Claims:1. An organic semiconductor molecule having formula(A)

Formula (A)
2. An organic semiconductor molecule having formula (I)

Formula (I)
3. An organic semiconductor molecule having formula (II)

Formula (II)
4. An organic semiconductor molecule having formula (III)

Formula (III)
5. A process for the synthesis of organic semiconductor molecule of formula (A) of claim1
comprising,
i) preparation of an acene-diketopyrropyrrole derivative based intermediate compound comprising, reacting acene with a diketopyrrolopyrole derivative to obtain the intermediate compound; and
ii) reacting acene-diketopyrropyrrole derivative based intermediate compound in presence of SnCl2.H2O for aromatization to obtain the compound of formula A.
6. The process as claimed in claim 5 wherein the acene is [(13-ethynyl-6,13-dimethoxy-6,13- dihydropentacen-6-yl) ethynyl]triisopropylsilanepentacene.
7. A device comprising the organic semiconductor of formula (A) proficient of singlet fission.

, Description:Field of invention:
The present invention relates to the field of organic electronics. More specifically, the invention relates to singlet fission based organic semiconductor molecules. In particular the invention relates to organic semiconductor molecules capable of singlet fission and a method for obtaining the organic semiconductors for singlet fission, for use in devices like solar cells.
Background of invention:
Singlet fission (SF) is a process in which an organic chromophore in an excited singlet state shares its excitation energy with a neighboring ground state chromophore and both are converted into triplet excited states. Singlet fission materials are observed to increase the efficiency of solar cells by producing two triplet excitons from each absorbed photon. Acenes such aspentacene and tetracene in particular are prominent candidates for singlet fission. Singlet fission in functionalized pentacene compounds has been observed experimentally. Intramolecular singlet fission in covalently linked pentacene and tetracenedimers has also been reported.
Zirzmeieret al in Proc. Natl. AcadSci USA 2015, April 28; 112(17); 5325-5330have reported the intramolecular singlet fission, in a series of pentacene dimers where the two pentacenes are linked via a phenylene spacer in an ortho-, meta-, and para-arrangement and observed triplet quantum yield reaching 156±5%. Another report by Sanders et alin J.Am.Chem. Soc. 2015, 137(28), pp 8965-8972describes a series of singlet fission dimers, pentacenes coupled at the 2-position with and without(oligo) phenylene spacers. Using these spacers, they varied the proximity and extent of conjugation of pentacenes and thereby controlled the rate of both singlet fission and triplet recombination. A triplet pair lifetime of 270ns is provided by this combination and it can find application in solar cells. The maximum efficiency of conventional single junction solar cells is limited to 33% by the thermodynamic process.
Patent document WO2016100754 provides soluble, stable singlet fission compounds, compositions, materials, methods of their use, and methods for their preparation that provide efficient intramolecular singlet fission and multiple excitons. The singlet fission compound may be a dimer, an oligomer, or a polymer of polyoligoacenes, for example, the material is selected from the group consisting of pentacene-hexacene, 2,2 bipentacene, pentacene-tetracene, an oligomer of 1-10 tetracenes, a polymer of 11-200 tetracenes, a polymer a heteropolymer of pentacenestetracenes, and/or hexacenes of 1-200monomers in length and their combinations.
Patent document 20080191199 relates to polyacene compounds, organic semiconducting formulations and layers comprising them, a process for preparing the formulation and layer and electronic devices, including organic field effect transistors (OFETs), comprising the same.
Patent document 20150034878 relates to organic copolymers and organic semiconducting compositions comprising these materials, including layers and devices comprising such organic semiconductor compositions. The invention is also concerned with methods of preparing such organic semiconductor compositions and layers and uses thereof.
The aforementioned documents reveal the usage of singlet fission materials; for example anthracene, tetracene, rubrene, and perylene,their derivatives as the singlet fission materials. Also, there is need for semiconductors with broader absorption range capable of inducing singlet fission, specifically overlapping with high energy part of the solar spectrum. It is also necessary to have a ecofriendly, facile process of preparation of the compounds to beget compounds with broader absorption range capable of inducing singlet fission, specifically overlapping with high energy part of the solar spectrum The present invention offers a solution by providing for organic semiconductor molecules for singlet fission which increase the efficiency, with broader absorption range capable of inducing singlet fission, involving simple and ecofriendly method of preparation.
