Primary processes in excited β-napthol systems: A pulsed laser photolysis study

Abstract

Using a pulsed N₂ laser the rates of formation of solvated electrons, and triplet molecules were measured for β‐naphtholate, β‐naphthol, and β‐naphthyl‐methyl‐ether in solution. The rate of electron formation is higher than the rate of vibrational relaxation to the lowest excited singlet state, from which intersystem crossing occurs. Quantum yields of triplet formation and rate constants for intersystem crossing were obtained from measurements of fluorescence yields, lifetimes and relative yields of triplets in oxygen free and oxygen containing solutions. For β‐naphthol in a high viscosity solvent the sum of the quantum yields of formation of solvated electrons and of population of the lowest excited singlet state is unity whereas the sum is less than unity in low viscosity solvents, indicating that the lowest excited singlet state of β‐naphthol is populated by charge recombination in high viscosity solvents but not in low viscosity solvents. A calculation of the energetics yields a maximum charge separation of 5 Å, a value consistent with the occurrence of effective charge recombination.