Organic dye for a dye sensitized solar cell

Abstract

Organic dye for a dye sensitized solar cell (DSSC) comprising at least one substituted pyrrole group. Said organic dye is particularly useful in a dye sensitized photoelectric transformation element which, in its turn, can be used in a dye sensitized solar cell (DSSC).

Claims

1. An organic dye having general formula (I): ##STR00077## wherein: D represents a triarylamine group having the following general formulae (VIII): ##STR00078## wherein R.sub.1 is selected from linear or branched C.sub.1-C.sub.20 alkoxyl groups, q is 1; P represents formulae (Ia):
-(T).sub.n-(P.sub.1).sub.m-(P.sub.2).sub.r-(P.sub.3).sub.s-(Ia) wherein: T represents a double carbon-carbon bond having general formula (XXVIII) or (XXIX): ##STR00079## wherein R.sub.6 and R.sub.7 each represent a hydrogen atom; n is 1; P.sub.1 represents a bivalent pyrrole group having general formula (XXII): ##STR00080## wherein: R.sub.5 is selected from linear or branched C.sub.1-C.sub.20 alkyl groups; R.sub.2 and R.sub.3, the same as each other, represent a hydrogen atom; m is 1 and r and s are 0; A represents a carboxycyanovinylene group having general formula (XLIV): ##STR00081## wherein R.sub.11 represents a hydrogen atom; and t is 2.

2. The organic dye according to claim 1, wherein R.sub.1 is a methoxyl group and R.sub.5 is a methyl group.

3. A dye-sensitized photoelectric transformation element, comprising at least one organic dye according to claim 1, said dye-sensitized photoelectric transformation element being supported on particles of a semiconductor oxide.

4. A dye-sensitized solar cell (DSSC) comprising the dye-sensitized photoelectric transformation element according to claim 3.

5. A dye-sensitized photoelectric transformation element, comprising at least one organic dye according to claim 2, said dye-sensitized photoelectric transformation element being supported on particles of a semiconductor oxide.

6. A dye-sensitized solar cell (DSSC) comprising the dye-sensitized photoelectric transformation element according to claim 5.

7. A compound of formula (F1): ##STR00082##

8. A dye-sensitized photoelectric transformation element, comprising a compound of formula (F1) according to claim 7, said dye-sensitized photoelectric transformation element being supported on particles of a semiconductor oxide.

9. A dye-sensitized solar cell (DSSC) comprising the dye-sensitized photoelectric transformation element according to claim 8.

10. The dye-sensitized solar cell (DSSC) of claim 6, wherein said DSSC has a photoelectric transformation efficiency () higher than or equal to 3.5%.

11. The dye-sensitized solar cell (DSSC) of claim 4, wherein said DSSC has a photoelectric transformation efficiency () higher than or equal to 3.5%.

12. The dye-sensitized solar cell (DSSC) of claim 9, wherein said DSSC has a photoelectric transformation efficiency () higher than or equal to 3.5%.

Description

EXAMPLES

(1) Reagents and Materials

(2) The reagents and materials used in the following examples of the invention, their optional pretreatments and producer are reported in the following list: tetrahydrofuran (THF) of Aldrich: anhydrified by distillation on lithium aluminium hydride (LiAlH.sub.4) in an inert atmosphere; potassium t-butoxide (t-BuOK) of Aldrich: used as such; dimethylformamide (DMF) of Aldrich: used as such; phosphorous oxychloride (POCl.sub.3) of Aldrich: used as such; 1,2-dichloroethane of Acros: used as such; 2-cyanoacetic acid of Aldrich: used as such; piperidine of Aldrich: used as such; chloroform (CHCl.sub.3) of Carlo Erba: used as such; dichloromethane (CH.sub.2Cl.sub.2) of Carlo Erba: used as such; ethyl acetate (AcOEt) of Carlo Erba: used as such; sodium sulfate (Na.sub.2SO.sub.4) of Carlo Erba: used as such; potassium carbonate (K.sub.2CO.sub.3) of Aldrich: used as such; tetramethylsilane (Me.sub.4Si) of Carlo Erba: used as such; deuterated dimethylsulfoxide (DMSO-d.sub.6) of Carlo Erba: used as such; deuterated chloroform (CDCl.sub.3) of Acros: used as such; N-methylpyrrole-2-carboxyaldehyde of Aldrich: used as such; 3-ethyl-2,4-dimethylpyrrole of Aldrich: used as such; pyridine of Carlo Erba: used as such; ethanol (EtOH) of Carlo Erba: used as such; sodium nitrite (NaNO.sub.2) of Aldrich: used as such; 4-aminobenzoic acid of Aldrich: used as such; hydrochloric acid at 37% (HCl) of Carlo Erba: used as such or in aqueous solution at 10%; petroleum ether (40 C.-70 C.) of Carlo Erba: used as such.

