Syntheses of boron containing donor-acceptor (D-A) organic materials and investigation of their properties

Until middle of 20th century, organic compounds were assumed to be non-conducting, and described in the same way. By the detection of their weak conductivity, many systematic studies have been bloomed. Especially, the studies on conjugated hydrocarbons and the structures containing heteroatoms have paved the way to take the name of "organic semi conducting". Serious and positive alterations has been observed by doping aromatic hydrocarbons with halogens. When it came to1990s, organic material chemistry has identified as OLED; "Organic Light-Emitting Device" materials with the discovery and development of the conjugated polymers. The acceleration in the progress of OLED has increased much with the improvement of plastic electronic, photodiods, solar cells, and field effect transistors. It is a known reality that inorganic conductors involving metal is superior in terms of energy conversion. However, OLED has been being the center of interest in comparison to LED with a series advantages; such as OLED efficiency up to 20 %, easy applicability, eco-friendly. Besides, it is possible to see that many intense and hopeful works in OLED fields. In OLED the properties of both conductor and emmisive layer are very crucial in terms of efficiency and activity. For this reason, more efficient organic conducting-layer materials have been designed and investigated. Recently, increasing energy demand, using energy effective and economics necessitate OLED materials. Fused and cyclic compounds rich in electron such as dithienothiophene (DTT), thienothiophene (TT) has found many applications in the fields of electronic, electroluminescence, photon absorbent, fluorescents, photochromism, optic chromophores, thin film transistors, radar absorbent, and conducting polymers. In the chemistry literature, it is well-known that TTs have many synthetic routes as DTTs have. But easy and effective synthesis of TTs is another important issue in this field. 1,8-diketone and mono-ketone ring closure reaction with P4S10, recently discovered by our research group, was utilized. This effective sythetic method is applicabile for both DTTs and TTs. It was an effective route to synthesize our electron rich and thiophene-based donors, and the reaction conditions are tried to improve as well. In the thesis study, sythesis of 3,5-dimethoxyphenyl dithieno[3,2-b: 2',3'-d] thiophene as DTT derivative (donor), N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxsaborolane-2-yl)phenyl)-N-phenyl benzenamine as triphenyl amine (TPA) derivative (donor) and their reactions with dimesityl boronfloride (DMBF) (acceptor) and building several donor-acceptor (D-A) nearly took a biennial period. However, synthesis period failed due to the extreme sensitivity of DMBF to moisture and air, tendency to obtainment of undesireable symmetric DTT product in coupling reactions, possible steric hinderence of electron donor DTT derivative. Upon those reasons, it was decided to synthesize sterically more comfortable new electron donor TT derivatives, so that TT derivatives would give reaction with dimethoxy mesityl borane and we would obtain new D-A polymers. Implementing mono-ketone ring closure reaction with P4S10, 3-phenylthieno[3,2-b]thiophene (13) and 3-(4-bromophenyl)thieno[3,2-b] thiophene (14) were successfully synthesized. By Suzuki coupling from two TT derivatives as lenear and cross thiophene coupled and totally four TT derivatives were prepared. Prepared donors firstly lithiated and then replacement reaction performed for overnight in order to D-A polymers including mesityl borane (acceptor). As a result, in the duration of the synthesis P1 (P(PhTT-MsB) (21), P2 P(PhTh2TT-MsB) (22), P3 P(PhTT-MsB2) (23) ve P4 P(PhTh2TT-MsB2) (24) as four D-A polymers were sythesized. The characterization of the sythesized TT derivatives and boron containing D-A polymers was confirmed by IR, 1H, 13C and 11B NMR and mass spectrometer. UV-visible, fluorescence spectroscopy analyses were carried out for both TT donors and their D-A polymers. For P1-4 quantum yields were calculated in company with convenient standards. Cyclic voltammograms of the polymers were taken, and reduction-oxidation potentials were determined. By means of reduction-oxidation potentials and UV spectrum, Eg and Eopt values were calculated, respectively and compared with each other. Properties of OLED materials prepared by D-A polymers were investigated and color coordinates were recorded. Furthermore, molecular weights of the polymers and their thermal gravimetric analyses were completed. When looking to the yields of ring closure reaction and Suzuki coupling reaction they are over 80 %. As for the polymers they are in the 40-60 % interval. In the UV spectra of donor TT derivatives it was determined that they had an absorption between 230-480 nm interval. It found to be around 225-580 nm interval for P1, P2, P3 and P4 in solution. Besides, four polymers had an interval about 300-600 nm when they were coated on ITO substrates. From TT to donor-acceptor polymers narrowing of optical band gap values were calculated for all polymers. Narrowing values were 0.10, 0.75, 1.40, 0.31 eV respectively when the donor TTs turned to P1, P2, P3 and P4. In the electrochemical studies, measurements in the areas of anodic and cathodic were taken under nitrogen atmosphere. In the cyclic voltammetry measurements 0.1 M Bu4NPF6 in THF as a supporting electrolyte was used. Glassy carbon as working, Pt as counter and Ag/AgCl as reference electordes were utilized. While taking measurements for polymers attached on glassy carbon, suitable electrolyte was determined as Bu4NPF6. Both oxidation and reduction potentials for P1 and P2 measured but for P3 and P4 were restricted with oxidation potential. Potentials were determined seperately by working in both anodic and cathodic. The oxidation potentials for P1, P2, P3 and P4 were 1.93, 1.40, 1.74, 1.36 V, respectively. Fluorescence measurement belonging to the four polymers were taken in both THF media and on ITO. Emission area of the polymers were determined for both solution and solid phase too. When we look into emission intervals, it is seen that they are higly broad for P1, P2, and P3. This issue repeated in solid phase emissions. However, in P2 the narrowing of emission interval and red shift were striking. Quantum yield calculations in company with coumarin1 and quinine sulphate the changes in 0.05-0.19 interval was found. Molecular weights of the donor-acceptor polymers taking from Light Scattering were calculated in the interval of 110-500 kda. The results of thermal gravimetric analysis (TGA) belonging to the polymers showed that they are thermally resistant till to 200oC, it was proved that there was not significant change in four polymers in mass. Especially,it can be said that P2 and P4 are thermally more resistant. Layer schemes for prepared OLEDs is ITO/PEDOT:PSS (50 nm)/P1-4 (70 nm) /TPBİ (30 nm)/LiF (6 nm)/Al (120 nm) layer by layer. The layers were utilized with spin coating method and thermal evaporation under vacuum were utilized. For four OLED electroluminescence-potential, luminescence efficiency-current density, external quantum efficiency- current density, current density-potential, color coordinates-potential changes were recorded. According to the result obtained, OLEDs prepared from P1, P2, and P3 gave white light emission. However, efficiencies OLED1, OLED2 ve OLED3 were 0.036, 0.036 ve 0.01, respectively. In conclusion the results such as successful synheses, applicability of OLED and white light emission were good and promising ones in spite of low luminescence efficiencies. New molecular designs can improve and promise for better emission efficiencies.