WO2012049167A1 - Novel oligothiophene derivatives, their process of preparation and their uses - Google Patents

Abstract

The present invention concerns novel oligothiophene derivatives bearing reactive functions, their process of preparation, their use for preparing electrically semi-conducting organic compounds, their preparation thereof and nanohybrid nanocomposite material containing them.

Description

NOVEL OLIGOTHIOPHENE DERIVATIVES, THEIR PROCESS

OF PREPARATION AND THEIR USES

Oligothiophenes are generally used to give access to a large range of molecules for industrial and commercial applications, in particular in optics, electronics and biology. They are considered as versatile substrates for preparations of more complex and dissymmetric molecules having generally semi-conducting properties, and linear and/or non linear optical properties.

However, the synthesis of desired dissymmetric oligothiophenes proved to be difficult and there is a need for selective methods. Further, an important problem of oligothiophenes is their poor solubility which makes their further chemical transformations and purifications burdensome. Very few starting materials allowing synthesis of dissymmetric oligothiophenes are commercially available, thus increasing the synthetic path length.

The columns used in oligothiophenes purification are expensive and limit yield of the target molecules. The purification of compounds on silica gel can also lead to their degradation depending on their chemical nature. Moreover, the use of large volumes of organic solvents, often toxic, requires the implementation of rigorous security conditions. Such problems are limited here, the process being environmentally friendly.

As a result of this poor selectivity and solubility, low yields are generally obtained.

There is therefore a need to provide oligothiophenes bearing reactive functions, that are soluble, thus suitable for easy further processing. Further, there is a need to provide convenient methods for the synthesis of such oligothiophene derivatives. According to a first object, the present invention thus concerns oligothiophene derivatives of formula (I):

(I)

wherein:

- n is an integer comprised between 2 and 10;

- X is chosen from the group consisting in H, a halogen atom, a CHO group, a Sn- (R)₃ group where Sn represents the Tin atom and where R is C1 -C6 alkyl,

- Y is a group of formula (II):

where each R1 , R2, R3, R4, R5, R6 are identical or different and independently chosen from H, C1 -C4 alkyl; is the bond linking Y to the thiophene moiety and

p, q and r are either 0 or 1 , provided that p + q + r = 2 or 3,

with the exception of the compound where n=2, X is Sn(n-Bu)3 and Y is a group of

formula

Preferably, the compounds of the invention are those of formula (I) above with the further exception of the compound where Br and Y is:

Preferably, the compounds of formula (I) are those of formula (I):

wherein:

- n is an integer comprised between 3 and 10;

- X is chosen from the group consisting in H, a halogen atom, a CHO group, a Sn- (R)₃ group where Sn represents the Tin atom and where R is C1 -C6 alkyl,

- Y is a group of formula (II):

(II) where each R1 , R2, R3, R4, R5, R6 are identical or different and independently chosen from H, C1 -C4 alkyl; is the bond linking Y to the thiophene moiety, and

p, q and r are either 0 or 1 , provided that p + q + r = 2 or 3.

Preferably, the compounds of the invention are those of formula (I) above with the exception of the compound where n is 3, Y is:

Preferably, in formula (\), X is chosen from a CHO group, a Sn-(R)₃ group where S represents the Tin atom and where R is C1 -C6 alkyl.

Preferably, Y is a group of formula:

where each p=q=r=1 and R1 , R2, R3, R4, R5, R6 are defined as above.

The general formula above encompasses any of the following preferred embodiments or any of their combination:

- n is 3, 4 or 5; and/or

- Y is (II), wherein q = 0 and p = r = 1 and R1 =R2=R5=R6=H; and/or

- X is a halogen; and/or

- X is Br; and/or

- X is Sn-Bu₃; and/or

- X is -CHO; and/or

- Y is a dioxane group optionally substituted by one or more C1 -C4 alkyl; and/or

- Y is 5,5-dimethyl-1 ,3 dioxane.

According to a particular embodiment, the present invention concerns a compound of formula (I) wherein:

- n is 2;

- X is -CHO;

- Y is a dioxane group optionally substituted by one or more C1 -C4 alkyl. According to the present invention, the terms below have the following meanings: a halogen atom corresponds to a fluorine, chlorine, bromine or iodine atom; an alkyl group corresponds to a saturated, linear or branched aliphatic group comprising 1 to 6 carbon atoms. The following examples may be cited: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertbutyl, pentyl, etc.

The following compounds are particularly preferred:

2-(5'-bromo-2,2'-bithien-5-yl)-5,5-dimethyl-1 ,3-dioxane

- Tributyl[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]stannane

- 5-bromo, 5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene

- Tributyl[5^,,-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2^,:5^,,2^,,-terthien-5-yl]stannane

- 5"-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene-5-carbaldehyde

- S^{^}-CS^-dimethyl-l ^-dioxan^-y ^^^&^^^^^{^}-quaterthiophene-S-carbaldehyde

- S^{^}-CS^-dimethyl-l ^-dioxan^-y ^^^&^^^^^{^}^^{^}^^{^}-quinquethiophene-S- carbaldehyde

- 5""-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2^,:5^,,2":5",2"^,:5"^,,2""-quinquethiophene-5- carbaldehyde

- [5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]acetaldehyde

A particular compound is that of formula:

The oligothiophenes of the invention are soluble in common organic solvents; they are versatile substrates for preparation of more complex dissymmetric molecules having generally semi-conducting properties, and linear and/or nonlinear optical properties.

According to another object, the present invention is also directed to the process of preparation of the oligothiophene derivatives of the invention.

According to the process of the invention, the compound of formula (I) may be obtained by a process comprising the step of coupling a corresponding compound of formula (III):

with a compound of formula (IV):

where n, X, Y, R are defined as in formula (I) and s is an integer comprised between 1 and 9.

Generally, said step is a Stille coupling. It may be generally carried out in the presence of Pd(PPh₃)₄ in the presence of a solvent such as DMF or THF or other polar aprotic solvents. Generally, this reaction is conducted at a temperature comprised between room temperature and the reflux temperature of the reaction mixture.

Said step may be carried out several times, depending on the starting products of formula (III) and (IV) available and the desired number n of thiophene units in the compound of formula (I).

Said compound of formula (III) may be obtained from a compound of formula (V):

in the presence of Sn(R)₃-Hal",

where Hal' and Hal", identical or different independently represent a halogen atom. This reaction may generally be carried out in the presence of a base, such as n-Butyllium, n- Hexyllithium or other alkyllithium, LDA or Phenyllithium, and in a solvent such as THF, DCM, dioxane or other polar aprotic solvents, at a temperature comprised between -78 °C and room temperature.

Said compound of formula (IV) may be obtained from a compound of formula (VI):

according to known procedures.

For example, this reaction may be conducted in the presence of Hal₂. Generally, this reaction may be conducted in the presence of a base such as NaHC0₃ in a solvent such as CHCI₃, at a temperature comprised between the room temperature and the reflux temperature of the solvent.

Compounds of formula (VI) where s is 2 or 3 are generally commercially available.

The compound of formula (V) may be obtained by coupling a compound of formula

(VII)

with a compound of formul

where p, q, r, R1 , R2, R3, R4, R5, R6 are defined as above.