(3) The following characterization methods were used in the following examples.

(4) Reactions and Products Obtained

(5) The reactions were checked by means of thin layer chromatography, on Polygram Sil G/UV254 silica gel having a thickness of 0.20 mm, revealing the blotches separated by irradiation of the supports with UV light (254 nm and 365 nm).

(6) The compounds obtained were purified by means of flash chromatography using Merck 9385 silica gel having a particle size ranging from 230 mesh to 400 mesh (40 mm-63 mm) and a pore size equal to 60 . Said flash chromatography was carried out as described by Still, W. C. et al. in Journal of Organic Chemistry (1978), Vol. 43, pages 2923-2925.

(7) NMR Spectra

(8) The NMR spectra of the compounds obtained were obtained using a NMR Bruker ANX-500 spectrometer.

(9) For this purpose, about 10 mg of the sample to be examined were dissolved in about 0.8 ml of a suitable deuterated solvent directly inside the glass tube used for the measurement. The scale of chemical shifts was calibrated with reference to the tetramethylsilane signal set at 0 ppm.

Example 1

(10) Preparation of the Compound F1

(11) ##STR00067##

(12) The compound F1 was obtained according to the following Scheme 1:

(13) ##STR00068##
wherein: (i) indicates [(1-methyl-1-H-pyrrol-2-yl)methyl]triphenylphosphonium iodide, potassium t-butoxide (t-BuOK), anhydrous tetrahydrofuran (THF); (ii) indicates dimethylformamide (DMF), phosphorous oxychloride (POCl.sub.3), 1,2-dichloroethane; (iii) indicates 2-cyanoacetic acid, piperidine, chloroform (CHCl.sub.3).

Synthesis of N,N-bis-{4-[N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (2)

(14) 0.497 g (1.5 mmoles) of N,N-bis-(4-formylphenyl)-p-methoxyaniline (1) [obtained as described by El-Khouly M. E. et al., in The Journal of Physical Chemistry B (2008), Vol. 112, pages 3910-3917], 1.55 g (3.2 mmoles) of [(1-methyl-1-H-pyrrol-2-yl)methyl]triphenylphosphonium iodide [obtained as described by Rawal V. H. et al., in The Journal of Organic Chemistry (1987), Vol. 52, pages 19-28] and 30 ml of anhydrous tetrahydrofuran (THF) were introduced into a 250 ml flask: 0.37 g (3.3 mmoles) of potassium t-butoxide (t-BuOK) were then added, in small portions, to the solution obtained. The reaction mixture obtained was left, under stirring, at room temperature (25 C.), for the whole night. The reaction was then quenched by adding 30 ml of water and subsequently 30 ml of ethyl acetate (AcOEt) and the whole mixture was left, under stirring, for 1 hour and then extracted with dichloromethane (CH.sub.2Cl.sub.2) (320 ml). The organic phase obtained was washed with water (315 ml) and dried on sodium sulfate (Na.sub.2SO.sub.4). After eliminating the solvent by evaporation at reduced pressure, a yellow-orange-coloured residue was obtained, which was purified by means of flash chromatography on silica gel, using dichloromethane (CH.sub.2Cl.sub.2) as eluent, obtaining 0.10 g (yield 14%) of N,N-bis-{4-[N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (2), as a yellow-orange solid.

(15) Said N,N-bis-{4-[N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (2) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6; Me.sub.4Si) obtaining the following spectrum: .sub.H 7.44 (4H, d, J=8.6 Hz), 7.06 (2H, J=8.9 Hz), 7.01 (2H, d, J=16.2 Hz), 6.95 (2H, d, J=8.9 Hz), 6.91 (4H, d, J=8.6 Hz), 6.80 (2H, d, J=16.2 Hz), 6.76 (2H, m), 6.42 (2H, m), 6.01 (2H, t), 3.77 (3H, s), 3.67 (6H, s).

