ULTRAFAST PHOTOINDUCED CHARGE-SHIFT REACTIONS IN ELECTRON DONOR-ACCEPTOR 9-ARYLACRIDINIUM IONS

Charge-shift species arising from intramolecular electron transfer hav e been identified for 9-aryl derivatives of the 10-methylacridinium io n through observation of red-shifted fluorescence emission bands and t he appearance of radical(ion) transients (CH3CN and CH2Cl2 solvents) u sing laser flash photolysis. Rates of forward and return charge-shift processes have been determined, the former occurring in the 1 ps time domain with small effects associated with changes in solvent and the e lectron donor substituent. Rates for return electron transfer were a s trong function of the donor oxidation potential and showed acceleratio n with decreased driving force (inverted behavior). The lifetimes for charge-shift intermediates could be 'tuned' over three orders of magni tude as the result of changes in acridinium structure and solvent.