Organik ışık yayan diodlar ve güneş pili uygulamaları için tiyenotiyofen ve bor türevli moleküllerin sentezi ve karakterizasyonu
Synthesis and characterization of thienothiphene and boron containing molecules for organic light emitting diodes and solar cell applications
Yazar: PELİN ULUKAN
Danışman: PROF. DR. TURAN ÖZTÜRK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Kimya = Chemistry

Özet:
Son yıllarda gelişen teknoloji ile organik moleküllerin OLED, biyosensör, kapasitör, elektrokromik cihazlar ve fotovoltaik uygulamalar gibi farklı alanlarda kullanımı oldukça önem kazanmıştır. Moleküllerin sahip oldukları fonksiyonel gruplara göre değişen absorpsiyon, emisyon ya da kapasitör davranışları bu malzemelerin hangi alanlarda kullanılacaklarını belirlemektedir.
Tiyenotiyofen (TT) yapıları uzun π konjugasyonuna sahip olmaları ve düzlemsel yapılarından dolayı materyal kimyasında oldukça sık kullanılmaktadırlar. Yapıdaki tiyofen halkasının kükürt atomu üzerindeki eşleşmemiş elektronlar yapıya donör özelliği katmaktadır. Bu durum, tiyenotiyofen yapılarının konjuge sistemlerde de kullanılabilmelerine sebep olmaktadır.
Bu çalışmada sentezlenen bazı moleküller, düşük bant aralığının oldukça önemli olduğu güneş pili uygulamaları için sentezlenmiştir. Ayrıca bu çalışmada, topaklanmaya bağlı emisyon kavramının uygulamasının da yapılması planlanmış topaklanmaya bağlı emisyon yapması beklenen moleküller sentezlenmiştir. OLED uygulamaları için sentezlenen bu malzemelerde beklenen topaklanmaya bağlı emisyon gözlemlenememiştir ve oldukça düşük kuvantum verimleri elde edilmiştir. Güneş pili uygulamalarında kullanılmak üzere sentezlenen moleküller ise yüksek kuvantum verimlerine sahip olmalarından ötürü OLED uygulamaları için de kullanılmalarına karar verilmiştir. Sentezlenen malzemeler arasından 33, 34 ve 35 numaralı moleküllerin OLED uygulaması için oldukça yüksek kuvantum verimlerine sahip oldukları gözlemlenmiştir. Güneş pili uygulamaları için ise 33. ve 35. Maddelerin UV-Vis spektrumlarında pik bacaklarının 500 nm' ye kadar uzanmasından dolayı güneş pili uygulamalarına en yakın malzemelerin bunlar olduğu görülmektedir. Ayrıca 31, 33, 34 ve 35 maddeleri ile döngülü voltametri ölçümleri yapılarak bulunan yükseltgenme ve indirgenme potansiyelleri üzerinden elektro kimyasal bant aralıkları hesaplanmıştır. Ölçümler sırasında çalışma ve karşıt elektrot olarak Pt teli, referans elektrot olarak ise Ag teli kullanılmıştır. Elektrolit ise 0.1 M TBAPF6 ve 10-3 M monomer içeren ACN/DCM çözücü karışımı hazırlanmıştır. Döngülü voltametri çalışmasından elde edilen grafiklere bakıldığı zaman iki adet oksidasyon potansiyeli olduğu görülmektedir.
Topaklanmaya bağlı emisyon amaçlanarak sentezlenen 54 ve 62 numaralı moleküllerde ise beklenen emisyon artışı gözlemlenememiştir. Bu iki molekül, daha önce araştırma grubumuzda sentezlenen ve içerisinde TPE grubu taşımayan iki molekülün TPE ile modifiye edilmiş halidir. Moleküllere takılan TPE grubunun topaklanmaya bağlı emisyon etkisinin görülememesinin sebebi, tiyenotiyofen ve TPE yapıları arasındaki fenil grubunun TPE'yi oldukça serbest bırakması ve beklenen sterik engeli yaratamaması olarak yorumlanmıştır. Bu iki molekül OLED uygulaması için başarısız olsa da, 62 numaralı malzemenin UV-Vis spektrumuna bakıldığında, pik bacağının 500 nm' ye kadar uzandığı ancak 54 numaralı malzemenin 500 nm'den geride kaldığı gözlemlenmiştir. Dolayısıyla bu iki molekül içerisinden 62 numaralı olan, güneş pili uygulamasına daha yakındır.