Synthesis of N,N-bis-{4-[(5-formyl-N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (3)

(16) 0.37 g (0.50 mmoles) of dimethylformamide (DMF) were introduced into a 100 ml flask, previously anhydrified and maintained under a flow of nitrogen (N.sub.2), and subsequently, after cooling to a temperature of 10 C., 0.80 g (0.50 mmoles) of phosphorous oxychloride (POCl.sub.3) were slowly added dropwise: the immediate formation of a colourless solid was observed and after 30 minutes, 5 ml of 1,2-dichloroethane were added. After the complete dissolution of the reaction mixture, 0.10 g (0.21 mmoles) of N,N-bis-{4-[N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (2), obtained as described above, dissolved in 10 ml of 1,2-dichloroethane, were added. The reaction mixture was left under stirring, at room temperature (25 C.), for the whole night. The reaction was then quenched by adding 30 ml of a saturated aqueous solution of potassium carbonate (K.sub.2CO.sub.3) and the whole mixture was left, under stirring, for 1 hour and then extracted with dichloromethane (CH.sub.2Cl.sub.2) (320 ml). The organic phase obtained was washed with water (215 ml), filtered and dried on sodium sulfate (Na.sub.2SO.sub.4). After eliminating the solvent by evaporation at reduced pressure, 0.05 g (yield 43%) of N,N-bis-{4-[(5-formyl-N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (3) were obtained as a dark orange solid.

(17) Said N,N-bis-{4-[(5-formyl-N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (3) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6; Me.sub.4Si) obtaining the following spectrum: .sub.H 9.45 (2H, s), 7.57 (4H, d, J 8.6), 7.25 (2H, d, J 16.1), 7.15 (2H, d, J 16.1), 7.09 (2H, d, J 8.9), 7.04 (2H, d, J 4.3), 7.01-6.95 (6H, m), 6.72 (2H, d, J 4.3), 4.00 (6H, s), 3.78 (3H, s).

(18) Synthesis of the Compound (F1)

(19) 0.05 g (0.09 mmoles) of N,N-bis-{4-[(5-formyl-N-methylpyrrol-2-yl)vin-2-yl]phenyl}-p-methoxyaniline (3), obtained as described above, and 10 ml of chloroform (CHCl.sub.3), were introduced into a 50 ml flask: 0.85 g (1.0 mmoles) of 2-cyanoacetic acid were then added to the solution obtained. The reaction mixture obtained was cooled to 0 C. with an ice bath and a solution of piperidine (0.102 g, 1.20 mmoles) in 5 ml of chloroform (CHCl.sub.3) were subsequently slowly added dropwise. At the end of the dripping, the reaction mixture was heated to the reflux temperature of the solvent, for 8 hours. The reaction mixture was then left to cool to room temperature (25 C.) and the formation of a precipitate was observed, which was recovered by filtration at reduced pressure obtaining a dark red solid which was subsequently dissolved in 20 ml of water and treated with 10 ml of a solution of hydrochloric acid at 10%: in this phase, the formation of a dark precipitate was observed, which was in turn recovered by filtration at reduced pressure, washed with water (215 ml) and dried under vacuum obtaining 0.026 g (yield 56%) of the compound (F1) as a purple solid.

(20) Said compound (F1) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6; Me.sub.4Si) obtaining the following spectrum: .sub.H 7.94 (2H, s), 7.57 (4H, d, J=8.9 Hz), 7.38 (2H, d, J=4.4 Hz), 7.23 (2H, d, J=16.2 Hz), 7.14 (2H, d, J=16.2 Hz), 7.02-6.94 (8H, m), 6.81 (2H, d, J=4.4 Hz), 4.00 (6H, s), 3.78 (3H, s).

