Dithiophene compound, preparation and its application in organic photovoltaics thereof

Abstract

The present invention disclosed a novel (4,8-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene-2,6-diyl)bis(trimethylstannane) compound, its preparation and use for the synthesis of polymers, which is used to build devices for capacitor and solar applications. The present invention further discloses to an improved process for the synthesis of DTBDT having improved yields.

Claims

1. A polymer of formula (II): ##STR00016## wherein, ##STR00017## ##STR00018## in which R is ##STR00019##

2. The polymer as claimed in claim 1, wherein the polymer is ##STR00020##

3. The polymer of claim 1, wherein the polymer is ##STR00021## in which R is ##STR00022##

4. The polymer of claim 1, wherein the polymer is ##STR00023## in which R is ##STR00024##

5. The polymer of claim 1, wherein the polymer is ##STR00025## in which R is ##STR00026##

6. The polymer of claim 1, wherein the polymer is ##STR00027## in which R is ##STR00028##

7. The polymer of claim 1, wherein the polymer is ##STR00029## in which R is ##STR00030##

8. The polymer of claim 1, wherein the polymer is ##STR00031## in which R is ##STR00032##

9. A process for the synthesis of the polymer of formula (II) of claim 1, wherein the process comprises the steps of: dissolving a monomer of formula (I) and BrArBr in a solvent to obtain a first reaction mixture: ##STR00033## in which Ar is defined in claim 1 and Br is a bromide group; degassing the first reaction mixture of step (a) and adding tetrakis(triphenylphosphine)palladium Pd(PPh.sub.3).sub.4) to the first reaction mixture to form a second reaction mixture, followed by heating the second reaction mixture at a temperature in the range of 100 to 110 C. for a period in the range of 70 to 74 hours; adding 2-bromothiophene and trimethyl(thiophen-2-yl)stannane to the second reaction mixture to form a third reaction mixture, followed by heating the third reaction mixture at a temperature in the range of 100 to 110 C. for a period in the range of 10 to 14 hours to produce with the polymer of formula (II).

10. The process as claimed in claim 9, wherein said solvent is toluene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: depicts Energy Level Diagram of Polymers (from CV).

(2) FIG. 2: depicts Normalized Absorbance Spectra of Polymers (in DCM).

(3) FIG. 3: depicts cyclic voltammograms of the films of the polymers on a Pt electrode in acetonitrile solution containing 0.1M Bu.sub.4NPF.sub.6 at a scan rate of 50 mV/s.sup.1.

(4) FIG. 4: depicts cyclic voltammograms of the films of the P6 on a Pt electrode in acetonitrile solution containing 0.1M Bu.sub.4NPF.sub.6 at a scan rate of 50 mV/s.sup.1.

(5) FIG. 5: depicts TEM images of Polymer 4.

(6) FIG. 6: depicts TEM images of Polymer 5.

DETAILED DESCRIPTION OF THE INVENTION

(7) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(8) In view of above, the present invention provides a novel dithiophene compound, preparation and its application in organic photovoltaics thereof.

(9) In an embodiment, the present invention provides a novel compound of formula (I);

(10) ##STR00007##

(11) In preferred embodiment, said compound of formula (I) is (4,8-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene-2,6-diyl)bis(trimethylstannane).

(12) In another embodiment, the present invention provides a process for the synthesis of compound of formula (I), wherein said process comprises the step of: a) Adding t-butyl lithium to a solution of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene in solvent to obtain the reaction mixture; b) Adding trimethyltin chloride in solvent to the reaction mixture of step (a) followed by work-up and purification to afford desired compound of formula (I).

(13) In preferred embodiment, said solvent is Tetrahydrofuran (THF).

(14) In another embodiment, the present invention provides a novel 2D soluble organic covalent polymer of formula (II);

(15) In preferred embodiment, said compound of formula (II) is selected from SCOF P1 to P7.

