formed polymer. Yagci and co-workers reviewed briefly the current status of photoinitiated polymerization reactions. Photoiniators working under UV light irradiation are well known in the art.

[003] Gruber and Fouassier separately reviewed the several classes of photoinitiators available for free radical polymerization reactions. Photoinitiators for free radical polymerization reactions can be divided into two types. Type I initiators decompose directly into two free radicals upon light irradiation while type II initiators react through a triplet excited state with a co-initiator (usually an alcohol or an amine) to generate a free radical through hydrogen transfer. Type II photoinitiators (typically derivatives of diarylketones and thioxanthone compounds) are preferably used in solution since their use requires the presence of a proton donor compound (alcohol or amine); this, in all, somehow prevents their use in bulk polymerization and in a broad range of applications. On the other hand, type I photoinitiators can be divided into three families of compounds: benzoin ether derivatives, phosphine oxide derivatives and organometallic species. The light absorption properties of benzoin ethers (s typically about 50-100 L-mol ¹ -cnr¹ at 360 nm and no absorption past 380 nm) are such that their use requires high-intensity UV irradiation. Phosphine oxides (s typically about 300- 1000 L-mol ¹ -cnr¹ at 400 nm and significant absorption until 440 nm) have the advantage of absorbing visible light and providing optically clear cured materials. However, they still require light sources of high intensity, such as mercury lamps, high- power LEDs, or lasers to efficiently initiate polymerization reactions. Organometallic complexes, such as titanocenes, in combination with sacrificial co-initiators, are often very efficient photoinitiators for a variety of controlled and uncontrolled polymerizations under visible light irradiation. However, a major drawback of this technique is the incorporation of the metal complex into the polymer matrix and their dependence on the presence of a co-initiator. Remarkably, none of these available photoinitiators allow for full control of the growth of the polymer chain, which in turn potentially leads to high index of polydispersity in the final polymer.

[004] A good index of polydispersity of the formed polymer is generally obtained when the free radical polymerization occurs through a living polymerization mechanism such as Reversible Addition Fragmentation chain Transfer (RAFT) mechanism. RAFT polymerization, as reported in patent AU2009900271 , is a mechanism where the propagation step involves a chain transfer agent that can reversibly and rapidly add to a certain polymer chain, which means that, when carried out under the control of a RAFT agent, the reaction mixture contains polymer chains with similar lengths, which allows for the formation of polymer with a narrow polydispersity and allows for carrying out block polymerization reactions in a reliable way. The chain transfer agent for the RAFT control typically results from the addition of the RAFT agent to a growing polymer in the free radical form. Such addition is typically triggered by thermal initiators, such as AI BN and other diazo compounds, or photoinitiators (irradiation with gamma rays or light). Consequently, the use of a RAFT agent typically requires the use of an external initiator. Typical RAFT agents are compounds of formula Z-CS2-R wherein the moiety of formula Z-CS2- acts as chain transfer agent. Typical RAFT agents, as reviewed by Rizzardo and co-workers, belong to the family of trithiocarbonates (general formula: Z- S-C(S)-S-R), dithioesters (general formula: Z-C(S)-S-R) or dithiocarbamates (general formula: Z-NR’-C(S)-S-R). Remarkably, RAFT agents are also usually good chain transfer agents for a narrow range of monomers and need to be carefully chosen in function of the polymer to be produced. For instance, Zhou and co-workers have reported families of dithiocarbamate compounds useful as RAFT agents when used with AIBN as initiation

[005] Although of high interest, RAFT polymerization initiated by light irradiation, also called photoRAFT, is a challenge given that RAFT agents are typically prone to UV degradation. As reviewed by X. Pan and co-workers, photoinitiators are often required in the implementation of light-mediated RAFT polymerization reactions in order to by- pass the degradation mechanism. When the above-mentioned UV degradation is slow or low, the photoinitiator is no longer necessary and the RAFT polymerization can be carried out with no need for an additional initiator, which is advantageous as it produces a more pure product according to the authors. As described by Xu and co-workers, certain dithiocarbonyl compounds undergo photoRAFT polymerization when irradiated with visible light (blue or green light). Noteworthy, the moiety responsible for the chain transfer in the RAFT agent being coloured, the prepared polymers also exhibit some coloration (absorbance in visible light). Also, initiator-free photoRAFT polymerization processes are reported to be slow with respect to photoRAFT processes carried out in the presence of a photoinitiator, and to lead to low conversion rates.

[006] Lalevee and co-workers reported in 2008 the use of certain xanthate derivatives as photoiniferters in controlled free radical polymerization reactions, in particular the compounds of formulae Ph-C(=0)-S-C(=S)-0-C₂H₅ (BEX) and Ph-C(=0)-S-C(=S)-N- (C₂H₅)₂ (BEC). The reported compounds exhibit moderate absorbance in the visible range of the light spectrum (molar absorption coefficient of 57 M ¹ -cnr¹ at 400 nm for BEX and 52 M ¹ -cnr¹ at 405 nm for BEC). It is particularly shown that the benzoyl free radical (due to the presence of a carbonyl group adjacent to the xanthate functionality in the photoiniferter compound BEX) provides an increased polymerization rate (with respect to the benzyl free radical). Lalevee also reports a carbazole-functionalized dithiocarbamate compound as photoiniferter, and generating a benzyl free radical upon irradiation (BCC). This BCC compound exhibits strong absorbance in the visible range and this feature is attributed to the presence of the carbazole moiety (if compared with the non-aromatic analog BDC). Such strong absorbance is transmitted to the final formed polymer, which will also absorb in the visible light range and be coloured (the carbazole bearing free radical is reported as a control agent of the polymerization). The authors report that these systems provide good control on polydispersity of the formed polymer as well as molecular weights in accordance with the expected kinetic chain length (each chain transfer agent is involved in a grown polymer chain).

[007] Cabannes-Boue and Poly reported in 2017 a dithiocarbamate compound with a N-carbazole group useful as a photoinitiator under visible light irradiation and capable of undergoing the RAFT polymerization mechanism through reverse photolysis with certain monomers. According to the authors, the reported compound is able to absorb light in the visible light range and undergo the initiation of a free radical polymerization (through the generation of a free radical) at a wavelength at which the chain transfer agent responsible for the controlled polymerization decomposes very slowly. This subtle balance allows the prepared compound to undergo both photoinitiation and controlled polymerization. The photolysis of the reported compound leads to the formation of two free radicals, one of which can trigger the polymerization and act as an initiator while the second one bearing a N-carbazole unit (it therefore strongly absorbs in the visible light range) recombines to act further as a chain transfer agent. The described dithiocarbamate compound is reported to initiate polymerization of butyl acrylate after an induction period of one hour in the prescribed conditions. The authors report that these systems provide good control on polydispersity of the formed polymer as well as molecular weights in accordance with the expected kinetic chain length (each chain transfer agent is involved in a grown polymer chain).

[008] On another aspect, Ates and co-workers have reported the preparation and characterization of a compound of formula (la) as well as its use as a monomer in the preparation of polymer-coated electrodes for use in energy storage devices.

Authors highlight the potential of the prepared thin film polymer to act as a supercapacitator when formulated in a composite film comprising carbon nanotubes. Authors are however silent about the potential use of this compound as a photoinitiator in polymerization reactions.

[009] In a separate document, Gumber et al. have reported the preparation and biological activity of the dithiocarbamate compound of formula (la’).

This compound is reported as exhibiting potential mycocidal activity. Authors are however silent about the potential use of this compound as a photoinitiator in polymerization reactions.

[010] From what is known in the art, it derives that there is still a need for providing improved photoinitiator compounds suitable for controlled polymerization reactions initiated by visible light irradiation and producing polymers with high molecular weight.

SUMMARY OF THE INVENTION

[011] The inventors have developed, after exhaustive research, a family of dithiocarbamate compounds comprising a carbonyl group appended to the dithiocarbamate functionality useful as photoinitiators of free radical reactions, especially polymerization reactions through a type I photoinitiation mechanism. The compounds of the invention exhibit strong absorbance in the visible range of the light spectrum and can be used as photoinitiators under visible light irradiation, i.e. at a wavelength in the range comprised from 400 to 800 nm. More precisely, the compounds of the invention exhibit strong absorbance at a wavelength in the range comprised from 400 to 500 nm, i.e. using blue light, which advantageously can be implemented through low intensity Light Emitting Diodes (LEDs) or through the use of ambient sunlight. Most compounds described in the state of the art exhibit low absorbance in this range of wavelength and strong absorbance at lower wavelengths, i.e. in the ultra-violet range of the spectrum, which typically requires sources of light of high intensity. The compounds of the invention therefore advantageously allow the use of light sources operating in the visible range of the light spectrum with low intensity, which advantageously conducts to a less energy consuming, and consequently more energy efficient, free radical reaction.

[012] Remarkably, and although exhibiting some colour (they absorb visible light), the photoinitiator compounds of the invention, when irradiated with light, dissociates into two free radical species that exhibit weaker absorbance in the visible range of the light spectrum. Thus, when the photoinitiator compounds of the invention are used as photoinitiators in free radical polymerization reactions, the produced polymer advantageously tends to present a decreased coloration. With the photoinitiators known in the art and exhibiting significant absorbance in the visible range of the light spectrum, coloured polymers are typically produced.

[013] The inventors have also found that the photoinitiators of the invention are suitable for living polymerization reactions induced by light. The inventors have found in particular that the polymerization progresses provided the polymerization system is irradiated with light. When the polymerization system is no longer irradiated with light, the growth of the polymer chain is stopped and when irradiation is restored, the growth of the polymer chain is resumed.

[014] The inventors have also found that the photoinitators of the invention provide polymers having a surprisingly high molecular weight, of about twice the expected value for standard photoinitiators of free-radical polymerization (M_n). Without being bond to theory, it is believed that, when the photoiniators of the invention are used, a re-combination of the grown polymer chains lead to the formation of polymers with higher molecular weights. Such re-combination may be due to the specific reactivity provided by the combination of the aromatic dithiocarbamate group with the carbonyl radical initiating moiety, which favours the re-combination of grown chains as a termination step. Thus, unlike the initiators described in the state of the art, which provide polymers with a molecular weight in accordance with the expectable kinetic chain length, the photoinitiators of the invention provide a product having about twice the molecular weight of the expected polymer obtainable through a free-radical polymerization process. The initiators of the invention are believed to favour a termination of the polymerization by combination of two active chain ends.