Example 2

(21) Preparation of the Compound F2

(22) ##STR00069##

(23) The compound F2 was obtained according to the following Scheme 2:

(24) ##STR00070##
wherein: (i) indicates 2-cyanoacetic acid, piperidine, ethanol (EtOH).
Synthesis of the Compound (F2)

(25) 1.00 g (9.2 mmoles) of N-methylpyrrole-2-carboxyaldehyde and 10 ml of ethanol (EtOH) were introduced into a 50 ml flask. 0.77 g (9.1 mmoles) of 2-cyanoacetic acid were then added to the solution obtained. The reaction mixture obtained was cooled to 0 C. with an ice bath and a solution of piperidine (0.85 g, 10.0 mmoles) in 5 ml of chloroform (CHCl.sub.3) were subsequently slowly added dropwise. At the end of the dripping, the reaction mixture was left under stirring at room temperature (25 C.), for 18 hours. After eliminating the solvent by evaporation at reduced pressure, a dark yellow oil was obtained, which was subsequently dissolved in 20 ml of water and treated with 10 ml of a solution of hydrochloric acid at 10%: in this phase, the formation of a bright yellow precipitate was observed, which was in turn recovered by filtration at reduced pressure, washed with water (215 ml) and dried under vacuum obtaining 1.27 g (yield 79%) of the compound (F2) as a bright yellow solid.

(26) Said compound (F2) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6) obtaining the following spectrum: .sub.H 13.33 (1H, bs), 8.06 (1H, s), 7.47 (1H d), 7.39 (1H, bs), 6.39 (1H, bs), 3.80 (3H, s).

Example 3

(27) Preparation of the Compound F3

(28) ##STR00071##

(29) The compound F3 was obtained according to the following Scheme 3:

(30) ##STR00072##
wherein: (i) indicates [(1-methyl-1-H-pyrrol-2-yl)methyl]triphenylphosphonium iodide, potassium t-butoxide (t-BuOK), anhydrous tetrahydrofuran (THF); (ii) indicates dimethylformamide (DMF), phosphorous oxychloride (POCl.sub.3); (iii) indicates 2-cyanoacetic acid, piperidine, chloroform (CHCl.sub.3).

Synthesis of (E)-3-ethyl-1,2,4-trimethyl-5-(2-(1-methyl-1H-pyrrol-2-yl)vinyl)-1H-pyrrole (6)

(31) 0.860 g (5.2 mmoles) of N-methyl-4-ethyl-3,5-dimethyl-1H-pyrrole-2-carbaldehyde (5) [obtained as described by D. Brown et al., in Journal of the Chemical Society, Perkin Transactions 1 (1986), pages 455-463], 1.06 g (2.2 mmoles) of [(1-methyl-1-H-pyrrol-2-yl)methyl]triphenylphosphonium iodide [obtained as described by Rawal V. H. et al., in The Journal of Organic Chemistry (1987), Vol. 52, pages 19-28] and 30 ml of anhydrous tetrahydrofuran (THF) were introduced into a 250 ml flask: 0.28 g (2.5 mmoles) of potassium t-butoxide (t-BuOK) were then added, in small portions, to the solution obtained. The reaction mixture obtained was left, under stirring, at room temperature (25 C.), for the whole night. The reaction was then quenched by adding 30 ml of water and subsequently 30 ml of ethyl acetate (AcOEt) and the whole mixture was left, under stirring, for 1 hour and then extracted with dichloromethane (CH.sub.2Cl.sub.2) (320 ml). The organic phase obtained was washed with water (315 ml) and dried on sodium sulfate (Na.sub.2SO.sub.4). After eliminating the solvent by evaporation at reduced pressure, a yellow-orange-coloured residue was obtained, which was purified by means of flash chromatography on silica gel, using dichloromethane (CH.sub.2Cl.sub.2) as eluent, obtaining 0.30 g (yield 54%) of (E)-3-ethyl-1,2,4-trimethyl-5-(2-(1-methyl-1H-pyrrol-2-yl)vinyl)-1H-pyrrole (6), as a yellow-orange solid.

(32) Said (E)-3-ethyl-1,2,4-trimethyl-5-(2-(1-methyl-1H-pyrrol-2-yl)vinyl)-1H-pyrrole (6) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6) obtaining the following spectrum: .sub.H 6.76 (1H, d, J=16.3 Hz), 6.71-6.68 (1H, m), 6.41 (1H, d, J=16.5 Hz), 6.35 (1H, m), 6.00-5.97 (1H, m), 3.60 (3H, s), 3.45 (3H, s), 2.34 (2H, q, J=7.4 Hz), 2.12 (3H, s), 2.09 (3H, s), 0.98 (3H, t, J=7.5 Hz).