This reaction may generally be carried out in a solvent such as toluene, at a temperature comprised between the room temperature and the reflux temperature of the reaction mixture, in the presence of an acid such as paratoluenesulfonic acid (APTS).

The compound of formula (I) where X is Hal may be similarly obtained from a compound of formula (IX):

(IX)

with a compound of formula (VII

where X is Hal and p, q, r, R1 , R2, R3, R4, R5, R6 are defined as above. Compounds of formula (I) where X is CHO may also be obtained from corresponding compounds of formula (I) where X is a Hal, in the presence of a base, such as n-BuLi. This reaction may be carried out in a suitable solvent such as THF, followed by the action of DMF. It is generally carried out at a temperature comprised between -78 °C and room temperature.

The compounds of formulae (VII) and (IX) above may be obtained form corresponding compound of formula (X) and (Χ'):

(X) (Χ')

by carrying out the same procedure as that leading to compound (IV) from compound (VI) discussed above.

The compounds of formula (VI) and (VIII) are generally commercially available or may be prepared by application or adaptation of known methods.

The process of the invention may be further adapted from methods well-known to those skilled in the art. The compounds can be synthesized, for example, by application or adaptation of the methods described above, or variations thereon as appreciated by the skilled artisan. The appropriate modifications and substitutions are readily apparent and well-known or readily obtainable from the scientific literature to those skilled in the art.

In particular, such methods can be found in R.C. Larock, Comprehensive Organic Transformations, VCH publishers, 1989.

It will be appreciated that the compounds of the present invention may contain one or more asymmetrically substituted carbon atoms, and may be isolated in optically active or racemic forms. Thus, all chiral, diastereomeric, racemic forms and all geometric isomeric forms of a structure are intended, unless the specific stereochemistry or isomeric form is specifically indicated. It is well-known in the art how to prepare and isolate such optically active forms. For example, mixtures of stereoisomers may be separated by standard techniques including, but not limited to, resolution of racemic forms, normal, reverse-phase, and chiral chromatography, preferential salt formation, recrystallization, and the like, or by chiral synthesis either from chiral starting materials or by deliberate synthesis of target chiral centers. The reagents and starting materials are commercially available, or readily synthesized by well-known techniques by one of ordinary skill in the arts. All substituents, unless otherwise indicated, are as previously defined. In the reactions described hereinafter, it may be necessary to protect reactive functional groups, for example hydroxy, amino, imino, thio or carboxy groups, where these are desired in the final product, to avoid their unwanted participation in the reactions. Conventional protecting groups may be used in accordance with standard practice, for examples see T.W. Green and P. G. M. Wuts in Protective Groups in Organic Chemistry, John Wiley and Sons, 1991 ; J. F. W. McOmie in Protective Groups in Organic Chemistry, Plenum Press, 1973.

Usually, reactions are carried out in a suitable solvent. A variety of solvents may be used, provided that it has no adverse effect on the reaction or on the reagents involved. Examples of suitable solvents include: hydrocarbons, which may be aromatic, aliphatic or cycloaliphatic hydrocarbons, such as hexane, cyclohexane, benzene, toluene and xylene; amides, especially fatty acid amides, such as dimethylformamide; and ethers, such as diethyl ether and tetrahydrofuran.

The reactions can take place over a wide range of temperatures. In general, we find it convenient to carry out the reaction at a temperature of from about 0°C to about Ι δΟ'Ό (more preferably from about room temperature to about 100 ). The time required for the reaction may also vary widely, depending on many factors, notably the reaction temperature and the nature of the reagents. However, provided that the reaction is effected under the preferred conditions outlined above, a period of from about 3 hours to about 20 hours will usually suffice.

The compound thus prepared may be recovered from the reaction mixture by conventional means. For example, the compounds may be recovered by distilling off the solvent from the reaction mixture or, if necessary after distilling off the solvent from the reaction mixture, pouring the residue into water followed by extraction with a water-immiscible organic solvent and distilling off the solvent from the extract. Additionally, the product can, if desired, be further purified by various well techniques, such as recrystallization, reprecipitation or the various chromatography techniques, notably column chromatography or preparative thin layer chromatography.

The process of the invention may also comprise the step of isolating the desired compound. The scheme below is given to illustrate a representative embodiment of the process of the invention:

1) THF, n-Buli, -78°C, 40 min

2) SnBu₃Cl, -78°C to RT

Scheme 1 : synthesis route toward dissymmetric oligothiophenes The title oligothiophenes can be prepared conveniently using commercially available starting materials following the efficient synthetic method disclosed herein. This method avoids long and expensive purification steps by column chromatography using silica gel and large volumes of solvents, offering an environmentally friendly approach. The described novel oligothiophenes give access to a large range of molecules for industrial and commercial applications in optics, electronics and biology.

The compounds of formula (I) can comprise one or more asymmetric carbon atoms. They can therefore exist in the form of enantiomers or diastereoisomers. These enantiomers and diastereoisomers, as well as their mixtures, including racemic mixtures, form part of the invention.

The compounds of formula (I) can be provided in the form of a free base or in the form of addition salts with acids, which also form part of the invention.

The oligothiophenes of the invention may be used to give access to a large scale of semi-conducting materials for electronic devices including transistors or solar cells. These compounds are dissymetrically end-capped with reactive functions such as acetal and carbonyl groups to introduce desired functional groups using the standard tools for synthetic organic chemists in order to diversify the structure and, hence, the properties of p-conjugated aromatic systems. Thus the access to distyryl oligothiophene semiconductors can be achieved.

In particular, the oligothiophenes derivatives of the invention may be advantageously used for preparing a hybrid nanocomposite material comprising electrically semi- conducting inorganic elongated nanocrystals grafted on at least part of the surface thereof with an electrically semi-conducting organic compound or with a mixture of at least two such electrically semi-conducting organic compounds (co-grafting).

Said hybrid nanocomposite material is disclosed in WO2009/083748 the disclosure of which is incorporated herein by reference.

According to a further object, the present invention thus concerns an electrically semi-conducting organic compound comprising an oligothiophene moiety of the invention. Preferably, said semi-conducting organic compound is obtainable from the oligothiophene derivatives of the invention.

According to a particular embodiment, said electrically semi-conducting organic compound is obtained from the bithiophene of the invention of formula:

wherein:

represents a double or triple bond;

t and u, identical or different, independently represent integers chosen from 0 or 1 to

20;

n is defined as in formula (I);

R7 and R8, identical or different, independently represent a group chosen from H, Halogen, a C1 -C6 alkyl, OR', NR'R", S(0)_mR', where alkyl is optionally substituted by one or more of Halogen, OR', NR'R", S(0)_mR', PR'₃

where m is 0, 1 or 2 and R', R" identical or different independently represent H, or a C1 -C6 alkyl;

w represents 0 or 1 ;

z represents 0 or 1 ;

and

A represents an anchoring p-conjugated electron withdrawing moiety.

~ represents preferably a double bond.

Preferably, t=u=1 .

Preferably, n is 2 to 10, in particular n=2.

Preferably, R7 and R8, identical or different, independently represent an OAlkyl. Preferably w=z=0.