[015] Thus, in a first aspect, the invention relates to a compound of formula (I)

wherein:

each of Xi, X₂, X₃, and X₄ is an atom independently selected from the group consisting of C and N;

I is 0 when X1 is N and I is 1 when X1 is C;

m is 0 when X₂ is N and m is 1 when X₂ is C;

n is 0 when X₃ is N and n is 1 when X₃ is C;

p is 0 when X₄ is N and p is 1 when X₄ is C;

q is 0 or 1 ;

each of R1, R₂, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Cr C6)alkylamino, (Ci-C6)perfluoroalkyl, halo, nitro, cyano and a substituent of formula R7 wherein R₇ is a substituent deriving from an aromatic ring system comprising from one to two fused rings, the rings comprising 5 or 6 members independently selected, where chemically possible, from the group consisting of C, CH, O, S, N and NRe, being Re hydrogen or (Ci-C₆)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (C1- C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano; or, alternatively,

one, two or three of the pairs R1 and R₂, R₂ and R3 and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to three rings, the rings being independently saturated, unsaturated or aromatic, the rings being isolated or fused, the rings comprising from 3 to 7 members independently selected from the group consisting of C, CH, CH₂, O, S, N and NRe, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Cr C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Cr C₆)alkylamino and cyano;

and wherein,

when q is 0,

Z is a substituent selected from the group consisting of (Ci-C₆)alkyl, (Ci- C₆)perfluoroalkyl, (C2-C6)alkenyl, and a substituent of formula Rg wherein Rg is a substituent deriving from an aromatic ring system comprising from one to two fused rings, the rings comprising 5 or 6 members independently selected, where chemically possible, from the group consisting of C, CH, O, S, N and NRe, being Re hydrogen or (Ci-C₆)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci- C₆)alkyloxy, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano;

when q is 1 ,

Z is a substituent selected from the group consisting of cyano, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)alkylaminocarbonyl being the (Ci-C₆)alkyl chain optionally substituted at any available position with one group selected from hydroxyl and carboxyl, an amidine group and a substituent of formula Rg;

R5 and R6 are each independently selected form the group consisting of hydrogen, (C1- C₆)alkyl optionally substituted at any available position with one group selected from hydroxyl and carboxyl, (Ci-C₆)alkyloxycarbonyl and (Ci-C₆)alkyloxy; or, alternatively, R5 and R6 together with the carbon atom to which they are attached form a (C₃- C₈)cycloalkyl ring;

and provided that the compound of formula (I) is other than the compounds of formulae

(la) and (la’)

[016] Upon light irradiation, the compounds of the invention dissociate into the free radicals of formulae

(II) (III) [017] Free radicals of formula (II) are useful for the initiation of free radical reactions, in particular of polymerization reactions, while free radicals of formula (III) may be useful chain transfer agents in free radical polymerization reactions, once recombined, especially through a RAFT mechanism as described above, the dithiocarbamate moiety in the free radical of formula (III) being a common structural feature in certain RAFT agents. When a RAFT polymerization takes place, good control on average molecular weight and polydispersity of the produced polymer can advantageously be achieved. Without being bound to theory, it is believed that the formation of the radicals of formulae (II) and (III) upon light irradiation is the result of an energy transfer process taking place on the excited state of the product of the bimolecular self-condensation of the compound of formula (I) in slow equilibrium with the compound of formula (I). It is thus believed that the rate of formation of the free radicals of formulae (II) and (III), hence the rate of this self-condensation equilibrium, is influencing the formation of the polymer through the establishment of an induction time, as reported in Cabannes-Boue and co-workers and as described in the Examples below. The presence of this induction time advantageously provides certain stability to light to a polymerizable composition comprising a compound according to the invention and a polymerizable monomer or oligomer.

[018] A second aspect of the invention thus relates to a photopolymerizable composition comprising:

a) a compound of formula (I) or of formula (la) or of formula (la’) as defined in the first aspect of the invention and at least one or more of

b) a monomer comprising at least in its molecular formula a carbon-carbon double bond, and

c) an oligomer comprising at least in its molecular formula a carbon-carbon double bond.

[019] Also, in a third aspect, the invention relates to the use of the compound as defined in the first aspect of the invention as a photoinitiator, preferably in polymerization reactions.

[020] Also, in a fourth aspect, the invention relates to the use of the compound as defined in the first aspect of the invention as a RAFT agent; preferably under light irradiation; and more preferably under visible light irradiation.

[021] A fifth aspect of the invention relates to a process for the preparation of a polymer comprising the step of contacting under light irradiation, preferably under visible light irradiation, a compound of formula (I) or of formula (la) or of formula (la’) as defined in the first aspect of the invention with at least one or more of a monomer comprising at least in its molecular formula a carbon-carbon double bond, and an oligomer comprising at least in its molecular formula a carbon-carbon double bond; or, alternatively, the step of submitting the photopolymerizable composition of the second aspect of the invention to light irradiation, preferably to visible light irradiation.

BRIEF DESCRIPTION OF THE FIGURES

[022] Figure 1 shows the evolution of conversion over time of the photoinitiator of formula (If) when irradiated with light at 405 nm (Example 8), as measured by UV-Vis spectroscopy and calculated with the following formula where A is the measured absorbance at the 358 nm wavelength at a given time and Ao is the initial absorbance at the 358 nm wavelength: Conversion = 100 x (Ao-A)/Ao

[023] Figure 2 shows the evolution of the molecular weight (in kDa) of polymethyl acrylate formed under thermal RAFT polymerization conditions in function of the conversion of the monomer (expressed as a percentage) and as described in Example 15 using compounds (ly) (diamond symbols), (It) (triangle symbols) and (If) (circle symbols) together with their respective linear correlation trendline (dashed lines) .

[024] Figure 3 shows the evolution of the polydispersity index of polymethyl acrylate formed under thermal RAFT polymerization conditions in function of the conversion of the monomer (expressed as a percentage) and as described in Example 15-1 using compounds (ly) (diamond symbols), (It) (triangle symbols) and (If) (circle symbols).

[025] Figure 4 shows the evolution of conversion, expressed as a percentage, over time, expressed in minutes, of methyl acrylate during its polymerization initiated by the compound of formula (li) in the conditions described in Example 15-2 using light intensities of 200 mW per cm² (circles) or 400 mW per cm² (triangles).

[026] Figure 5 shows the evolution of the molecular weight, expressed in kDa, of the formed polymethyl acrylate as a function of the conversion of methyl acrylate, expressed as a percentage, during its polymerization initiated by the compound of formula (li) in the conditions described in Example 15-2 using light intensities of 200 mW per cm² (circles) or 400 mW per cm² (triangles).

[027] Figure 6 shows the evolution of the polydispersity index of the formed polymethyl acrylate as a function of the conversion of methyl acrylate, expressed as a percentage, during its polymerization initiated by the compound of formula (li) in the conditions described in Example 15-2 using light intensities of 200 mW per cm² (circles) or 400 mW per cm² (triangles).

[028] Figure 7 shows the evolution over time (minutes) of the conversion (%) of methyl acrylate in a bulk polymerization experiment initiated with blue light and each of the compounds (lu), (Iv), (VII) and (laa) in the conditions described in Example 17.

[029] Figure 8 shows the evolution over time (minutes) of the conversion (%) of methyl acrylate in a bulk polymerization experiment initiated with blue light and each of the compounds (VIII), (Iv) and (VII) in the conditions described in Example 17.

[030] Figure 9 shows the evolution over time (seconds) of ln([Mo]/[M]) in a bulk polymerization experiment of methyl acrylate using the compound (Iv) as initiator where light is repeatedly switched on and off at different intervals of time.

DETAILED DESCRIPTION OF THE INVENTION

[031] All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions for certain terms as used in the present application are as set forth below and are intended to apply uniformly through-out the specification and claims unless an otherwise expressly set out definition provides a broader definition.

[032] For the purposes of the invention, any ranges given include both the lower and the upper end-points of the range. Ranges given, such as temperatures, times, and the like, should be considered approximate, unless specifically stated.

[033] In the context of the invention, the term “free radical” refers to a molecule bearing an atom with an unpaired valence electron.

[034] In the context of the invention, the term“halo” or“halogen” refers to an halogen radical, it thus refers to fluoro, chloro, bromo or iodo.

[035] In the context of the invention, the term“alkyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims. Examples of alkyl groups include, but are not limited to: methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, tert-butyl, pentyl, and hexyl.

[036] In the context of the invention, the term“alkenyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims and at least one carbon-carbon double bond.

[037] In the context of the invention, the term“cycloalkyl” refers to a saturated cyclic hydrocarbon group having the number of carbon atoms indicated in the description or in the claims and wherein the carbon atoms forming the cyclic hydrocarbon may be substituted with linear or branched alkyl groups.

[038] In the context of the invention, the term“perfluoroalkyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims wherein all the hydrogen atoms are replaced by a fluoro group. Examples of perfluoroalkyl groups include, but are not limited to: trifluoromethyl, and pentafluoroethyl.

[039] In the context of the invention, the term“alkyloxy” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through an ether group (-0-).

[040] In the context of the invention, the term“alkylcarbonyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through a carbonyl group (C=0).

[041] In the context of the invention, the term“alkylcarbonyloxy” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through a carboxyl group (-COO-) and wherein the alkyl chain is attached to the carbon atom of the carboxyl group.

[042] In the context of the invention, the term“alkyloxycarbonyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through a carboxyl group (-OOC-) and wherein the alkyl chain is attached to the oxygen atom of the carboxyl group and the C atom of the carboxyl group is attached to the remainder of the formula.

[043] In the context of the invention, the term “alkylaminocarbonyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through an aminocarbonyl group (-NH-CO-) and wherein the alkyl chain is attached to the nitrogen atom of the aminocarbonyl group and the C atom of the aminocarbonyl group is attached to the remainder of the formula. The term “(Ci- C₆)alkylaminocarbonyl” thus refers to a substituent of formula -C(0)-NHR wherein R is a (Ci-C₆)alkyl chain as defined above.

[044] In the context of the invention, the term “dialkylaminocarbonyl” refers to a saturated linear or branched hydrocarbon group having the number of carbon atoms indicated in the description or in the claims which is attached to the remainder of the formula through an aminocarbonyl group (-N(-)-CO-) and wherein the alkyl chain is attached to the nitrogen atom of the aminocarbonyl group and the C atom of the aminocarbonyl group is attached to the remainder of the formula. The term“di(Ci- C₆)alkylaminocarbonyl” thus refers to a substituent of formula -C(0)-NRR’ wherein R and R’ are each a (Ci-C₆)alkyl chain as defined above.

[045] In the context of the invention, the term“hydroxyl” refers to a group of formula -OH.

[046] In the context of the invention, the term“carboxyl” refers to a group of formula -COOH.

[047] In the context of the invention, the term“cyano” refers to a group of formula - CN.

[048] In the context of the invention, the term“amidine” refers to a group of formula -C(=NH)-NH2 and any of its known salts or solvates.

[049] In the context of the invention, the term“light irradiation” refers to the fact that a sample is submitted to the irradiation of an electromagnetic wave such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X- rays and gamma rays. More typically, it refers to the fact that a sample is submitted to the irradiation of visible light or ultraviolet radiation. Visible light typically refers to an electromagnetic radiation having a wavelength comprised from 400 to 800 nm. Ultraviolet (UV) radiation typically refers to an electromagnetic radiation having a wavelength comprised from 10 nm to 400 nm.

[050] In the context of the invention, two rings of a ring system are designated as “isolated” when one member of one ring is connected to a member of the other ring through a single bond. For example, biphenyl is a ring system comprising two isolated phenyl rings.

[051] In the context of the invention, two rings of a ring system are designated as “fused” when said rings share two members in common. For example, naphthyl is a ring system comprising two fused phenyl rings.

