Comparison of donor-acceptor-donor type conjugated systems with cross-exchange of donor units

Eroğlu, Deniz
In this thesis study, a series of new donor-acceptor donor type monomers were synthesized. For this purpose,benzothiadiazole (B) was used as the acceptor unit. Donor units, carbazole (C) and thiophene(T), were combined to B unit both symmetrically (CBCand CTBTC) and unsymmetrically (CBT) to understand the effect of cross exchange of donor units on the opto-electronic properties of monomers.The monomers were characterized using Nuclear Magnetic Resonance (NMR) and High-Resolution Mass (HRMS) spectroscopies. Optical properties of monomers were investigated by using UV-visible and fluorescence spectroscopy. Replacing oneof the symmetrical carbazole units in CBCmonomer with thiophene unit results in about 8 nm red shift in optical absorption. Having both carbazole and thiophene units symmetrically in the monomer structure increases the conjugation and exhibits about 70 nm red shift in the optical absorption.On the other, electrochemical behaviour of monomers were investigated utilizing cyclic and differential pulse voltammetry techniques. As a result of these studies, CTBTCmonomer was found to have the lowest oxidation potential and it has the lowest band gap energy (both optical and electronic) due to increased conjugation. After their characterization, monomers were polymerized electrochemically and properties of vipolymers were also investigated to understand the effectof symmetrical (D-A-D type) and unsymmetrical (D-A-D'type) combination of donor units.Polymerization of CBT and CTBTCmonomers was successfully achieved, and PCTBTCshows multichromic behavior however, its stability was lower than the stability of PCBT.The percent transmittance value of PCBTwas measuredas 12% at 530 nm and the switching time was calculated as 3 s at 95% of the full contrast. For PCTBTC, on the other hand, at 576 nm, percent transmittanceand the switching time was found as 8% and 4.2 s,respectively. It was observed that PCTBTChas the lowest optical band gap value and this value was calculated as 1.44 eV. For PCBT, the optical band gap wascalculated as 1.81 eV.
Citation Formats
D. Eroğlu, “Comparison of donor-acceptor-donor type conjugated systems with cross-exchange of donor units,” M.S. - Master of Science, Middle East Technical University, 2020.