EP3328846A1

EP3328846A1 - Novel compounds exhibiting photophysical properties upon formation of lewis acid-base adducts using non-chelating boranes, method for producing the same and devices including the same

Info

Publication number: EP3328846A1
Application number: EP16747729.8A
Authority: EP
Inventors: Max Martin HANSMANN; A. Stephen K. Hashmi; Carlos ROMERO-NIETO; Alicia LÓPEZ-ANDARIAS; Eva RETTENMEIER; Carolina EGLER-LUCAS
Original assignee: Universitaet Heidelberg
Current assignee: Universitaet Heidelberg
Priority date: 2015-07-29
Filing date: 2016-07-18
Publication date: 2018-06-06
Also published as: WO2017016653A1

Abstract

The present invention relates to novel compounds exhibiting photophysical properties upon formation of Lewis acid-base adducts using non-chelating boranes and methods for producing the same as well as devices that include such Lewis acid-base adducts of the following general formula (I).

Description

Novel compounds exhibiting photophysical properties upon formation of Lewis acid-base adducts using non-chelating boranes, method for producing the same and devices including the same

The present invention relates to novel compounds exhibiting photophysical properties upon formation of Lewis acid-base adducts using non-chelating boranes and methods for producing the same. In addition, the present invention relates to devices that include such Lewis acid-base adducts. In particular, the novel compounds according to the present invention are fluorescent materials, both in solution and solid-state, and may also have piezochromism.

Organic luminescent solids are attracting increasing interest in various fields of application. Modification or alteration of the chemical structures of their component molecules is the most common approach for tuning their luminescence properties. Solid-state luminescent materials are of utmost importance because of their application e.g. in light-emitting diodes (LEDs),^[1) lasers^[2] and luminescent sensors^ as well as organic light-emitting diodes (OLEDs). Thus, materials research has focused over the last decades on establishing the key factors that lead to the best emission performances. As a result, it is well established that:

a) ideally in luminescent materials, intermolecular interactions must restrict non- radiative relaxation processes; namely intramolecular rotations.¹⁴¹ The energy levels can then rearrange, generating extremely efficient photo-induced emission;

b) the presence of halogens, some transition metals and carbonyl groups must be avoided. Their η-π* transitions typically promote efficient intersystem crossings and thus deactivate fluorescent decays.^[5]

The latter deductions have certainly limited the diversity of efficient solid-state emitting materials. Most of molecular dyes exhibit reduced or quenched luminescence when increasing the molecular density from diluted solutions to the solid state. This is namely attributed to intermolecular interactions or intersystem crossings that dissipate the absorbed energy.¹⁶¹ Recently, boranes have been investigated so as to provide a possible approach for overcoming the aforementioned drawbacks. A myriad of chelating four-coordinated organoboron compounds have been reported. ^[7] For instance, the preparation of organoboranes from β-diketonates with extraordinary solid-state photophysical properties, i.e. morphology and stimuli dependent fluorescence, have been described.¹⁸¹

However, examples of non-chelating boranes are rather scarce. The coordination properties of tris(pentafluorophenyl)borane (B(C6Fs)3) to several carbonyl group- containing compounds including their solid-state structures have been reported by Piers et al. years ago.^[9] Apart therefrom, the utilization of such Lewis acids was restricted to frustrated Lewis pair chemistry!¹⁰' or catalysis-related applications. US 2011/0028656 A1 generally discloses a method for altering the electronic and/or optical properties of a chemical compound having a bandgap and a framework that comprises π-delocalized electrons by complexing a Lewis acid to a basic site within the framework to form a Lewis acid-base adduct. In particular, US 2011/0028656 A1 describes that the absorption properties of benzothiadiazole-containing compounds can be modified by coordination of Lewis acids, such as B(C6Fs)3, to the nitrogen atoms of the benzothiadiazole moieties. Based on the well know tendency of boranes to bind harder nitrogen bases over softer bases such as sulfur counterparts, it is described in US 2011 /0028656 A1 that B-N adducts are formed. The formation of B-N adducts leads to a reduction of the optical bandgap, and thus to absorption features in the near infrared.^

However, preparing chelating organoboron compounds as well as the synthesis of the structures based on benzothiadiazole-containing compounds described in US 201 /0028656 A1 require multi-step and tedious methods.

Therefore, the object underlying the present invention is to provide novel compounds having fluorescence, particularly solid-state fluorescence, which can be straightforwardly prepared and which allow a gradual variation of the optical bandgap.

The solution to the above technical problem is achieved by the embodiments characterized in the claims.

In particular, the present invention provides a compound of the following general formula (1 ) in which the oxygen atom of the carbonyl group of the carbonyl compound is coordinated to a non-chelating borane in terms of a Lewis acid-base adduct

wherein each X, which may be the same or different from another, represents a halogen atom, a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched C1-C15 alkoxy group, a halogenated linear or branched C1-C15 alkoxy group, a C3-C15 cycloalkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated C3-C15 cycloalkyl group, a C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N including ferrocene, or a halogenated C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N;

said ring moiety A represents a cyclic aromatic ring or an aromatic heterocyclic ring, preferably phenyl, naphthyl, thienyl, benzothienyl, more preferably phenyl and benzothienyl, each R¹, which may be the same or different from another, represents a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from 0, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom; and

n represents an integer of 1 to 5.

Preferably, the present invention provides a compound of the following general formula (1 ) in which the oxygen atom of the carbonyl group of the carbonyl compound is coordinated to a non-chelating borane in terms of a Lewis acid-base adduct

wherein each X, which may be the same or different from another, represents a halogen atom, a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched C1-C15 alkoxy group, a halogenated linear or branched C1-C15 alkoxy group, a C3-C15 cycloalkyi group which may contain one or more heteroatoms selected from O, S and N, a halogenated C3-C15 cycloalkyi group, a C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N including ferrocene, or a halogenated C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N;

R represents a hydrogen atom, a linear or branched C1-C15 alkyl group, a C3-C15 cycloalkyl group, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more halogen atoms;

each R¹, which may be the same or different from another, represents a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom; and

n represents an integer of 1 to 5.

In another preferred embodiment, there are provided compounds of the following general formula (3) in which the oxygen atom of the carbonyl group of the carbonyl compound is coordinated to a non-chelating borane in terms of a Lewis acid-base adduct

wherein each X, which may be the same or different from another, represents a halogen atom, a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from 0, S and N, a linear or branched C1-C15 alkoxy group, a halogenated linear or branched C1-C15 alkoxy group, a C3-C15 cycloalkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated C3-C15 cycloalkyl group, a C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N including ferrocene, or a halogenated C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N;

each R¹, which may be the same or different from another, represents a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched unsaturated G2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom; and

n represents an integer of 1 to 5.

According to the present invention, the compounds of the general formula (1 ) (hereinafter simply referred to as "compound(s) 1 ") and also the compounds of the general formula (3) (hereinafter simply referred to as "compound(s) 3") surprisingly exhibit photoluminescence in the solid state and from concentrated solutions (hereinafter also referred to as "luminescence"), even though the uncoordinated carbonyl compound, i.e. the carbonyl compound not coordinated to the Lewis acid BX3, is non-emissive. Thus, according to the present invention, it is possible to provide a straightforward approach to efficiently turn on luminescence of non-emissive carbonyl materials by simple coordination of Lewis acids. Further, variation into the electronic properties of the aldehyde and ketone moieties, respectively, allow modulating the emission colors.

Compound 1 can be efficiently prepared in a straightforward manner simply by reacting the following carbonyl compound (1a) with a non-chelating borane BX3 to form a Lewis acid-base adduct of compound 1. Accordingly, the present invention further relates to a method for producing the compound 1 , comprising reacting the following carbonyl compound (1a) with a non-chelating borane BX3 to form a Lewis acid-base adduct having the general formula (1 )

The variants X, R, R¹ and n are defined as above.

