Oled Uygulamaları İçin Ditiyeno[3,2-b;2′,3′-d]tiyofen (dtt) Temelli Moleküllerin Sentezleri Ve Özellikleri

Abstract

Organik elektronik, elli yıl içinde özellikle fizik ve kimya alanında bilimsel araştırmacıların artan bir eğilimle ilgi odağı olmuştur. Bu artan ilginin ana nedeni organik moleküllerin yapılarının kolay değiştirilebilmesi ve bu değişikliğe bağlı olarak organik materyalin özelliklerinin direk olarak değişmesidir. 1980 yıllarının ortalarına kadar, organik materyallerin kararlılığı ve performansı, silikon ve galyum arsenik temelli materyallerin gerisinde kalmasına rağmen, düşük voltaj ve etkin ince film ışık saçan organik diyotların optoelektronik alanında kullanılabileceğinin gösterilmesi ile yeni bir pencere açılmış oldu. Günümüzde organik ince filmlerin pek çok uygulamada kullanılabileceği bilinmektedir. Bunlar arasında, renkli ekranlarda kullanılan organik materyallerle organik ışık saçan cihazlar (organic light emitting diode, OLED) en başarılı durumda olanlardır. Bunun yanında, organik ince film transistörler ve düşük maliyetli ve etkin güneş hücreleri (solar cells), yapılmakta olan yoğun araştırmalarla OLED’ler gibi uygulamaya geçilmeye yakın durumdadırlar. Organik lazerler ve hafızalar konusunda yoğun araştırmalar devam etmekle birlikte, kısa zamanda diğer uygulamaları yakalayacağı beklemektedir. Genel anlamda küçük organik moleküller ve polimerler olmak üzere iki grup organik materyaller elektronik ve optoeletronik cihaz yapımında kullanılmaktadır. Bu materyallerde anahtar sorun organik materyalin elektronik yapısını anlayarak yeni yüksek performansa sahip optik ve elektronik materyallerin dizayn edilmesidir. Organik molekülün yapısında yapılacak ufak gözükebilen bazı eklemeler, molekülün uygulamadaki özelliğini büyük oranda değiştirebilmektedir. Günümüzde moleküler düzeyde organik moleküllerin yapısında değişiklikler yaparak elektronik ve optoelektronik özelliklerini değiştirmek son derece zor ve önemli bir konudur. Tiyofen temelli organik materyaller, moleküler mühendislikle, fonksiyonel özelliklerinin kaba ve ince ayar yapılarak değiştirilebilmesinden dolayı ümit vadeden moleküller arasında en üstlerde yer almaktadır. Bir örnek olarak, tiyofenler, oligomerleri ve polimerleri ışık saçan materyaller olarak, düşük elektron afiniti ve düşük katı-hal fotolüminesans özelliklerinden dolayı uygun olmamalarına rağmen, S,S-dioksit’e çevrildiklerinde, özellikle oligomerleri, ince film fotolüminesans ve moleküler enerji seviyelerinde büyük etkinlik kazanarak uygun olmaları verilebilir. Organik elektronik ve optoelektronik materyallerin özelliklerini geliştirmede bor kullanımı son zamanlarda gelişme göstermekte ve önemli sonuçlar vermektedir. Bunun başlıca nedeni, pz orbitali boş olan bor atomu üçlü bağ yaptığında güçlü elektron çekici karakter kazanmaktadır ve organik “” konjuge sistemine entegre olduğunda güçlü elektron delokalize edebilmesidir. Organik materyal kimyasında konjuge organoboran polimerler, geniş uygulama alanları ile yeni organik materyal sınıfını oluşturarak yeni ve etkili elektronik, optoektronik ve sensör materyallerin geliştirilmesinde yer almaktadırlar. Donör-Akseptör (D-A) polimer sistemi, bromlanmış iki farklı donörün n-BuLi ile reaksiyona girerek karbanyon oluşturmasının ardından tek basamakta akseptör olan 2,4,6-timetilfenildimetoksiboran ortama ilave edilmesi ile sentezlenmiştir. Oluşan D-A polimerlerinin ilk olarak elektronik ve optik özellikleri incelenmiştir. Döngülü Voltametri (Cyclic Voltammetry) ile oksidasyon ve indirgeme potansiyelleri ölçülmüş, elektronik band-gapleri hesaplanmıştır. UV-Vis ve FL spektrofotometre cihazları ile polimer filmi kaplanmış İTO’ların ve tetrahidrofuran (THF) içindeki polimerlerin absorpsiyonları ve floresansları ölçülmüştür, ele geçen verilerden kuantum verimleri ve optik band-gapleri hesaplanmıştır. Bu analizlerden farklı olarak 11Bor-Nükleer Manyetik Rezonans (NMR), termogravimetrik analiz (TGA), Light Scattering ölçümleri alınarak yapısal incelemeleri tamamlanmıştır. Grubumuzca geliştirilen, yeni bir yöntemle aromatik halkalar taşıyan ditiyenotiyofen (DTT) ve tiyenotiyofen (TT) sentezi, literatürde bilinen en iyi yöntemi oluşturmaktadır. DTT’ler üç tiyofen halkasının ve TT’ler iki tiyofen halkasının yan yana gelmesiyle oluşan heterosiklik bileşiklerdir. Bu çalışmada geliştirdiğimiz yöntemle elde edecegimiz DTT, DTT-S,S-dioksit ve TT moleküllerin bor içeren polimerleri hazırlanacaktır. Hazırlanan materyallerin döngülü voltmetre (cyclic voltammetry), kapasitör, ultra-viyole (UV), ultraviyole-döngülü voltmetre (UV-CV), sensör ve floresans çalışmaları yapılarak sensör, elektronik ve optoelektronik özellikleri açıklanacaktır. Bu çalışma, ülkemizde son derece bol olan bor elementinin, yeni gelişmekte olan ve önemi son zamanlarda fark edilen organoboranın materyal kimyasında kullanımını artırmaya ve yeni organik elektronik, optoelektronik ve sensör materyalleri geliştirmeye yöneliktir.