Summary of invention:
Accordingly, the present invention is related to organic semiconductor molecules which are potential materials for singlet fission. The molecules are diketopyrropyrrole derivatives with two pentacene molecules coupled via acetylene bridge thus enabling two sites for triplet formation in the same molecule and profound optoelectronic properties. The invention also relates to a method of synthesis of said singlet fission material and their usage.
Brief description of Figures:
The features of the present invention can be understood in detail with the aid of appended figures. It is to be noted however, that the appended figures illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope for the invention.
Figure 1: shows proton NMR spectra for 3,6-bis(4-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)phenyl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione- [OMe)PEN-PDPP-PEN(OMe)].
Figure 2: shows proton NMR spectrafor2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)phenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione[PEN-PDPP-PEN]
Figure 3: shows Carbon-13 NMR spectra for PEN-PDPP-PEN
Figure 4: shows Matrix assisted laser desorption studies of PEN-PDPP-PEN
Figure5: shows proton NMR spectra for 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)thiophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione[(OMe)PEN-TDPP-PEN(OMe)
Figure 6: shows proton NMR spectra for2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione[PEN-TDPP-PEN]
Figure 7: shows Matrix assisted laser desorption ionization (MALDI) mass spectrum of PEN-TDPP-PEN
Figure8: shows proton NMR spectra for 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)selenophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione [(OMe)PEN-SeDPP-PEN(OMe)
Figure 9: shows proton NMR spectrafor2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacene-6-yl)ethynyl)selenophen-2-yl-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione [PEN-SeDPP-PEN]
Figure 10: shows Matrix assisted laser desorption studies of PEN-SeDPP-PEN
Figure 11: shows absorption spectra for PEN-PDPP-PEN
Figure 12:shows absorption spectra for PEN-TDPP-PEN
Figure 13: shows absorption spectra for PEN- SePDPP-PEN
Figure 14: provides data to establish singlet fission in solution of the compound which can lead to improved efficiency when incorporated in conventional solar cells
Detailed description of invention:
The foregoing description of the embodiments of the invention has been presented for the purpose of illustration. It is not intended to be exhaustive or to limit the invention to the precise form disclosed as many modifications and variations are possible in light of this disclosure for a person skilled in the art in view of the Figures, description and claims. It may further be noted that as used herein and in the appended claims, the singular “a” “an” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by person skilled in the art.
Abbreviations:
a) (OMe)PEN-PDPP-PEN(OMe) for 3,6-bis(4-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)phenyl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.
b) PEN-PDPP-PEN for 2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)phenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.
c) (OMe)PEN-TDPP-PEN(OMe) for 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl) ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)thiophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.
d) PEN-TDPP-PEN for2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.
e) (OMe)PEN-SeDPP-PEN(OMe)for 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)selenophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.
f) PEN-SeDPP-PEN for2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacene-6-yl)ethynyl)selenophen-2-yl-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione.

The present invention is in relation to an organic semiconductor molecule having formula(A)

Formula (A)

The present invention is also in relation to an organic semiconductor molecule having formula (I)

Formula (I)
The present invnetion is also in relation to an organic semiconductor molecule having formula (II)

Formula (II)
The present invention is also in relation to an organic semiconductor molecule having formula (III)