Abstract:
In the last few years, with the recent developments in technology, the applications of organic molecules in OLEDs, biosensors, capacitors, electrochromic devices and organic photovoltaics became very important. Different functional groups on molecules provide different absorption, emission or capacitor characteristics and determine their usage areas.
Thienothiophene (TT) molecules with long π conjugation and planar structures have many applications in material chemistry. Because of the nonbonding electrons on sulfur atom of thiophene ring, TT structures are in donor characteristic. Thus, they can be used in conjugate systems. In this thesis work, molecules with low band gaps for solar cell applications have been synthesized. In addition to solar cell applications, some molecules which are expected to have aggregation induced emission (AIE) for OLED applications have been synthesized. However, AIE could not be observed in these molecules.
In this study, molecules which have been designed for solar cell devices demonstrated very high quantum yields and we have observed that these molecules are mainly useful for OLED applications. It is observed that the structures 33, 34, and 35 with very good quantum yields are potential OLED structures. In the UV-Vis spectra of molecules 33 and 35, it is observed that the peak tails reach upto 500 nm. As a result, these two are the most suitable ones for solar cell applications compared to the other structures. Also cyclic voltammetry measurements of molecules 31, 33, 34 and 35 have been studied and the electrocehmical band gaps were calculated by using oxidation and reduction potentials. In these measurements, a Pt wire was used as working and counter electrodes. As a reference electrode a Ag wire was used. A 0.1 M TBAPF6 and 10-3 M monomer consisting of ACN/DCM solvent mixture were prepared as the electrolyte. In cyclic voltammograms, it is noticed that there are two oxidation potentials. According to the literature, the first one belongs to TPA molecule.
On the other hand, molecules 54 and 62 which were synthesized for AIE could not have expected emissions. In our research group, these two molecules lacking of TPE and phenyl group between TPE and TT were synthesized previously. The structures 54 and 62 are the modified versions of those two molecules which have extremely low quantum yields. In 54 and 62, it was expected to have an increase in quantum yields with the AIE effect of TPE group. However, the phenyl group between TT and TPE prevented the expected steric hindrance, thus, hampering AIE. Although these two molecules are not suitable for OLED applications, in the UV-Vis spectrum of molecule 62, it is observed that the peak tail reaches 500 nm. However, for the molecule 54, it is observed that the peak tail could not reach 500 nm. So, molecule 62 is closer to solar cell applications compared to the molecule 54.
In this work different TT derivatives were synthesized containing TPA (triphenylamine), TPE (tetraphenylethene) and dimesityl borane.
	1-(4-Fluorophenyl)-2-(thiophene-3-ylthio)ethanone (22): 3-Bromothiophene (3.00 g) was solved in dry diethyl ether under N2 atmosphere. Reaction was cooled down to -78 °C and at this temperature n-BuLi (8.00 mL, 20.0 mmol) was added to the reaction mixture. After 45 min elemental sulphur (640 mg, 20.0 mmol) was added and stirred for 60 min. Then, the reaction was transferred into an ice bath. At 0 °C, 2-bromo-4-fluoroacetophenone (4.39 g, 19.3 mmol) was added to the reaction mixture. The reaction was stirred overnight under N2 atmosphere and the day after, it was extracted with DCM/water mixture. Organic phase was dried over Na2SO4 and then the solvent was evaporated under atmospheric pressure furnishing a brown oily product in 86% yield.
	3-(4-Fluorophenyl)thieno[3,2-b]thiophene (23): Polyphosphoric acid (2.91 g, 29.7 mmol) was weighed in a round bottomed flask and 5.00 mL chloro-benzene was added. The mixture was heated up to 135 °C. At this temperature, 22 (500 mg, 2.02 mmol) in 5.00 mL chloro¬benzene solvent was added to the reaction mixture dropwise. After five hours, chlorobenzene phase is separated from the PPA phase and chlorobenzene was evaporated. Then, the product was extracted with DCM-NaHCO3 solution. The product was purified with column chromatography over silica gel using n-hexane as eluent giving rise to 390 mg (84%) of a white solid product.