The anchoring moiety may be chosen among reactive functions generally used for grafting organic molecules on metal or metal oxide substrates. The anchoring moiety may be chosen in particular from the group consisting in carboxylic acid, phosphonic acid, sulfonic acid, phosphate, acetyl aceton ate (acac), hydroxamic acid.

A is a C(=0)OH in particular.

The compounds of formula (A) may be in particular chosen from the compounds of formula (Aa):

(Aa)

where R7, R8, n are defined as above.

Said electrically s rticular of formula (A1 ):

(A1 )

and is referred to herein as DMC-2T (DiMethoxyCarbazole-biThiophene).

According to a further object, the present invention also concerns the process of preparation of a compound of formula (Aa), comprising:

i) reacting a compound of formula (D):

(D)

where R7, R8 are defined as in formula (A),

with HBrPPh3, followed by

ii) coupling the obtained compound of formula (C):

with an oligothiophene of formula (I) of the invention where X is CHO and Y is a group of formula (II),

and

iii) reacting the obtained compound of formula (B)

(B)

with cyanoacetic acid.

Step i) is generally conducted in a solvent such as chloroform, at a temperature comprised between the room temperature and the reflux temperature of the reaction mixture.

Step ii) may be conducted in the presence of a base such as t-BuOK, in a solvent such as THF, at room temperature, followed by acidic treatment (e.g. with CF₃COOH) to cleave the group of formula (II) in the intermediate compound of formula :

Step iii) may be conducted in the presence of piperidine, in a solvent such as acetonitrile.

Said compound of formula (D) may be obtained by reducing the corresponding compound of formula (E):

Said reduction may be in particular conducted with NaBH₄ in usual conditions.

Said compound of formula (E) may be obtained by reacting a compound of formula

with benzaldehyde, by application or adaptation of procedures described in particular by M. Sigalov, A. Ben-Asuly, L. Shapiro, A. Ellern and V. Khodorkovsky, Tetrahedron Lett 2000, 41 , 8573.

The compound of formula (F) may be obtained by application or adaptation of procedures described in particular in Holzapfel et al J. Phys. Chem. C 2008, 1 12(4), 1227- 1243.

Compounds C, D and E are novel. The present invention thus also concerns the compounds of formula (G):

(G)

where:

T and U form together a >C=0 group with the carbon atom to which they are attached; or

one of T and U is H and the other is OH or a P⁺Ph₃/Br ^" group. Compounds of formula (G) are useful as intermediates in the synthesis of compounds of formula (A):

A representative process of preparation of a compound of formula (A) is illustrated in scheme 2 below:

According to a further object, the present invention thus concerns a hybrid nanocomposite material comprising an electrically semi-conducting inorganic elongated nanocrystals grafted on at least part of the surface thereof with an electrically semiconducting organic compound of the invention.

Said hybrid nanocomposite material of the invention is generally such that the elongated nanocrystals are nanowires, nanorods, nanotubes, nanodipods, nanotripods, nanotetrapods or nanostars or nanospheres.

The elongated nanocrystals may be in particular semiconductors or metals. Most often, the nanocrystals will be n-type or p-type semiconductors, depending on the conception of the device.

Such nanocrystals may be made of a large collection of inorganic compounds, including in particular: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, osmium, cobalt, nickel, copper, silver, gold, zinc, cadmium, scandium, yttrium, lanthanum, boron, gallium, indium, arsenic, thallium, silicon, germanium, tin, lead, magnesium, calcium, strontium, barium and aluminum, and the simple or mixed chalcogenides, in particular oxides and sulfides, thereof. The semiconductors may be elemental materials such as silicon and germanium, eventually doped, or compound semiconductors such as gallium arsenide and indium phosphide, or alloys such as silicon germanium or aluminium gallium arsenide.

Preferred metal conductors are those having high charge carrier mobility such as gold, silver, copper and indium doped tin oxide (ITO).

Preferred semiconductors have a band gap between 0,4 eV and 4,1 eV, particularly a band gap close the solar spectrum. The band gap may then further be tuned by varying the diameter of the elongated nanocrystal or by additional doping. Particularly preferred semi-conductors are zinc oxide, zinc sulfide and titanium dioxide.

According to a preferred embodiment, the invention concerns a hybrid nanocomposite material comprising a ZnO nanorod grafted with the semi-conducting organic compound DMC-2T of formula (A1 ) as defined above.

According to a further object, the present invention thus also concerns a device comprising a thin film of a hybrid nanocomposite material of the invention.

Said device may be in particular a solar cell or an electronic switching device.

More particularly, the present invention concerns a solar cell comprising a thin film of the hybrid nanocomposite material comprising a ZnO nanorod grafted with the semiconducting organic compound DMC-2T of formula (A1 ) as defined above.

FIGURES

Figure 1 shows the structure of a solar cell of the invention. Figures 2 shows l-V curves in the dark (solid line) and under illumination (dashed line) of DMC2T-ZnO solar cells.

Figure 3 shows EQE spectrum of DMC2T-ZnO solar cells.

Figure 4 shows l-V curves in the dark and under illumination of solar cells obtained with C212.

Figure 5 shows the EQE spectrum of C212-ZnO solar cells using different mass ratios.

The examples below are given for illustrative, non-limiting purpose.

EXAMPLES

General remarks

Reagents were obtained from standard commercial suppliers and were used directly without further purification. Solvents were distilled under adequate drying agent prior to use and experiments were carried out under argon. ¹ H and ¹³C NMR spectra were recorded on a Bruker AC 250 operating at 250 MHz and 62 MHz respectively, using CDCI₃ or DMSO as solvent and referenced to residual non-deutered one. Chemical shifts are reported in δ units, in parts per million (ppm). Splitting patterns are designed as s, singlet; d, doublet; dd, double of doublets; t, triplet; q, quadruplet; m, multiplet; br, broad. ESI mass spectral analyses were recorded on a 3200 QTRAP (Applied Biosystems SCIEX) mass spectrometer. Compounds 2, 6 were synthesized according to published procedures (2: Wei, Y.; Yang, Y.; Yeh, J.-M. Chem. Mater. 1996, 8, 2659. 6: Wei, Y.; Wang, B.; Wang, W.; Tian, J. Tetrahedron Letters 1995, 36, 665).

In Examples 1 -8 below, compounds are referred to by the reference number used in Scheme 1 above.

Example 1 : 2-(5'-bromo-2, ioxane (3)

A solution of 5'-bromo-2,2'-bithiophene-5-carbaldehyde 2 (20 g, 73.2 mmol, 1 eq), p-toluenesulfonic acid (0.31 g, 1 .6 mmol, 0.052 eq) and 2,2-dimethyl-1 ,3-propanediol (1 15 g, 1 .1 mol, 15 eq) in toluene (700 mL) was refluxed during 6 h using a dean-stark apparatus and then cooled down to room temperature. The organic phase was washed one time with an aqueous solution of NaHC0₃ and three times with water, and then dried over MgS0₄ and condensed under vacuum. The crude product was recrystallized in ethanol, cooled at 0°C and filtered. This process was repeated two or three times, until no impurity remained on TLC. The product was obtained as pure white needles (24.5 g, 93%): mp=105-106 °C.¹H NMR (CDCI₃, ppm): 6=7.02 (dd, 1H, J1= 3.6 Hz, J2=0.63 Hz, 3'-H), 6.98 (dd, 2H, J1= 5.5 Hz, J2=3.8 Hz, 3-H,4'-H), 6.90 (1H, d, J= 3.8 Hz, 3'-H), 5.67 (s, 1H, CH), 3.79-3.95 (m, 4H, 2xCH2), 1.57 (s, 3H, CH3), 1.11 (S, 3H, CH3).

