ENERGY-GAP DEPENDENCES OF CHARGE RECOMBINATION PROCESSES OF ION-PAIRS PRODUCED BY EXCITATION OF CHARGE-TRANSFER COMPLEXES - SOLVENT POLARITY EFFECTS

The energy pp dependences Of k(CR) (charge recombination rate constant) of CIPs (compact ion pairs) produced by exciting CT complexes of acid anhydride-aromatic hydrocarbon systems were investigated in solutions of different polarities and compared with those of the intramolecular IP states in distance-fixed porphyrin-quinone dyads10 as well as those of aromatic ligand to ligand intramolecular ET (electron transfer) states in Re(I) complexes.16b,c,17b No or very little solvent polarity effect on the k(CR) vs (energy gap) relation of CIPs was observed, which was very similar to the result of the intramolecular ET systems10,17b and suggested a dominant effect of the high-frequency quantum modes in the ET process. A ln(k(CR)) vs (energy pp) linear relation was observed for CIPs and interpreted on the basis of the weak coupling limit in the radiationless transition, including the important contributions of the multimode effects and the equilibrium displacements enhanced by ET, which was also very similar to the case of the Re(I) complexes.