A similar method applies to the compounds according to the above general formula 3.

The luminescence of the compounds 1 (as well as 3) according to the present invention is based on the intermolecular interactions from the Lewis acid as will be discussed in more detail below. As mentioned above, molecular dyes commonly exhibit reduced or quenched luminescence when increasing the molecular density from diluted solutions to the solid state, which can be attributed to intermolecular interactions or intersystem crossings that dissipate the absorbed energy.

According to the present invention, it has been found that the compounds of general formula (1 ) and (3) not only show luminescence in concentration solution, but also in solid state. Thus, according to a preferred embodiment, the compounds of general formula (1 ) and (3) exhibit solid-state luminescence based on intermolecular interactions between the non-emissive carbonyl compound and the Lewis acid BX3. According to the present invention, the emission maxima of the compounds 1 are bathochromically shifted in the solid state with respect to concentrated solutions. This reveals that additional intermolecular interactions are involved.

The present invention further provides an electronic or optoelectronic device containing compound 1 and/or (3) according to the present invention. In particular, the electronic or optoelectronic device according to the present invention includes LEDs, lasers and luminescent sensors as well as OLEDs, LCDs, optical waveguides, switch devices, field effect transistors, electrochromic devices, electrochemical supercapacitors, photovoltaic cells and applications such as bioimaging pressure sensors, inks, etc.

The present invention will be described in more detail herein-below with respect to the following embodiments along with the accompanying drawings, wherein

Fig. 1 a) illustrates frontier orbitals distribution of ortho derivatives 1 b-f and 2b-f; b) frontier orbitals distribution of para derivatives 1g-k and 2g-k;

Fig. 2 shows the optimized geometry (left) and electronic density distribution of frontier orbitals: LUMO (center) and HOMO (right) of compounds 2b-f; Fig. 3 shows the optimized geometry (left) and electronic density distribution of frontier orbitals: LUMO (center) and HOMO (right) of compounds 2g-k;

Fig. 4 shows absorption spectra of compounds 1 b-f (dashed lines) and compounds 2b- f (solid lines) in dilute dichloromethane solutions;

Fig. 5 shows absorption spectra of compounds 1 g-k (dashed lines) and compounds 2g-k (solid lines) in dilute dichloromethane solutions; Fig. 6a) shows the absorption spectrum of compound 2b from concentrated dichloromethane solution; b) excitation spectrum monitored at 475 nm (left), and emission spectrum excited at 400 nm (right) of compound 2b from concentrated dichloromethane solutions;

Fig. 7a) shows the absorption spectrum of compound 2c from concentrated dichloromethane solution; b) excitation spectrum monitored at 500 nm (left), and emission spectrum excited at 400 nm (right) of compound 2c from concentrated dichloromethane solutions;

Fig. 8a) shows the absorption spectrum of compound 2d from concentrated dichloromethane solution; b) excitation spectrum monitored at 540 nm (left), and emission spectrum excited at 425 nm (right) of compound 2d from concentrated dichloromethane solutions;

Fig. 9a) shows the absorption spectrum of compound 2e from concentrated dichloromethane solution; b) excitation spectrum monitored at 575 nm (left), and emission spectrum excited at 445 nm (right) of compound 2e from concentrated dichloromethane solutions;

Fig. 10a) shows the absorption spectrum of compound 2f from concentrated dichloromethane solution; b) excitation spectrum monitored at 625 nm (left), and emission spectrum excited at 475 nm (right) of compound 2f from concentrated dichloromethane solutions;

Fig. 11a) shows the absorption spectrum of compound 2g from concentrated dichloromethane solution; b) excitation spectrum monitored at 440 nm (left), and emission spectrum excited at 375 nm (right) of compound 2g from concentrated dichloromethane solutions;

Fig. 12a) shows the absorption spectrum of compound 2h from concentrated dichloromethane solution; b) excitation spectrum monitored at 450 nm (left), and emission spectrum excited at 475 nm (right) of compound 2h from concentrated dichloromethane solutions; Fig. 13a) shows the absorption spectrum of compound 2i from concentrated dichloromethane solution; b) excitation spectrum monitored at 475 nm (left), and emission spectrum excited at 400 nm (right) of compound 2i from concentrated dichloromethane solutions; Fig. 14a) shows the absorption spectrum of compound 2j from concentrated dichloromethane solution; b) excitation spectrum monitored at 525 nm (left), and emission spectrum excited at 425 nm (right) of compound 2j from concentrated dichloromethane solutions; Fig. 15a) shows the absorption spectrum of compound 2k from concentrated dichloromethane solution; b) excitation spectrum monitored at 590 nm (left), and emission spectrum excited at 450 nm (right) of compound 2k from concentrated dichloromethane solutions; Fig. 6 shows a representative absorption spectra of compound 2k from concentrated (solid line) and diluted (dashed line) solutions; inset: progressive fading of the emerging absorption band after addition of methanol;

Fig. 17 shows normalized emission spectra of compounds 2b-k from concentrated dichloromethane solutions;

Fig. 18a) shows solid-state emission spectra of compounds 2b-k - from left to right, 2b, 2g, 2c, 2h, 2d, 2i, 2e, 2j, 2f and 2k; b) CIE color coordinates from the solid-state emission of compounds 2b-k;

Fig. 19 shows the evolution of the aggregate absorption band after addition of one drop of methanol of compounds 2b to 2g; Fig. 20 shows the evolution of the aggregate absorption band after addition of one drop of methanol of compounds 2h to 2k; Fig. 21 shows the normalized excitation spectrum monitored at 490 nm, and emission spectrum excited at 390 nm of compound 2b from the solid state;

Fig. 22 shows the normalized excitation spectrum monitored at 510 nm, and emission spectrum excited at 440 nm of compound 2c from the solid state;

Fig. 23 shows the normalized excitation spectrum monitored at 520 nm, and emission spectrum excited at 430 nm of compound 2d from the solid state;

Fig. 24 shows the normalized excitation spectrum monitored at 550 nm, and emission spectrum excited at 460 nm of compound 2e from the solid state;

Fig. 25 shows the normalized excitation spectrum monitored at 600 nm, and emission spectrum excited at 490 nm of compound 2f from the solid state; Fig. 26 shows the normalized excitation spectrum monitored at 460 nm, and emission spectrum excited at 370 nm of compound 2g from the solid state;

Fig. 27 shows the normalized excitation spectrum monitored at 460 nm, and emission spectrum excited at 370 nm of compound 2h from the solid state;

Fig. 28 shows the normalized excitation spectrum monitored at 500 nm, and emission spectrum excited at 430 nm of compound 2i from the solid state;

Fig. 29 shows the normalized excitation spectrum monitored at 550 nm, and emission spectrum excited at 400 nm of compound 2j from the solid state;

Fig. 30 shows the normalized excitation spectrum monitored at 630 nm, and emission spectrum excited at 500 nm of compound 2k from the solid state;

Fig. 31a) shows solid-state colors of compounds 2b-f under ambiente light (up) and under UV irradiation, 366 nm (down); b) solid-state colors of compounds 2g-k under ambiente light (up) and under UV irradiation (down); and

Fig. 32 shows the changes into the solid-state photoluminescence of compound 2k and color change from orange to red (inset) upon increasing the pressure. The Lewis acid BX3 of compound 1 according to the present invention is not particularly limited as long as non-chelating borane adducts can be formed with the carbonyl compound 1a. Examples of suitable Lewis acids of the present invention include boron halides such as BF3, BCI3, BBr3 and BI3. Linear or branched C1 -C15 alkyl groups which may contain one or more heteroatoms selected from O, S and N, optionally halogenated can equally be used. For example, BEt3, ΒΟΜβ3, BOE.3 and any higher homologs which may be halogenated can be used as Lewis acid. Also the following compounds may be used as Lewis acid:

Similarly, boranes having perfluorinated alkyl groups such as B(CF3)3 can suitably be used. From the perspective of systematic modulation of the Lewis acidity of the boron compounds, it is preferred to use triarylboranes. However, as mentioned above, according to the present invention, the substituents of the boron atom may also be different from another. Examples of triarylboranes include, but are not limited to the following compounds:

According to a preferred embodiment of the present invention, at least one of the ligands X of the borane compound represents a C6-C20 aryl group containing at least one fluorine atom. Examples of such preferred Lewis acids include, but are not limited to the following compounds:

Among those, tris(pentafiuorophenyl)borane, tris(2,3,5,6-tetrafluorophenyl)borane, tris(2,3,4,5-tetrafluorophenyl)borane, tris(3,4,5-trifluorophenyl)borane, tris(2,3,4-tri- fluorophenyl)borane, phenylbis(pentafluorophenyl)borane are preferred, and tris(pentafluorophenyl)borane (B(C6F5)3) is particularly preferred.

