Flash-photolysis studies of trans-[Cr(cyclam)(CN)(2)]ClO4 (cyclam = 1,4,7,11-tetraaza-cyclotetradecane) complex: Dependence of its luminescence lifetime on solvents, concentration and temperature

The luminescence lifetime (tau(lum)) Of the title complex (I) has been dete rmined in eight solvents. It has been found that in spite of former assumpt ions the luminescence lifetime of I depends on the concentration of the com plex. The self-quenching and Stem-Volmer constants, and the relative values of luminescence quantum yields have been determined in eight solvents. The re is no measurable self-quenching in 1,2-ethane-diol and N,N-dimethylforma mide, dynamic self-quenching has been found (K-SV values are 50-180 M-1) in N,N-dimethylacetamide, dimethylsulphoxide, water, propylene carbonate and pyridine. In acetonitrile the presence of both dynamic and static self-quen ching has been assumed based on high Stern-Volmer constant (K-SV = 2600 M-1 ) and low luminescence quantum yield which decreases further when the compl ex concentration increases. The apparent activation energies have also been studied; they decrease when the self-quenching becomes faster.