	2-Bromo-3-(4-fluorophenyl)thieno[3,2-b]thiophene (24): To a solution of 23 (200 mg, 850 mol) in DMF (3-5 mL), NBS (150 mg, 850 mol) was added. The reaction was carried to an ice bath and it was protected from light. After 12 h, the reaction solvent was evaporated and the product was extracted with DCM-NaHCO3 solution. Organic layer was dried over Na2SO4, filtered and evaporated by using rotary evaporator. The product was purified with column chromatography using n-hexane as mobile phase providing 54% of 24.
	4-(5-(3-(4-Fluorophenyl)thieno[3,2-b]thiophene-2-yl)thiophene-2-yl)-N,N-diphenylaniline (31): 24 (350 mg, 1.12 mmol) and 30 (1.03 g, 1.68 mmol) were weighed and taken into a coupling reactor. The reaction was stirred under nitrogen atmosphere. Then, a 5 M K2CO3 solution and THF (30 mL) were added intro the reactor. Then Pd(0)(PPh3)4 (64.0 mg, 55.4 mmol) was added to the reaction mixture as a catalyst. The reactor was closed tightly and stirred for 48 h at 80 °C. After 48 h, reaction was filtered through celite pad, and THF was evaporated. The product was precipitated from cold methanol and 530 mg (85%) of an orange solid product was obtained.
	4-(5-(5-(Dimesitylboryl)-3-(4-fluorophenyl)thieno[3,2-b]thiophen-2-yl)thiophen-2-yl)-N,N-diphenylaniline(33): 31 (350 mg, 632 mol) was solved in THF under N2 atmosphere. At -78 °C, t-BuLi (1.43 mL, 2.72 mmol) was added dropwise. After 45 minutes, dimesitylboron fluoride (670 mg, 2.72 mmol) was added. After 3 hours, the reaction was allowed to warm up to room temperature and stirred overnight under N2 atmosphere. Reaction was extracted with DCM-NaCl solution. 360 mg (70%) of the product was obtained after purification with column chromatography using n-hexane as esluent.
	4-(3-(4-fluorophenyl)thieno[3,2-b]thiophen-2-yl)-N,N-diphenylaniline(34): 24 (340 mg, 1.09 mmol) and 28 (520 mg, 1.42 mmol) were taken into a coupling reactor under N2 atmosphere. Then, 5 M K2CO3 and THF (30 mL) were added into the reactor. Pd(PPh3)4 (62.0 mg) was added and reactor was closed tightly. Reaction was stirred for 48 h at 80 °C. After 48 h it was filtered through celite. The product was purified by column chromatography using  n-hexane/DCM (15:1) Furnishing 58% (300 mg) of 34 as a pale yellow product.
	4-(5-(dimesitylboryl)-3-(4-fluorophenyl)thieno[3,2-b]thiophen-2-yl)-N,N-diphenylaniline (35): 34 (400 mg, 830 mol) was dissolved in THF (30 mL) under N2 atmosphere. The reaction was cooled down to -78 °C and t-BuLi (1.58 mL, 3.52 mmol) was added dropwise. After 45 minutes, 940 mg of dimesityboron fluoride was added and the reaction mixture was stirred for 4 h at the same temperature. Then, it was allowed to wamp up to room temperature and stirred overnight under inert atmosphere. It was extracted with DCM-NaCl solution and the crude product was purified with column chromatography using hexane solvent as mobile eluent, yielding 180 mg (28%) of green solid product.
	2,2':5',2''-Terthiophene (37): 26 (1.50 g, 7.14 mmol) was taken into a coupling reactor under inert atmosphere. 36 (0570 mg, 2.38 mmol), 5 M K2CO3 and THF (30 mL) were added into the reactor. Then, Pd2(dba)3 catalyst (180 mg, 230 mol) and tri(o-tolyl)phosphine ligand (180 mg, 4.76 mmol) were added to the reaction mixture. The reactor was closed tightly and stirred for 48 h at 80 °C. After 2 days, reaction mixture was filtered through celite and the product was purified by column chromatography using n-hexane as eluent giving rise to a pale yellow solid in 37% yield (0.22 g).