1³C NMR (CDCI₃, ppm): δ= 140.57 (1C, CS), 138.67 (1C, CS), 136.54 (1C, CS), 130.55 (1C, CH), 125.69 (1C, CH), 123.87 (1C, CH), 123.32 (1C, CSBr), 111.01 (1C, CH), 97.96 (C, HC02), 77.48 (2C, OCH2C), 30.23 (1C, CCH3CH3), 22.98 (1C, CH3), 21.84 (1C, CH3).

Compound 2 (5'-bromo-2,2'-bithiophene-5-carbaldehyde) was obtained as follows:

To a solution of 5-formyl-2,2'-bithiophene (18 g, 92.8 mmol) and sodium bicarbonate

(8.4 g, 97.4 mmol, 1.05 eq) in dry chloroform (160 mL) was added dropwise a solution of bromine (15.57 g, 97.4 mmol, 1.05 eq) in dry chloroform (84 mL) over a period of 1 h. The reaction mixture was refluxed for 4 h, cooled to room temperature and poured into cold water. A large volume of CHCI₃ was added and the organic phase washed with a saturated aqueous solution of NaHC0₃. Upon drying on Mg₂S0₄ and evaporation of solvent, the crude product was recrystallized twice in toluene and rinsed with pentane. The pure product was obtained as a yellow solid (19 g, 75 %): no melting point, decomposition at 145 ^<Ό.¹H NMR (CDCI₃, ppm): δ= 9.87 (s, 1H, CHO), 7.66 (d, J=3.9 Hz, 1H, 4'-H), 7.18 (d, J=4.0 Hz, 1H, 3'-H), 7.11 (d, J= 3.9 Hz, 4-H), 7.04 (d, J=4.0 Hz, 1H, 3- H). ¹³C NMR (CDCI₃, ppm): δ= 181.68 (1C, CHO), 145.77 (1C, CS), 141.92 (1C, CS), 137.36 (1C, CS), 137.23 (1C, CH), 131.16 (1C, CH), 126.17 (1C, CH), 124.34 (1C, CH), 114.12 (1C, CBr). Example 2: Tri butyl [5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]stannane (4)

A solution of n-BuLi in hexane (0.57 ml, 0.917 mmol, 1 .6 M) was added dropwise into a stirred solution of 2-(5'-bromo-2,2'-bithien-5-yl)-5,5-dimethyl-1 ,3-dioxane 3 (0.3 g, 0.834 mmol) in dry THF (10 ml) at -78°C. After 40 min, tri-n-butylchlorostannane (0.249 ml, 0.917 mmol) was added slowly at -60 °C and the mixture was left to reach room temperature. The reaction was followed by TLC and. When the starting product was consumed (about 1 h after the Bu₃SnCI addition), the mixture was added to water (50 ml) and extracted with diethyl ether (200 ml). The combined organic layers were dried over magnesium sulfate, and the solvent was removed in vacuum to give the corresponding product as colorless oil. This product was used in the Stille coupling without further purification. ¹ H NMR (CDCI₃, ppm): 6=7.17 (d, 1 H, J= 3.32 Hz, 4'-H), 6.93 (m, 3H,3-H,3 -

H, 4'-H), 5.51 (s, 1 H, CH), 3.60 (m, 4H, 2xCH2), 1 .43-1 .52 (m, 5H, 3x(CH2)2CH2CH3),

I .16-1 .31 (m, 12H, 3x(CH2)2CH2CH3), 0.77-1 .04 (m, 16H, 3x(CH2)2CH2CH3).

Example 3: 5-bromo, 5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene (7)

Compound 6 may be prepared from compound 5 according to the method disclosed by Wei Y., Wang B., Wang W. and Tian J., Tetrahedron Letters, Vol. 36, No. 5, pp. 665- 668, 1995.

A solution of 6(2 g, 5.63 mmol), p-toluenesulfonic acid (55.7 mg, 0.29 mmol) and 2,2-diethylpropane-1 ,3-diol (1 1 .16 g, 84.44 mmol) in dry toluene was refluxed under argon during 6 h using a dean-stark apparatus and cooled to room temperature. The reaction mixture was condensed under vacuum and methanol (100 mL) was added. After 30 min of vigorous stirring, the precipitate was filtered and washed with methanol. 7 was obtained as a yellow powder (2.34 g, 89 %): mp=136-137^<O. ¹ H NMR (CDCI₃, ppm): 6=0.81 (t, ³J= 7.58 Hz, 3H), 0.89 (t, ³J= 7.58 Hz, 3H), 1 .14 (q, ³J= 7.58 Hz, 2H), 1 .82 (q, ³J= 7.58 Hz, 2H), 3.59 (dt, ²J= 1 1 .69 Hz, ⁴J= 1 .42 Hz, 2H), 3.95 (dt, ²J= 1 1 .69 Hz, ⁴J= 1 .42 Hz, 2H), 5.61 (s, 1 H), 6.90 (d, ³J= 3.79 Hz, 1 H), 6.97 (d, ³J= 3.79 Hz, 1 H), 6.99 (d, ³J= 3.79 Hz, 1 H), 7.02 (d, ³J= 3.79 Hz, 1 H), 7.04 (d, ³J= 3.79 Hz, 1 H), 7.05 (d, ³J= 3.79 Hz, 1 H). Anal, calcd for C₂₀H₂₁ BrO₂S₃: C, 51 .17; H, 4.51 ; O, 6.82; S, 20.49. Found: C, 51 .27; H, 4.43; O, 6.97, S, 19.62. Mass spectrum (ESI-MS): 468.9 [M+H]⁺. ¹³C NMR (CDCI₃, ppm): 6=6.61 (1 C, CHS), 7.55 (1 C, CHS).

Example 4: Tri butyl [5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthien-5-yl]stannane (8)

A solution of n-BuLi in hexane (0.479 ml, 0.767 mmol, 1 .6 M) was dropped into a stirred solution of 2-(5"-bromo-2,2':5',2"-terthien-5-yl)-5,5-diethyl-1 ,3-dioxane 7 (0.3 g, 0.639 mmol) in dry THF (10 ml) at -78 ^<Ό. After 40 min, tri-n-butylchlorostannane (0.191 ml, 0.703 mmol) was added slowly at -60 °C and the mixture was left to reach room temperature. The reaction was followed by TLC. When the starting product was consumed (about 45 min after the Bu₃SnCI addition), the mixture was added to water (50 ml) and extracted with diethyl ether (200 ml). The combined organic layers were dried over magnesium sulfate, and the solvent was removed in vacuum to give the corresponding product as colorless oil. This product was used in the Stille coupling without further purification.