(16) ##STR00008## ##STR00009## ##STR00010## ##STR00011##

(17) In still another embodiment, the present invention provides a process for the synthesis of polymer of formula (II), wherein said process comprises the steps of: a) Dissolving monomer of formula (I) and BrArBr in solvent to obtain the reaction mixture; b) Degassing the solution of step (a) and adding Pd(PPh3)4 followed by heating the reaction mixture at temperature in the range of 100 to 110 C. for the period in the range of 70 to 74 hrs; c) Adding 2-bromothiophene and trimethyl(thiophen-2-yl)stannane followed by heating the reaction mixture at temperature in the range of 100 to 110 C. for the period in the range of 10 to 14 hrs.

(18) In preferred embodiment, said solvent is Toluene.

(19) The above process for synthesis of compound and its polymer is shown below in Scheme A:

(20) ##STR00012## ##STR00013##

(21) In an aspect, the present invention provides the characterization data of synthesized polymers wherein FIG. 1 represents Energy Level Diagram of Polymers (from CV); FIG. 2 represents Normalised Absorbance Spetra of Polymers (in DCM); FIG. 3 shows the cyclic voltammograms of the films of the polymers on a Pt electrode in acetonitrile solution containing 0.1M Bu.sub.4NPF.sub.6 at a scan rate of 50 mV/s.sup.1; FIG. 4 shows the cyclic voltammograms of the films of the P6 on a Pt electrode in acetonitrile solution containing 0.1M Bu.sub.4NPF.sub.6 at a scan rate of 50 mV/s.sup.1; FIGS. 5 and 6 shows the TEM images of Polymer 4 and Polymer 5 respectively.

(22) In another aspect, the present invention provides the electrochemical and optical properties of synthesized polymers as shown below in Table 1.

(23) TABLE-US-00001 TABLE 1 E.sub.g HOMO LUMO E.sub.g .sub.max .sub.onset (from UV) Polymer (ev) (ev) (ev) (nm) (nm) (ev) P1 5.89 3.15 2.74 427 549 2.26 P2 5.93 3.85 2.08 429 557 2.23 P3 4.88 3.68 1.2 343 502 2.47 P4 5.89 3.92 1.97 379 530 2.34 P5 6.07 3.71 2.36 361 527 2.36 P6 5.09 3.26 1.83 382 680 1.83

(24) In one embodiment, the present invention provides a one pot gram scale synthesis of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (DTBDT) by using simple well known Grignard reaction. The compound is useful to synthesize monomers, which are then polymerized and used to build useful devices for various applications.

(25) In preferred embodiment, the present invention provides a one pot process for the synthesis of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (DTBDT) comprising the steps of: a) Adding a solution of 2-bromothiophene in solvent to a suspension of magnesium and iodine in solvent at 0 C. followed by refluxing for the period in the range of 1 to 2 hr; b) Adding 4,8-dehydrobenzo[1,2-b:4,5-b]dithiophene-4,8-dione to the reaction mixture of step (a) followed by stirring reaction mixture at temperature in the range of 50 to 60 C. for the period in the range of 5 to 7 hours; c) Cooling the mixture of step (b) to temperature at 25 C. and adding a solution of tin chloride in HCl followed by stirring for the period in the range of 1 to 2 hours to afford 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (DTBDT).

(26) In preferred embodiment, said solvent is tetrahydrofuran (THF).

(27) The process for the synthesis of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (DTBDT) by using simple well known Grignard reaction is as depicted in scheme 2:

(28) ##STR00014##

(29) The process disclosed herein leads to over 40% yield of the desired product.

(30) In a preferred embodiment, the process yields over 60% of DTBDT.

(31) The compound synthesized, DTBDT, was characterized by determining melting point, .sup.1H NMR, .sup.13C NMR and MALDI-TOF.

(32) In an aspect, the invention provides a process for the synthesis of DTBDT up to gram scale, and the process leads to the desired product with the same yield, purity and other characteristics.