	5-Bromo-2,2':5',2''-terthiophene (38): To a concentrated solution of 37 (150 mg, 600 mol) in DMF (10 mL), NBS (110 mg, 600 mol) was added in an ice bath and in the dark medium. After 12 h, a saturated solution of NaHCO3 was poured into the reaction flask and the product was precipitated as a pale yellow solid. It was used in the next step without further purification.
	4-([2,2':5',2''-Terthiophene]-5-yl)-N,N-diphenylaniline (39): 38 (180 mg, 560 mol) and 28 (210 mg, 560 mol) were weighed and transferred into a coupling reactor under N2 atmosphere. A solution of 5 M K2CO3 and THF (30 mL) were added into the reactor. Then, Pd(PPh3)4 (65.0 mg, 56 mol) was added and the reaction was stirred for 48 h at 80 °C. After 48 h, it was filtered through celite. The product was purified by column chromatography using n-hexane as eluent furnishing 22% (60.0 mg) of 39.
	N,N-diphenyl-4-(5''-(tributylstannyl)-[2,2':5',2''-terthiophene]-5-yl)aniline (40): 39 (160 mg, 340 mol) was dissolved in dry THF (30 mL), under inert atmosphere. The reaction was cooled down to -78 °C and t-BuLi (360 L, 680 mol) was added dropwise. After 45 minutes, tributyltin chloride (180 l, 680 mol) was added to the reaction. After 30 minutes, it was allowed to warm up to room temperature and stirred overnight under N2 atmosphere. The product was extracted with DCM-NaHCO3 and it was used in the next reaction without further purification.

	4-(5''-(3-(4-Fluorophenyl)thieno[3,2-b]thiophene-2-yl)-[2,2':5',2''-terthiophene]-5-yl)-N,N-diphenylaniline (41): 39 (748 mg, 960 mol) and 24 (250 mg, 800 mol) were added into a coupling reactor under N2 atmosphere. Then, THF (30 mL) and Pd(PPh3)4 (46.0 mg, 39.0 mol) catalyst were added respectively. The reactor was closed tightly and stirred for 48 h at 80 °C. After 48 h, reaction was filtered through celite and the product was purified by column chromatography using n-hexane as a mobile phase providing 84.0 mg (15%) orange color solid product. 

	N,N-diphenyl-4-(thiophen-2-yl)aniline (29): 27 (1.50 g, 4.60 mmol) and 26 (1.45 g, 6.90 mmol) were weighed and taken into a coupling reactor under N2 atmosphere. A 5 M solution of K2CO3 and THF (25 mL) were added into the reaction medium. Then, Pd(PPh3)4 (260 mg, 230 mol) was added and reactor was closed tightly. The reaction was stirred for 48 h at 80 °C. After 2 days, it was filtered through celite and purified by column chromatography with  the eluent hexane:dcm (8:1)furnishing 29 (1.49 g)  in 67% yield. 
	N,N-diphenyl-4-(5-(tributylstannyl)thiophene-2-yl)aniline (30): 29 (1.00 g, 3.10 mmol) was dissolved in dry THF (35 mL) under nitrogen atmosphere. The reaction medium was cooled down to -78 °C and  t-BuLi (3.59 ml, 6.10 mmol) was added dropwise. After 1 h, at about -50 °C, tributyltin chloride (1.65 mL, 6.10 mmol) was added. Reaction was stirred overnight under N2 atmosphere. The product was extracted with DCM-NaCl solution, organic layer was dried over Na2SO4 and solvent was evaporated by using rotary evaporator. The product was used in the next step without further purification.
	4,4,5,5-Tetramethyl-2-(thiophene-2-yl)-1,3,2-dioxaboralane (26): Thiophene (3.00 g, 35.7 mmol) and THF (30 mL) were added into a three necked flask under inert atmosphere. The reaction was cooled down to -78 °C and n-BuLi (15.7 mL, 39.2 mmol) was added dropwise. After 30 minutes, it was allowed to warm up to room temperature and stirred overnight under N2 atmosphere. Solvent was evaporated and the residue was extracted with DCM-NaHCO3 solution. The organic layer was dried over Na2SO4 and DCM was evaporated under atmospheric pressure. The product was precipitated from cold methanol giving  4.89 g product (65.3% yield) .
