Optical characterisation of poly-2,5-diheptyl-1,4-phenylene-alt-2,5-thienylene

We have investigated the electronic properties and the photoluminescence (P L) decay of the poly-2,5-diheptyl-1,4-phenylene-alt-2,5-thienylene (PDHPT) copolymer made up by the regular alternation of high and low band-gap units . Experimental data show that the large twisting of the neighbouring consti tuents of the polymer chain leads to a considerable shift of the optical tr ansitions towards high energies. This blue shift is much more pronounced th an the expected band-gap lowering caused by the low-gap thiophene units. Tr ansient PL experiments show that inter-chain migration of excitons towards centers where excitons decay non-radiatively reduces the PL quantum yield ( QY). (C) 2000 Elsevier Science S.A. All rights reserved.