Effect of Thiophene Units on the Properties of Donor Acceptor Type Monomers and Polymers Bearing Thiophene-Benzothiadiazole- Scaffolds

Abstract

In this article, a series of benzothiadiazole and thiophene based donor-acceptor-donor (D-A-D) type monomers and their corresponding polymers, via potential cycling, were reported. Effect of increasing number of thiophene units in the electron rich donor segment on the electrochemical and photophysical properties of the monomers and their corresponding polymers were reported. Electrochemical and optical properties were determined by cyclic voltammetry, UV-Vis and emission spectrometry. Monomers with one, two and three thiophene units on both sides of benzothiadiazole (TBz, T2Bz, T3Bz) exhibited better conjugation and intramolecular charge transfer with increasing thiophene length. On the other hand, the inverse trend was observed in their corresponding polymers (PTBz, PT2Bz, PT3Bz). Blue shift of the absorption edge in polymer thin films resulted in wider optical bandgap (from 1.70 eV to 1.99 eV) with increasing donor/ acceptor ratio on the polymer chain. Based on our experimental and theoretical studies, molecular weight or branching on these polymers together with degree of stiffness and conformational degree of freedom might be an explanation for these controversial observations. (C) 2016 The Electrochemical Society. All rights reserved.