Example 5: 5"-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene-5-carbaldehyde (9)

To a deoxygenated solution of freshly distilled 5-bromo-2-thiophenecarboxaldehyde (4.79 mmol, 0.567 mL) and tributyl[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5- yl]stannane 4 (5.28 mmol, 3.01 g) in DMF (15 ml) was added Pd(PPh₃)₄ (0.095 mmol, 1 10 mg). The mixture was heated at 60 °C until the starting material was consumed according to TLC analysis (~4 h). The reaction mixture was cooled to room temperature and poured into water. The resulting yellow suspension was filtered and washed with water, diethyl ether and pentane. The product was obtained as yellow crystals (1 .44 g, 77 %): mp=174- 175^<Ό. Anal. Calcd. for Ci₉H₁₈0₃S₃: C, 58.43; H, 4.65; O, 12.29; S, 24.63. Found: C, 58.30; H, 4.70; O, 12.9, S, 24.81 . Mass spectrum (ESI-MS): 391 .1 [M+H]⁺, 413.1 [M+Na]⁺. ¹ H NMR (CDCI₃, ppm): 6=9.84 (s, 1 H, CHO), 7.64 (d, 1 H, J= 3.9 Hz, 3-H), 7.24 (d, J=3.7 Hz, 1 H, 4-H), 7.22 (d, J=3.9 Hz, 1 H, 3"-H ), 7.03-7.1 1 (m, 3H,3"-H,4'-H,4"-H), 5.61 (s, 1 H, CH), 3.62- 3.78 (m, 4H, 2xCH₂), 1 .28 (s, 3H, CH3), 0.80(s, 3H, CH3).

Example 6: 5"'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2^,:5',2":5",2^,"-quaterthiophene-5- carbaldehyde (10)

The synthesis of this compound was performed using the same procedure as described for 9, starting from 5'-bromo-2,2'-bithiophene-5-carbaldehyde 2 (0.984 g, 3.60 mmol), tributyl[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]stannane 4 (2.26 g, 4 mmol), and Pd(PPh₃)₄ (208 mg, 0.18 mmol). At the end of the reaction, the mixture was cooled to room temperature and filtered. The crude product was dissolved in a large volume of CHCI₃ and the solution was filtered over celite. The solvent was evaporated under vacuum and the as obtained solid was recrystallized with a minimum volume of CHCI₃. The product was obtained as orange crystals (1 .27 g, 74.7 %): mp=234-236°C. Anal, calcd for C₂₃H₂o0₃S₄: C, 58.44; H, 4.26; O, 10.15; S, 27.14. Found: C, 58.04; H, 4.33; S, 27.18. Mass spectrum (ESI-MS): 472.9 [M+H]⁺. ¹ H NMR (CDCI₃, ppm): 6=9.79 (s, 1 H, CHO), 7.61 (d, 1 H, J= 3.9 Hz, 3-H), 7.21 (d, J=3.9 Hz, 1 H, 4-H), 7.17 (d, J=4.10 Hz, 1 H, 3"'-H ), 6.99-7.06 (m, 5H,3'-H, 3"-H, 4'-H, 4"-H, 4"'-H), 5.56 (s, 1 H, CH), 3.60- 3.73 (m, 4H, 2xCH₂), 1 .23 (s, 3H, CHS), 0.74(s, 3H, CH3).

Example 7: 5""-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2':5',2":5",2"':5"',2""- quinquethiophene-5-carbaldehyde (11 )

To a deoxygenated solution of 5"-bromo-2,2':5',2"-terthiophene-5-carbaldehyde 6 (0.69 mmol, 245 mg) and tributyl[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5- yl]stannane 4 (0.79 mmol, 449 mg) in DMF (5 ml) was added Pd(PPh₃)₄ (3.5x10^"3 mmol, 4.0 mg). The mixture was heated at 60 °C until the starting material was consumed according to TLC analysis (-20 h). The reaction mixture was cooled to room temperature and added to water. The orange suspension formed was filtered and washed with water, diethyl ether and pentane. The product was then recrystallized in dichlorobenzene, filtered and washed with pentane to afford orange crystals. The product was obtained as orange crystals (263 mg, 68.7 %). Anal. Calcd. for C₁₉H₁₈0₃S3: C, 58.45; H, 4.00; O, 8.65; S, 28.90. Found: C, 58.15; H, 3.99; O, 8.42, S, 29.21 . Mass spectrum (ESI-MS): 554.9 [M+H]⁺.

Example 8: 5""-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2^,:5',2":5",2"^,:5"',

2""-quinquethiophene-5-carbaldehyde (12)

To a deoxygenated solution of 5'-bromo-2,2'-bithiophene-5-carbaldehyde 2 (0.581 mmol, 156 mg) and tributyl[5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthien-5-yl]stannane 8 (0.639 mmol, 434 mg) in DMF (5 ml) was added Pd(PPh₃)₄ (3.1 x10^~3 mmol, 3.68 mg). The mixture was heated at 60 °C until the starting material was consumed according to TLC analysis (-20 h). The reaction mixture was cooled to room temperature and added to water. The orange suspension formed was filtered and washed with water, diethyl ether and pentane. The product was then recrystallized in toluene, filtered and washed with pentane to afford orange crystals (95.8 mg, 28.3 %). Anal, calcd for C₁₉H₁₈0₃S3: C, 59.76; H, 4.50; O, 8.24; S, 27.51 . Found: C, 55.52; H, 4.26; O, 8.82, S, 25.16. Mass spectrum (ESI-MS): 583 [M+H]⁺.

Example 9:

[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]acetaldehyde 13

To a solution of 2-(5'-bromo-2,2'-bithien-5-yl)-5,5-dimethyl-1 ,3-dioxane 3 (1 .6 g, 4.45 mmol) in THF (48 mL) maintained at -78 °C was added dropwise a solution of n-BuLi in hexane (2.14 mL, 5.34 mmol, 2.5 M). After 30 min at -78 °C, a solution of DMF (1 .03 mL, 13.4 mmol) in THF (15 mL) was added dropwise and the mixture was left to reach slowly room temperature. The reaction was monitored by TLC. After 4 h, diethyl ether (60mL) and a saturated aqueous solution of NH₄CI (60 mL) were added. The aqueous layer was extracted with diethyl ether. The ether layers were combined, dried over MgS0₄ and evaporated to dryness under vacuum. The crude solid was washed with diethyl ether and pentane to give a white powder corresponding to pure acetal derivative (1 .20 g, 89 %): mp=126-127 °C. Anal. Calcd. for C₁₅H₁₆0₃S₂: C, 58.41 ; H, 5.23; S, 20.79. Found: C, 58.13; H, 5.29; S, 20.75. Mass spectrum (ESI-MS): 309.2 [M+H] ⁺. ¹ H NMR (CDCI₃, ppm): 6=9.83 (s, 1 H, CHO), 7.64 (d, 1 H, J= 3.9 Hz, 3-H), 7.22-7.24 (m, 2H, 4-H, 3'-H ), 7.06 (dd, 1 H, J1 =3.80 Hz, J2=0.64 Hz, 4'-H), 5.60 (s, 1 H, CH), 3.61 - 3.77 (m, 4H, 2xCH₂), 1 .26 (s, 3H, CH₃), 0.79 (s, 3H, CH₃). ¹³C NMR (CDCI₃, ppm): δ= 181 .61 (1 C, CHO), 147.01 (1 C, CS), 143.10 (1 C, CSCOO), 141 .72 (1 C, CS), 137.35 (1 C, CH), 136.07 (1 C, CS), 126.09 (1 C, CH), 125.52 (1 C, CH), 124.27 (1 C, CH), 97.75 (1 C, C0₂), 77.45 (2C, 0CH₂C), 30.17 (1 C, CCH₃CH₃), 22.87 (1 C, CH₃), 21 .73 (1 C, CH₃). Example 10: Synthesis of a semi-conducting oligothiophene

The synthesis is carried out according to Scheme 2 above. The compounds are referred to by the reference number used in Scheme 2.