Synthesis of (E)-5-(2-(4-ethyl-1,3,5-trimethyl-1H-pyrrol-2-yl)vinyl)-1-methyl-1H-pyrrole-2-carboxaldehyde (7)

(33) 0.10 g (1.36 mmoles) of dimethyl formamide (DMF) were introduced into a 100 ml flask, previously anhydrified and maintained under a flow of nitrogen (N.sub.2), and subsequently, after cooling to a temperature of 10 C., 0.21 g (1.36 mmoles) of phosphorous oxychloride (POCl.sub.3) were slowly added dropwise: the rapid formation of a colourless solid was observed and after 30 minutes, 10 ml of dimethyl formamide (DMF) were added. After the complete dissolution of the reaction mixture and after cooling to a temperature of 10 C., 0.30 g (1.24 mmoles) of (E)-3-ethyl-1,2,4-trimethyl-5-(2-(1-methyl-1H-pyrrol-2-yl)vinyl)-1H-pyrrole (6), obtained as described above, dissolved in ml of dimethyl formamide (DMF), were slowly added dropwise. The reaction mixture was left under stirring, at 10 C., for 10 minutes. The reaction was then quenched by adding 100 ml of a saturated aqueous solution of potassium carbonate (K.sub.2CO.sub.3) and the whole mixture was left, under stirring, for 1 hour, and then extracted with dichloromethane (CH.sub.2Cl.sub.2) (320 ml). The organic phase obtained was washed with water (215 ml), filtered and dried on sodium sulfate (Na.sub.2SO.sub.4). After eliminating the solvent by evaporation at reduced pressure, a yellow-orange-coloured residue was obtained, which was purified by means of flash chromatography on silica gel using dichloromethane/ethyl acetate (CH.sub.2Cl.sub.2/AcOEt) (95:5 v/v) as eluent, obtaining 0.20 g (yield 62%) of (E)-5-(2-(4-ethyl-1,3,5-trimethyl-1H-pyrrol-2-yl)vinyl)-1-methyl-1H-pyrrole-2-carboxaldehyde (7) as a dark orange solid.

(34) Said (E)-5-(2-(4-ethyl-1,3,5-trimethyl-1H-pyrrol-2-yl)vinyl)-1-methyl-1H-pyrrole-2-carboxaldehyde (7) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6) obtaining the following spectrum: .sub.H 9.45 (2H, s), 7.57 (4H, d, J=8.6 Hz), 7.25 (2H, d, J=16.1 Hz), 7.15 (2H, d, J=16.1 Hz), 7.09 (2H, d, J=8.9 Hz), 7.04 (2H, d, J=4.3 Hz), 7.01-6.95 (6H, m), 6.72 (2H, d, J=4.3 Hz), 4.00 (6H, s), 3.78 (3H, s) (some signals are covered by the signal of the solvent).

(35) Synthesis of the Compound (F3)

(36) 0.10 g (0.37 mmoles) of (E)-5-(2-(4-ethyl-1,3,5-trimethyl-1H-pyrrol-2-yl)vinyl)-1-methyl-1H-pyrrole-2-carboxaldehyde (7), obtained as described above, and 10 ml of chloroform (CHCl.sub.3) were introduced into a 50 ml flask: 0.32 g (3.7 mmoles) of 2-cyanoacetic acid were then added to the solution obtained. The reaction mixture obtained was cooled to 0 C. with an ice bath and a solution of piperidine (0.34 g, 4.0 mmoles) in 5 ml of chloroform (CHCl.sub.3) were subsequently slowly added dropwise. At the end of the dripping, the reaction mixture was heated to the reflux temperature of the solvent, for 4 hours. The reaction mixture was then left to cool to room temperature (25 C.) and the formation of a precipitate was observed, which was recovered by filtration at reduced pressure obtaining a dark red solid which was subsequently dissolved in 20 ml of water and treated with 10 ml of a solution of hydrochloric acid at 10%: in this phase, the formation of a dark precipitate was observed, which was in turn recovered by filtration at reduced pressure, washed with water (215 ml) and dried under vacuum obtaining 0.08 g (yield 64%) of the compound (F3) as a purple solid.