Organic electronics has been the focus of growing number of the researchers particularly in the fields of physics and chemistry for more than 50 years. The main attraction of this field comes from the ability to modify the chemical structure of the organic compounds in a way that the properties of the materials could directly be affected. Until the mid-1980s, their stability and performance fell short of those devices based on materials such as silicon or gallium arsenide. This situation was changed since then with the demonstration of a low voltage and efficient thin film light emitting diode, which opened the door of the possibility of using organic thin films for a new generation of optoelectronics devices. It has now proven that organic thin films are useful in a number of applications. Among them, organic light emitting diodes (OLED) is the most successful one, which is used now in color displays. Organic thin film transistors and low cost and efficient organic solar cells are not far behind OLEDs. Moreover, devices such as organic lasers and memories might be seen eventually. In general, two groups of organic materials, small molecules and polymers, are used in electronic and optoelectronic devices. Understanding of their electronic structure is the key to the design of high performance optical and electronic organic devices, and some important tunings in structure or composition of an organic material can markedly alter its bulk properties. Currently, modification of the molecular structure of the conjugated materials to tune their optoelectronic properties is a challenging topic. Thiophene-based organic materials are among the most promising compounds with tuneable functional properties by proper molecular engineering. For example, thiophenes and their oligomers and polymers are not proper materials for applications in light emitting devices as they have low electron affinities and low solid-state photoluminescence efficiencies. On the other hand, converting oligothiophenes into the corresponding oligothiophene-S,S-dioxides has been shown to be useful for increasing both thin film photoluminescence efficiencies and molecular energy levels. The use of boron to alter the properties of organic electronic and optoelectronic materials has started recently and given interesting results. The reason for that is the presence of empty pz orbital of boron which behaves as strong electron withdrawing atom when it makes three bonds. It delocalizes electrons strongly when integrated to “” systems. In organic material chemistry, conjugated organoborane polymers are now considered as new class of organic materials with their widespread applications in electronics, optoelectronics and sensors. The method developed by our group for the syntheses of ditihenothiophene (DTT) and thienothiophene (TT) having aromatic groups is among the best methods available in the literature. DTTs and TTs are the heterocyclic rings, formed by fused three and two thiophene rings, respectively. In this work, polymers of DTTs, DTT-S,S-dioxides and TTs, prepared by our methods, consisting of boron atoms will be prepared. Cyclic voltammetry (CV), capacitor, ultra-viole (UV), ultra-violet-cyclic voltammetry (CV-UV), sensor and fluorescent properties of the materials will be studied to understand their sensor, electronics and optoelectronics properties. The aim of this study is to enhance the use of boron in new developing organoborane material chemistry and to develop new organic electronics, optoelectronics and sensor materials as our country is rich in boron element. Synthesis of organic oligomers and polymers, having advanced electronic and optoelectronic properties, is important task in material chemistry. The main fascination of this field is adjusting the properties of the materials easily by modifying chemical structures of the organic compounds. Since the derivatives of thiophene-based compounds are easily prepared, and their physical properties emerged from high -electron conjugation, they have a wide range of applications. Dithienothiophenes (DTT), constructed by three fused thiophene units, provides important electronic and optoelectronic properties for applications in material chemistry. Oxidation of thiophene with hydrogen peroxide or m-chloroperbenzoic acid (mCPBA) results in the formation of thiophenes with increased electron affinity and fluorescence quantum yield. Unlike an aromatic thiophene, thiophene-S,S-dioxide has diene properties. In this work, four DTT and DTT-S,S-dioxide derivatives were synthesized as a donor; • Synthesis of 2,6-dibromo-3,5-diphenyldithieno[3,2-b;2′,3′-d]thiophene (Donor 1): To a solution of 3,5-diphenyldithieno[3,2-b;2′,3′-d]thiophene (500 mg, 1.43 mmol) in DMF (60 mL) was added NBS (560 mg, 3.20 mmol) protected from light portion wise at 0ᵒC. After 4 h, the reaction mixture was poured into cold water to precipitate the crude product, which was