Formula (III)
The present invention is also in relation to a process for the synthesis of organic semiconductor molecule of formula (A) of claim1, said process comprising acts of,
i) preparation of an acene-diketopyrropyrrole derivative based intermediate compound comprising, reacting acene with a diketopyrrolopyrole derivative to obtain the intermediate compound; and
ii) reacting acene-diketopyrropyrrole derivative based intermediate compound in presence of SnCl2.H2O for aromatization to obtain the compound of formula A.
In an embodiment of the present invention, the acene is [(13-ethynyl-6,13-dimethoxy-6,13- dihydropentacen-6-yl) ethynyl]triisopropylsilanepentacene.
The present invention is also in relation to a device comprising the organic semiconductor of formula (A) proficient of singlet fission.
The present invention is in relation to organic semiconductor molecules, a series of molecules for singlet fission based electronic devices, for example solar cells and a method for the synthesis of the semiconductor molecules. The molecules undergo singlet fission with a rapid time scale of subpicoseconds and is found to undergo singlet fission across the solar spectrum. Typically, the organic semiconductor molecule exhibits an absorption range of 350nm to 850nm and induces singlet fission for wavelengths ranging from 480nm to 670nm as evidenced using transient absorption spectroscopy.
The semiconductor molecule comprises two acenes linked through a spacer of Donor -Acceptor -Donor character. The acene chosen in the present invention is pentacene and the acceptor molecule is Diketopyrrolopyrrole. The three different donors used are phenyl, thiophene and selenophene.
The basic structure of the organic semiconductor molecule of the present invention which functions as a singlet fission material for use in electronic devices is given in scheme Iand is represented by Formula A

Scheme I
Experimental:
The process for the synthesis of organic semiconductor molecule comprising coupling of two pentacene molecules with a series of diketopyrropyrrole derivatives via acetylene bridge to form singlet fission system represented as PEN-XDPP-PEN, where XDPP is derivative of diketopyrropyrole is given below in scheme II:

Scheme-II
Typically the following compounds were prepared and analysed the potential as a singlet fission material.

Formula (I) Formula (II) Formula (III)