[052] In the context of the invention, the term“light absorption coefficient” refers to the measurement of how strongly a chemical species attenuates light at a given wavelength and is determined by Beer-Lambert’s law. It is designated as e and is measured in L. mol ¹. cm ¹.

[053] In the context of the invention, the term “photopolymerization” and its derivatives refers to a process initiated thanks to light irradiation and through which a polymer is formed.

[054] In the context of the invention, the term“photoinitiator” refers to a substance which, when submitted to light irradiation, is able to generate reactive species and trigger a chemical transformation, such as a free radical polymerization process. [055] In the context of the invention, the term“RAFT agent” refers to a substance or reagent for free radical polymerization processes controlled through the RAFT mechanism. RAFT polymerization is a reversible-deactivation radical polymerization process. It makes use of RAFT agent to afford control over the generated molecular weight and polydispersity during a free-radical polymerization. RAFT polymerization typically uses thiocarbonylthio compounds, such as dithioesters, thiocarbamates, and xanthates, to mediate the polymerization via a reversible chain-transfer process.

[056] According to the first aspect of the invention, the invention relates to a compound of formula (I) as defined above. The compound of the invention typically consists of three moieties which are adjacent one with another: (i) a chromophore moiety consisting of a N-heterocyclic ring, (ii) a core moiety consisting of a dithiocarboxylic functional group and (iii) an acyl group able to generate an initiating radical. The combination of these three features allow the compound of the invention to exhibit higher absorbance in the visible light range than the compounds of the state of the art. This is in particular attributed to the presence of the carbonyl group adjacent to the dithiocarboxyl functional group which shifts the absorbance of the chromophore moiety in the visible range. Upon light irradiation, the compound of formula (I) undergoes homolytic cleavage between the acyl group and dithiocarboxyl functional group, which provides free radicals that exhibit lower absorbance in the visible range than the compound of formula (I) and accounts for the photobleaching of the compounds of formula (I) when irradiated with light. This homolytic cleavage in turn provides an acyl free radical which can act as a free radical initiator of chemical reactions, such as a free radical polymerization. On the other hand, the dithiocarboxyl free radical may act as chain transfer agents in RAFT polymerization processes. This specific combination is also believed to favour a termination of polymerization by combination of grown polymer chains, providing polymers with high molecular weight.

[057] Thus, in a particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described below, the compound of formula (I) dissociates into the free radicals of formula (II) and (III)

(II) (III) when submitted to light irradiation. Preferably, the compound of formula (I) dissociates into the free radicals of formula (II) and (III) as defined above when submitted to ultraviolet or visible light irradiation. More preferably, the compound of formula (I) dissociates into the free radicals of formula (II) and (III) as defined above when submitted to visible light irradiation.

[058] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least one of Xi, X₂, X₃ and X₄ is a carbon atom; preferably wherein at least two of X₁, X₂, X₃ and X₄ are carbon atoms; more preferably wherein at least three of X₁, X₂, X₃ and X₄ are carbon atoms.

[059] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein each of R1, R₂, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (C1- C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (C1- C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

[060] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least two of X1, X₂, X₃, and X₄ are carbon atoms and each of R1, R₂, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Cr C₆)alkylamino and cyano.

[061] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least three of X₁, X₂, X₃, and X₄ are carbon atoms and each of R₁, R₂, R₃ and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, di(Cr C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, (Ci- C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

[062] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein one or two of the pairs Ri and R₂, R₂ and R3 and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to three aromatic rings, the rings being isolated or fused, the rings comprising from 5 to 6 members independently selected from the group consisting of C, CH, O, S, N and NRe, being Re hydrogen or (Ci-C6)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (C1- C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (C1- C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

[063] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least two of X1, X₂, X₃, and X₄ are carbon atoms and one or two of the pairs R1 and R₂, and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to two aromatic rings, preferably one ring, the rings being isolated or fused, the rings comprising from 5 to 6 members independently selected from the group consisting of C, CH, and N the rings being further optionally substituted at no more than two available positions with a substituent selected from the group consisting of (Ci-C₆)alkyl, (C1- C₆)alkyloxy, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

[064] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least three of X1, X₂, X₃, and X₄ are carbon atoms and one or two of the pairs R1 and R₂, and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to two phenyl rings, preferably one ring, the rings being isolated or fused, the rings being further optionally substituted at no more than two available positions with a substituent selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)perfluoroalkyl, halo, di(Ci-C₆)alkylamino and cyano.

[065] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein at least three of Xi, X₂, X₃, and X₄ are carbon atoms and one of the pairs R1 and R₂, and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to two phenyl rings, preferably one ring, the rings being isolated or fused, the rings being further optionally substituted at no more than two available positions with a substituent selected from the group consisting of (Ci-C6)alkyl, (Ci-C6)alkyloxycarbonyl, (Ci-C6)perfluoroalkyl, halo, di(Ci-C6)alkylamino and cyano.

[066] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

18

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below and wherein Ri, R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, (C1- C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (C1- C₆)perfluoroalkyl, halo, nitro, cyano and phenyl; and wherein, preferably, none, one or two of the substituents R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ are different from hydrogen. More preferably, R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R_I2’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, bromo and (Ci-C₆)alkyloxycarbonyl; and wherein, preferably, none or one of the substituents R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ is different from hydrogen.

[067] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

[068] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below and wherein R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, (Ci- C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (Ci- C₆)perfluoroalkyl, halo, nitro, cyano and phenyl; and wherein, preferably, none, one or two of the substituents Ri, R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ are different from hydrogen. More preferably, R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, RI₂’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, bromo and (Ci-C₆)alkyloxycarbonyl; and wherein, preferably, none or one of the substituents R1 , R₂, R3, R₄, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ is different from hydrogen.

[069] The compounds described in the above embodiment are advantageous as they strongly absorb in the visible light range.

[070] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below.

[071] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below and wherein Ri, R₂, Rio, Rn, R12, and R13 are each a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (C1- C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and phenyl; and wherein, preferably, none, one or two of the substituents Ri, R2, R10, R11 , R12, and R13, are different from hydrogen. More preferably, R1 , R₂, R10, R11 , R_I2, and R13 are each a substituent independently selected from the group consisting of hydrogen, bromo and (Ci-C₆)alkyloxycarbonyl; and wherein, preferably, none or one of the substituents Ri, R₂, R10, R11 , R12 and R13, is different from hydrogen.

[072] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below and wherein Ri, R₂, R3, and R₄ are each a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (C1- C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and phenyl; and wherein, preferably, none, one or two of the substituents Ri, R₂, R3 and R₄, are different from hydrogen. More preferably, Ri, R₂, R3, and R₄ are each a substituent independently selected from the group consisting of hydrogen, bromo and (Ci-C₆)alkyloxycarbonyl; and wherein, preferably, none or one of the substituents R1 , R2, R3, and R₄ is different from hydrogen.

[073] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein R₅, R₆, q and Z are as defined in any of the embodiments described above and below and wherein R10, Rn, R12, R13, R10’, R11’, R12’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, (C1- C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (C1- C₆)perfluoroalkyl, halo, nitro, cyano and phenyl; and wherein, preferably, none, one or two of the substituents R10, R11 , R12, and R13, are different from hydrogen. More preferably, R1 , R2, R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ are each a substituent independently selected from the group consisting of hydrogen, bromo and (C1- C₆)alkyloxycarbonyl; and wherein, preferably, none, one or two of the substituents R10, R11 , R12, R13, R10’, R11’, R12’ and R13’ is different from hydrogen.

[074] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

[075] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae

[076] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein:

when q is 1 ,

Z is a substituent selected from the group consisting of cyano, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)alkylaminocarbonyl being the (Ci-C₆)alkyl optionally substituted at its terminal carbon atom with one group selected from hydroxyl and carboxyl, amidine, pyridyl and phenyl optionally substituted at any position with one or more groups selected from the group consisting of (Ci-C₆)perfluoroalkyl, halo, and nitro; and,

R5 and R6 are each independently selected from the group consisting of hydrogen, (C1- C₆)alkyl optionally substituted with one group selected from hydroxyl, carboxyl and (C1- C6)alkyloxy; or, alternatively, R5 and R6 together with the carbon atom to which they are attached form a cyclohexyl ring;

when q is 0,

[077] Z is a substituent selected from the group consisting of (Ci-C₆)alkyl, pyridyl and phenyl optionally substituted at any position with one or more groups selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)perfluoroalkyl, halo, and nitro. [078] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein:

when q is 1 ,

R5 and R6 are each independently selected from the group consisting of hydrogen, (C1- C₆)alkyl optionally substituted at its terminal carbon atom with one group selected from hydroxyl and carboxyl and (Ci-C6)alkyloxy; or, alternatively, R5 and R6 together with the carbon atom to which they are attached form a cyclohexyl ring;

when q is 0,

Z is a substituent selected from the group consisting of (Ci-C₆)alkyl, pyridyl and phenyl optionally substituted at any position with one or more groups selected from the group consisting of (Ci-C₆)perfluoroalkyl, halo, and nitro.

[079] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein q, Z, R₅ and R₆ are such that the compound of formula (I) is selected from the group consisting of the compounds of formulae

w vvh 1e c

embodiments described above and below. [080] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein q, Z, R₅ and R₆ are such that the compound of formula (I) is selected from the group consisting of the compounds of formulae

wherein I, m, n, p, X₁, X₂, X₃, X₄, R₁, R₂, R₃ and R₄ are as defined in any of the embodiments described above and below.

[081] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein q, Z, R₅ and R₆ are such that the compound of formula (I) is selected from the group consisting of the compounds of formulae

[082] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein q is 0 and Z is 2,4,6-trimethylphenyl and wherein I, m, n, p, X₁, X₂, X₃, X₄, R₁, R₂, R₃ and R₄ are as defined in any of the embodiments described above and below.

[083] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein I, m, n, p, Xi, X₂, X₃, X₄, R₁, R₂, R₃ and R₄ are such that the compound of formula (I) is selected from the compounds of formulae

and wherein R₅, R₆, q and Z are such that the compound of formula (I) is selected from the compounds of formulae

[084] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein I, m, n, p, Xi, X₂, X3, X₄, R1, R2, R3 and R₄ are such that the compound of formula (I) is selected from the compounds of formulae

[085] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is that wherein I, m, n, p, X₁, X₂, X₃, X₄, R₁, R₂, R₃ and R₄ are such that the compound of formula (I) is selected from the compounds of formulae

and wherein

q and Z are such that the compound of formula (I) is selected from the compounds of formulae

[086] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae (lb), (lc), (Id), (le), (If), (Ig), (Ih), (li), (Ij), (Ik), (II), (Im), (In), (lo), (Ip), (Iq), (Ir), (Is), (It), (lu), (Iv), (Iw), (lx), (ly), (laa) and (Iz)

(Id)

[087] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) is selected from the group consisting of the compounds of formulae (lb), (lc), (Id), (le), (If), (Ig), (Ih), (li), (Ij), (Ik), (II), (Im), (In), (lo), (Ip), (Iq), (Ir), (Is), (It), (lu), (Iv), (Iw), (lx), (ly) and (Iz)

[088] The compounds of the invention exhibits strong absorption in the visible range of the light spectrum and in the UV region, which makes them suitable as photoiniators under irradiation of UV-visible light.