The above boranes are either commercially available or their synthesis is described in literature and represent well known protocols to the person skilled in the art.

According to the present invention, the compounds of formula (1 ) represent either Lewis acid-base adducts of substituted benzaldehydes according to which R in formula (1 ) represents a hydrogen atom, or Lewis acid-base adducts of respective ketone compounds in which R in formula (1 ) is not hydrogen. Non-limiting examples of ketone derivatives of compound 1 include those in which R is -Ch (Me), -CH2CH3 (Et), -CH2CH2CH3 (Pr), -CH(CH3)2 (iPr), and higher homologs thereof. R in formula (1 ) may also represent a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds. Said aikenyl group may be further substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms. Apart therefrom, R in formula (1 ) may be a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more halogen atoms.

Preferably, in case R≠ H, R in formula (1 ) represents Me, Et, a linear or branched unsaturated C2-C10 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds, a substituted or unsubstituted C6-C18 aryl group optionally containing one or more halogen atoms, such as a phenyl group, an alkyl or alkoxy substituted phenylene group, a biphenyl group, a terphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a tolane moiety (diphenylecatylene) which may be substituted with an alkyl or alkoxy group, or a stilbene moiety (1 ,2-diphenylethene including the trans and cis isomer) which may be substituted with an alkyl or alkoxy group.

Preferably, compound 1 according to the present invention is a Lewis acid-base adduct of a substituted benzaldehyde, i.e. the substituent R of formula (1 ) represents a hydrogen atom. According to the present invention, it has been found that substituted benzaldehyde-borane adducts exhibit strong photoluminescence. Depending on the nature of the Lewis acid and the corresponding substituted benzaldehyde, it is possible to adjust the emission maxima range over the entire visible spectrum. The emission maxima are determined by the nature of the peripheral groups; increasing the electron donating capacity leads to a red shift of the borane adducts' emission features.

According to a further preferred embodiment of the present invention, the substituent R¹ of the compound 1 of the present invention represents a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom.

Further preferred residues for R¹ in formula ( ) are selected from the following residues a to f :

a b e d e f wherein each R', which may be the same or different from another, represents a linear or branched C1-C10 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C10 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched Ci- C10 alkoxy group, or a C6-C20 aryl group.

The number of substituents R¹ and R' of the compound 1 is not particularly limited and may be 1 , 2, 3, 4, or 5. Suitably, the phenyl moiety of compound 1 contains 1 , 2, 3 of 4 substituents R¹, preferably 1 to 3, and most preferably 1 or 2 substituents which may be the same or different from another.

A particularly preferred embodiment of the present invention is represented by the following general formula (2)

wherein Ar^F represents a C6 aryl group containing at least one fluorine atom, such as tris(pentafluorophenyl)borane, tris(2,3,5,6-tetrafluorophenyl)borane, tris(2,3,4,5-tetra- fluorophenyl)borane, tris(3,4,5-trifluorophenyl)borane, tris(2,3,4-trifluorophenyl)borane, or phenylbis(pentafluorophenyl)borane; and

R² represents a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C2-C15 hydrocarbon group or at least one halogen atom, forming a conjugated system with the benzaldehyde moiety. In a particularly preferred embodiment, R² is selected from the above residues a to f.

If the substituent R² forms a conjugated system with the benzaldehyde moiety, strong luminescence over a broad spectrum can be obtained. According to the present invention, due to the intermolecular interactions upon coordination of the Lewis acid BX3 to the aldehyde and ketone moieties, respectively, compounds having strong solid-state luminescence can be obtained, even though the educts, i.e. the Lewis acid and base, are non-luminescent. The coordination of the boron atom of the Lewis acid lowers the HOMO and LUMO levels and, accordingly, results to a reduction of the optical bandgap. In turn, the electronic densities rearrange so that the LUMO contains the carbonyl moiety and the HOMO is located on the borane group.

Carbonyl-containing compounds are commonly known to exhibit fluorescence quantum yields (QYs) rather low (Φ < 0.05); η-ττ^* transitions funnel photo-excited electrons into the ττ-ττ* triplet state, preventing from efficient fluorescent decays. In the compounds 1 according to the present invention, however, it is assumed that the electronic rearrangement provoked by the O-B coordination suppresses the aforementioned photo-induced process, promoting improved luminescence. Preferably, the compounds 1 of the present invention exhibit solid-state fluorescence quantum yields of at least 0.10, more preferably of at least 0.15. Quantum yields Φ were measured with a calibrated Ulbricht sphere. Fluorescence quantum yields represent average values from at least two independent measurements.

To this extent, it should be noted that the spectroscopic features of compounds 1 according to the present invention represents a reversible phenomenon. For instance, the addition of methanol upon which the Lewis acid-base adduct is considered to be decomposed, results in a progressively fading away of the luminescent properties of compounds (1 ). Furthermore, the compounds (1 ) of the present application are present as discrete aggregates, as demonstrated by a lack of shifts in the absorption maxima upon addition of methanol.

Moreover, according to the present invention, it has been found that the coordination of a Lewis acid, such as B(C6Fs)3, to carbonyl groups do not prevent radiationless processes in individual molecules, and that discrete intermolecular interactions in the ground state are required to circumvent non-radiative deactivation processes and, therefore, enable photoluminescence to the solid state. It is important to note that, after aggregation, the energy distribution of the carbonyl-borane adducts rearranges leading to an emissive state of lower energy. A rationale infers the latter redistribution to be responsible for preventing the radiationless transitions.

According to a particularly preferred embodiment of the present invention, the compounds 1 exhibit solid-state piezochromism, which is even more surprising. That means, upon pressure variations of e.g. <1 bar the compounds according to the present invention show a visible color change. Thus, increasing the pressure on solid materials of the compounds of the present invention induces piezochromism, i.e. for instance a red shift of the emission maxima, which correlates with a color change from orange to red as shown in Fig. 31. Importantly, grinding of the sample lead to recovering the initial spectroscopic features.

Compound 1 can be efficiently prepared in a straightforward manner simply by reacting the carbonyl compound (1a) with a non-chelating borane BX3 to form a Lewis acid- base adduct of compound 1. Preferably, the reaction is carried out in solution using an aprotic polar or non-polar solvent. Non-limiting examples include pentane, hexane, cyclohexane, benzene, toluene, tetrahydrofuran, chloroform and preferably methylene chloride. Furthermore, the reaction can be carried out in an ordinary temperature range, e.g. from 0 °C to 60 °C, preferably at ambient temperature. Commonly, the Lewis acid-base adducts are quantitatively formed within 1 to 2 hours, preferably within 30 min. In particular, the addition of an equimolar amount of the Lewis acid to the aldehyde and ketone moieties is preferred.

