TICT AND TRIPLET-STATES OF TRIARYLPYRYLIUM CATIONS

Triarylpyrylium cations bearing an electron donating group an studied in solution by two pump-probe techniques with picosecond and nanosecon d resolution. The transient spectra recorded on the picosecond time-sc ale as a function of solvent viscosity are in agreement with the forma tion of a TICT (twisted intramolecular charge transfer) state, predict ed by quantum chemistry calculations. The ground state relaxation from the twisted conformation is observed. It is shown that the tripler st ate is formed only in solid matrices where the non-radiative decay of the excited singlet to the ground state is slowed down. (C) 1997 Elsev ier Science B.V.