purified by column chromatography over silica gel using a mixture of n-hexane/DCM (3:1) as eluent to give the Donor 1 (581 mg, 1.14 mmol) in 80% yield as a yellow-white crystal. • Synthesis of 2,6-Dibromo-3,5-diphenyldithieno[3,2-b;2′,3′-d]thiophene-S,S-dioxide (Donor 2): To a solution of 2,6-dibromo-3,5-diphenyldithieno[3,2-b;2′,3′-d]thiophene (400 mg, 790 µmol), dissolved in DCM (60 mL), was added m-CPBA (680 mg, 2.76 mmol, 70%) at ambient temperature. The reaction was then left stirring at room temperature for 2 days. The solution was extracted with 200 mL 10% KOH, 200 mL 10% NaHCO3 and 100 mL of brine. Organic layer was dried over Na2SO4, filtered and the solvent was evaporated under atmospheric pressure. The crude product was purified by column chromatography over silica gel using a mixture of n-hexane/DCM (4:1) as eluent to give the Donor 2 (332 mg, 620 µmol) in 78% yield as a yellow powder. In addition, boron derivatives were synthesized as an acceptor in this work. • Synthesis of 2,4,6-trimethylphenyldimethoxyborane: Trimethoxyborane was distilled over CaH2 to avoid moisture. 2-mesitylmagnesium bromide (15.0 mL, 1M) was added dropwise to a solution of trimethoxyborane (6.44 mL, 57.7 mmol) in 80 mL of diethyl ether solution at -78ᵒC under N2 atmosphere. After the reaction was stirred at -78ᵒC for 3 h, it was allowed to warm up to room temperature and left to stir overnight. The solution was then filtered under N2 and the precipitated salts were washed off with dry n-pentane (20 mL). The filtrates were combined, concentrated and distilled under vacuum (1 mmHg, 72ᵒC) to give dimethoxymesitylborane (11.1 g, 57.79 mmol) in 57% yield as colorless viscous liquid. Furthermore, four donor-acceptor (D-A) polymers were synthesized using one pot synthesis for WOLED application. • n-BuLi (2.05 eq.) was added dropwise to a solution of brominated donors (1 eq) in 40 mL of THF at -78°C inert atmosphere. The reaction was stirred at -78ᵒC for 1 h. Then, 2,4,6-trimethylphenyldimethoxyborane in 20 mL THF was added dropwise to the reaction medium. The reaction was warmed up to room temperature, and allowed to stir overnight. The solvent was evaporated under reduced pressure. The crude product was adsorbed on silica gel and then purified by removing donors and oligomers by column chromatography over silica gel, eluting with a mixture of n-hexane/DCM (2:1). D-A polymers were extracted from silica gel using THF. The THF solutions were concentrated under vacuum. The D-A polymers were precipitate into cold n-hexane to give the long chain polymer. • Synthesis of p-Br Ph2DTT-Boron Polymer (1): n-BuLi (518 µL, 1.24 mmol, 1.6 M) was added dropwise to a solution of donor (300 mg, 593 µmol) in 40 mL of THF at -78°C under N2. The reaction was stirred at -78ᵒC for an hour. Then acceptor (79,6 mg, 414 µmol) in 20 mL THF was added dropwise to the reaction medium. The reaction was warmed up to room temperature, and left to stir overnight. The solvent was evaporated under reduced pressure. The crude product was adsorbed on silica gel and then purified by removing donors and oligomers by column chromatography over silica gel, eluting with a mixture of n-hexane/DCM (2:1). Polymer 1 was extracted from silica gel using THF. The THF solution was concentrated under reduced condition. Polymer was precipitated into cold n-hexane to give the long chain polymer. • Synthesis of p-Br Ph2DTT-S, S-dioxide-Boron Polymer (2): n-BuLi (739 µL, 1.12 mmol, 1.6 M) was added dropwise to a solution of donor (302 mg, 531 µmol) in 40 mL of THF at -78ᵒC under N2. The reaction was stirred at -78ᵒC for an hour. Then acceptor (107 mg, 558 µmol) in 20 mL of THF was added dropwise to the reaction medium. The reaction was warmed up to room temperature, and left to stir overnight. The solvent was evaporated under reduced pressure. The crude product was adsorbed on silica gel and then purified by removing monomers and oligomers by column chromatography over silica gel, eluting with a mixture of n-hexane/DCM (2:1). Polymer 2 was extracted from silica gel using THF. The THF solution was concentrated under vacuum. Polymer was precipitated into cold n-hexane to give the long chain polymer. (dn/dc: 0.246; Mw: 1.220 105; Mn: 1.087 105; Mw/ Mn: 1.122 (THF, 25oC)) All D-As were analyzed with cyclic voltammetry (CV), ultra-violet (UV) and fluorescent (FL) to understand their sensor, electronics and optoelectronics properties. Apart from these measurements, their TGA, LS, 11Boron NMR analyses were carried out. Based on TGA analysis, they were thermally stable up to 350oC. Their molecular weight were approximately 30000 Da. Their calculated optical and electronical band gap energies were suitable for WOLED applications, but aggregation-caused quenching was observed for all D-A polymers. Therefore, they had small quantum efficiencies of less than %10. Due to low quantum yields, none of them were designed to be used for diod applications.