Photophysics of trans-stilbene analogues: Indolo[3,2-b]indole and its heterosubstituted sulfur and selenium derivatives Original Research Article

The rates of radiative and nonradiative depopulation channels of the lowest excited singlet and triplet states have been determined for indolo[3,2-b]indole and its derivatives in which one or two nitrogen atoms have been replaced by sulfur or selenium. Introduction of the heavy atom leads to activation of both S0 ← S1 internal conversion and T1 ← S1 intersystem crossing. The nonradiative rates of T1 depopulation are affected much more strongly than the radiative ones. The results are interpreted in terms of a trans-stilbene-like character of excited indoloindoles containing heavy heteroatoms. The evidence for the geometry change upon excitation is also provided by the results of luminescence anisotropy measurements.