Excited state relaxation properties of donor–acceptor-bithiophene and related compounds

Thiophene containing biaryls of ionic and nonionic character are investigated with respect to their photophysical properties and their ground and excited state hypersurfaces. The ionic dimethylamino-thiophene-pyridinium derivative showed a strong nonradiative deactivation channel assigned to intramolecular twisting and charge shift by analogy with a related biphenyl-type compound and based on the quantum chemical results. Implications for the induction of molecular photodiode behaviour and the possible construction of molecular photoswitches are discussed.