Structural and electronic effects of 1,3,4-thiadiazole units incorporated into polythiophene chains

Pang, Hao and Skabara, Peter and Crouch, David J. and Duffy, Warren and Heeney, Martin and McCulloch, Iain and Coles, Simon J. and Horton, Peter N. and Hursthouse, Michael B. (2007) Structural and electronic effects of 1,3,4-thiadiazole units incorporated into polythiophene chains. Macromolecules, 40 (18). pp. 6585-6593. ISSN 0024-9297

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Abstract

A series of conjugated triaryl compounds have been synthesized, consisting of thiophene or selenophene peripheral units and a central 1,3,4-thiadiazole (TDA) heterocycle. X-ray crystallographic studies on four of the materials reveal that the molecules are planar in the solid state and feature an array of intramolecular (heteroatomic) and intermolecular (heteroatomic and π−π) noncovalent close contacts. Electrochemical oxidative polymerization affords insoluble polymers for EDOT-TDA-EDOT and EDTT-TDA-EDTT. The band gaps of the polymers have been deduced by cyclic voltammetry and electronic absorption spectroscopy and were found to be 1.8−1.9 eV. Both polymers show good stability toward n-doping and the EDTT analogue is more readily reduced than the EDOT-containing system. The enhanced stability toward n-doping, compared with the homopolymers PEDTT and PEDOT, is attributed to the presence of the electron deficient thiadiazole unit. The LUMO of poly(EDTT-TDA-EDTT) is 0.3 eV lower than that of poly(EDOT-TDA-EDOT), demonstrating that the substituent effect of the chalcogen atom is an important contributor to the electronic properties of the polymers.