Tailoring of light emission properties of functionalized oligothiophenes

We investigate theoretically the light emission properties of short oligoth iophenes containing a thienyl-S,S-dioxide moiety, which have recently been shown to exhibit strong photoluminescence efficiency and tunability. We fin d that the dioxide substitution tends to increase the torsion angle between rings and strongly affects the states at the optical band edges, in a way depending on the position of the substituted ring. We have identified a low -energy transition which is optically active only when the dioxide unit is inserted between two thiophene rings, as a result of increased inter-ring t orsional angle also in the excited state. With the dioxide unit in a termin al position, planarity is favored in the excited state, and the transition is optically inactive. For short oligomers, this can lead to nonradiative d ecay quenching the luminescence. (C) 2001 American Institute of Physics.