[089] Thus, in another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) has a light absorption coefficient of at least 500 L. mol ¹. cm ¹; preferably of at least 1000 L. mol ¹. cm ¹; at a wavelength comprised in the visible region of the spectrum.

[090] The compounds of the invention undergo photolytic cleavage upon light irradiation to generate free radicals of formulae (II) and (III) as defined above. In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the free radicals of formula (II) and (III) described above each have a light absorption coefficient of no more than 1000 L. mol ¹. cm ¹; preferably of no more than 500 L. mol ¹. cm ¹ at a wavelength comprised in the visible region of the spectrum. When a compound of formula (I) having these absorption properties is used as photoinitiator in polymerization reactions, the produced polymer advantageously presents little colouration.

[091] Thus, in another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) has a light absorption coefficient of at least 500 L. mol ¹. cm ¹; preferably of at least 1000 L. mol ¹. cm ¹; at a wavelength comprised in the visible region of the spectrum; and wherein the free radicals of formula (II) and (III) described above each have a light absorption coefficient of no more than 1000 L.mol ¹.cnr¹; preferably of no more than 500 L.mol ¹. cm ¹ at a wavelength comprised in the visible region of the spectrum.

[092] In another particular embodiment of the first aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) has a light absorption coefficient of at least 10 L.mol ¹. cm ¹ at a wavelength comprised in the range from 500 to 650 nm. It is advantageous as it allows using green or yellow light to promote the formation of the free radicals of formula (II) and (III).

[093] It is advantageous as, upon photolytic cleavage of the compound of formula (I), uncouloured free radicals are generated and the compound of formula (I) undergoes photobleaching in the visible light region, which allows the use of these compounds as initiators in the preparation of uncoloured polymer materials using visible light irradiation to initiate the polymerization reaction.

[094] Thus, the second aspect of the invention relates to a photopolymerizable composition comprising:

a) a compound of formula (I) or of formula (la) or of formula (la’) as defined in any of the embodiments above and at least one or more of

[095] In another particular embodiment of the second aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the photopolymerizable composition comprises:

a) a compound of formula (I) as defined in any of the embodiments above and at least one or more of

b) a monomer, or mixture of monomers, comprising at least in its molecular formula a carbon-carbon double bond, and

[096] Suitable monomers for photopolymerization are known in the art and will become apparent to the skilled person. In another particular embodiment of the second aspect of the invention, optionally in combination with one or more of the embodiments described above or below, the monomer comprised in the photopolymerizable composition is selected from the group consisting of styrene, acrylates, methacrylates, cyanoacrylates, ethylene, propylene, acrylamides, methacrylamides, urea acrylamides and carbonate acrylates, vinyl esters, unsaturated polyesters.

[097] The photopolymerizable composition of the second aspect of the invention may comprise an oligomer comprising at least in its molecular formula a carbon-carbon double bond. Such oligomer may be selected from the group consisting of the oligomers of styrene, acrylates, methacrylates, cyanoacrylates, ethylene, propylene, acrylamides, methacrylamides, urea acrylamides and carbonate acrylates, vinyl esters, unsaturated polyesters. For certain applications, preferred oligomers are those being liquid in normal conditions of pressure and temperature.

[098] As further shown below in the Examples, the compound of formula (I) is useful in controlled living polymerization. When a composition according to the second aspect of the invention is irradiated with light, polymerization takes place as long as light is provided to the composition. In the absence of light irradiation, no polymerization is taking place. It is advantageous as it provides stable compositions in normal conditions of storage (ambient light irradiation) and provides for a full control over the polymerization process and the molecular weight of the formed polymer. When the composition of the second aspect of the invention comprises an oligomer as defined above, said oligomer may thus be obtained by irradiating a composition comprising a compound of formula (I), or of formula (la), or of fomula (la’) and a monomer or a mixture of monomers as defined above in suitable conditions so as to form the oligomer. It is advantageous as it may provide an oligomer with suitable properties for the formulation of curable resins. Such oligomer may be used as a latent curing agent.

[099] The composition of the second aspect of the invention may further comprise further photoinitiators or initiators. For instance, the composition of the second aspect of the invention may further comprise further photoinitiators of formula (I) as defined above.

[100] In addition, the composition of the second aspect of the invention may further comprise further components known in the art for the formulation of curable resins, such as stabilizers, dyes, binders, fillers, dispersing agents, thickening agents and polymerization inhibitors.

[101] In preferred embodiments of the second aspect of the invention, the composition of the second aspect of the invention comprises a compound of formula (I) as defined in any of the particular and preferred embodiments of the first aspect of the invention.

[102] In preferred embodiments of the second aspect of the invention, the composition of the second aspect of the invention comprises a monomer selected from the group consisting, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, dimethylacrylamide and mixtures thereof.

[103] In preferred embodiments of the second aspect of the invention, the composition of the second aspect of the invention is such that the molar ratio of the compound of formula (I) or of formula (la) or of formula (la’) to the monomer, oligomer or mixture thereof is in the range of 1 :1000 to 1 :100. Preferably, it is in the range of 1 :500 to 1 :100. The inventors have found that the photopolymerization of a composition as defined in the second aspect of the invention comprises the following steps:

(i) an induction step; and

(ii) a polymer chain growth step.

Inventors have found in particular that the amount of initiator in photopolymerizable composition determines the rate of each of these phases. In particular, it was found that low amounts of initiators favour a short induction period along with a moderate rate of chain growth, while higher amounts of initiators provide longer induction periods along with high rates of growth of polymer chain. As described above, intensity of light irradiation was also found to have an impact on the respective rates of both steps.

[104] The compound of formula (I) or of formula (la) or of formula (la’) as defined in any of the embodiments above presents similar structural features common to known RAFT agents and photoiniferter compounds.

[105] The third aspect of the invention thus relates to the use of the compound of formula (I) or of formula (la) or of formula (la’) as defined in any of the embodiments above as a photoinitiator, preferably in polymerization reactions.

[106] When used in photopolymerization reactions, concurrently with the initiation mechanism, the compound of formula (I) or of formula (la) or of formula (la’) is able to control the polymerization mechanism through a RAFT mechanism acting as reversible chain transfer agent. It is advantageous as it allows using one sole compound under visible light irradiation to initiate a controlled living polymerization process.

[107] The fourth aspect of the invention thus relates to the use of the compound of formula (I) or of formula (la) or of formula (la’) as defined in any of the embodiments above as a RAFT agent; preferably under light irradiation; and more preferably under visible light irradiation.

[108] In another particular embodiment of the invention, optionally in combination with one or more of the embodiments described above or below, the compound of formula (I) or of formula (la) or of formula (la’) is used both as a photoinitiator in polymerization reactions and as a RAFT agent under visible light irradiation.

[109] In a fifth aspect, the invention relates to a process for the preparation of a polymer comprising the step of contacting under light irradiation, preferably under visible light irradiation, a compound of formula (I) or of formula (la) or of formula (la’) as defined in any one of the embodiments described above with at least one or more of a monomer comprising at least in its molecular formula a carbon-carbon double bond, and an oligomer comprising at least in its molecular formula a carbon-carbon double bond; or, alternatively the step of submitting the photopolymerizable composition of the second aspect of the invention to light irradiation, preferably to visible light irradiation.

[110] A suitable source of visible light irradiation is selected from the group consisting of sunlight, blue light-emitting diodes, green light-emitting diodes, neon tubes, light bulbs and compact fluorescent lamp (CFL). The wavelength of the light source is preferably comprised from 300 nm to 800 nm. Light source is preferably at a light intensity in the range of 0.1 to 10 W. More preferably, light source is at a light intensity in the range of 0.1 to 5 W; even more preferably of 0.1 to 2 W; and even more preferably of 0.1 to 1 W. The use of low intensity of light is advantageous in terms of energy efficiency of the process and safety of operation.

[111] The process of the fifth aspect of the invention may be carried out in the presence or in the absence of a solvent. The process of the fifth aspect of the invention may be carried out in a temperature range such that the reaction medium is liquid, preferably at a temperature comprised from 0 °C to 50 °C and more preferably at room temperature.

[112] In particular embodiments of the fifth aspect, the process for the preparation of a polymer preferably provides a polymer having a polydispersity index in the range of 1 to 2. In more particular embodiments, when a solvent is used, the process for the preparation of a polymer preferably provides a polymer having a polydispersity index in the range of 1 to 1.6.

[113] In particular embodiments of the fifth aspect, when the process for the preparation of a polymer comprises the step of contacting under light irradiation, preferably under visible light irradiation, a compound of formula (I) or of formula (la) or of formula (la’) as defined in any one of the embodiments described above with a monomer comprising at least in its molecular formula a carbon-carbon double bond, the process provides a polymer having a molecular weight higher than the value P, being P the result of the calculation P = x * M , where M is the molecular weight of the monomer and x is the ratio of the molar amount of monomer to the molar amount of the compound of formula (I), or of formula (la), or of formula (la’).

[114] A process for the preparation of a compound of formula (I) or of formula (la) or of formula (la’) is also part of the invention, said process comprising the steps of:

(i) contacting a compound of formula (V)

with carbon disulfide in the presence of a base;

(ii) contacting the product obtained in step (i) with a compound of formula (VI)

wherein Y is Cl or a moiety of formula (VI’)

and (iii) isolating the compound of formula (I) or of formula (la) or of formula (la’); wherein, in the compound of formula (V) I, m, n, p, Xi, X₂, X3, X₄, R1, R2, R3 and R₄ are as defined in any of the embodiments described above and below; and, in the compound of formula (VI) R₅, R₆ , q and Z are as defined in any of the embodiments described above and below.

[115] A suitable base for carrying out step (i) of the preparation process of the compound of formula (I) is selected from the group consisting of alkali carbonate salts, alkali hydroxide salts and alkali (Ci-C₆)allkyloxides. Preferably, the base is potassium tert-butoxide or potassium hydroxide.

[116] Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. EXAMPLES

Preparative Example 1 : Preparation of potassium 5-bromo-1 H-indole-1-carbodithioate

(!Ya)

[117] In an oven dried round bottom flask under an atmosphere of argon, 5- bromoindole (1 eq) was dissolved in a minimal amount of THF (commercial synthesis grade; 10 mL.g ¹). The flask was cooled to 0°C in an ice-water bath and potassium tert- butoxide (1 ,1 eq) was added portionwise. The mixture turned a slight yellow/orange color and was left to stir for 30 minutes. Still at 0°C, carbon disulfide (1 ,5 eq) was added dropwise via syringe addition. The mixture immediately turned a bright orange color and was left to stir for one hour at 0°C. After warming up to room temperature, THF was evaporated carefully on a rotary evaporator to a thick syrupy consistence. Toluene was added and evaporated to obtain a yellow solid residue. The residue was suspended in a 1 :1 mixture of pentane and diethyl ether and stirred vigorously to obtain a fine suspension. The yellow solid was then filtered under a flow of argon, washed twice with a small amount of 1 : 1 mixture of pentane and diethyl ether and further dried overnight under high vacuum to obtain the desired product as a yellow powder. This reaction has been performed on various scales (5 to 55 mmol of starting 5- bromoindole) with isolated yields ranging from 88 to 95%.