(37) Said compound (F3) was characterized by means of .sup.1H-NMR (500 MHz; DMSO-d.sub.6) obtaining the following spectrum: .sub.H 7.97 (1H, s), 7.61 (1H, bs), 7.30 (1H, d, J=15.6 Hz), 7.02 (1H, bs), 6.54 (1H, d, J=15.8 Hz), 3.72 (3H, s), 3.56 (3H, s), 2.17 (6H, bs), 0.99 (3H, m) (some signals are covered by the signal of the solvent).

Example 4

(38) Preparation of the Compound F4

(39) ##STR00073##

(40) The compound F4 was obtained according to the following Scheme 4:

(41) ##STR00074##
wherein: (i) indicates hydrochloric acid (HCl), sodium nitrite (NaNO.sub.2), 4-amino benzoic acid, pyridine, water (H.sub.2O), ethanol (EtOH).
Synthesis of the Compound F4

(42) 0.90 g (6.6 mmoles) of 4-amino benzoic acid were introduced into a 150 ml flask and suspended in 16 ml of water: 4 ml of hydrochloric acid at 37% were added to the suspension obtained. 0.50 g (7.2 mmoles) of sodium nitrite in 10 ml of water were added to the solution obtained, cooled to 0 C. with an ice bath and kept under magnetic stirring, obtaining a solution comprising a diazonium salt.

(43) 0.81 g (6.6 mmoles) of 3-ethyl-2,4-dimethylpyrrole and 6 ml of pyridine were dissolved, separately, in 60 ml of ethanol, in a 100 ml flask: the solution of diazonium salt prepared as described above was slowly added dropwise to the solution obtained, maintaining the temperature between 0 C. and 5 C. At the end of the dripping, the reaction mixture obtained was left to warm up to room temperature (25 C.) and kept under stirring for 18 hours. The reaction mixture was then concentrated by evaporation of the solvent at reduced pressure observing the formation of a precipitate which was filtered at reduced pressure obtaining a dark solid. The dark solid obtained was dissolved in 3 ml of acetic acid, precipitated by adding 20 ml of petroleum ether and filtered at reduced pressure obtaining 0.04 g (yield 2%) of compound (F4) as a dark solid.

(44) Said compound (F4) was characterized by means of .sup.1H-NMR (500 MHz; CDCl.sub.3) obtaining the following spectrum: .sub.H 8.13 (2H, d, J=8.4 Hz), 7.3 (2H, d, J=8.5 Hz), 2.61 (3H, s), 2.49 (2H, q, J=8.2 Hz), 2.38 (3H, s), 0.88 (3H, t, J=6.8 Hz).

Example 5

(45) Preparation of the Compound F5

(46) ##STR00075##

(47) The compound F5 was obtained according to the following Scheme 5:

(48) ##STR00076##
wherein: (i) indicates hydrochloric acid (HCl), sodium nitrite (NaNO.sub.2), 4-amino benzoic acid, pyridine, water (H.sub.2O), ethanol (EtOH).
Synthesis of the Compound F5

(49) 0.45 g (3.3 mmoles) of 4-amino benzoic acid were introduced into a 100 ml flask and suspended in 8 ml of water: 2 ml of hydrochloric acid at 37% were added to the suspension obtained. 0.25 g (3.6 mmoles) of sodium nitrite in 5 ml of water were added to the solution obtained, cooled to 0 C. with an ice bath and kept under magnetic stirring, obtaining a solution comprising a diazonium salt.

(50) 0.36 g (3.3 mmoles) of N-methylpyrrole-2-carboxyaldehyde and 3 ml of pyridine were dissolved, separately, in 30 ml of ethanol, in a 50 ml flask: the solution of diazonium salt prepared as described above was slowly added dropwise to the solution obtained, maintaining the temperature between 0 C. and 5 C. At the end of the dripping, the reaction mixture obtained was left to warm up to room temperature (25 C.) and kept under stirring for 18 hours. The reaction mixture was then concentrated by evaporation of the solvent at reduced pressure observing the formation of a precipitate which was filtered at reduced pressure obtaining a dark solid. The dark solid obtained was dissolved in 3 ml of acetic acid, precipitated by adding 20 ml of petroleum ether and filtered at reduced pressure obtaining 0.47 g (yield 57%) of compound (F5) as a dark solid.