Example 1:
I] Synthesis of PEN-PDPP-PEN singlet fission material:
The organic semiconductor molecules are synthesized by a two step processes, initially through Sonogashira coupling reaction between [(13-ethynyl-6,13-dimethoxy-6,13-dihydropentacen-6-yl)ethynyl]triisopropylsilane (M1) and 2,5-dihexyl-3,6-bis(4-iodophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (M2) using Pd(PPh3)4 as the catalyst to get intermediate compound 3,6-bis(4-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)phenyl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione[(OMe)PEN-PDPP-PEN(OMe)] and then further treated for aromatization in presence of SnCl2.2H2O to get desired product 2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)phenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (PEN-PDPP-PEN) as represented in scheme III. The intermediate and final compound is purified through silica gel chromatography; structures and their purity are verified by 1H, 13C NMR, MALDI-TOF and elemental analysis
A] Synthesis of 3,6-bis(4-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)phenyl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
[(OMe)PEN-PDPP-PEN(OMe)]
To a two-neck round bottomed flask 0.2g, (0.36mmol) of[(13-ethynyl-6,13-dimethoxy-6,13-dihydropentacen-6-yl)ethynyl]triisopropylsilane (M1),0.13g, (0.18mmol)of 2,5-dihexyl-3,6-bis(4-iodophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (M2), 10mg of CuI and 40ml of, tetrahydrofuran and diisopropyllamine solvent of which the proportion is 1:1 are added. The mixture thus obtained is deoxygenated with argon for 20 min. 15mg of Pd(PPh3)4which acts as catalyst is added under argon. The reaction mixture is maintained at 45 oC for 24hand then cooled down to room temperature. 100ml water is then added and the resulting mixture is extracted with dichloromethane (3 x 50ml). The organic phase is dried over anhydrous Na2SO4 and filtered. After removing the solvent from the filtrate, the residue is purified by column chromatography on silica gel using ethyl acetate/hexane (2:8) as the eluent yielding a orange solid (0.25mg, 80%).
Proton NMR spectroscopic data of (OMe)PEN-PDPP-PEN(OMe)(Figure 1 )
1H NMR (400 MHz, CDCl3), d 8.79 (d, J = 4 Hz, 2H), 8.76 (s, 4H), 8.44 (s, 4H), 8.01-7.98 (m, 4H), 7.94-7.91 (m, 4H), 7.58-7.56 (m, 8H), 7.16-7.15 (d, 2H), 3.91-3.87 (m, 4H), 3.13 (s, 6H), 3.09 (s, 6H), 1.56 (br, s, 12H), 1.30-1.28 (m, 30H), 1.28 (br, s, 10H), 1.22-1.21 (m, 6H), 0.82-0.78 (t, J = 8 Hz, 6H) ppm.
B] Synthesis of 2,5-dihexyl-3,6-bis(4-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)phenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (PEN-PDPP-PEN).
To a solution of 3,6-bis(4-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)phenyl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, 0.2g, (0.13mmol) in 20 ml of dry THF (20mL) that has been deoxygenated by argon for 20 min, 0.14g, (0.64mmol)SnCl2.H2O is added followed by 0.5ml of 10% aq H2SO4. The reaction mixture is wrapped in aluminum foil to limit light exposure. This reaction mixture is further deoxygenated for 10 min. The reaction mixture is stirred at room temperature for 6 h. The resulting reaction mixture is filtered through pad of celite and the solvent is removed under reduced pressure. The crude product is purified by column chromatography on silica gel using ethyl acetate/hexane(1:9) as the eluent yielding a dark blue solid (0.13g, 70%).
Proton NMR spectroscopic data of PEN-PDPP-PEN (Figure 2):
Proton NMR spectra for 1H NMR (400 MHz, CDCl3), d 8.79 (d, J = 4 Hz, 2H), 8.88 (s, 4H), 8.76 (s, 4H), 7.99 (s, 8H), 7.84-7.82 (d, 8H), 7.38-7.34 (t, J = 8 Hz, 4H), 7.11-7.08 (t, J = 8 Hz, 4H), 4.02-3.98 (m, 4H), 1.63-1.62 (br, s, 6H), 1.49-1.47 (m, 30H), 1.30 (br, s, 6H), 0.92-0.89 (t, J = 8 Hz, 6H) ppm.
Carbon-14 spectroscopic data of PEN-PDPP-PEN (Figure 3):
13C NMR (100 MHz, CDCl3) d 162.49, 148.02, 132.65, 129.50, 129.47, 129.25, 128.68, 127.93, 125.67, 125.43, 118.00, 116.89, 110.08, 107.15, 106.45, 105.11, 104.74, 104.59, 41.59, 31.34, 29.16, 26.54, 19. 14, 13.99, 11.85 ppm.
Matrix assisted laser desorption studies of PEN-PDPP-PEN(Figure 4):
MALDI_Scalculated for C100H100N2O2Si2: m/z: 1417.73; found: 1417.84.