Said aldehyde and ketone moieties of formula (1a) may be prepared by literature known syntheses, such as simple Sonogashira and Suzuki-Miyaura cross-coupling, respectively, from commercially available reactants. Due to the intriguing characteristics of the compounds 1 of the present invention, i.e. facile preparation and enhanced solid-state fluorescence and, remarkably, piezochromism, said compounds can be used in a wide range of applications including electronic and optoelectronic devices. The present invention will be described in more detail herein-below with respect to the following non-limiting examples. Examples

General procedures

With the exception of the synthesis of starting materials, all reactions and manipulations were carried out under an atmosphere of dry, O2-free nitrogen using standard double-manifold techniques with a rotary oil pump. An argon-filled glove box (MBRAUN) was used to manipulate solids including the storage of starting materials, room temperature reactions, product recovery and sample preparation for analysis. Molecular sieves (4 A) were dried at 120 °C for 24 h prior to use. All solvents (toluene, CH2CI2, THF, pentane, hexane) were dried by employing a solvent purification system MB SPS-800, degassed and stored over molecular sieves under a nitrogen atmosphere. Chemicals were purchased from commercial suppliers and used as received. B(C6Fs)3 was prepared based on a slightly modified synthesis reported in the literature.'¹³¹

Theoretical calculations

Computational studies were carried out using DFT calculations on Gaussian09^[14] using the B3LYP/6-31+ G^* level of theory. Steady-state spectroscopy

Absorption and emission spectra were recorded using a Jasco V660 and Jasco FP6500 spectrometer, respectively.

Fluorescence lifetimes

The fluorescence decays were recorded with a HORIBA Scientific Fluorocube single photon counting system operated with HORIBA Scientific DataStation version 2.2. Lifetimes were calculated by an exponential fit according to the least mean square with commercially available software HORIBA Scientific Decay Data Analyses 6 (DAS6) version 6.4.4. Fluorescence lifetimes from concentrated solutions were measured from samples with optical density below 0.1. Quantum yields Φ:

Quantum yields were measured with a calibrated Ulbricht sphere. Fluorescence quantum yield are average values from at least two independent measurements. Synthesis of starting materials

2-((Perfluorophenyl)ethynyl)benzaldehyde (1 b)

To a solution of 1 ,2,3,4,5-pentafluoro-6-iodobenzene (693 mg, 2.36 mmol, 1.0 equiv.), Pd(PPhs)4 (54.5 mg, 47.2 μιτιοΙ, 2 mol%) and Cul (18.0 mg, 94.4 mol, 4 mol%) in degassed NEt3 (30 mL), was added 2-ethynylbenzaldehyde (400 mg, 3.07 mol, 1.3 equiv.). After the reaction was stirred at 60 °C over night the solvent was removed under reduced pressure. The crude material was purified by flash column chromate- graphy (S1O2; petrolether : ethylacetate = 50:1 ) to afford the title compound 1b as colorless solid (573 mg, 1.93 mmol, 82%).

2-((4-(Trifluoromethyl)phenyl)ethynyl)benzaldehyde (1c)

To a solution of 4-iodo-(trifluoromethyl)-benzene (691 mg, 2.54 mmol, 1.0 equiv.), PdCl2(PPh3)2 (35.7 mg, 50.8 pmol, 2 mol%) and Cul (19.3 mg, 102 pmol, 4 mol%) in degassed NEt3 (25 mL), was added 2-ethynylbenzaldehyde (430 mg, 3.30 mmol, 1.3 equiv.). The reaction was stirred at room temperature over night and the solvent was removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 40:1 ) to afford the title compound 1c as colorless solid (582 mg, 2.12 mmol, 84%). 2-(Phenylethynyl)benzaldehyde (1d)

To a solution of 2-bromobenzaldehyde (6.68 g, 36.1 mmol, 1.0 equiv.), PdC (PPh3)2 (512 mg, 729 μιηοΙ, 4 mol%) and Cul (280 mg, 1.47 mmol, 2 mol%) in degassed NEt3 (70 ml_) was added phenylacetylene (4.41 g, 43.2 mmol, 1.3 equiv.). After the reaction was stirred at room temperature over night the solvent was removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 20:1 ) to afford the title compound 1d as slightly yellow oil (2.84 g, 13.8 mmol, 38%).

(E)-2-styrylbenzaldehyde (1 e)

To a solution of 2-bromobenzaldehyde (1.00 g, 5.40 mmol) in a degassed solvent mixture of dioxane/water (40 mL/10 ml_) was added Pd(PPh3)4 (187 mg, 0.16 mmol, 3 mol%), followed by CS2CO3 (3.52 g, 10.8 mmol, 2eq.) and irans-2-phenylvinylboronic acid (960 mg, 6.49 mmol, 1.2 eq.). The solution was heated under reflux for 26 h, cooled down and H2O (30 ml_) added. The layers were separated and the aqueous phase extracted with CH2CI2 (2x 50 ml_). The combined organic layers were dried over MgS04, filtered and concentrated under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 40:1 to 20:1 ) to afford the title compound 1e as slightly yellow oil (352 mg, 1.69 mmol, 31 %). 2-((4-Methoxyphenyl)ethynyl)benzaldehyde (1f)

To a solution of 4-iodo-anisole (2.76 g, 11.8 mmol, 1.0 equiv.), PdCl2(PPh)2 (166 mg, 236 Mmol, 2 mol%) and Cul (89.0 mg, 472 Mmol, 4 mol%) in degassed NEt3 (100 mL), was added 2-ethynylbenzaldehyde (2.00 g, 15.4 mmol, 1.3 equiv.). After the reaction was stirred at room temperature over night the solvent was removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 40:1 to 35:1 ) followed by recrystallization in ChbC /pen- tane to afford the title compound 1f as colorless solid (2.49 g, 0.5 mmol, 89%).

4-((Perfluorophenyl)ethynyl)benzaldehyde (1g)

To a solution of 1-iodo-4-(trifluoromethyl)benzene (267 pL, 2.00 mmol, 1.0 equiv.), PdCl2(PPh3)2 (42.0 mg, 0.06 mmol, 3 mol%) and Cul (7.6 mg, 0.04 mmol, 2 mol%) in degassed NEt3 (25 mL), was added 4-ethynylbenzaldehyde (260 mg, 2.00 mmol, 1.0 equiv.). The reaction was stirred at 60 °C over night. Water (25 mL) was added and the aqueous layer extracted with CH2CI2 (3 x 50 mL). The combined organic phases were dried over MgS04, filtered and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 25:1 to 20:1 ) to afford the title compound 1g as white foamy solid (320 mg, 1.08 mmol, 54%). 4-((4-(Trifluoromethyl)phenyl)ethynyl)benzaldehyde (1 h)

To a solution of 1-iodo-4-(trifluoromethyl)benzene (400 mg, 1.47 mmol, 1.0 equiv.), PdCl2(PPh3)2 (31.0 mg, 0.05 mmol, 3 mol%) and Cul (5.7 mg, 0.03 mmol, 2 mol%) in degassed NEt3 (25 mL), was added 4-ethynylbenzaldehyde (191 mg, 1.47 mmol, 1.0 equiv.). After the reaction was stirred at 60 °C over night the solvent was removed under reduced pressure. The crude material was purified by flash column chromate- graphy (S1O2; petrolether : ethylacetate = 25:1 to 20:1 ) and recrystallized from hot pentane to afford the title compound 1h as colorless solid (260 mg, 0.95 mmol, 64%).

