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

The luminescence lifetime (tau(lum)) of the title complex (1) was determine d in 8 solvents. We found that in spite of former assumptions tau(lum) of I depends on the concentration of the complex. We determined the self-quench ing- and Stern-Volmer constants (K-SV), and the relative values of luminesc ence quantum yields in 8 solvents. There was no measurable self-quenching i n 1,2-ethanediol and N,N-dimethyl-formamide, dynamic self-quenching was fou nd (the concentration dependence of tau(lum) and phi(lum) was the same) in N,N-dimethyl-acetamide, dimethylsulfoxide, water, propylene-carbonate, pyri dine. In acetonitrile we found both dynamic and static self-quenching 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 ap parent activation energies were also studied, they decreased when the self- quenching became faster.