3,6-dimethoxy-9H-carbazole 7

This compound is described in literature (Holzapfel, M.; Lambert, C. J. Phys. Chem. C, 2008, 112 (4), 1227-1243).

To a solution of 3,6-dibromo-9/-/-carbazole 8 (4 g, 12.3 mmol) and Cul (9.85 g, 51 .7 mmol) in dry DMF (130 mL) under argon atmosphere was added MeONa (24.6 mmol in 67 mL of MeOH). The reaction mixture was refluxed for 3 h under argon atmosphere and cooled down to room temperature. Ethyl acetate (300 mL) was added and the reaction mixture was filtered on Celite. The filtrate was washed with water (200 mL) and the aqueous phase was extracted with ethyl acetate (2 x 100 mL). The combined organic layers were then washed with brine and dried over MgS0₄. After evaporation of the solvents under reduced pressure, the crude product was subjected to column chromatography on silica gel eluting with heptane/dichloromethane (70/30 v:v) to pure dichloromethane. Compound 7 was obtained as a white powder (2.02 g, yield 73 %), in agreement with published data.

RMN ¹ H (CDCI₃): 5=3.94 ppm (s, 6H), 5=7.04 ppm (dd, ³J(H,H)=8.69 Hz, 2H), 5=7.29 ppm (m, 2H), 5=7.51 ppm (s, 2H).

4-(3,6-dimethoxy-9H-carbazol-9-yl)benzaldehyde 6

A mixture of 3,6-di-methoxycarbazole 7 (2.66 g, 8.54 mmol, 1 eq.), 4- bromobenzaldehyde (1 .74 g, 9.392 mmol, 1 .1 eq.), K₂C0₃ (3.541 g, 25.62 mmol, 3 eq), tri- tert-butylphosphine (51 .8 mg, 0.256 mmol, 3 mol%) and Pd(OAc)₂ (19.17 mg, 0.0854 mmol, 1 mol%) in toluol (10 ml) was boiled under reflux until the starting product has disappeared (overnight). Then the reaction mixture was cooled to RT and filtered through Celite. Water (100 ml) was added to the filtrate and the mixture was extracted with Et₂0 (2x200 ml), then the combined extracts were washed with brine (200 ml), dried with MgS0₄ and concentrated under reduced pressure until the precipitation begin to form. The filtered product 6 was then recrystallized from heptane (50 ml) and dried under vacuum overnight (2.33g, 7.03 mmol, yield 82.3 %).

RMN ¹ H (CDCI₃): 5=3.94 ppm (s, 6H), 5=7.03 ppm (dd, ³J(H,H)=9.04 Hz, 2H), 5=7.39 ppm (d, ³J(H,H)=9.04 Hz, 2H), 5=7.55 ppm (d, ⁴J(H,H)=2.53 Hz, 2H), 5=7.66 ppm (d, ³J(H,H)=8.53 Hz, 2H), 5=8.02 ppm (d, ³J(H,H)=8.53 Hz, 2H), 5=10.02 ppm (s, 1 H).

(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)methanol 5

NaBH₄ (74.9 mg, 1 .98 mmol) was added to a solution of 6 (330 mg, 0.99 mmol) in ethanol (10 mL). The reaction mixture was refluxed for 30 min and cooled down to room temperature. After removing the solvent under reduced pressure, the residue was taken with dichloromethane (50 mL) and the solution was washed with saturated aqueous NH₄ ⁺CI^". The aqueous layer was extracted with dichloromethane (2 x 50 mL). The combined organic layers were dried over MgS0₄ and evaporated to dryness under vacuum. Compound 5 was obtained as a white powder (305 mg, yield 92 %).

RMN ¹ H (CDCI₃): 5=3.95 ppm (s, 6H), 5=4.81 ppm (s, 2H), 5=7.03 ppm (dd, ³J(H,H)=9.04 Hz, 2H), 5=7.2 ppm (d, ³J(H,H)=9.04 Hz, 2H), 5=7.56 ppm (m, 6H).

(E)-5'-(4-(3,6-dimethoxy-9H-carbazol-9-yl)styryl)-2,2'-bithiophene-5-carbaldehyde 2

HBrPPh3 (403.62 mg, 1 .18 mmol) was added to a solution of 5 (280 mg, 0.84 mmol) in dry chloroform (7 mL). The solution was refluxed for 48 h and filtered. The white powder (4-(3,6-dimethoxy-9H-carbazol-9-yl)benzyl)triphenylphosphonium bromide 4) was used in the following step without further purification. A mixture of compound 4 (461 .4 mg, 0.70 mmol), 5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithiophene-5-carbaldehyde prepared according to example 9 (218.9 mg, 0.61 mmol), f-BuOK (595.7 mg, 48.7 mmol) in THF (75 mL) was stirred 3 h at RT under argon atmosphere. After addition of water (200 mL), the mixture was extracted 3 times with dichloromethane (75 mL). The combined organic layers were dried over MgS0₄. Evaporation of the solvent under reduced pressure and addition of heptane (100 mL) led to the precipitation of the acetal derivative. After filtration and washing of the solid with pentane, the compound was subjected to an acidic treatment to effect aldehyde deprotection, using a mixture of H₂0 (10 mL) and CF₃COOH (12 mL) in CHCI₃ (50 mL). The reaction mixture was stirred for 4 h at room temperature. A saturated solution of NaHC0₃ was carefully added and the organic phase was washed 3 times with sat. NaHC0₃ then with water. The organic layer was dried over MgS0₄ and evaporated to dryness. The crude product was then dissolved in dichloromethane (50 mL), and MeOH (100 mL) was added. Dichloromethane evaporation led to the precipitation of an orange powder which was recovered by filtration. Subsequent chromatography of the solid on silica gel eluting with pure dichloromethane afforded compound 2 as an orange powder (130.8 mg, yield 30 % over 3 steps).

