Tiyenotiyofen Ve Bor İçeren Floresans Materyallerin Sentez Ve Karakterizasyonları

Abstract

Son yılarda iletken polimerlerin gelişen teknoloji üzerindeki önemi daha da artmaktadır. Birçok cihaz farklı fonksiyonel gruplar içeren organik yapılardan yapılmaktadır. Bu fonksiyonel gruplar absorpsiyon, emisyon ya da kapasitor davranışlarını değiştirerek materyalin kullanım alanını belirlemektedir. Organik moleküllerin biosensör, OPV (organik fotovoltaik), OLED, kapasitör, elektrokromik cihazlarda kullanımına ilişkin yeni bir araştırma alanı oluşturmaktadır. Materyal kimyasında TT (tiyenotiyofen) ve DTT (Ditiyenotiyofen) sıklıkla kullanılmaktadır. Bunun başlıca nedeni uzun π konjugasyonuna sahip olması ve esnek olmayan , dayanıklı, düzlemsel yapısıdır. Tiyofen halkasında bulunan kükürt üzerinde ki ortaklaşmamış elektronların sayesinde iyi bir donor görevi gömektedir. Bu sayede konjuge sistemlerde moleküler arası iletişim yüksek olmakta ve düşük band aralığı için yararlı olmaktadır. Teknolojinin gelişmesiyle birlikte moleküllerin sentez ve karakterizasyonu kolaylaşmış bu sayede küçük moleküller üzerinde de donor akseptör sistemler birlikte kullanılarak fonksiyonlandırma çalışmaları başlamıştır. Bu durum cihaz yapım prosesinde büyük kolaylıklar sağlamaktadır. Polimerik malzemelerin çoğu zaman çözünürlük sıkıntısı olması cihaz yapım sürecinde çeşitli zorluklar oluşturmaktadır. Bu nedenle küçük yapıda oligomerik materyallerin kullanımı yaygınlaşmaktadır. Ancak elbetteki HOMO-LUMO seviyelerinin ve bant aralıklarının uygun olması koşulu bu işlemdede kısıtlamalara neden olmaktadır. Bu kapsamda kullanılacak iyi donor ve iyi akseptör bileşiklerine duyulan ihtiyaç artmaktadır. Bu projede amacımız OLED ve güneş hücresi olabilecek, elektronca zengin tiyofen türevleri içeren donör molekülerle, elektronca fakir olan bor atomu ile oluşturulacak, donör-akseptör (D-A) sistemine sahip organik materyaller geliştirilecektir. Tiyofen türevleri olan DTT ve TT moleküllerinin grubumuzca geliştirilmiş olmaları ve borun ilk defa organik güneş pillerinde akseptör olarak kullanılması projenin özgün değerini oluşturmaktadır. Tüm bu bilgilerle OLED ve güneş hücresi olabilecek moleküllerin sentezine başlanmıştır. Ne yazık ki OLED için tasarlanan moleküllerde reaksiyon prosedürü ile ilgili sıkıntı meydana gelmiş ve sentez başarısız olmuştur. Ancak çalışmalar sırasında elde edilmiş olan 20 nolu molekül elektropolimerleştirilerek ECD ve kapasitör özellikleri incelenmiştir. Malzeme CV ile Pt elektrot üzerinde polimerleştirilmiştir. Sistemde Ag tel referans elektrot olarak kullanılmış, elektrolit 0.1M TBAPF6 (tetrabütilamonyum hekzafloro fosfat)’ın DCM-ACN karışımında hazırlanmasıyla elde edilmiştir. Monomer konsantrasyonu 1x10-3 M olacak şekilde ayarlanmıştır. Polimerleşme olduğu görüldüğünde benzer sistem ile İTO üzerine kaplama gerçekleştirilmiş ve CV-UV çalışması ile ECD özellikleri incelenmiştir. Daha sonra Pt xxii disk üzerine kaplamalar alınarak farklı potansiyeller için kapasitif davranışlarına bakılmıştır. Güneş hücresi olarak tasarlanan malzemeler ise Suzuki , Stille kenetlenme reaksiyonları yardımı ile sentezlenmiş ve 1H NMR, 13C NMR ile karakterizasyonları yapılmıştır. Optik ve elektronik özellikleri incelenmiş ve Gaussian09 hesaplamalı kimya programı kullanılarak DFT metodu ile moleküllerin yapılarının optimizasyonu hesaplanmıştır. Molekül sisteminde HOMO-LUMO dağılımlarına bakılmıştır. Optik, elektronik ve hesaplamalı bant aralıkları bulunmuştur. Optik ölçümlerde moleküllerin THF içerisi de alınan UV-Vis spektrumlarında pik 500nm’ye kadar uzamakta olan geniş absorpsiyonu güneş hücresinde donor molekül olarak kullanılabilecek olduğunu göstermektedir. Ayrıca UV-Vis spektrum üzerinden hesaplanmış olan optik bant aralıkları 2.41 ile 2.61 eV arasında bulunmuştur. Döngülü voltametre yardımı ile p-n doping uygulanmış ve moleküllerin oksidayon, redüksiyon noktaları tespit edilerek, elektronik bant aralıkları 1.83-2.98eV aralığında bulunmuştur. Tüm bu sonuçlarla görülmektedir ki 31 nolu molekülün UV-Vis spektrumu güneş hücresi olabilecek en yakın moleküldür. Bu durum arada bulunan tiyofen halkasının konjugasyona katılması yardımı ile olmaktadır. Projenin bir sonraki adımı aradaki tiyofen sayısını 2 ve 3 olarak artırmak olacaktır. Böylelikle UV spektrumda 500-600nm aralığında yakalanacağı ve güneş hücreleri için ideal dalgaboyuna erişilebileceği düşünülmektedir. Bu sistemi destekleyebilecek olan hesaplamalı kimya çalışmaları yapılmış TD metodu ile tahmini UV-Vis spekturumu elde edilmiş ve burada 700-800nm’ye kadar uzanan geniş bir absorpsiyon aralığı elde edilmiştir.