(33) In another aspect, the effect of the ratio of the Grignard reagent used with respect to the amount of 4,8-dehydrobenzo[1,2-b:4,5-b]dithiophene-4,8-dione (BDT) taken was studied for its effect on the yield of DTBDT. BDT: Grignard reagent may be varied between 1:2 to 1:6, preferably 1:4.

(34) The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

EXAMPLES

Example 1: Synthesis of (4-(5-(tetramethyl-15-stannyl)thiophen-2-yl)-8-(5-trimethylstannyl) thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene-2,6-diyl)bis(trimethylstannane) (I)

(35) ##STR00015##

(36) To a solution of 400 mg (10 mmol) of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene in 15 mL of dry THF under argon at 78 C., was added 2.67 ml (1.9M, 42 mmol) of t-butyl lithium drop wise. The reaction mixture was warmed at rt for 2 h, cooled to 0 C., followed by addition of 1.01 g (42 mmol) of trimethyltin chloride in THF (1M) dropwise. The mixture was warmed to room temperature. After 24 h, the reaction mixture was quenched with water, extracted with Diethyl ether and washed with water three times. The organic phase was dried with sodium sulfate and the solvents were removed under reduced pressure to give crude product. Recrystallization from hexane gave monomer I as a yellow crystal. (953 mg, 84% yield).

(37) .sup.1H NMR (500 MHz, CDCl.sub.3, ppm): 7.70 (s, 2H), 7.66 (d, J=3.11 Hz, 2H), 7.34-7.40 (m, 2H), 0.42 (m, 18H), 0.48 (m, 18H); .sup.13C NMR (125 MHz, CDCl.sub.3, ppm): 146.30, 143.16, 142.24, 138.72, 137.25, 135.37, 131.21, 129.04, 122.34, 8.03, 8.31; MALDI-TOF/TOF-MS (in DHB matrix): m/z=1005.6575 [M], calcd. for C.sub.30H.sub.42S.sub.4Sn.sub.4: 1005.7460.

Example 2: General Procedure for the Synthesis of SCOF P1

(38) Under the protection of Argon atmosphere in a sealed tube, monomer I (1 mmol) was dissolved in 2 mL dried toluene, 2,5-dibromo-3,4-dibutylthiophene (2 mmol) dissolved in 2 ml dried toluene was added to the reaction mixture. The solution was degassed with argon for 10 min, and then 10 mol % of Pd (PPh.sub.3).sub.4 were added. After that did the freeze thaw cycles 3 times, the reactant was heated to 110 C. for 72 h. The reaction solution was cooled to room temperature, then 2-bromothiophene and trimethyl(thiophen-2-yl) stannane was added as an end capping group. Further reaction mixture was heated to 110 C. for 12 h.

Example 3: General Procedure for the Synthesis of SCOF P2 to P7

(39) Under the protection of Argon atmosphere in a sealed tube, monomer I (1 mmol) was dissolved in 2 mL dried toluene, XArX (2 mmol) dissolved in 2 ml dried toluene was added to the reaction mixture. The solution was degassed with argon for 10 min, and then 10 mol % of Pd (PPh.sub.3).sub.4 were added. After that did the freeze thaw cycles 3 times, the reactant was heated to 110 C. for 72 h. The reaction solution was cooled to room temperature, then 2-bromothiophene and trimethyl(thiophen-2-yl) stannane was added as an end capping group. Further reaction mixture was heated to 110 C. for 12 h.

(40) The reaction mixture cooled to room temperature and then passed through celite pad washed with dichloromethane. Then solution was concentrated on rotary evaporator to remove the solvent. Again dissolved crude reaction mixture in minimum amount of dichloromethane and then added methanol drop wised, formed precipitate filter through whatmann filter paper. The crude product subjected to Soxhlet extraction with pet ether, ethyl acetate and chloroform. The polymer was recovered from chloroform fraction, and the fraction was precipitated into methanol to afford the product solid (82 to 96% yield), P1 to P7 respectively.

