Excited singlet state reactions of triphenylpyrylium ion with electron donors: Evidence for electron transfer and the observation of Marcus inverted region for the charge shift in the radical pair

The excited singlet state of 2,4,6-triphenylpyrylium ion reacts with benzene derivatives by the electron transfer mechanism, and the radical yield was measured using the flash photolysis technique. A poor correlation is observed between experimental and theoretical k(q) values calculated using k(d) from the Debye expression. The observed quenching constants are in good agreement with the k(q) values calculated using k(d) = 3.7 x 10(10) M(-1) s(-1), which is obtained from Smoluchowski expression and Delta G(double dagger) from the Rehm-Weller expression. The back electron transfer rate constant is determined from the quantum yield of the radical. Marcus inverted region is observed for the back electron transfer rate constants in the highly exothermic region of Delta G(b).