Scheme -III

II ] Synthesis of PEN-TDPP-PEN singlet fission material (scheme-IV):
A] Synthesis of 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)thiophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione [(OMe)PEN-TDPP-PEN(OMe)]
To a two-neck round bottomed flask 0.2g, (0.31mmol) of [(13-ethynyl-6,13-dimethoxy-6,13-dihydropentacen-6-yl)ethynyl]triisopropylsilane, 0.12g, (0.19mmol) of 3,6-bis(5-bromothiophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, 10 mg ofCuI and 40 ml of THF/DIPA solvent of which the proportion is 1:1 are added. The mixture is deoxygenated with argon for 20 min. 15 mg of Pd(PPh3)4is added under argon. The reaction mixture is maintained at 45 oC for 24 h and then cooled down to room temperature. 100 ml of water is then added and the resulting mixture is extracted with dichloromethane (3 x 50ml). The organic phase is dried over anhydrous Na2SO4 and filtered. After removing the solvent from the filtrate, the residue is purified by column chromatography on silica gel using ethyl acetate/hexane (2:8) as the eluent yielding an orange solid (0.18mg, 75%).
Proton NMR spectroscopic data of (OMe)PEN-TDPP-PEN(OMe) (Figure 5):
1H NMR (400 MHz, CDCl3), d 8.79 (d, J = 4 Hz, 2H), 8.76 (s, 4H), 8.44 (s, 4H), 8.01-7.99 (m, 4H), 7.94-7.91 (m, 4H), 7.58-7.56 (m, 8H), 7.16 (d, J=4Hz, 2H), 3.91-3.87 (m, 4H), 3.13 (s, 6H), 3.09 (s, 6H), 1.56 (br, s, 12H), 1.30-1.28 (m, 30H), 1.28 (br, s, 10H), 1.22-1.21 (m, 6H), 0.82-0.78 (t, J = 8 Hz, 6H) ppm.
B] Synthesis of 2,5-dihexyl-3,6-bis(5-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (PEN-TDPP-PEN).
To a solution of 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)thiophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione 0.16g (0.1mmol), in 20ml of dry THF that has been deoxygenated by argon for 20 min, 0.11g, (0.51mmol) SnCl2.H2Ois added followed by 0.5mL of 10% aq H2SO4. The reaction mixture is wrapped in aluminum foil to limit light exposure. This reaction mixture is further deoxygenated for 10 min. The reaction mixture is stirred at room temperature for 6 h. The resulting reaction mixture is filtered through pad of celite and the solvent is removed under reduced pressure. The crude product is purified by column chromatography on silica gel using ethyl acetate/hexane (1:9) as the eluent yielding a dark green solid (0.13g, 70%).
Proton NMR spectroscopic data of PEN-TDPP-PEN (Figure 6):
1H NMR (400 MHz, CDCl3), d 9.29-9.28 (d, J = 4 Hz, 2H), 8.81 (s, 4H), 8.73 (s, 4H), 7.85-7.83 (d, J = 8 Hz 4H), 7.69-7.68 (d, J = 4 Hz 2H), 7.60-7.58 (d, J = 8 Hz, 4H), 7.40 (t, J = 8 Hz, 4H), 7.21 (t, J = 8 Hz, 4H), 4.25-4.23 (m, 4H), 1.93 (br, s, 4H), 1.62-1.52 (m, 12H), 1.40 (br, s, 41H), 0.99 (t, J = 8 Hz, 6H) ppm.
Matrix assisted laser desorption studies of PEN-TDPP-PEN is given in Figure 7. MALDI-MS calculated for C96H96N2O2S2Si2: m/z: 1429.64; found: 1429.70.

