EXCITED SINGLET-STATE REACTIONS OF THIOPYRYLIUM WITH ELECTRON-DONORS - ELECTRON-TRANSFER, INDUCTION OF TRIPLET BY INTERNAL AND EXTERNAL HEAVY-ATOM EFFECT, AND COMPARISON OF PYRYLIUM AND THIOPYRYLIUM REACTIONS

The free energy dependence on the fluorescence quenching of 2,4,6-trip henylthiopyrylium tetrafluoroborate (TPTP) by a variety of halogenated benzenes, toluenes, and anisoles were studied in acetonitrile. The k( q), values calculated using Delta G double dagger from the Levine expr ession and the k(d) value of 5.4 x 10(10) M-1 s(-1). from the Smolucho wski expression are in good agreement with the experimental k(q) value s. The observation of the TPTP. signal at 550 nm and the correlation o f k(q) with Delta G(et) expound the possibility of an electron-transfe r mechanism. The radical yield and intersystem-crossing rate constants are evaluated using flash photolysis techniques. The influence of sul fur atom in the triplet induction is reflected in the intersystem-cros sing rate constant and radical yield values. The recombination rate co nstants k(b) obtained from the radical yield values are compared with the k(b) values calculated using the semiclassical expression.