	1-(4-Bromophenyl)-2-(thiophene-2-ylthio)ethanone (43): 25 (2.50 g, 15 mmol) was dissolved in dry diethyl ether (40 mL )under N2 atmosphere. The reaction medium was cooled down to -78 °C and n-BuLi (12.5 mL, 20.0 mmol) was added dropwise. After 45 minutes, elemental sulphur (640 mg, 20.0 mmol) was added and stirred for 30 minutes. Then, the cooler was turned off and at about -20 °C, 43 (5.55 g, 20.0 mmol) was added. The reaction was stirred overnight under N2 atmosphere. The product was extracted with DCM-Water mixture and organic phase was dried overNa2SO4. The product was obtained by precipitation from n-hexane/methanol (1:1) mixture in32% yield as a brown solid.
	3-(4-Bromophenyl)thieno[2,3-b]thiophene (44): PPA (2.94 g, 30.0 mmol) was weighed in a two necked round bottomed flask and 5.00 mL of chlorobenzene solvent was added on PPA. The PPA-chlorobenzene mixture was heated up to 135 °C and started to reflux. At this temperature, 43 (500 mg, 2.00 mmol) in 5.00 mL of chlorobenzene was added into the reaction mixture. The reaction was stirred for 72 h and  then chlorobenzene phase was separated. The solvent was evaporated under reduced pressure. The solid product was extracted with DCM-NaHCO3 solution and it was purified with column chromatography using n-hexane as eluent rendering 66% (310 mg) of 44 as a white solid.
	3-(4'-(1,2,2-Triphenylvinyl)-[1,1'-biphenyl]-4-yl)thieno[2,3-b]thiophene (51): 44 (540 mg, 1.83 mmol) and 50 (1.01 g, 2.20 mmol) were weighed and transferred into a coupling reactor under N2 atmosphere. A 5 M K2CO3 solution and toluene (30 mL) were added into the reactor and the reaction mixture was degassed with excess N2. After the reactor was saturated with N2 atm, Pd(PPh3)4 (110 mg, 92.0 mol) was added and the reactor was closed tightly. The reaction was stirred for 48 h at 110 °C. After 48 h, reaction mixture was filtered through celite and the product was precipitated in cold methanol furnishing beige color 51 in 74% (730 mg) yield.
	2,5-Dibromo-3-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-il)thieno[2,3-b]thiophene (52): NBS (180 mg, 10.0 mmol) was added into a concentrated solution of 51 (200 g, 410 mol) in chloroform. The reaction was performed in an ice bath and dark medium. It was stirred overnight and then, the chloroform was evaporated. Product was extracted with DCM-NaHCO3 solution and it was precipitated from cold methanol providing 52 in 77% (280 mg) yield as a pale yellow solid product.
	2,5-Di(thiophene-2-yl)-3-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)-thieno[2,3-b]thiophene (53): 52 (200 mg, 300 mol) and 26 (240 mg, 1.20 mmol) were transferred into a coupling reactor under N2 atmosphere. Then, a 5 M solution of K2CO3 and THF (30 mL) were added into the reaction mixture. Under N2 atmosphere, Pd(PPh3)4 (16.0 mg, 15.0 mol) was added and the reactor was closed tightly. It was stirred for 48 h at 80 °C. After 48 h, the reaction mixture was filtered through celite and the product was precipitated from cold n-hexane giving rise to pale brown 160 mg (76%)  of 53.
	(5,5'-(3-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-il)thieno[2,3-b]thiophene-2,5-diyl)bis(thiophene-5,2-diyl))bis(dimesitylborane) (54): 53 (150 mg, 210 mol) was dissolved in dry THF under N2 atmosphere. The medium was cooled down to -78 °C, and t-BuLi (740 L, 1.26 mmol) was added dropwise. After 60 minutes, dimesitylboron fluoride (320 mg, 1.47 mmol) was added into the reaction mixture. After 60 minutes, the cooler was turned off and the reaction was stirred overnight under N2 atmosphere. The product was extracted with DCM-NaHCO3 solution. It could not be purified with column chromatography.
