Flash-photolysis studies of trans-[Cr(cyclam)(CN)(2)]ClO4 (cyclam = 1,4,7,11-tetraaza-cyclotetradecane) complex - Part 2 - Unexpected self-quenching and its connection to the apparent activation energies of the complex

The luminescence lifetime (tau(lum)) of the title complex I was determined in eight solvents. We found that in spite of former assumptions, tau(lum) o f I depends on the concentration of the complex. We determined the self-que nching- and Stern-Volmer constants (K-SV), and the relative values of lumin escence quantum yields in eight solvents. There was no measurable self-quen ching in 1,2-ethane-diol and N,N-dimethyl-formamide, dynamic self-quenching was found (the concentration dependence of tau(lum) and phi(lum) was the s ame) in N,N-dimethylacetamide, dimethylsulfoxide, water, propylene-carbonat e, pyridine. In acetonitrile we found both dynamic and static self-quenchin g based on the different concentration dependence of tau(lum) and phi(lum) of I; K-SV and the association constant of I in acetonitrile were computed. The apparent activation energies were also studied, they decreased when th e self-quenching became faster. (C) 1999 Elsevier Science S.A. All rights r eserved.