TICT and triplet states of triarylpyrylium cations

Triarylpyrylium cations bearing an electron donating group are studied in solution by two pump-probe techniques with picosecond and nanosecond resolution. The transient spectra recorded on the picosecond time-scale as a function of solvent viscosity are in agreement with the formation of a TICT (twisted intramolecular charge transfer) state, predicted by quantum chemistry calculations. The ground state relaxation from the twisted conformation is observed. It is shown that the triplet state is formed only in solid matrices where the non-radiative decay of the excited singlet to the ground state is slowed down.