RMN ¹ H (DMSO): 5=3.92 ppm (s, 6H), 5=7.08 ppm (dd, ³J(H,H)=8.85 Hz, ⁴J(H,H)=2.53 Hz, 2H), 5=7.22 ppm (d, ³J(H,H)=16.27 Hz, 1 H), 5=7.35 ppm (d, ³J(H,H)=3.95 Hz, 1 H), 5=7.40 ppm (d, ³J(H,H)=9 Hz, 2H), 5=7.61 ppm (d, ³J(H,H)=16.27 Hz, 1 H), 5=7.60 ppm (d, ³J(H,H)=3.95 Hz, 1 H), 5=7.63 ppm (d, ³J(H,H)=3.79 Hz, 1 H), 5=7.63 ppm (d, ³J(H,H)=8.37 Hz, 2H), 5=7.87 ppm (d, ⁴J(H,H)=2.53 Hz, 2H), 5=7.89 ppm (d, ³J(H,H)=8.83 Hz, 2H), 5=8.05 ppm (d, ³J(H,H)=4.1 1 Hz, 1 H), 5=9.93 ppm (s, 1 H). (E)-2-cyano-3-(5'-(4-(3,6-dimethoxy-9H-carbazol-9-yl)styryl)-2,2'-bithiophen-5- yl)acrylic acid 1

To a solution of compound 2 (120 mg, 0.23 mmol) in acetonitrile (8 mL) was added cyanoacetic acid (46 mg, 0.46 mmol) and then piperidine (79.3 μί). The reaction mixture was refluxed overnight under argon atmosphere. After cooling of the mixture down to room temperature and filtration, the precipitate was washed with acetonitrile. The product was dispersed in dichloromethane (40 mL) using sonication. Reducing of the solvent volume to 5 mL under reduced pressure led to the precipitation of compound 1 as an orange solid (142.3 mg, 92 %). The structural analyses indicate the solid so-obtained is a stoichiometric mixture of one piperidine molecule and one molecule 1. It was used without further purification to produce the nanohybrids.

RMN ¹ H (DMSO): 5=1 .56 ppm (m, 2H), 5=1 .66 ppm (m, 4H), 5=3.01 ppm (t, 4H), 5=3.36 ppm (s, 1 H), 5=3.88 ppm (s, 6H), 5=7.04 ppm (dd, ³J(H,H)=9 Hz, ⁴J(H,H)=2.53 Hz, 2H), δ=7.18 ppm (d, ³J(H,H)=16.1 1 Hz, 1 H), 5=7.28 ppm (d, ³J(H,H)=3.95 Hz, 1 H), 5=7.37 ppm (d, ³J(H,H)=9 Hz, 2H), 5=7.48 ppm (d, ³J(H,H)=3.95 Hz, 2H), 5=7.57 ppm (d, ³J(H,H)=16.1 1 Hz, 1 H), 5=7.60 ppm (d, ³J(H,H)=9 Hz, 2H), 5=7.70 ppm (d, ³J(H,H)=4.27 Hz, 1 H), 5=7.83 ppm (d, ⁴J(H,H)=2.53 Hz, 2H), 5=7.85 ppm (d, ³J(H,H)=9 Hz, 2H), 5=8.09 ppm (s, 1 H), 5=9.09 ppm (s, 1 H). Anal. Calcd. for (C₃₄H_{24 2}O₄S₂ + 1 eq. of piperidine): C, 69.51 ; H, 5.24; O, 9.50; S, 9.52; N, 6.24. Found: C, 68.25; H, 5.20; O, 9.26; S, 9.40; N, 6.07. Mass spectrum ESI-MS, positive mode: 589.1 [M+H]⁺, 606.2 [M+NH₄]⁺, 61 1 .1 [M+Na]⁺, 627.2 [M+K]⁺. Mass spectrum ESI-MS, negative mode: 587.2 [M-H]^~. Example 1 1 : Assembly of the DMC2T-ZnO nanorods and characterization of the photovoltaic properties in solution-processed devices

Assembly: DMC2T-ZnO nanorods are produced by simply mixing ZnO nanorods and the compound DMC2T in chlorobenzene at room temperature. Under these conditions, the DMC2T molecules graft via the COOH- groups onto the surface of the ZnO nanorods. This process leads to self-assembled core-shell structures, which represents a coaxial p-n heterojunction. The ZnO nanorods used in the experiments were prepared according to a published procedure. [C. Martini, G. Poize, D. Ferry, D. Kanehira, N. Yoshimoto, J. Ackermann, F. Fages, ChemPhysChem 2009, 10, 2465]. The nanorods were separated from the seed solution by several precipitation and washing steps using methanol and transferred to chlorobenzene.

Solar cell fabrication and characterization: Solar cells were prepared on top of ITO glass substrate that has a sheet resistivity of 30 Ohm/SQ. A thin layer (~100nm) of PEDOT:PSS (poly(ethylenedioxythiophene): polystyrenesulfonate) (H-Starck, Germany) was spin coated (5000 rpm for 50 seconds) on top of the ITO to serve as a hole-only transport layer while also aiding to smooth out the ITO surface. The PEDOT:PSS layer was subsequently annealed in air at 140 °C during 10 minutes. Then DMC2T and ZnO NR were mixed in chlorobenzene with DMC2T mass ratio of R=5 (that is 5 mol/mg ZnO) in DMC2T:ZnO using a ZnO concentration of 30 mg/ml. The photoactive solution was continuously sonicated in a water bath at 50°C before spin coating. The DMC2T-ZnO solution was spin coated (1500 rpm for 20 seconds) on top of the PEDOT:PSS layer and left drying under Argon. The final step is the deposition of electrodes through evaporation of aluminum (80 nanometers) under vacuum. Figure 1 represents the device structure. l-V measurements were performed in the dark and under 100 mW/cm₂ of AM1 .5 illumination using a 150 W class AAA simulator from Oriel. External Quantum Efficiency measurements (EQE) were measured in air using a white-light halogen tungsten source combined with a Cornerstone monochromator with the spectral intensity calibrated using a reference silicon solar cell.

Photovoltaic properties of DMC2T-ZnO nanorod layers. Table 1 lists the photovoltaic parameters of the solar cells obtained with active layers of DMC2T-ZnO nanorods, while Figures 2 and 3 show the corresponding l-V curves and EQE spectrum.

Cell Voc Jsc F.F. Efficiency(%) R_Series (Q) Rshunt (Ω)

(Volts) (mA/cm²)

DMC2T- 0.66 -1 .59 34.26 0.360 175.44 727.27

ZnO Table 1 : Photovoltaic Properties of a typical DMC2T-ZnO solar cell

The DMC2T-ZnO devices show clearly pronounced photovoltaic behavior: diode like rectifying behavior in the dark, photocurrent density Jsc = 1 ,59 mA/cm2 and open circuit voltage Voc = 0,66 V under illumination. Especially the high EQE value of 34 % at 450 nm indicates that the solar energy conversion of DMC2T layer is efficient.

Example 12: Comparison of DMC2T with prior art

The properties of DMC2T were compared with those of C212, a dye known to give specially high efficiencies up to 6,1 % in Dye sensitized solar cells (DSSCs based on Ti02; ref: D. Shi, Y. Cao, N. Pootrakulchote, Z. Yi, M. Xu, S. M. Zakeeruddin, M. Graetzel, J. Phys. Chem. C 2008, 1 12, 17478.)

To study the photovoltaic properties of C212 molecule after grafting onto ZnO nanorod surface, active layer solutions of nanohybrids with different organic:inorganic mass ratios R4-R8 were prepared in chlorobenzene and sonicated in a 40 °C heat bath before spin coating on top of the PEDOT covered with ITO's. The solubility of the organic molecule C212 was not sufficient when working at high concentrations (R6 and R8) despite heat and sonication treatments. Therefore spin coating of the C212-ZnO solution lead to the presence of non-dissolved clusters in the films of mass ration R6 and R8.

The Table 2 and Figures 4 and 5 show the photovoltaic characteristics of the solar cells obtained with C212. Only devices using mass ratio R6 and R8 show photovoltaic properties.