1H NMR (400 MHz, d6-DMSO) d 6.39 (d, J= 3.5 Hz, 1 H), 7.25 (dd, J= 9, 2.1 Hz, 1 H), 7.68 (d, J=2.1 Hz, 1 H), 8,69 (d, J= 3.5 Hz, 1 H), 9,28 (d, J= 9 Hz, 1 H)

HRMS (ESI negative^'): calculated for CgHsBrlS^ (M): 269.9052, found 269.9044.

Example 1 : Preparation of 5-bromo-1 H-indole-1-carbothioic pivaiic thioanhvdride ( lb )

[118] In an oven dried round bottom flask cooled to 0°C with an ice-water bath, pivaloyl chloride was dissolved in acetonitrile (265 mg, 2.2 mmol, 1.2 eq) then potassium 5-bromo-1 H-indole-1-carbodithioate (621 mg, 2 mmol, 1 eq) was added portionwise over 10 minutes. After stirring for an additional 15 minutes, the majority of the volatiles was carefully evaporated on a rotary evaporater then the orange residue was diluted with ethyl acetate (25 mL) and water (15 mL) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel, the phase separated and the aqueous layer extracted twice with 5ml_ of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange solid. The residue was then dissolved in 1 :20 mixture of ethyl acetate and heptane and the solvent slowly evaporated in a rotary evaporator under reduced pressure (240 mbar at 40°C) until orange cristals appeared, leaving a mostly colorless liquid phase. The crystalline orange solid was filtered, washed further with heptane and dried overnight under high vacuum (430 mg, 60% yield)

¹H NMR (400 MHz, CDCIs) d 8.88 (d, J=9 Hz, 1 H); 7.84 (d, J=3.8 Hz, 1 H); 7.70 (d, J=2 Hz, 1 H); 7.47 (dd, J=2, 9 Hz; 1 H); 6.60 (d, J=3.8 Hz, 1 H); 1.33 (s, 9H)

e (358 nm, MeCN): 10.040 L. mol ¹. cm ¹

e (405 nm, MeCN): 2.580 L. mol ¹. cm ¹

When a 0.001 M solution of compound (lb) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (lb) exhibits absorption (i.e. absorption is not 0) is of 595 nm.

Example 2: Preparation of benzoic 5-bromo-1 H-indole-1-carbothioic thioanhydride (lc)

[119] In an oven dried round bottom flask cooled to 0°C with an ice-water bath, benzoyl chloride was dissolved in acetonitrile (309 mg, 2.2 mmol, 1.2 eq) then potassium 5-bromo-1 H-indole-1-carbodithioate (IVa) (621 mg, 2 mmol, 1 eq) was added portionwise over 10 minutes. After stirring for an additional 15 minutes, the majority of the volatiles was carefully evaporated on a rotary evaporater then the orange residue was diluted with ethyl acetate (25 mL) and water (15 mL) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel , the phase separated and the aqueous layer extracted twice with 5mL of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange solid. The residue was then dissolved in 1 :20 mixture of ethyl acetate and heptane and the solvent slowly evaporated in a rotary evaporator under reduced pressure (240 mbar at 40°C) until orange cristals appeared, leaving a mostly colorless liquid phase. The cristaline orange solid was filtered, washed further with heptane and dried overnight under high vacuum (532 mg, 70% yield).

¹H NMR (400 MHz, CDCIs) d 8.93 (d, J=9 Hz, 1 H); 7.99-7.92 (m, 3H); 7.72 (d, J=1.8

Hz, 1 H); 7.68 (app t, J=7.5 Hz, 1 H); 7.54 (t, J=7.7 Hz, 2 H); 7.49 (dd, J=1 .8, 9 Hz; 1 H); 6.62 (d, J=3.9 Hz, 1 H)

s (358 nm, MeCN): 12.100 L.mo .cm ¹

(405 nm, MeCN): 3.600 L. mol ¹. cm^-1

When a 0.001 M solution of compound (lc) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (lc) exhibits absorption (i.e.

absorption is not 0) is of 518 nm.

Example 3: Preparation of 5-bromo-1 H-indole-1 -carbothioic 2-phenylacetic thioanhydride (Id):

[120] In an oven dried round bottom flask cooled to 0°C with an ice-water bath, 2- phenylacetyl chloride was dissolved in acetonitrile (170 mg, 1.1 mmol, 1 .2 eq) then potassium 5-bromo-1 H-indole-1 -carbodithioate (IVa) (310 mg, 1 mmol, 1 eq) was added portionwise over 10 minutes. After stirring for an additional 15 minutes, the majority of the volatiles was carefully evaporated on a rotary evaporater then the orange residue was diluted with ethyl acetate (25 ml.) and water (15 ml.) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel , the phase separated and the aqueous layer extracted twice with 5ml_ of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange solid. The residue was then dissolved in 1 :20 mixture of ethyl acetate and heptane and the solvent slowly evaporated in a rotary evaporator under reduced pressure (240 mbar at 40°C) until orange cristals appeared, leaving a mostly colorless liquid phase. The cristaline orange solid was filtered, washed further with heptane and dried overnight under high vacuum (150 mg, 38% yield).

¹H NMR (400 MHz, CDCIs) d 8.79 (d, J=9 Hz, 1 H); 7.72 (d, J=3.8 Hz, 1 H); 7.68 (d, J=2 Hz, 1 H); 7.45-7.36 (m, 4 H); 7.35-7.31 (m, 2H); 6.56 (app d, J=3.8 Hz, 1 H); 3.95 (s,

2H)

e (358 nm, MeCN): 13.000 L. mol ¹. cm ¹ e (405 nm, MeCN): 3.370 L.mol ¹.cnrr¹

When a 0.001 M solution of compound (Id) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (Id) exhibits absorption (i.e. absorption is not 0) is of 628 nm

Example 4: Preparation of acetic 5-bromo-1 H-indole-1-carbothioic thioanhydride (le):

[121] In an oven dried round bottom flask cooled to 0°C with an ice-water bath, 2- phenylacetyl chloride was dissolved in acetonitrile (170 mg, 1.1 mmol, 1.2 eq) then potassium 5-bromo-1 H-indole-1-carbodithioate (IVa) (310 mg, 1 mmol, 1 eq) was added portionwise over 10 minutes. After stirring for an additional 15 minutes, the majority of the volatiles was carefully evaporated on a rotary evaporator then the orange residue was diluted with ethyl acetate (25 ml.) and water (15 ml.) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel, the phase separated and the aqueous layer extracted twice with 5ml_ of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange solid that was further dried overnight under high vacuum (150 mg, 38% yield).

¹H NMR (300 MHz, CDCIs) d 8.88 (d, J=9 Hz, 1 H); 7.87 (d, J=3.8 Hz, 1 H); 7.70 (d, J=2 Hz, 1 H); 7.47 (dd, J=2, 9 Hz, 1 H); 6.61 (d, J=3.8 Hz, 1 H); 2.48 (s, 3H)

e (358 nm, MeCN): 12.960 L. mol ¹. cm ¹

e (405 nm, MeCN): 2.990 L. mol ¹. cm^-1

When a 0.001 M solution of compound (le) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (le) exhibits absorption (i.e. absorption is not 0) is of 572 nm.

Example 5: Preparation of 1 H-indole-1-carbothioic pivalic thioanhydride (If)

[122] In an oven dried round bottom flask, indole (586 mg, 5 mmol, 1 eq) was dissolved in THF (10 ml.) then tBuOK (589 mg, 5.25 mmol, 1.05 eq) was added and the resulting mixture stirred for 15 minutes. Carbon disulfide (453 mI_, 7.5 mmol, 1.5 eq) was then added and the resulting orange mixture stirred for 15 minutes. Pivaloyl chloride was then added in one portion and the mixture stirred for an additional 15 minutes. The orange mixture was diluted with ethyl acetate (25 ml.) and water (15 ml.) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel, the phases separated and the organic layer layer extracted twice with 25ml_ of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange oil. Column chromatography ((20% AcOEt in hexanes containing 1 % NEt3 as eluant) provided the pure compound as an orange oil (630 mg, 45% yield)

¹H NMR (300 MHz, CDCIs) d 9.06-8.96 (m, 1 H); 7.83 (d, J= 3.8 Hz, 1 H); 7.60-7.52 (m, 1 H); 7.42-7.30 (m, 2H); 6.66 (d, J= 3.8 Hz, 1 H); 1.33 (s, 9H)

e (358 nm, MeCN): 9.950 L. mol ¹. cm ¹

e (405 nm, MeCN): 3.590 L.mo .cm ¹

When a 0.001 M solution of compound (If) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (If) exhibits absorption (i.e. absorption is not 0) is of 562 nm.

Example 6: Preparation of pivalic 1 H-pyrrole-1-carbothioic thioanhydride (Iq)

[123] In an oven dried round bottom flask, indole (349 mI_, 5 mmol, 1 eq) was dissolved in THF (10 ml.) then tBuOK (589 mg, 5.25 mmol, 1.05 eq) was added and the resulting mixture stirred for 15 minutes. Carbon disulfide (453 mI_, 7.5 mmol, 1.5 eq) was then added and the resulting orange mixture stirred for 15 minutes. Pivaloyl chloride was then added in one portion and the mixture stirred for an additional 15 minutes. The orange mixture was diluted with ethyl acetate (25 ml.) and water (15 ml.) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel, the phases separated and the organic layer layer extracted twice with 25ml_ of ethyl acetate. The combined organic phases were dried (MgS04) and concentrated to black semisolid residue. Column chromatography (10% AcOEt in hexanes containing 1% NEt3 as eluant) provided the pure compound (Ig) as an orange oil (430 mg, 60% yield).