(51) Said compound (F5) was characterized by means of .sup.1H-NMR (500 MHz; CDCl.sub.3) obtaining the following spectrum which proved to contain two stereoisomers E and Z, which are indicated hereunder as A and B as signals could not be assigned to either structure:

(52) Isomer A: .sub.H 9.62 (1H, s), 8.18 (2H, d, J=8.2 Hz), 7.55 (2H, d, J=8.2 Hz), 7.01 (1H, d, J=4.1 Hz), 6.39 (1H, d, J=4.1 Hz), 3.97 (3H, s);

(53) Isomer B: .sub.H 9.75 (1H, s), 8.23 (2H, d, J=8.4 Hz), 7.95 (2H, d, J=8.2 Hz), 7.03 (1H, d, J=4.6 Hz), 6.76 (1H, d, J=4.5 Hz), 4.34 (3H, s).

Example 6

(54) Preparation of a Dye Sensitized Solar Cell (DSSC)

(55) The titanium dioxide (TiO.sub.2) electrodes were prepared by the deposition (doctor blade technique) of a colloidal paste containing titanium dioxide (TiO.sub.2) having a dimension of 20 nm (TiO.sub.2 paste DSL 18NR-T-Dyesol) on FTO conductive glass (Hartford Glass Co., TEC 8, having a thickness of 2.3 mm and a sheet resistance of 6 /cm.sup.2-9 /cm.sup.2), previously cleaned with water and ethanol, treated with a plasma cleaner, at 100 W, for 10 minutes, immersed in a freshly prepared aqueous solution of titanium tetrachloride (TiCl.sub.4 of Aldrich) (4.510.sup.2 M), at 70 C., for 30 minutes, and finally washed with ethanol.

(56) After a first drying at 125 C., for 15 minutes, a diffusion reflecting layer containing particles of titanium dioxide (TiO.sub.2) with dimensions >100 nm (Ti-Nanoxide R/SP-Solaronix), was deposited (doctor blade technique) on the first layer of titanium dioxide (TiO.sub.2) and sintered at 500 C., for 30 minutes. The glass coated with the film of titanium dioxide (TiO.sub.2) was cooled to room temperature (25 C.) and immersed again in a freshly prepared aqueous solution of titanium tetrachloride (TiCl.sub.4) (4.510.sup.2 M), at 70 C., for 30 minutes, finally washed with ethanol and sintered again at 500 C., for 30 minutes, obtaining a final thickness of the electrode ranging from 8 m to 12 m.

(57) After sintering, the glass coated with titanium dioxide (TiO.sub.2) film, was cooled to about 80 C.-100 C. and immediately immersed in a solution in dichloromethane (CH.sub.2Cl.sub.2) (510.sup.4 M) of the compound (F1) obtained as described in Example 1, at room temperature (25 C.), for 24 hours. The glass coated with coloured titania was washed with ethanol and dried at room temperature (25 C.), under a flow of nitrogen (N.sub.2).

(58) A Surlyn spacer having a thickness of 50 m (TPS 065093-50-Dyesol) was used for sealing the photo-anode obtained as described above and the counter-electrode consisting of platinized FTO glass (Hartford Glass Co., TEC 8, having a thickness of 2.3 mm and a sheet resistance of 6 /cm.sup.2-9 /cm.sup.2). The cell was subsequently filled, through a hole previously prepared in the platinized FTO glass, with the commercial electrolyte solution HPE of Dyesol.

(59) The active area of the cell, calculated by means of a microphotograph, was 0.1336 cm.sup.2.

(60) The photovoltaic performance of the cell was measured with a solar simulator (Abet 2000) equipped with a 300 W xenon light source, the light intensity was calibrated with a standard silicon solar cell (VLSI Standard SRC-1000-RTD-KGS), the current-voltage characteristics were obtained by applying an external voltage to the cell and measuring the photocurrent generated with a Keithley 2602A digital multimeter (3A DC, 10A Pulse). The following results were obtained: Voc (open-circuit photovoltage)=0.59 V; FF (Fill Factor)=70.8%; Jsc (short-circuit current density)=9.8 mA/cm.sup.2; (photoelectric transformation efficiency): 4.1%.