Cell (NR Voc Jsc F.F. Efficiency(%) Rseries (Ω) Rshunt (Ω) 50 nm) (Volts) (mA/cm²)

R6 0.62 -1 .01 29.16 0.183 400.00 769.23

R8 0.8 -0.67 25.96 0.139 1081 .08 1333.33

Table 2: Summary of photovoltaic parameters for best performing devices C212-ZnO

Clearly, the performance of C212-ZnO solar cells was lower than that of devices obtained with DMC2T. Photocurrent J_sc and the fill factor are clearly lower. The low J_sc is also reflected in the low EQE values with a maximum 18 % at 455 nm. One major problem represents the low solubility of the C212 molecules, which hinders the formation of an efficient bulk heterojunction. In conclusion, C212 is not as efficient for coaxial heterojunction solar cells as DMC2T, although when applied to dye sensitized solar cells more than 6% efficiency can be obtained. This justifies the superiority of DMCT with respect to the "Nanohyba" application, as compared to structurally-related dyes which are known as reference compounds in DSSC technology. This can be explained that the fact that the requirements the dye compound must fulfil is different, although the chemical structures are somewhat close, depending on the kind of application targeted, either DSSC or "Nanohyba"-type solar cells.

Claims

1 . An oligothiophene derivative of formula (I):

wherein:

- n is an integer comprised between 2 and 10;

- X is chosen from the group consisting in H, a halogen atom, a CHO group, a Sn- (R)₃ group where Sn represents the Tin atom and where R is C1 -C6 alkyl,

- Y is a group of formul

where each R1 , R2, R3, R4, R5, R6 are identical or different and independently chosen from H, C1 -C4 alkyl; is the bond linking Y to the thiophene moiety and

p, q and r are either 0 or 1 , provided that p + q + r = 2 or 3,

with the exception of the compound where n=2, X is Sn(n-Bu)3 and Y is a group of

formula

2. The derivative according to claim 1 , wherein, in formula (\), X is chosen from a CHO group, a Sn-(R)₃ group where Sn represents the Tin atom and where R is C1 -C6 alkyl.

3. The derivative according to anyone of the preceding claims, wherein Y is a group of formula:

where each p=q=r=1 and R1 , R2, R3, R4, R5, R6 are defined as in anyone of the preceding claims.

4. The derivative according to anyone of the preceding claims, wherein n is 3, 4 or 5.

5. The derivative according to anyone of the preceding claims, wherein Y is 5,5- dimethyl-1 ,3 dioxane.

6. The derivative according to anyone of the preceding claims, wherein it is chosen from

- 2-(5'-bromo-2,2'-bithien-5-yl)-5,5-dimethyl-1 ,3-dioxane

- Tributyl[5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]stannane

- 5-bromo, 5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene

- Tributyl[5"-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2':5^,,2"-terthien-5-yl]stannane

- 5"-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2':5',2"-terthiophene-5-carbaldehyde

- 5"'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2':5',2":5",2"^,-quaterthiophene-5-carbaldehyde

- S^-CS^-dimethyl-l ^-dioxan^-y ^^^&^^^^^{^}!^^^{^}-quinquethiophene-S- carbaldehyde

- 5""-(5,5-diethyl-1 ,3-dioxan-2-yl)-2,2^,:5^,,2":5",2"^,:5"^,,2""-quinquethiophene-5- carbaldehyde

- [5'-(5,5-dimethyl-1 ,3-dioxan-2-yl)-2,2'-bithien-5-yl]acetaldehyde

7. Process of preparation of a derivative of formula (I) according to anyone of the preceding claims comprising the step of coupling a corresponding compound of formula

(III)

with a compound of formula (IV):

where n, X, Y, R are defined as in anyone of claims 1 to 6 and s is an integer comprised between 1 and 9.

8. Process of preparation of a compound of formula (I) according to anyone of claims 1 to 6 where X is CHO comprising reacting a corresponding compound of formula (I) where X is Hal with a base, followed by the action of DMF.

9. Process of preparation of a compound of formula (I) according to anyone of claims 1 to 6 where X is Hal comprising reacting a corresponding compound of formula (IX):

(IX)

with a compound of formula (VII

where X is Hal and p, q, r, R1 , R2, R3, R4, R5, R6 are defined as in anyone of claims 1 to 6.

10. An electrically semi-conducting organic compound of formula (A):

(A) wherein:

~ represents a double or triple bond;

t and u, identical or different, independently represent integers chosen from 0 or 1 to

20;

n is an integer comprised between 2 and 10;

R7 and R8, identical or different, independently represent a group chosen from H, Halogen, a C1 -C6 alkyl, OR', NR'R", S(0)_mR', where alkyl is optionally substituted by one or more of Halogen, OR', NR'R", S(0)_mR', PR'₃

where m is 0, 1 or 2 and R', R" identical or different independently represent H, or a C1 -C6 alkyl;

w represents 0 or 1 ;

z represents 0 or 1 ;

and

A represents an anchoring p-conjugated electron withdrawing moiety.

1 1 . The electrically semi-conducting compound according to claim 10 wherein the anchoring moiety A is chosen from the group consisting in carboxylic acid, phosphonic acid, sulfonic acid, phosphate, acetylacetonate (acac), hydroxamic acid.

12. The electrically semi-conducting compound according to claim 10 or 1 1 which is of formula (Aa):

(Aa)

where R7, R8, v are defined as in claim 10 or 1 1 .

13. The electrically semi-conducting organic compound according to claim 10, 1 1 or 12 which is of formula (A1 ):

and is referred to herein as DMC-2T (DiMethoxyCarbazole-biThiophene).

14. The process of preparation of a compound of formula (Aa) according to anyone of claims 10 to 13 comprising:

i) reacting a compound of formula (D):

(D)

where R7, R8 are defined as in claim 10,

with HBrPPh3, followed by

ii) coupling the obtained compound of formula (C):

(C)

with an oligothiophene of formula (I) as defined in anyone of claims 1 to 6 where X is CHO and Y is a group of formula (II), and

iii) reacting the obtained compound of formula (B)

(B)

with cyanoacetic acid.

15. The process according to claim 14, wherein said compound of formula (D) is obtained by reducing the corresponding compound of formula (E):

(E)

where R7, R8 are defined as in claim 12.

16. A compound of formula (G):

where:

R1 and R2 form together a >C=0 group with the carbon atom to which they are attached; or

one of R1 and R2 is H and the other is OH or a P⁺Ph₃ Br^" group, and

where R7, R8 are defined as in claim 10.

17. A hybrid nanocomposite material comprising an electrically semi-conducting inorganic elongated nanocrystals grafted on at least part of the surface thereof with an electrically semi-conducting organic compound according to anyone of claims 10 to 13.

18. The hybrid nanocomposite material according to claim 17 comprising a ZnO nanorod grafted with the semi-conducting organic compound according to claim 13.

19. A device comprising a thin film of a hybrid nanocomposite material according to claim 17 or 18.

20. The device according to claim 19 chosen from a solar cell and an electronic switching device.

21 . The device according to claim 19 or 20, which is a solar cell comprising a thin film of the hybrid nanocomposite material of claim 16 or 17.