4-(Phenylethynyl)benzaldehyde (1 i)

To a solution of 4-bromobenzaldehyde (250 mg, 1.35 mmol, 1.0 equiv.), PdCl2(PPh3)2 (19.0 mg, 27.0 prnol, 4 mol%) and Cul (10.3 mg, 54.0 Mmol, 2 mol%) in degassed NEt.3 (12 mL) was added phenylacetylene (180 mg, 1.76 mmol, 1.3 equiv.). The reaction was stirred at 60 °C over night and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 50:1 ), followed by recrystallization in ChteCte/pentane, to afford the title compound 1i as colorless solid (223 mg, 1.08 mmol, 80%).

(E)-4-styrylbenzaldehyde (1j)

To a solution of 4-bromobenzaldehyde (1 .00 g, 5.40 mmol) in a degassed solvent mixture of dioxane/water (40 mL/10 mL) was added Pd(PPh3)4 (187 mg, 0.16 mmol, 3 mol%), followed by CS2CO3 (3.52 g, 10.8 mmol, 2eq.) and frans-2-phenylvinylboronic acid (960 mg, 6.49 mmol, 1.2 eq.). The solution was heated under reflux for 26 h, cooled down and H2O (30 mL) added. The layers were separated and the aqueous phase extracted with CH2CI2 (2x 50 mL). The combined organic layers were dried over MgSO_4> filtered and concentrated under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 40:1 to 20:1 ) to afford the title compound 1j as colorless solid (400 mg, 1.92 mmol, 36%).

4-((4-Methoxyphenyl)ethynyl)benzaldehyde (1 k)

To a solution of 4-bromobenzaldehyde (250 mg, 1.35 mmol, 1.0 equiv.), PdCl2(PPh3)2 (19.0 mg, 27.0 pmol, 4 mol%) and Cul (10.3 mg, 54.0 Mmol, 2 mol%) in degassed NEt.3 (12 mL) was added 4- 1-ethynyl-4-methoxybenzene (233 mg, 1 .76 mmol, 1 .3 equiv.). The reaction was stirred at 60 °C over night and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 50:1 ) followed by recrystallization in Ch C /pentane to afford the title compound 1k as colorless solid (254 mg, 1.08 mmol, 80%).

Synthesis of products

General procedure A

To a solution of the corresponding benzaldehyde (0.30 mmol) dissolved in CH2CI2 (2.5 mL) was added B(C6Fs)3 (153.4 mg, 0.30 mmol). The solution was mixed for ca. 15 min and the solvent removed under reduced pressure. Pentane (0.5 mL) was added and removed under reduced pressure to afford the Lewis acid-base adducts quantitatively as solids. ((perfluorophenyl)ethynyl)benzaldehyde (2b)

According to general procedure A, 2-((perfluorophenyl)ethynyl)benzaldehyde (88.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeFs)3 (153,4 mg, 0.30 mmol) added. The Lewis adduct 2b was isolated quantitatively as white solid.

BCF-2-((4-(trifluoromethyl)phenyl)ethynyl)benzaldehyde (2c)

According to general procedure A, 2-((4-(trifluoromethyl)phenyl)ethynyl)benzaldehyde (82.3 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeFs)3 (153.4 mg, 0.30 mmol) added. The Lewis adduct 2c was isolated quantitatively as slightly yellow solid.

BCF-2-(phenylethynyl)benzaldehyde (2d)

According to general procedure A, 2-(phenylethynyl)benzaldehyde (61.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeF₅)3 (153.4 mg, 0.30 mmol) added. The Lewis adduct 2d was isolated quantitatively as green/yellow solid. BCF-(E)-2-styrylbenzaldehyde (2e)

According to general procedure A, (E)-2-styrylbenzaldehyde (62.5 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(C-6Fs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct 2e was isolated quantitatively as a yellow solid.

BCF-2-((4-methoxyphenyl)ethynyl)benzaldehyde (2f)

₀^ B(C₆F₅)₃

According to general procedure A, 2-((4-methoxyphenyl)ethynyl)benzaldehyde (70.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeF₅)3 (153.4 mg, 0.30 mmol) added. The Lewis adduct 2f was isolated quantitatively as an orange solid.

BCF-4-((perfluorophenyl)ethynyl)benzaldehyde (2g)

According to general procedure A, 4-((perfluorophenyl)ethynyl)benzaldehyde (88.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeFs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct 2g was isolated quantitatively as a white solid.

BCF-4-((4-(trifluoromethyl)phenyl)ethynyl)benzaldehyde (2h)

According to general procedure A, 4-((4-(trifluoromethyl)phenyl)ethynyl)benzaldehyde (82.3 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeF₅)3 (153.4 mg, 0.30 mmol) added. The Lewis adduct 2h was isolated quantitatively as a slightly yellow solid. BCF-4-(phenylethynyl)benzaldehyde (2i)

According to general procedure A, 4-(phenylethynyl)benzaldehyde (61.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeF₅)3 (153.4 mg, 0.30 mmol) added. The Lewis adduct 2i was isolated quantitatively as a yellow solid. BCF-(E)-4-styrylbenzaldehyde (2j)

According to general procedure A, (E)-4-styrylbenzaldehyde (62.5 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(CeF5)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct 2j was isolated quantitatively as a yellow solid.

BCF-4-((4-Methoxyphenyl)ethynyl)benzaldehyde (2k)

According to general procedure A, 4-((4-Methoxyphenyl)ethynyl)benzaldehyde (47.2 mg, 0.20 mmol) was dissolved in 1.5 mL CH2CI2 and B(CeFs)3 (102.0 mg, 0.20 mmol) added. The solvent was removed under reduced pressure and pentane (1 mL) added. The solvent was removed via syringe and the remaining solid dried under reduced pressure to give the Lewis adduct 2k as a bright orange solid (125.2 mg, 84 %).

DFT Calculations

HOMO and LUMO levels of compounds 1 b-k and 2b-k are shown in Fig. 1. The energy values from frontiers orbitals HOMO and LUMO of compounds 1 b-k and 2b-k are shown in Table 1. Table 1

DFT calculations (B3LYP/6-31G+(d) level of theory) show a gradual variation of the HOMO and LUMO frontier orbitals within the ortho and para series. Bonding of the boron atom of the Lewis acid leads in all cases to lower the HOMO and LUMO levels and, accordingly, to a reduction of the optical bandgap. In turn, the electronic densities rearrange so that the LUMO contains the carbonyl moiety and the HOMO is located on the borane group as shown in Figs. 2 and 3. To evaluate the photophysical properties of the borane adducts, steady-state spectroscopy has been carried out. The Absorption spectra from diluted solutions of compounds 2b-k in dichloromethane are shown in Figs. 4 and 5, while corresponding spectra of concentrated dichloromethane solutions as well as excitation spectra and emission spectra are shown in Figs. 6 to 15 for each of the compounds 2b-k.

Dichloromethane solutions of compounds 2a-k indicate a negligible effect of the O-B coordination into the spectroscopic features. Namely, the absorption spectra from diluted solutions exhibit identical absorption maxima in the UV range, between 260 and 341 nm (Figs 4 and 5). In turn, emission properties remain unaltered, i.e. Φ < 0.02. A different scenario emerged when increasing the concentration above 0^"5 M. Increasing the concentration of compounds 2b-k correlates with the formation of a new and less energetic absorption band as shown in Figs. 6 to 15 as well as Fig. 16. Again, these new emerging absorption bands are responsible for a prominent luminescent process; excitation spectra corroborate the latter as shown in Figs. 6 to 15. Thus, concentrated solutions exhibit maxima that range from 437 to 613 nm, as function of the different peripheral groups as illustrated in Fig. 17. The excitation and emission maxima thereof are given in Table 2.

Table 2

A rationale infers the formation of aggregates in the ground state, which lead to the newly formed spectroscopic features. To investigate the nature of the latter aggregation, the reversibility of the phenomena has been evaluated. The addition of methanol progressively fades away the additional absorption bands as shown in Fig. 16, inset and Figs. 19 and 20. The lack of shifts in the absorption maxima is consistent with the formation of discrete aggregates. Massive molecular aggregation generally leads to a gradual displacement of absorption peaks.