¹H NMR (500 MHz, CDCIs) d 7.60-7.57 (m, 2H); 6.38-6.34 (m, 2H); 1.33 (s, 9H) e (358 nm, MeCN): 2.400 L. mol ¹. cm ¹

e (405 nm, MeCN): 210 L. mol ¹. cm ¹

When a 0.001 M solution of compound (Ig) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (Ig) exhibits absorption (i.e. absorption is not 0) is 567 nm. Example 7: Preparation of l-ffbenzoylthiolcarbonothiovP-l H-indole-3-carboxylic methanesulfonic anhydride Oh^'):

[124] In an oven dried round bottom flask cooled to 0°C with an ice-water bath, benzoyl chloride was dissolved in acetonitrile (155 mg, 1.1 mmol, 1.2 eq) then potassium 3-(methoxycarbonyl)-1 H-indole-1-carbodithioate (289 mg, 1 mmol, 1 eq) was added portionwise over 10 minutes. After stirring for an additional 15 minutes, the majority of the volatiles was carefully evaporated on a rotary evaporaterm then the orange residue was diluted with ethyl acetate (25 ml.) and water (15 ml.) and the resulting biphasic mixture stirred vigorously for 5 minutes. The mixture was then transferred to an extraction funnel , the pase separated and the aqueous layer extracted twice with 5ml_ of ethyl acetate. The combined organic phases were dried (MgS0₄) and concentrated to an orange solid. The residue was then purified by chromatography (20% AcOEt in hexanes as eluant) to obtain the pure product as an orange solid (96 mg, 27% yield)

1H NMR (300 MHz, CDCIs) d 8.97-8.91 (m, 1 H); 8.59 (s, 1 H); 8.25-8.20 (m, 1 H); 7.98- 7.93 (m, 1 H); 7.72-7.67 (td, J=7.5, 1 Hz, 1 H); 7.57-752 (m, 2H); 3.95 (s, 3H) e (358 nm, MeCN): 10.680 L.mol Tcm ¹

e (405 nm, MeCN): 4.900 L. mol ¹. cm ¹

When a 0.001 M solution of compound (Ih) in MeCN is placed in a 1 mm long UV cuvette, the longest wavelength at which compound (Ih) exhibits absorption (i.e. absorption is not 0) is of 582 nm. Example 8: Preparation of the compounds of formulae (linin^')

[125] General one pot synthetic procedure: To an oven dried 250-mL round bottom flask, containing argon and equipped with a stir bar and a septum, was added indole (1 g, 8.54 mmol, 1 equiv.) and f-BuOK (1.006 g, 8.96 mmol, 1.05 equiv.). The flask was cooled in ice-water bath and anhydrous THF (20 ml.) was added. The mixture was stirred for 30 minutes, and then, carbon disulfide (0.774 ml_, 12.80 mmol, 1.5 equiv.) was added dropwise via syringe. The stirring was continue in the ice-water bath for 90 minutes and the respective acyl chloride (8.96 mmol, 1.05 equiv.) was added dropwise. The reaction mixture was protected from light using aluminum foil and stirred for 15 min in the ice bath and 45 minutes more at room temperature. Deionized water (20 ml.) was added to the reaction, and the mixture was portioned between ethyl acetate and water in a separatory funnel. The mixture was washed with water (25 ml_, 3x), brine (1x), and dried over anhydrous Na₂S0₄. The oily products were purified by column chromatography (silica, ethyl acetate : petroleum ether : triethylamine 20:80:1 ), and solid products were purified by recrystallization from ethyl acetate/heptanes or ethyl ether/petroleum ether. lndole-1-carbothioic pivalic thioanhydride (li). Purification by column chromatography (Silica, AcOEhPetroleum Ethe EtsN 20:80:1 ), orange-red paraffin-like solid, 69% yield. ¹H-NMR (CDCI3) 1.32 (9H, s), 6.64 (1 H, d, J=3.84 Hz), 7.35 (1 H, q, J=7.54 Hz), 7.54 (1 H, d, J=1.72 Hz), 7.56 (1 H, d, J=0.92 Hz), 7.82 (1 H, d, J=3.88 Hz), 9.01 (1 H, d, J=8.04 Hz).

Indole-1 -carbothioic 2-phenylacetic thioanhydride (Ij). Purification by recrystallization from heptanes:ethyl acetate, orange solid, 65% yield. ¹H NMR (400 MHz, Chloroform- d) d 8.93 (d, J = 9.4 Hz, 1 H), 7.70 (d, J = 3.9 Hz, 1 H), 7.53 (d, J = 8.9 Hz, 1 H), 7.45 - 7.25 (m, 7H), 6.61 (d, J = 3.9 Hz, 1 H), 3.94 (s, 2H).

Indole-1 -carbothioic 2,4,6-trimethylbenzoic thioanhydride (Ik). Purification by recrystallization from heptanes: ethyl acetate , fine orange powder, 70 % yield.¹ H NMR (400 MHz, Chloroform-d) d 9.23 - 8.96 (m, 1 H), 8.00 (d, J = 3.9 Hz, 1 H), 7.67 - 7.49

(m, 1 H), 7.38 (pd, J = 7.3, 1.5 Hz, 2H), 6.95 - 6.84 (m, 2H), 6.70 (dd, J = 3.9, 0.7 Hz, 1 H), 2.42 (s, 6H), 2.31 (s, 3H).

2-acetoxy-2-methylpropanoic 1 H-indole-1-carbothioic thioanhydride (II). Purification by column chromatography (Silica, AcOEhPetroleum Ethe EtsN 25:75:1 ), dark orange- red oil, 56% yield. Ή NMR (400 MHz, Chloroform-d) d 9.03 (dd, J = 8.0, 1.5 Hz, 1 H), 7.83 (d, J = 3.9 Hz, 1 H), 7.54 (dd, J = 7.2, 1.8 Hz, 1 H), 7.35 (ddd, J = 6.3, 4.0, 1.7 Hz,

3H), 6.66 (dd, J = 4.0, 0.7 Hz, 1 H), 2.16 (s, 3H), 1.65 (s, 7H).

indole-1 -carbothioic 3-methoxy-2,2-dimethyl-3-oxopropanoic thioanhydride (Im). Purification by column chromatography [silica, ethyl acetate : petroleum ether : triethylamine 25:75:1] afforded a dark orange-red oil, 50% yield. ¹H NMR (400 MHz, Chloroform-d) d 9.02 (d, J = 7.7 Hz, 1 H), 7.86 (t, J = 3.3 Hz, 1 H), 7.57 (d, J = 7.2 Hz, 1 H), 7.39 (q, J = 7.4 Hz, 3H), 6.68 (t, J = 3.3 Hz, 1 H), 3.84 (t, J = 1.8 Hz, 3H), 1.69 - 1.51 (m, 6H).

2-cyano-2-methylpropanoic-indole-1 -carbothioic thioanhydride (In). Red dense oil, crude yield >70%. ¹H NMR (400 MHz, Chloroform-d) d 9.02 - 8.94 (m, 1 H), 7.80 (d, J = 3.9 Hz, 1 H), 7.61 - 7.53 (m, 1 H), 7.38 (tt, J = 7.4, 5.7 Hz, 2H), 6.69 (dd, J = 3.9, 0.8

Hz, 1 H), 1.69 (s, 7H).

Example 9: Preparation of 3-methyl-1 H-indazole-1 -carbothioic pivalic thioanhydride (lo).

[126] Step 1 : To a solution of ground potassium hydroxide

(1 ,517 g, 23 mmol, 1.0 equivalents) in tetrahydrofuran (50 ml.)

at room temperature was added 4-chloro-3,5-dimethylpyrazole

(3.04 g, 23 mmol). The mixture was stirred at room temperature

until all the hydroxide dissolved. The mixture was cooled to 5 °C,

and carbon disulfide (1.8 ml_, 2.276 g, 29.9 mmol, 1.3 equivalents) was added slowly. The reaction mixture was stirred at 5 °C for 3 min and then at room temperature for 90 min. The mixture was filtered and the orange solid washed with THF and diethyl ether, and dried under vacuum overnight to yield a yellow solid, 4.76 g, 84% yield.

[127] Step 2: In an oven dried round bottom flask cooled to 5 °C with an ice-water bath, pivaloyl chloride (0.15 ml_, 1.218 mmol, 1 equiv.) was dissolved in acetonitrile then the potassium 3-methyl-1 H-indazole-1 -carbodithioate (0.3 g, 1.218 mmol, 1 equiv.) was added portionwise. After stirring for an additional 2h (mixture turned orange), ethyl acetate was added and the mixture was partitioned between water and ethyl acetate (50 ml_), washed with water (2x), brine (1x), and dried over Na₂S0₄. Purification by column chromatography (Silica, ethyl acetate : cyclohexane : triethylamine 10:90:1 ) produced an orange oil (0.085 mg, 23% yield). ¹H NMR (400 MHz, Chloroform-d) d 9.04 (d, J = 8.5 Hz, 1 H), 7.64 (d, J = 7.8 Hz, 1 H), 7.57 (d, J = 8.6 Hz, 1 H), 7.42 (t, J = 7.5 Hz, 1 H), 2.53 (s, 3H), 1.34 (s, 9H).

[128] Compound (Iz) was prepared following a similar procedure as for compound (lo).

2-acetoxy-2-methylpropanoic 3-methyl-1 -indazolyl-1-carbothioic

thioanhydride (Iz). 39% yield. ¹H NMR (300 MHz, Chloroform-c/) d

9.03 (d, J = 8.5 Hz, 1 H), 7.71 - 7.56 (m, 2H), 7.44 (ddd, J = 8.0,

7.2, 0.9 Hz, 1 H), 2.55 (s, 3H), 2.13 (s, 3H), 1.72 (s, 6H).

Example 10: Preparation of the compounds (Ip)-(ls)

[129] General procedure: In an oven dried round bottom flask cooled to 0-5 °C with an ice-water bath, potassium 5-bromo-1-indolyl-1 -carbodithioate (0.927g, 2.99 mmol) was dispersed in ethyl acetate. Then, the corresponding acid chloride (1 eq, 2.99 mmol) was added dropwise. The mixture was stirred for 5 min in the ice bath, and additional 40-60 minutes at room temperature. The reaction mixture was partitioned between water and ethyl acetate, washed with 1 % HNaCC>3 (2x), water (3x), brine (1 x), and dried over Na₂S0₄. The solvent was removed by rotary evaporation, and the residue was recrystallized accordingly.

5-bromo-1-indole-1 -carbothioic 2,4,6-trimethylbenzoic thioanhydride (Ip). 71 % yield. ¹H NMR (400 MHz, Chloroform-d) d 8.95 (d, J = 9.0 Hz, 1 H), 8.00 (d, J = 3.9 Hz, 1 H), 7.70 (d, J = 2.0 Hz, 1 H), 7.47 (dd, J = 9.0, 2.1 Hz, 1 H), 6.88 (s, 2H), 6.63 (d, J = 3.9 Hz, 1 H), 2.40 (s, 6H), 2.31 (s, 3H).

2-acetoxy-2-methylpropanoic 5-bromo-1 -indole-1 -carbothioic thioanhydride (Iq). Red oil, 82% crude yield. ¹H NMR (300 MHz, Chloroform-d) d 8.89 (dt, J = 8.9, 0.6 Hz, 1 H), 7.84 (d, J = 3.9 Hz, 1 H), 7.67 (d, J = 2.0 Hz, 1 H), 7.44 (ddd, J = 9.0, 2.1 , 0.5 Hz, 1 H), 6.59 (dd, J = 3.9, 0.7 Hz, 1 H), 2.16 (s, 3H), 1.64 (s, 6H).

5-bromo-1 -indole-1 -carbothioic 3-methoxy-2,2-dimethyl-3-oxopropanoic thioanhydride (lr). A dense red oil, 85% crude yield. ¹H NMR (300 MHz, Chloroform-c/) d 8.86 (dt, J = 9.0, 0.6 Hz, 1 H), 7.84 (d, J = 3.9 Hz, 1 H), 7.68 (d, J = 2.0 Hz, 1 H), 7.45 (dd, J = 8.9, 2.1 Hz, 1 H), 6.59 (dd, J = 3.9, 0.7 Hz, 1 H), 3.81 (s, 3H), 1 .55 (s, 6H). 5-bromo-1 -indole-1 -carbothioic 2-cyano-2-methylpropanoic thioanhydride (Is). 83% yield. 1 H NMR (400 MHz, Chloroform-d) d 8.82 (d, J = 9.0 Hz, 1 H), 7.80 (d, J = 3.9 Hz, 1 H), 7.67 (d, J = 2.0 Hz, 1 H), 7.45 (dd, J = 8.9, 2.0 Hz, 1 H), 6.61 (d, J = 3.9 Hz, 1 H), 1.69 (s, 6H).