In recent years, conducting polymers have an important role for the development of the technology. Many devices made by organic compounds, which are different in properties which depends on the their functional groups. Each functional groups with their ability absorption, emmision or capacitive behaviour will conclude as a material for the compounds applications. This is a new area, in which the organic coumpounds are used in biosensors, OPVs (Organic Photovoltaics), OLEDs (Organic Light Emmiting Diodes), capasitors, ECDs (Elktrocromic Devices) etc. In material chemistry, TT (thienothiophene) and DTT (Dithienothiophene) are used often because of their unique properties, their long π conjugation and rigid, unflexible structures. These fused tiophene ring systems to have nonbonding electrons on the sulfurs so they have donor character on the polymers. These significant features results in low band gap and high intromolecular interactions. Synthesis and characterization of organic molecules are easier by the new technological developments so small organic molecules which include donor and acceptor group on their structure can have low band gap as polymers. This stituation is very big advantage for prosesing steps of making devices. The proposed project aims to design and synthesize materials for OLED and solar cell applications posessing thiophene derivatives as donors and, electron deficient boron atom as acceptor. Design and syntheses of the thiophen derivatives, DTTs and TTs, have been developed by our group and the boron atom will be used in solar cell materials for the first time, which make the project original. In this work different TT derivatives were synthesized contain TPA (triphenylamine) and dimesityl borane.  Synthesis of 2-bromo-3-(4-bromophenyl)thieno[3,2-b]thiophene (17a) To a solution of 4-bromophenyl)thieno[3,2-b]thiophene (0.39g) in DMF (3-5ml) was added NBS (0.25 g) protected from light at 0 ⁰C. After the reaction extracted with DCM-%10 NaHCO3. Organic layer dried by Na2SO4, filtered and solvent evaporeted. Then product was purified by coloumn chromatography over silica gel using hexane. %60-70 yield as a white solid.  Synthesis of 2-bromo-3-phenylthieno[3,2-b]thiophene (17b). following the similarly reaction . Reaction mixture was poured cold water to precipitate. %80-90 yield as a white solid.  Synthesis of N,N-diphenyl-4'-(thieno[3,2-b]thiophene-3-il)-[1,1'-biphenyl]-4-amine (20). In a reactor mixture of 17a (0.5g) and N,N-diphenyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)aniline (18) (0.76g) solved in THF and xxiv added K2CO3(2M) , Pd(PPh3)4 was degassed with N2 for 15-20 minutes.Then the mixture stirred at 70-80⁰C for 2 days. It was filtered through celite and evoporated. Reaction mixture precipiteted in methanol. %70-80 yield.  Synthesis of N,N-diphenyl-4-(3-phenylthieno[3,2-b]thiophene-2-yl)aniline (21). following the similarty reaction prosedure 20. %60 yield.  Synthesis of N,N-diphenyl-4-(3-phenyl-5-(tributilkalay)thieno[3,2-b]thiophene-2-yl)aniline (23) t-BuLi (0.63ml, 1.7M) was added dropwise to THF of 25g 21. The reaction stirred at -78 ⁰C for 40 minnutes. 0.23 ml tributhyl tin chloride was added to reaction medium. After the 2 hours reaction was warmed room temperature and stired overnight. The product used without further purification.  Synthesis of (5-bromo-6-phenylthieno[3,2-b]thiophene-2-yl)dimesitilborane (27) 0.5 g 17b was solved in THF (15 ml) and LDA (0.93ml, 2M) added dropwise at -78 ⁰C under N2. 1 hours later 0.48g dimesithyl boron floride was added. After 2 hours reaction was warm to room temperature slowly and strired overnight. Purification by preparatif tin layer chromotography for characterization.  Synthesis of (5-(dimesitilboranil)-3-phenylthieno[3,2-b]thiophene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (28) n-BuLi was added by dropwise to 0.4g 27in THF at -78 ⁰C under N2. After 45 minutes, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxoborolane(0.15 ml). Then the reaction medium was warmed to room temperature slowly and stired overnight. Saturated brine added to reaction mixture and extracted with DCM-water. Organic layer dried by Na2SO4. Purification by tin layer chromotography for characterization. Note: this product could decomposition at high teperature( 40⁰C and more).  