Temperature dependence of a process competing with S2-S1 internal conversion in indole and phenol in aqueous solutions

Abstract

The drop in phi/sub f/ with decreasing excitation wavelength, previously attributed to ionization from the S/sub 2/ state, increases substantially with increasing temperature for both indole and phenol in aqueous solution. Addition of 2-propanol to the solvent reduces the drop in phi/sub f/ but not its activation energy which on the other hand depends significantly on the solute. phi/sub eaq/-measured upon excitation of the S/sub 2/ state of indole in H/sub 2/O increases from 0.09 at 25/sup 0/C to 0.17 at 65/sup 0/C. The results are interpreted in terms of an intermediate charge transfer to solvent state (CTTS) populated from S/sub 2/. In the 2-propanol-water solvent the formation of this CTTS state appears to be governed primarily by interaction of the excited solute with water molecules. (auth)