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. (c) 2005 Elsevier B.V. All rights reserved.