Example 1 1 : Preparation of compounds (It)-(ly) and (laa)

[130] General procedure: In an oven-dried round-bottom flask, equipped with a stir bar and with argon atmosphere, potassium carbazole-9-carbodithioate (0.637 g, 2.263 mmol) was dispersed in ethyl acetate (10 ml_). The flask was cooled to 0°C with an ice- water bath, and acid chloride (1 eq, 2.263 mmol) was added dropwise. The mixture was stirred for 20 min in the ice bath, and additional 40 minutes at room temperature. The reaction mixture was partitioned between water and ethyl acetate and 2% aqueous HNaC03 (1x), washed with water (2x), brine (1x), and dried over Na2S04. The solvent was removed by rotary evaporation.

9-carbazolyl-9-carbothioic pivalic thioanhydride (It). 75% yield. ¹H NMR (300 MHz, Chloroform-c/) d 8.65 - 8.23 (m, 2H), 8.15 - 7.75 (m, 2H), 7.41 (ddd, J = 6.4, 4.2, 1 .7 Hz, 4H), 1.13 (s, 9H).

9-carbazolyl-9-carbothioic 2-phenylacetic thioanhydride (lu). 73% yield. 1 H NMR (500 MHz, Chloroform-d) d 8.32 (d, J = 8.1 Hz, 2H), 7.95 (dd, J = 7.6, 1.4 Hz, 2H), 7.42 - 7.28 (m, 7H), 7.20 - 7.09 (m, 2H), 3.70 (s, 2H).

9-carbazolyl-9-carbothioic 2,4,6-trimethylbenzoic thioanhydride (Iv). 71 % yield. ¹H NMR (300 MHz, Chloroform-d) d 8.55 - 8.39 (m, 2H), 8.05 - 7.89 (m, 2H), 7.42 (tt, J = 7.3, 5.7 Hz, 4H), 6.70 (s, 2H), 2.18 (s, 3H), 2.16 (s, 6H).

2-acetoxy-2-methylpropanoic 9-carbazolyl-9-carbothioic thioanhydride (Iw). 82% yield. ¹H NMR (300 MHz, Chloroform-d) d 8.52 - 8.33 (m, 2H), 8.03 - 7.89 (m, 2H), 7.48 - 7.35 (m, 4H), 2.12 (d, J = 0.6 Hz, 3H), 1.50 (d, J = 0.7 Hz, 6H).

9-carbazolyl-9-carbothioic 3-methoxy-2,2-dimethyl-3-oxopropanoic thioanhydride (lx). 68% yield. ¹H NMR (300 MHz, Chloroform-d) d 8.43 (d, J = 8.7 Hz, 2H), 8.04 - 7.88 (m, 2H), 7.48 - 7.33 (m, 4H), 3.67 (d, J = 0.8 Hz, 3H), 1.40 (d, J = 0.9 Hz, 6H).

9-carbazolyl-9-carbothioic 2-cyano-2-methylpropanoic thioanhydride (ly). 74% yield. NMR showed the expected product and a bit of carbazole. ¹H NMR (300 MHz, Chloroform-d) d 8.52 - 8.37 (m, 2H), 8.06 - 7.91 (m, 2H), 7.56 - 7.35 (m, 4H), 1.46 (s, 6H).

9-carbazolyl-9-carbothioic benzoic thioanhydride (laa). 86% yield. ¹H NMR (400 MHz, Chloroform -d) d 8.56 - 8.45 (m, 2H), 8.01 - 7.91 (m, 2H), 7.79 - 7.71 (m, 2H), 7.61 - 7.52 (m, 1 H), 7.45 - 7.33 (m, 6H). ¹³C NMR (101 MHz, CDCIs) d 189.19, 185.1 1 , 140.70, 135.07, 134.62, 129.16, 127.90, 127.26, 126.60, 124.86, 120.17, 1 15.25.

Example 12: Polymerization of methylmetacrylate using compound (If) under visible light irradiation

[131] Kinetic measurements: A solution of 0.01 M of compound (If) in acetonitrile was prepared. The resulting solution was diluted with methylmethacrylate such that the concentration of (If) is 0.001 M. A sample of the resulting solution was placed in a UV- Vis cuvette and sample was irradiated at 405 nm wavelength and 40 mW.cnr² of irradiation power. UV-Vis spectra were recorded at regular intervals of time (every 30 seconds). The conversion of the photoinitiator, expressed as a percentage, was calculated for each time according to the following formula where A is the measured absorbance at a given time at the 358 nm wavelength and Ao is the initial absorbance at the 358 nm wavelength:

Conversion = 100 x (Ao-A)/Ao

Figure 1 shows the evolution of conversion over time of the photoinitiator, indicating that the compound of formula (If) undergoes photolysis upon irradiation with light.

Example 13: Bulk polymerization of methylmethacrylate under light irradiation

[132] A sample of each of the compounds of formulae (Ib)-(lh) were each diluted in methylmethacrylate under a molar ratio of 1 :4000. Aliquots of the resulting solutions were placed in 1 ml. cylindrical vials and irradiated with a 5W power blue LED strip inside a crystallizing dish at a temperature of 40 °C. Table 1 below indicates the time at which the solution was fully cured (formation of a solid mass - inversion of the vial did not result in inversion of the mixture).

[133] Table 1.

photoinitiators for the bulk polymerization of methylmethacrylate carried out under blue LED irradiation.

Example 14: Bulk polymerizations

[134] General procedure A: Polymerization inhibitor was removed by filtering each monomer through a pad of basic alumina, then all the monomers and solvents were degassed by pump-freeze thaw. The polymerization components were mixed in a glove box, minimizing the exposition to ambient light. Transparent glass vials (2-mL) were used for the irradiation experiments and 2-mL amber vials for RAFT polymerization using thermal initiators (e.g. AIBN). Initiator was weighted directly inside the HPLC vial using a microbalance, then the vial was transferred to a glove box, where 0.2 mL of monomer was added producing a thickness of around 4 mm (see general experimental section). The HPLC vial was equipped with a cap (with septum) and placed inside a photo-reactor such that the vial is protected from external light sources. All the photo- reactors have the same circular irradiation aperture (9.6 mm diameter). Blue LEDs (460 nm wavelength) were located around 1-cm distance from the reaction vial and equipped with a heatsink. The reaction mixture was irradiated with a light intensity of 0.4 W per cm², calibrated with a photodiode BPW-21 (OSRAM Opto semi-conductors).

The reaction was stopped by turning off the LED. Samples for GPC and NMR were taken by either cutting the jelly or solid polymer or by dissolving the entire polymer in the vials using DCCI₃ or THF. Conversion was determined by ¹H NMR spectroscopy while molecular weight and polydispersity index were determined by Gel Permeation Chromatography.

Gel permeation chromatography (GPQ

[135] The polymer molecular weights were determined by gel permeation chromatography (GPC) using an Agilent 1200 series HPLC equipped with an Agilent G1362A 1260 Infinity II Series Refractive Index detector (RID). Samples were eluted with tetrahydrofuran at a flow rate of 1 ml/min at 30°C through a PSS SDV Linear M 5- micron Column. Column calibration was carried out using polystyrene polymer standards of narrow mass distribution. Data analyses were carried out using Agilent GPC Data Analysis Software.

Several bulk polymerization experiments were carried out following General Procedure A with different compounds of formula (I), monomers and different reaction times. Results shown in Table 2 (molecular weight M_n, polydispersity index and conversion) were obtained using a ratio of compound of formula (I) to monomer of 1 :500. Entries 8-9, 17-18 and 35-36, are comparative examples carried out with initiators known in the art.

Table 2

1 : AIBN = azoisobutyronitrile, light irradiation was replaced by thermal i at 80 °C; 2: BAPO = phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

Example 15: Living controlled polymerization of methyl acrylate (RAFT)

1 ) Thermal initiation

[136] General Procedure B: The compound of formula (I) (0.01 eq) was weighted directly in an amber HPLC vial using a microbalance, then the vial was transferred to a glove box. Methyl acrylate (1 eq) was added using a syringe. An azoisobutyronitrile AIBN stock solution (2 mg/mL in dry acetonitrle) was prepared for the initiator addition (0.002 eq); then, dry acetonitrile was added to complete the volume to produce a 3M monomer concentration reaction. The brown HPLC vial was equipped with a cap (with septum) and placed inside of a aluminum-block holder pre-heated to 80 °C. Aliquots (5 mί) were taken for GPC and NMR analysis after several reaction times to determine the conversion, molecular weight of the polymer (M_n) and polydispersity (PDI).

[137] Table 3 below shows the results obtained at different times of reaction and using different compounds of formula (I).

Table 3

The results of Table 3, together with the comparative examples of entries 21-22 show that the compounds of formula (I) are useful as RAFT agents. This is further confirmed by Figures 2 and 3 showing a linear correlation between molecular weight and conversion and a homogeneous polydispersity during the progress of the polymerization. The results of figures 2 and 3 were obtained by analyzing aliquots of reaction of polymerization of methyl acrylate using General Procedure B and three different RAFT agents of formula (I) ((ly), (It) and (If)) by ¹H NMR and GPC at different times of reaction to determine conversion, molecular weight and polydispersity of the samples.

2) Photochemical initiation using the compound of formula (li)

[138] The compound of formula (li) (0.01 eq) was weighted directly in a transparent HPLC vial using a microbalance, then the vial was transferred to a glove box. Methyl acrylate (1 eq) was added using a syringe. Dry acetonitrile was added to produce a 3- Molar monomer concentration reaction . The HPLC vial was equipped with a cap (with septum) and placed inside the photo-reactor described in Example 14. Reaction mixture was irradiated with a blue LED (460 nm wavelength) and different intensities of light (measured as described in Example 14). The reaction was stopped by turning off the LED. Aliquots (5 mί) were taken for GPC and NMR analysis in order to determine the conversion, the molecular weight of the polymer and the polydispersity index.

[139] Figures 4, 5 and 6 represent the results obtained in such experimentsusing a light intensity of 200 mW per cm² or 400 mW per cm². Figure 4 shows that the polymerization does not take place until an induction period has lapsed and that said induction period depends on the intensity of light irradiated. This is advantageous as it provides resin formulation stable to irradiation of low intensities. Figures 5 and 6 show that the compound of formula (li) is useful as photo-RAFT agent, as a linear correlation between molecular weight and conversion and a homogeneous polydispersity during the progress of the polymerization are observed.

Example 16: Bulk polymerization of methyl acrylate

[140] Methyl acrylate was polymerized following General Procedure A (as described in Example 14), using a ratio of photoinitiator to methyl acrylate of 1 :100 and using as photoinitiator one of the following compounds:

Table 4 shows the properties of the formed polymer after one hour of reaction, as measured by GPC and ¹H NMR spectroscopy.

