Molecular twisting and relaxation in the excited state of triarylpyrylium cations

Excited-state twisting and relaxation of triarylpyrylium cations is studied with various substituents attached to different parts of the molecule by means of femtosecond pump-probe absorption spectroscopy. The modeling shows that a broad population distribution along the twisting angle in the ground state is transferred to the excited state, causing strong fluorescene broadening, while competition between the excited-state twisting and solvation determines a subsequent reaction path.