Furthermore, to get better insight into the involved species, solid-state spectroscopic properties have been investigated. As found in concentrated solutions, substituted benzaldehyde-borane adducts exhibit strong photoluminescence. Emission maxima range the entire visible spectrum, i.e. from 444 nm for compound 2b to 625 nm for compound 2k as shown in Fig.18a). Thus, the emission maxima are determined by the nature of the peripheral groups; increasing the electron donating capacity leads to a red shift of the borane adducts emission features. The color coordinates given in Fig. 18b) and Table 3 provide additional information on the observed fluorescent colors of the solids as shown in Figs. 31a) and b).

Table 3

Solid-state fluorescence quantum yields of the borane derivatives differ from 0.64 for compound 2d to 0.15 for compound 2k as given in Table 4, presumably due to the stronger donor-acceptor character of the later adduct. Nevertheless, it is important to remark that neither the free Lewis acid B(C6Fs)3 nor compounds 1 b-k exhibit any significant spectroscopic feature in the solid state.

Table 4

Overall, emission maxima are bathochromically shifted in the solid state with respect to concentrated solutions. This indicates that additional intermolecular interactions are at work. Fluorescence decays, nevertheless, remain biexponential when increasing the molecular density from concentrated solutions to the solid state as given in Table 4. It should be noted that fluorescence decays in the solid state are generally multi- exponential due to the diversity of deactivation pathways.

To further investigate the intermolecular interactions, X-ray spectroscopy has been carried out on compounds 2b-d, 2h and 2i. Analyses of the three-dimensional arrangements reveal a strong predilection of the B(C6Fs)3 moieties to interact with one another. Short contacts between borane groups are found in all cases. The shortest distances arise from F-F interactions and range from 2.83 to 2.94 A. Thus, the negatively charged boron center, surrounded by highly polarized C6F5 groups, drives the intermolecular interactions. This leads, for example in compound 2i, to dimeric structures. This observation, together with our spectroscopic investigations, point to: a) the coordination of B(C6Fs)3 to carbonyl groups do not prevent radiationless processes in individual molecules; b) discrete intermolecular interactions in the ground state are required to circumvent non-radiative deactivation processes and, therefore, enable photoluminescence to the solid state. It is important to note that, after aggregation, the energy distribution of the carbonyl-borane adducts rearranges leading to an emissive state of lower energy. A rationale infers the latter redistribution to be responsible for preventing the radiationless transitions.

Accordingly, interfering into the intermolecular interactions would modify the photophysical properties of the solid state. To verify said hypothesis, the spectroscopic measurements have been reproduced applying an increasing pressure. Compounds with narrower optical band gap ease the identification of batho- or hypsochromic changes. Thus, increasing the pressure on solid compounds 2e induces piezochromism, i.e. a red shift of the emission maxima from 569 nm to 590 nm as shown in Fig. 32, which correlates with a color change from orange to red (cf. Fig. 32; inset). Importantly, grinding of the sample lead to recovering the initial spectroscopic features.

Synthesis of starting benzothiophene materials ylethynyl)benzo[b]thiophene-2-carbaldeh de (MHCA2)

To a solution of 3-bromobenzo[b]thiophene-2-carbaldehyde (1.00 g, 4.15 mmol), PdCI₂(PPh3)2 (87.3 mg, 0.124 mmol, 3 mol%) and Cul (23.7 mg, 0.124 mmol, 3 mol%) in degassed NEt3 (20 mL) was added phenylacetylene (501 μΙ_, 4.56 mmol, 1.1 eq.). The reaction was stirred at 60 °C over night and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 40:1 to 20:1 ), followed by recrystallization in Ch C /pentane, to afford the title compound as slightly yellow solid (513 mg, 1.96 mmol, 47%). The spectral data is in accordance with previously reported data (A. K. Verma , S. K. R. Kotla, D. Choudhary, M. Patel, R. K. Tiwari, J. Org. Chem. 2013, 78, 4386-4401 )

¹H NMR (300 MHz, CDCb, 298 K): 10.48 (s, 1 H), 8.20-8.14 (m, 1 H), 7.92-7.87 (m, 1 H), 7.69-7.62 (m, 2H), 7.61 -7.49 (m, 2H), 7.47-7.41 (m, 3H); ³C NMR { H} (75 MHz, CDCb, 298 K): 184.6 (s), 143.6 (s), 141 .2 (s), 139.6 (s), 132.1 (s, 2C), 129.7 (s), 129.0 (s), 128.8 (s, 2C), 127.9 (s), 125.8 (s), 125.2 (s), 123.5 (s), 122.1 (s), 99.2 (s), 80.7 (s).

3-(p-tolylethynyl)benzo[b]thiophene-2-carbaldehyde (MHCA4)

To a solution of 3-bromobenzo[b]thiophene-2-carbaldehyde (1 .00 g, 4.15 mmol), PdCI₂(PPh3)2 (87.3 mg, 0.124 mmol, 3 mol%) and Cul (23.7 mg, 0.124 mmol, 3 mol%) in degassed NEt3 (20 ml_) was added 4-ethynyltoluene (727 μΙ_, 5.74 mmol, 1 .4 eq.). The reaction was stirred at 60 °C overnight and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petroletherethylacetate = 40:1 to 20:1 ), followed by recrystallization in CH2Cl2/pentane, to afford the title compound as colorless solid (736 mg, 2.66 mmol, 64%). The spectral data is in accordance with previously reported data (R. R. Jha, R. K. Saunthwal, A. K. Verma, Org. Biomol. Chem. 2014, 12, 552-556.)

¹H NMR (300 MHz, CDCb, 298 K): 10.47 (s, 1 H), 8.19-8.14 (m, 1 H), 7.91-7.86 (m, 1 H), 7.60-7.49 (m, 4H), 7.24 (d, J = 8.0 Hz, 2H), 2.42 (s, 3H); ¹³C. NMR {¹H} (75 MHz, CDCb, 298 K): 184.7 (s), 143.3 (s), 141 .2 (s), 140.1 (s), 139.6 (s), 132.0 (s, 2C), 129.6 (s, 2C), 129.0 (s), 128.2 (s), 125.7 (s), 125.2 (s), 123.5 (s), 1 19.0 (s), 99.6 (s), 80.2 (s), 21 .8 (s). 3-((4-(trifluoromethyl)phenyl)ethyn l)benzo[b]thiophene-2-carbaldehyde (MHCA3)

To a solution of 3-bromobenzo[b]thiophene-2-carbaldehyde (1.10 g, 4.56 mmol), PdCl2(PPh₃)2 (98.3 mg, 0.140 mmol, 3 mol%) and Cul (26.7 mg, 0.140 mmol, 3 mol%) in degassed NEt3 (25 mL) was added 1-ethynyl-4-(trifluoromethyl)benzene (826 μΙ_, 5.10 mmol, 1.1 eq.). The reaction was stirred at 60 °C overnight and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petroletherethylacetate = 40:1 to 20:1 ), followed by recrystallization in CHhC /pentane, to afford the title compound as yellow solid (1.04 g, 3.14 mmol, 69%). The spectral data is in accordance with previously reported data.

¹H NMR (600 MHz, CD2CI2, 298 K): 10.46 (s, 1 H), 8.17-8.10 (m, 1 H), 7.93-7.86 (m, 1 H), 7.75 (d, J = 8.4 Hz, 2H), 7.68 (d, J = 8.4 Hz, 2H), 7.61-7.50 (m, 2H); ¹⁹F NMR (470 MHz, CD2CI2, 298 K): -62.9 (s); ¹³C NMR {¹H} (150 MHz, CD2CI2, 298 K): 184.2 (s), 144.5 (s), 141.2 (s), 139.4 (s), 132.3 (s), 131.3 (q, JCF = 33 Hz), 129.1 (s), 126.7 (s), 125.9 (s), 125.8 (s), 125.7 (q, JCF = 4 Hz), 125.0 (s), 123.9 (q, JCF = 272 Hz), 123.5 (s), 97.2 (s), 82.8 (s).