Table 4

ntry 1 represents a comparative example with a photoiniferter as described in the state of the art.

Example 16 shows that the photoinitiators of the invention provide polymers with a higher molecular weight than similar iniferters described in the art.

Example 17: Kinetic measurements of bulk polymerization of methyl acrylate

[141] General Procedure D: The initiator was weighted in a HPLC vial using a microbalance, then the vial was transferred to a glove box, where 0.1 ml. of methyl acrylate was added. The molar ratio of initiator to monomer is 1 :200. The reaction mixture was transferred to a 1-mm width quartz cell, and the cell was equipped with a cap, and covered with aluminum foil until it was placed in a cell holder designed to allow a 45° cell rotation so as to permit both irradiation with light and measurement by Near Infra-Red spectroscopy. The mixture was irradiated as soon as possible with a blue LED (460 nm) equipped with a focusing lens and a heatsink, and located at 3 cm distance from the reaction vial, with an irradiance of 400 mW per cm². Once the irradiation period was done, the entire reaction crude was dissolved in the quartz cell using DCCI3, and then samples were taken to be analyzed by GPC and NMR. The deuterated chloroform solvent was removed in vacuum for the GPC samples. 1 ) Several experiments were carried out with the following compounds used as initiators:

Table 5 shows the properties of the formed polymer at different degrees of conversion of the monomer as measured by IR spectroscopy (the consumption of the monomer is quantified by integration at a given time of the reaction of the absorption band corresponding to the carbon-carbon double bond of the monomer).

Table 5

[142] Entries 1-4 of Table 5 are comparative examples carried out with initiators described in the art. Table 5 shows that the compounds of the invention, when used as photoinitiators, produce a polymer with higher molecular weight than when the initiators known in the art are used. It is believed that the combination of an aromatic dithiocarbamate moiety combined with the presence of an acyl radical in a compound of formula (I) favours a mechanism of termination of the free radical polymerization by re-combination of two growing chains while still keeping a low PDI value.

[143] Figures 7 and 8 show the evolution of the conversion (%) over time (in minutes) with different initiating systems and compared with the comparative initiators known in the art.

[144] Figure 9 shows the pseudo first order plot (evolution of ln([M]o/[M]) as a function of time (in seconds)) in experiments where light irradiation is stopped several times, with respective intervals of 20, 25 and 20 minutes. Mo is the initial concentration of monomer and M is the concentration of monomer at a given time. This figure shows that polymerization takes place only when the reaction system is irradiated with light.

2) Following General Procedure D and using compound (Iv) as an initiator, polymerization of methyl acrylate was carried out during one hour with different molar ratios of initiator to monomer. Table 6 below summarizes the obtained results for kinetics of polymerization (observed inhibition period and time of growth of polymer up to 2 and 90% conversion) and properties of formed polymer.

Table 6

The results of Table 6 show that the molar ratio of the compound of formula (I) or of formula (la) or of formula (la’) affects the duration of the induction period: the higher the amount of initiator with respect to the monomer the higher the induction time. The results of Table 6 also show that the molar ratio of the compound of formula (I) or of formula (la) or of formula (la’) affects the rate of growth of the polymer chain: the higher the amount of initiator with respect to the monomer the higher the rate of growth of the polymer chain.

CITATION LIST

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4. Rizzardo E., Moad G., Thang S.H. (2008) RAFT Polymerization in Bulk Monomer or in (Organic) Solution in Handbook of RAFT polymerization (ed Christopher Barner- Kowollik) John Wiley & Sons, Inc., ISBN: 978-3-527-31924-4

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10. Patent AU2009900271

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Claims

1. A compound of formula (I)

wherein:

I is 0 when Xi is N and I is 1 when Xi is C;

m is 0 when X₂ is N and m is 1 when X₂ is C;

n is 0 when X₃ is N and n is 1 when X₃ is C;

p is 0 when X₄ is N and p is 1 when X₄ is C;

q is 0 or 1 ;

each of Ri, R₂, R₃ and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C6)alkyl, (Ci-C6)alkyloxy, (Ci-C6)alkyloxycarbonyl, di(Cr C6)alkylamino, (Ci-C6)perfluoroalkyl, halo, nitro, cyano and a substituent of formula R7 wherein R₇ is a substituent deriving from an aromatic ring system comprising from one to two fused rings, the rings comprising 5 or 6 members independently selected, where chemically possible, from the group consisting of C, CH, O, S, N and NR₃, being R₃ hydrogen or (Ci-C6)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (C1- C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano; or, alternatively,

one, two or three of the pairs R1 and R₂, R₂ and R₃ and R₃ and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to three rings, the rings being independently saturated, unsaturated or aromatic, the rings being isolated or fused, the rings comprising from 3 to 7 members independently selected from the group consisting of C, CH, CH₂, O, S, N and NR₃, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Cr C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci- C₆)alkylamino and cyano;

and wherein,

when q is 0,

Z is a substituent selected from the group consisting of (Ci-Ce)alkyl, (Ci- C₆)perfluoroalkyl, (C2-C6)alkenyl, and a substituent of formula Rg wherein Rg is a substituent deriving from an aromatic ring system comprising from one to two fused rings, the rings comprising 5 or 6 members independently selected, where chemically possible, from the group consisting of C, CH, O, S, N and NRe, being Re hydrogen or (Ci-C₆)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci- C₆)alkyloxy, (Ci-C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano;

when q is 1 ,

and provided that the compound of formula (I) is other than the compounds of formulae (la) and (la’)

2. The compound according to claim 1 that dissociates into the free radicals of formula (II) and (III)

(II) (III)

when submitted to light irradiation; preferably when submitted to ultraviolet or visible light irradiation; more preferably when submitted to visible light irradiation.

3. The compound according to any one of claims 1 and 2 wherein at least one of Xi, X₂, X₃ and X₄ is a carbon atom; preferably wherein at least two of X₁, X₂, X₃ and X₄ are carbon atoms; more preferably wherein at least three of X₁, X₂, X₃ and X₄ are carbon atoms.

4. The compound according to any one of claims 1 to 3 wherein

each of R1, R2, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Cr C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Cr C₆)alkylamino and cyano;

or, alternatively,

one or two of the pairs R1 and R2, R2 and R3 and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to three aromatic rings, the rings being isolated or fused, the rings comprising from 5 to 6 members independently selected from the group consisting of C, CH, O, S, N and NRe, being Re hydrogen or (Ci-C₆)alkyl, the rings being further optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyl, (C1- C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

5. The compound according to any one of claims 1 to 4 wherein:

at least two of X₁ , X₂, X₃, and X₄ are carbon atoms; each of Ri, R₂, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, di(Cr C₆)alkylamino, (Ci-C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)alkylcarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Cr C₆)alkylamino and cyano;

or, alternatively,

one or two of the pairs R1 and R₂, and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to two aromatic rings, preferably one ring, the rings being isolated or fused, the rings comprising from 5 to 6 members independently selected from the group consisting of C, CH, and N the rings being further optionally substituted at no more than two available positions with a substituent selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxy, (C1- C₆)alkylcarbonyl, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (C1- C₆)perfluoroalkyl, halo, nitro, di(Ci-C₆)alkylamino and cyano.

6. The compound according to any one of claims 1 to 5 wherein:

at least three of X1, X₂, X₃, and X₄ are carbon atoms;

each of R1, R₂, R3 and R₄ is a substituent independently selected from the group consisting of hydrogen, (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, di(Ci-C₆)alkylamino, (C1- C₆)perfluoroalkyl, halo, nitro, cyano and a phenyl substituent optionally substituted at any available position with one or more substituents selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)perfluoroalkyl, halo, nitro, di(Cr C₆)alkylamino and cyano;

or, alternatively,

one or two, preferably one, of the pairs R1 and R₂, and R3 and R₄, together with the carbon atoms to which they are attached form a ring system comprising from one to two phenyl rings, preferably one ring, the rings being isolated or fused, the rings being further optionally substituted at no more than two available positions with a substituent selected from the group consisting of (Ci-C₆)alkyl, (Ci-C₆)alkyloxycarbonyl, (C1- C₆)perfluoroalkyl, halo, di(Ci-C₆)alkylamino and cyano.

7. The compound according to any one of claims 1 to 6 wherein

when q is 1 , Z is a substituent selected from the group consisting of cyano, (Ci-C₆)alkyloxycarbonyl, (Ci-C₆)alkylcarbonyloxy, (Ci-C₆)alkylaminocarbonyl being the (Ci-C₆)alkyl optionally substituted at its terminal carbon atom with one group selected from hydroxyl and carboxyl, amidine, pyridyl and phenyl optionally substituted at any position with one or more groups selected from the group consisting of (Ci-C₆)perfluoroalkyl, halo, and nitro; and,

when q is 0,

8. The compound according to any one of claims 1 to 7 wherein q, Z, R₅ and R₆ are such that the compound of formula (I) is selected from the group consisting of the compounds of formulae

9. The compound according to any one of claims 1 to 8 wherein Xi, X₂, X₃, X₄, R₁, R₂, R₃ and R₄ are as defined in claim 6 and q, Z, R₅ and R₆ are as defined in claim 8.

10. The compound according to claim 9 that is selected from the group consisting of the compounds of formulae (lb), (lc), (Id), (le), (If), (Ig), (Ih), (li),

(Ij), (Ik), (II), (Im), (In), (lo), (Ip), (Iq), (Ir), (Is), (It), (lu), (Iv), (Iw), (lx), (ly) and (Iz)

1 1 . The compound according any one of the claims 2 to 10 having a light absorption coefficient of at least 500 L. mol ¹. cm ¹; preferably of at least 1000 L. mol ¹. cm ¹ ; at a wavelength comprised in the visible region of the spectrum; and wherein the free radicals of formula (II) and (III) each have a light absorption coefficient of no more than 1000 L. mol ¹. cm ¹; preferably of no more than 500 L. mol ¹. cm ¹ at a wavelength comprised in the visible region of the spectrum.

12. A photopolymerizable composition comprising:

a) a compound of formula (I) or of formula (la) or of formula (la’) as defined in any one of the claims 1 to 1 1 and at least one or more of

13. Use of the compound of formula (I) or of formula (la) or of formula (la’) according to any one of the claims 1 to 1 1 as a photoinitiator, preferably in polymerization reactions.

14. Use of the compound of formula (I) or of formula (la) or of formula (la’) according to any one of the claims 1 to 1 1 as a RAFT agent; preferably under light irradiation; and more preferably under visible light irradiation.

15. A process for the preparation of a polymer comprising the step of contacting under light irradiation, preferably under visible light irradiation, a compound of formula (I) or of formula (la) or of formula (la’) as defined in any one of the claims 1 to 10 with at least one or more of a monomer comprising at least in its molecular formula a carbon-carbon double bond, and an oligomer comprising at least in its molecular formula a carbon- carbon double bond; or , alternatively the step of submitting the photopolymerizable composition of claim 1 1 to light irradiation, preferably to visible light irradiation.