Synthesis of (3,3'-diphenyl-[2,2'-bithieno[3,2-b]thiophene]-5,5'-diyl)bis (dimesitil borane)(29). 27 and 28 was solved in THF and added 2ml K2CO3 (2M), Pd(II)(OAc)2 to reactor. Then reaction dagased with N2 for 30 minutes and stired at room temperature for 2 days. It was filtered through Celite and solvent extracted with DCM-water, organic layer dried over Na2SO4, filtered and solvent evaporated under pressure. The product was purification by column chromatography over the silica gel with DCM-Hexane mixture.  Synthesis of 2,5-bis(5-(dimesitilboranil)-3-phenylthieno[3,2-b]thiophene-2-yl)thiophene (31). In a reactor, 0.02 g of 27 , 2,5-dipinacolborylthiophene (30)(0.07 g), K2CO3 and Pd(PPh3)4 in THF was degassed with N2 for 20minutes. Then the mixture was stired at 70 ⁰C for 3 days. It was filtered through celite and solvent evaporated under reduced pressure. It was extracted DCM-water and organic layer dried with Na2SO4, filtered and the solvent evaporated. Product purification by tin layer chromatography for characterization.  Synthesis of 4-(5'-(dimesitylboranil)-3,3'-difenil-[2,2'-bithieno[3,2-b]tiyofen]-5-yl)-N,N-diphenylaniline (32). 0.15g 27 and 23 was solved in THF. It was degased with N2 for 30 minutes after adding the catalayst Pd(PPh3)4. The reactor stired at 70 ⁰C for 2 days. It was filtered through celite and solvent evoporated under reduced pressure. The crude product extracted with DCM-water, organic layer dried by Na2SO4. Then product prification with thin layer chromotography for characterization. xxv  Synthesis of 4,4'-(6,6'-diphenyl-[2,2'-bithieno[3,2-b]thiophene]-5,5'-diil)bis(N,N-diphenylaniline) (33) dried 0.2 g 21 solved in THF and strired at -78 ⁰C and added 0.24ml t-BuLi (1.7M) drop by drop. After 50 minutes 0.058g CuCl2, then the reaction refluxed for 6 hours. It was ended with asidic water and exracted with DCM-water. Organic layer dried with Na2SO4 and evoporated under reduced pressure. Then the product purification by tin layer chromotography for characterization. With all the information obtained by the literature search we focused on the synthesis of molecules that can be used in OLED and solar cell in future. Unfortunatly some prosedures were failed because of the problems occured during the reactions. Then we decided not to use this compound for OLED applications, on the other hand, this monomer (20) is used to prepare an electropolymer. This monomers quantum efficiency (QY) in solvent is higher than solid state, but its electropolymer have ECD and capasitive behaviours. Compound 20 was electropolymerized on Pt electrode by CV (cyclic voltametry). In these experiments Ag wire used as reference electrode and electroytes were chosen 0.1M TBAPF6 (tetrabuthylammonium hexaflorophosphate) in DCM-ACN mixture. Monomer concentrations were adjusted 1x10-3M and scan rate 0.1V/s. After the successful polymerization on Pt wire, polimerization on ITO (Indium Tin Oxide) were with using the same conditions. Polymer coated ITO was used for ECD measurements for spectro-electrchemistry (CV-UV experiments). Then Pt disc electrode coated with these methode and determined its capasitive behaviours for different potantials. The materials that are used for the design of solar cells are synthesized and investigated in this thesis. Molecules were characterized by 1H NMR and 13C NMR. Their optical and electronical behaviours were examined after synthesis and their optimized structure calculated with Gaussian09. All band gaps, namely Egopt, EgCV, Egcalculation are determined by relevant methods. Optical measurement show that their UV-vis spectrum peaks were between 400-500 nm and optical band gaps 2.41-2.61 eV. Electronic band gaps were found between 1.83-2.98 eV by using cyclic voltametry. As a result of the UV-Vis spectrum, 31 molecule is the best molecule for making solar cell because its conjugation is longer than others. Because of that, it ispossible to designe new molecules which include 2 or 3 thiophene ring between the two TT-BorMes2. It is believed the new molecules that are synthesized according to proposed method will support the solar cell condition which is the photon absorption between 500-600 nm wave length.