Aggregation and thermally induced photo-physics and structural ordering of thiophene-quinoxaline copolymer

Abstract

Aggregation and thermally induced photo-physics of a low band gap thiophene-quinoxaline copolymer (TQ1) was investigated. The S0 ⟶ S1 transition of TQ1 in solution is found to be due to an intra-molecular charge transfer state while the excited state in aggregated TQ1 chains was due to intra and inter-chain excitons. On the other hand, the emission of TQ-1 recorded at 85 °C for more than 300 h confirmed that thermal stress hampers the inter-chain interaction as confirmed by the disappearance of the vibronic shoulder ascribed to it in the PL. In addition, it was observed that the PL intensity has drastically decreased while its absorption showed smaller change due to annealing for less than 40 h which confirmed either the introduction of new non-radiative channels or coiling of the copolymer due to thermal stress. The evolution XRD traces of TQ1 with thermal stress confirmed that it takes higher energy to break the long-range order than the molecular bonds in the copolymer.