3-((4-methoxyphenyl)ethynyl)benzo[b]thiophene-2-carbaldehyde (MHCA1 )

e

To a solution of 3-bromobenzo[b]thiophene-2-carbaldehyde (1.10 g, 4.56 mmol), PdCl2(PPh₃)2 (98.3 mg, 0.140 mmol, 3 mol%) and Cul (26.7 mg, 0.140 mmol, 3 mol%) in degassed NEt3 (25 mL) was added 4-methoxyethynylbenzene (674 mg, 5.10 mmol, 1 .1 eq.). The reaction was stirred at 60 °C over night and the solvent removed under reduced pressure. The crude material was purified by flash column chromatography (S1O2; petrolether : ethylacetate = 20:1 to 5:1 ), followed by recrystallization in Ch C /pentane, to afford the title compound as yellow solid (1 .00 g, 3.42 mmol, 75%). The spectral data is in accordance with previously reported data (V. Rustagi, R. Tiwari, A. K. Verma, Eur. J. Org. Chem. 2012, 24, 4590-4602). H NMR (300 MHz, CDCI3, 298 K): 10.45 (s, 1 H), 8.18-8.12 (m, 1 H), 7.89-7.84 (m, 1 H), 7.61-7.47 (m, 4H), 6.98-6.92 (m, 2H), 3.87 (s, 3H); ³C NMR {¹ H} (75 MHz, CDCb, 298 K): 184.7 (s), 160.8 (s), 142.9 (s), 141 .2 (s), 139.5 (s), 133.7 (s, 2C), 128.9 (s), 128.4 (s), 125.6 (s), 125.2 (s), 123.4 (s), 1 14.5 (s, 2C), 1 14.0 (s), 99.6 (s), 79.8 (s), 55.6 (s).

Synthesis of benzo[b]thiophene products

BCF-3-(phenylethynyl)benzo[b thiophene-2-carbaldehyde (MH814B)

According to general procedure A, 3-(phenylethynyl)benzo[b]thiophene-2- carbaldehyde (78.7 mg, 0.30 mmol) was dissolved in 2.5 ml_ CH2CI2 and B(C6Fs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct was isolated quantitatively as orange solid.

IR (thin film) vmax = 2201 cnr , 1643, 1595, 1564, 1515, 1454, 1407, 1378, 1318, 1299, 1286, 1 169, 1 104, 1071 , 1040, 970, 889, 849, 789, 774, 760; ¹H NMR (600 MHz, CD2CI2, 298 K): 9.61 (s, 1 H), 8.32 (d, J = 8.4 Hz, 1 H), 8.03 (d, J = 8.3 Hz, 1 H), 7.84- 7.80 (m, 1 H), 7.69-7.65 (m, 1 H), 7.58-7.54 (m, 1 H), 7.53-7.46 (m, 4H); ⁹F NMR (470 MHz, CD2CI2, 298 K): -133.8 (dd, JFF = 23.0 Hz, 7.8 Hz, 6F, o-CeFs), -156.8 (t, JFF = 20.1 Hz, 3F, p- CeFs), -164.0 (m, 6F, m- CeFs); ¹¹B NMR (160 MHz, CD₂CI_2> 298 K): 2.91 (brs.); ¹³C NMR {¹H} (150 MHz, CD2CI2, 298 K): 187.0 (s), 148.8 (brs.), 148.7 (dm, JCF = 242 Hz, C-F), 143.4 (brs.), 141.1 (dm, JCF = 250 Hz, C-F), 139.7 (s), 137.9 (dm, JCF = 250 Hz, C-F), 136.6 (brs.), 134.5 (brs.), 132.8 (s), 131.9 (s), 129.6 (s), 128.0 (s), 127.9 (s), 124.5 (s), 120.7 (s), 1 16.8 (m, C-B),108.6 (brs.), 81 .0 (s); HRMS-FAB (+) (m/z): calcd for C29H10BF10OS [M-CeFs]*, 607.0386; found, 607.0399.

BCF-3-(p-tolylethynyl)benzo[b]thiophene-2-carbaldehyde (MH814D)

According to general procedure A, 3-(p-tolylethynyl)benzo[b]thiophene-2- carbaldehyde (82.9 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(C6Fs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct was isolated quantitatively as orange solid. IR (thin film) Vmax = 2188 cm-¹, 1646, 1557, 1518, 1457, 1380, 1316, 1285, 1 103, 1035, 977, 890, 856, 817, 792, 772, 735; ¹H NMR (600 MHz, CD₂CI_2> 298 K): 9.58 (brs., 1 H), 8.30 (d, J = 8.5 Hz, 1 H), 8.01 (d, J = 8.4 Hz, 1 H), 7.83-7.79 (m, 1 H), 7.67-7.64 (m, 1 H), 7.39 (d, J = 8.2 Hz, 2H), 7.30 (d, J = 8.2 Hz, 2H), 2.44 (s, 3H); ⁹F NMR (470 MHz, CD2CI2, 298 K): -133.8 (dd, JFF = 23.0 Hz, 7.4 Hz, 6F, o-CeFs), -156.9 (t, JFF = 20.5 Hz, 3F, p- CeFs), -164.1 (m, 6F, m- CeFs); ¹¹B NMR (160 MHz, CD₂CI₂, 298 K): 2.90 (s); ¹³C NMR {¹H} (150 MHz, CD₂CI₂, 298 K): 186.8 (s), 148.8 (brs.), 148.7 (dm, JCF = 243 Hz, C-F), 144.0 (brs.), 143.2 (s), 141.0 (dm, JCF = 251 Hz, C-F), 139.6 (s), 137.7 (dm, JCF = 251 Hz, C-F), 136.2 (brs.), 134.5 (brs.), 132.8 (s), 130.4 (s), 128.0 (s), 127.8 (s), 124.5 (s), 117.6 (s), 1 16.8 (m, C-B), 109.7 (brs.), 81 .0 (s), 22.2 (s). HRMS-FAB (+) (m/z): calcd for C₃oHi₂BFioOS [M-CeFs]*, 621 .0542; found, 621.0564. BCF-3-((4-(trifluoromethyl)phenyl)ethynyl)benzo[b]thiophene-2-carbald (MH814C)

According to general procedure A, 3-((4-

(trifluoromethyl)phenyl)ethynyl)benzo[b]thiophene-2-carbaldehyde (99.1 mg, 0.30 mmol) was dissolved in 2.5 mL CH2CI2 and B(C6Fs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct was isolated quantitatively as yellow solid.