Where X= S
Scheme-IV

III] Synthesis of PEN-SeDPP-PEN singlet fission material (Scheme-V):
A] Synthesis of 3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)selenophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H, 5H)-dione [(OMe)PEN-SeDPP-PEN(OMe)]
To a two-neck round bottomed flask 0.22g, (0.4mmol) [(13-ethynyl-6,13-dimethoxy-6,13-dihydropentacen-6-yl)ethynyl]triisopropylsilane, 0.15g (0.2mmol) of 3,6-bis(5-bromoselenophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, 10mg of CuI and 40ml of THF/DIPA solvent of which the proportion is 1:1 are added. The mixture is deoxygenated with argon for 20 min. 15mg Pd(PPh3)4is added under argon. The reaction mixture is maintaining at 45 oC for 24 hand then cooled down to room temperature. 100ml of Water is added and the resulting mixture is extracted with dichloromethane (3 x 50ml). The organic phase is dried over anhydrous Na2SO4 and filtered. After removing the solvent from the filtrate, the residue is purified by column chromatography on silica gel using ethyl acetate/hexane (2:8) as the eluent yielding an orange solid (0.25mg, 73%).
Proton NMR spectroscopic data of (OMe)PEN-SeDPP-PEN(OMe) is given in Figure 8.
1H NMR (400 MHz, CDCl3), d 8.76 (s, 5H), 8.74 (s, 1H), 8.43 (s, 4H), 8.01-7.98 (m, 4H), 7.94-7.92 (m, 4H), 7.58-7.56 (m, 8H), 7.33 (d, J = 8 Hz, 2H), 3.85-3.81 (m, 4H), 3.13 (s, 6H), 3.09 (s, 6H), 1.57 (br, s, 10H), 1.30-1.28 (m, 42H), 1.26 (br, s, 6H), 0.83 (t, J = 8 Hz, 6H) ppm.
B]Synthesis of 2,5-dihexyl-3,6-bis(5-((13-((triisopropylsilyl)ethynyl)pentacen-6-yl)ethynyl)selenophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (PEN-SeDPP-PEN).
To a solution of 0.16g, 0.1mmol3,6-bis(5-((6,13-dimethoxy-13-((triisopropylsilyl)ethynyl)-6,13-dihydropentacen-6-yl)ethynyl)selenophen-2-yl)-2,5-dihexylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione in 20ml of dry THF that had been deoxygenated by argon for 20 min,0.1g, (0.48mmol) of SnCl2.H2O followed by o.5ml of 10% aq H2SO4. The reaction mixture is wrapped in aluminum foil to limit light exposure. This reaction mixture is further deoxygenated for 10 min. The reaction mixture is stirred at room temperature for 6 h. The resulting reaction mixture is filtered through pad of celite and the solvent is removed under reduced pressure. The crude product is purified by column chromatography on silica gel using ethyl acetate/hexane (1:9) as the eluent yielding a dark green solid (0.10g, 68%).
Proton NMR spectroscopic data of PEN-SeDPP-PEN is given in Figure 9.
1H NMR (400 MHz, CDCl3), d 9.10 (d, J = 4 Hz, 2H), 8.97 (s, 4H), 8.86 (s, 4H), 7.89-7.87 (m, 8H), 7.75 (d, J = 8 Hz,2H), 7.41 (t, J = 8 Hz, 8H), 4.21-4.18 (m, 4H), 1.55 (br, s, 6H), 1.40-1.38 (br, s, 42H), 1.26 (br, s, 10H), 1.0 (t, J = 8 Hz, 6H) ppm.
Matrix assisted laser desorption studies of PEN-SEDPe-PEN is given in Figure 10. MALDI-MS calculated for C96H96N2O2Se2Si2: m/z: 1523.53; found: 1523.62.

Where X= Se
Scheme-V
Spectroscopic analysis of the organic semiconductor molecule.Transient absorption studies establish singlet fission in the molecule. The rise of triplet absorption at 504 nm (B) and ground state bleach rise around 620 (A) nm are of the same order which is typical of the timescale for singlet fission process. This serves as an evidence for singlet fission. Hence we believe incorporation of a layer of material capable of singlet fission into solar cells can boost its efficiency.
The steady state absorption spectral studies (Figures 11-13) and the transient absorption spectral studies (Figure-14) verify that the singlet fission based organic semiconductor molecules of the present invention, when incorporated in devices optimize the efficiency of the device. The organic semiconductor molecules that undergo single fission can be included as a film in optoelectronic devices such as solar cells, photodetectors, photosensors and the like. A solar cell with an ideal singlet fission material can have an increased efficiency up to 44%.
The experimentally verified broadened window of excitation serves as a proof for modified electronic structural properties achieved by the chemical tuning of acenes with DPP derivatives.
Thus, the present invention relates to the synthesis of organic semiconductor molecules for singlet fission. The invention couples two pentacene molecules with a series of diketopyrrolopyrrole derivatives to form Singlet fission systems with improved absorption properties and two sites for triplet formation in the same molecule. Incorporation of the singlet fission material in solar cells increases the efficiency of the electronic devices as well as provides broader absorption range capable of inducing singlet fission.
The aforesaid description is enabled to capture the nature of the invention. It is to be noted however that the aforesaid description and the appended figures illustrate only a typical embodiment of the invention and therefore not to be considered limiting of its scope for the invention may admit other equally effective embodiments.
It is an object of the appended claims to cover all such variations and modifications as can come within the true spirit and scope of the invention.