WAVELENGTH DEPENDENCE AND SOLVENT EFFECTS ON THE LIGAND-FIELD PHOTOCHEMISTRY - THE RING-CLOSURE PROCESS IN THE EXCITED [FE(CN)(5)(TN)](3-) COMPLEX

The solvent composition and wavelength effects on the quantum yield of the photoinduced ring closure process of the [Fe(CN)(5)(tn)](3-) comp lex (tn = 1,3-diaminopropane) were investigated. The reactivity was sh own to be controlled by the macroscopic properties of water-glycerol m ixtures. A sharp decrease in quantum yields with increasing medium vis cosity was observed for all the irradiation wavelengths employed (313, 334, 365, 404, and 434 nm). The observed quantum yields ranged from 0 .24 (lambda(irr) = 313 nm, 66.48 wt.% of acetonitrile) to 0.010 (lambd a(irr) = 404 or 434 nm, 61.85 wt.% of glycerol). The overall efficienc y is a complex function of the dynamics of radical recombination and d issociation pathways. The proposed cage model for the deactivation dyn amics of the excited states illustrates that the decrease in medium vi scosity favors a diffusional escape of the cyanide from the solvent ca ge.