IR (thin film) vmax = 2200 cm^"1, 1648, 1573, 1519, 1457, 1381 , 1322, 1286, 1 178, 105, 1068, 1034, 1018, 971 , 889, 845, 788, 775; ¹H NMR (500 MHz, CD2CI2, 298 K): 9.64 (brs., 1 H), 8.31 (d, J = 8.3 Hz, 1 H), 8.05 (d, J = 8.3 Hz, 1 H), 7.86-7.81 (m, 1 H), 7.75 (d, J = 8.2 Hz, 2H), 7.71 -7.64 (m, 3H); ¹⁹F NMR (470 MHz, CD2CI2, 298 K): -63.5 (s, 3F), -133.8 (dd, JFF = 23.0 Hz, 4.8 Hz, 6F, o-CeFs), -156.6 (t, JFF = 20.5 Hz, 3F, p- C₆F₅), - 164.0 (m, 6F, m- C₆F₅); ¹¹B NMR (160 MHz, CD2CI2, 298 K): 3.23 (brs.); ³C NMR {¹H} (150 MHz, CD2CI2, 298 K): 187.3 (s), 148.7 (dm, J_CF = 239 Hz, C-F), 148.6 (brs.), 141.1 (dm, JCF = 250 Hz, C-F), 139.8 (s), 137.8 (dm, JCF = 250 Hz, C-F), 137.5 (brs.), 134.5 (brs.), 133.1 (s), 132.9 (q, J_CF= 33 Hz), 128.1 (s), 127.8 (s), 126.5 (q, JCF = 4 Hz), 124.6 (brs.), 124.6 (s), 124.2 (q, J_CF = 264 Hz, CF3), 1 16.6 (m, C-B), 105.3 (brs.), 82.3 (s); HRMS-FAB (+) (m/z): calcd for C30H9BF13OS [M-C6F₅]⁺, 675.0260; found,675.0230.

BCF-3-((4-methoxyphenyl)ethynyl)benzo[b]thiophene-2-carbaldehyde (MH814A)

According to general procedure A, 3-((4-methoxyphenyl)ethynyl)benzo[b]thiophene-2- carbaldehyde (87.7 mg, 0.30 mmol) was dissolved in 2.5 ml_ CH2CI2 and B(C6Fs)3 (153.4 mg, 0.20 mmol) added. The Lewis adduct was isolated quantitatively as dark red solid.

IR (thin film) v_max = 2181 cm^"1 , 1647, 1601 , 1565, 1516, 1456, 1379, 1317, 1287, 1257, 1 170, 1 103, 1037, 1017, 972, 887, 853, 831 , 790, 769; ¹H NMR (600 MHz, CD2CI2, 298 K): 9.55 (brs., 1 H), 8.29 (d, J = 8.3 Hz, 1 H), 8.00 (d, J = 8.3 Hz, 1 H), 7.82-7.78 (m, 1 H), 7.66-7.62 (m, 1 H), 7.45 (d, J = 8.1 Hz, 2H), 6.99 (d, J = 8.2 Hz, 2H), 3.90 (s, 3H); ¹⁹F NMR (470 MHz, CD2CI2, 298 K): -133.8 (dd, JFF = 23.0 Hz, 7.0 Hz, 6F, o-C₆F₅), - 156.9 (t, JFF = 20.5 Hz, 3F, p- C₆F₅), -164.1 (m, 6F, m- CeFs); ¹¹B NMR (160 MHz, CD2CI2, 298 K): 2.60 (brs.); ³C NMR {¹H} (150 MHz, CD2CI2, 298 K): 186.3 (s), 162.9 (s), 148.9 (brs.), 148.7 (dm, JCF = 242 Hz, C-F), 144.5 (brs.), 141 .1 (dm, JCF = 253 Hz, C-F), 139.6 (s), 137.9 (JCF = 240 Hz, C-F), 135.8 (brs.), 134.9 (s), 134.6 (brs.), 128.0 (s), 127.7 (s), 124.5 (s), 1 17.0 (m, C-B), 1 15.4 (s), 1 12.5 (s), 110.5 (brs.), 81 .3 (s), 56.2 (s); HRMS-FAB (+) (m/z): calcd for C30H12BF10O2S [M-C₆F₅]⁺, 637.0491 ; found, 637.0510.

In conclusion, the present invention provides a straightforward protocol to efficiently turn on solid-state luminescence of non-emissive carbonyl materials by simple coordination of Lewis acids, such as B(C6Fs)3. Said method is compatible with materials containing both double and triple bonds. Intermolecular interactions promoted by B(C6Fs)3 enable, moreover, intriguing phenomena such as piezochromism. The commercial availability of B(C6Fs)3 and the simplicity of the method according to the present invention allow the facile preparation of novel materials with enhanced solid-state fluorescence properties, preventing the tedious preparation of borane chelating reactants.

References

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Claims

1. A compound of the following general formula (1 ) in which the oxygen atom of the carbonyl group of the carbonyl compound is coordinated to a non-chelating borane in terms of a Lewis acid-base adduct

said ring moiety A represents a cyclic aromatic ring or an aromatic heterocyclic ring, preferably phenyl, naphthyl, thienyl, benzothienyl, more preferably phenyl and benzothienyl,

n represents an integer of 1 to 5.

2. The compound according to claim 1 which has the following general formula (1 )

wherein each X, which may be the same or different from another, represents a halogen atom, a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched Ci- C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched C1-C15 alkoxy group, a halogenated linear or branched C1-C15 alkoxy group, a C3-C15 cycloalkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated C3-C15 cycloalkyl group, a C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N including ferrocene, or a halogenated C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N;

R represents a hydrogen atom, a linear or branched C1-C15 alkyl group, a C3-C15 cycloalkyl group, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15

hydrocarbon group optionally containing one or more halogen atoms;

each R¹, which may be the same or different from another, represents a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom; and n represents an integer of 1 to 5.

3. The compound according to claim 1 which has the following general formula (3)

wherein each X, which may be the same or different from another, represents a halogen atom, a linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C15 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched C1-C15 alkoxy group, a halogenated linear or branched C1-C15 alkoxy group, a C3-C15 cycloalkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated C3-C15 cycloalkyl group, a C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N including ferrocene, or a halogenated C6-C20 aryl group which may contain one or more heteroatoms selected from P, O, S and N; R represents a hydrogen atom, a linear or branched C1-C15 alkyl group, a C3-C15 cycloalkyl group, a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1-C15 hydrocarbon group optionally containing one or more halogen atoms;

n represents an integer of 1 to 5.

4. The compound according to claim 1 , 2 or 3 which is in the solid state, exhibiting solid state luminescence based on intermolecular interactions between the non- emissive carbonyl compound and the Lewis acid BX3.

5. compound according to any one of claims 1 to 4, wherein at least one X represents a C6-C20 aryl group containing at least one fluorine atom.

6. The compound according to any one of claims 1 to 5, wherein R represents a hydrogen atom.

7. The compound according to any one of claims 1 to 6, wherein R¹ represents a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one substituted or unsubstituted C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C1 -C15 hydrocarbon group optionally containing one or more heteroatoms selected from O, S and N or at least one halogen atom.

8. The compound according to any one of claims 1 to 7, wherein R¹ is selected from t

a b c d e f wherein each R\ which may be the same or different from another, represents a linear or branched C1-C10 alkyl group which may contain one or more heteroatoms selected from O, S and N, a halogenated linear or branched C1-C10 alkyl group which may contain one or more heteroatoms selected from O, S and N, a linear or branched Ci - C10 alkoxy group, or a C6-C20 aryl group.

9. The compound according to any one of claims 1 to 8 having the following general formula (2)

BAr^F ₃

t

wherein Ar^F represents a C-6 aryl group containing at least one fluorine atom; and R² represents a linear or branched unsaturated C2-C15 hydrocarbon group having one or more carbon-carbon double bonds and/or one or more carbon-carbon triple bonds which may be substituted with at least one C6-C20 aryl group optionally containing one or more halogen atoms, or a C6-C20 aryl group which may be substituted with at least one saturated or unsaturated C2-C15 hydrocarbon group or at least one halogen atom, forming a conjugated system with the benzaldehyd moiety.

10. The compound according to any one of claims 1 to 9, wherein BX3 and BAr^F3

1,1. A method for producing the compound according to any one of claims 1 to 10, comprising reacting the following carbonyl compound (1a) with a non-chelating borane BX3 to form a Lewis acid-base adduct having the general formula (1 )

wherein X, R, R¹ and n are defined as above.

12. An electronic or optoelectronic device containing the compound according to any one of claims 1 to 10.