(41) The electrochemical and optical properties of synthesized polymers are shown below in Table 2.

(42) TABLE-US-00002 TABLE 2 E.sub.g HOMO LUMO E.sub.g .sub.max .sub.onset (from UV) Polymer (ev) (ev) (ev) (nm) (nm) (ev) P1 5.89 3.15 2.74 427 549 2.26 P2 5.93 3.85 2.08 429 557 2.23 P3 4.88 3.68 1.2 343 502 2.47 P4 5.89 3.92 1.97 379 530 2.34 P5 6.07 3.71 2.36 361 527 2.36 P6 5.09 3.26 1.83 382 680 1.83

Example 4: Synthesis of 4,8-Di(thien-2-yl)-benzo[1,2-b:4,5-b]dithiophene

(43) A solution of 2.96 g (18.16 mmol) of 2-bromothiophene in 40 mL of dry THF was added dropwise to a suspension of 0.45 g (18.16 mmol) of magnesium and I.sub.2 (cat.) in 10 mL of dry THF at 0 C. The Grignard reagent was refluxed for 1 hours up to complete Mg dissolved. Subsequently, 4,8-dehydrobenzo[1,2-b:4,5-b]dithiophene-4,8-dione (1.0 g, 4.54 mmol) was quickly added, and the reaction mixture was stirred at 50 C. for 6 hours. Then the reaction mixture was cooled to ambient temperature. A solution of SnCl.sub.2 (8.2 g, 36.3 mmol) in 10% HCl (10 mL) was then added. The reaction mixture was stirred for an additional 1.5 hours and poured into ice water. The mixture was extracted twice with petroleum ether. The organic phase was dried over Na.sub.2SO.sub.4 and concentrated. The crude product was purified by silica gel chromatography using petroleum ether as the eluent to yield the pure product as a yellow solid (1.08 g, yield 67%).

(44) m.p. 207-210 C.; .sup.1H NMR (500 MHz, CDCl.sub.3, ppm): 7.59 (d, J=5.7 Hz, 2H), 7.53-7.54 (m, 2H), 7.49-7.50 (m, 2H), 7.46 (d, J=5.7 Hz, 2H), 7.25-7.26 (m, 2H); .sup.13C NMR (125 MHz, CDCl.sub.3, ppm): 139.60, 139.24, 136.72, 128.05, 127.77, 127.42, 126.40, 123.86, 123.22; MALDI-TOF/TOF-MS: m/z=353.882 [M]+, calcd. for C.sub.18H.sub.10S.sub.4: 353.9660.

Example 5: Effect of the Quantity of Bromothiophene

(45) The effect of the quantity of Bromothiophene Grignard used on the yield of the final product, DTBDT, was studied and the results are tabulated o in Table 3. The process followed was as enlisted in example 1.

(46) TABLE-US-00003 TABLE 3 Effect of the quantity of Bromothiophene Grignard used on the yield of the final product: 2-Bromothiophene Sr. No. BDT Grignard % of Product 1. 1 eq 2.2 eq 45 2. 1 eq 4.0 eq 67 3. 1 eq 6.0 eq 68

(47) When 2.2 equivalent of 2-Bromothiophene Grignard with respect to BDT was used 45% yield of DTBDT was observed. By increasing the equivalents of Grignard reagent up to 4 equivalents the yield was improved to 67%. However further increase in Grignard reagent amount to six equivalences, no improvement in yield was observed.

ADVANTAGES OF INVENTION

(48) a. Novel compound and its polymer.

(49) b. One pot synthesis of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene.

(50) c. Applications in organic photovoltaics.

(51) d. Polymers can be used to build devices for capacitor and solar applications.

(52) e. One pot process

(53) f. Standardized up to gm scale

(54) g. Process provides good yields