	1-(4-Bromophenyl)-2-(thiophene-3-ylthio)ethanone (57): 55 (2.50 g, 15.0 mmol) was dissolved in dry diethyl ether (35 mL) under N2 atmosphere. The reaction medium was cooled down to -78 °C and n-BuLi (12.5 mL, 15.0 mmol) was added dropwise. After 60 minutes elemental sulphur (640 mg, 20.0 mmol) was added and reaction mixture was stirred for 45 minutes. Then, the cooler was turned off and at about -20 °C, 56 (5.58 g, 20.0 mmol) was added. The reaction was stirred overnight under N2 atmosphere. The product was extracted with DCM-water mixture and organic layer was dried over Na2SO4 and DCM was evaporated by using rotary evaporator. The product was precipitated from cold n-hexane yielding 80% of 57 as a yellow solid.
	3-(4-Bromophenyl)thieno[3,2-b]thiophene (58): PPA (3.13 g, 20.0 mmol) was weighed in a round bottomed flask and chlorobenzene (5 mL) was added into the flask. It was heated up to 135 °C and started to reflux. Then, 57 (500 mg, 1.00 mmol) was added into the reaction medium. The reaction was stirred for 5 h and then the chlorobenzene phase is removed from the PPA phase. The product was extracted with DCM-NaHCO3 solution and organic layer was dried over Na2SO4 and evaporated. 58 was obtained as a white solid in 90% yield after column chromatography using n-hexane as eluent.
	3-(4'-(1,2,2-Triphenylvinyl)-[1,1'-biphenyl]-4-yl)thieno[3,2-b]thiophene (59): 58 (200 mg, 830 mol) and 52 (450 mg, 910 mol) were added into a coupling reactor and the reactor was taken to the nitrogen atmosphere. A 5 M solution of K2CO3 and THF were added into the reactor. Then, Pd(PPh3)4 (48.0 mg, 42.0 mol) was added and the reaction was stirred for 48 h at 80 °C. After 48 h, the reaction mixture was filtered through celite and THF was evaporated. The product was precipitated from cold methanol furnishing beige color 59 in 75% yield.
	2,5-Dibromo-3-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)thieno[3,2-b]thiophene (60): NBS (180 mg, 1.00 mmol) was added into a concentrated solution of 59 (220 mg, 410 mol) in an ice bath. The reaction was stirred for 12 h in a dark medium. After 12 h, chloroform was evaporated and the product was extracted with DCM-NaHCO3 solution. Dried product was precipitated from cold methanol yielding 60 (77%)  as a pale yellow product.
	2,5-Di(thiophene-2-yl)-3-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)-thieno[3,2-b]thiophene (61): 60 (220 mg, 300 mol) and 26 (250 mg, 1.20 mmol) were weighed and were taken into a coupling reactor. Then the reactor was transferred into the N2 atmosphere. A 5 M solution of K2CO3 and THF (30 mL) were added into the reactor. After the reactor was saturated with N2 gas, Pd(PPh3)4 (35.0 mg, 30.0 mol) was added as a catalyst. The reactor was closed tightly and stirred for 48 h at 80 °C. After that, the reaction was filtered through celite. The product was extracted with DCM-NaHCO3, the organic layer was dried over Na2SO4 and DCM was evaporated. The product was precipitated from cold n-hexane giving rise to pale brown solid  61 in 57% yield.
	(5,5'-(3-(4'-(1,2,2-Triphenylvinyl)-[1,1'-biphenyl]-4-yl)thieno[3,2-b]¬thiophene-2,5-diyl)bis(thiophene-5,2-diyl))bis(dimesitylborane) (62): 61 (150 mg, 210 mol) was dissolved in dry THF (25 mL) under N2 atmosphere. The reaction medium was cooled down to -78 °C and t-BuLi (680 L, 1.15 mmol) was added dropwise. The reaction was stirred for 30 minutes and dimesitylboron fluoride (280 mg, 1.05 mmol) was added into the reaction medium. After 45 minutes, the cooler was turned off and the reaction was stirred overnight under N2 atmosphere. It was extracted with DCM-NaHCO3 solution. The product could not be purified by column chromatography.