Wavelength dependence and solvent effects on the ligand field photochemistry: the ring closure process in the excited [Fe(CN)5(tn)]3− complex

Abstract

The solvent composition and wavelength effects on the quantum yield of the photoinduced ring closure process of the [Fe(CN)5(tn)]3− complex (tn = 1,3-diaminopropane) were investigated. The reactivity was shown to be controlled by the macroscopic properties of water–glycerol mixtures. A sharp decrease in quantum yields with increasing medium viscosity was observed for all the irradiation wavelengths employed (313, 334, 365, 404, and 434 nm). The observed quantum yields ranged from 0.24 (λirr = 313 nm, 66.48 wt.% of acetonitrile) to 0.010 (λirr = 404 or 434 nm, 61.85 wt.% of glycerol). The overall efficiency is a complex function of the dynamics of radical recombination and dissociation pathways. The proposed cage model for the deactivation dynamics of the excited states illustrates that the decrease in medium viscosity favors a diffusional escape of the cyanide from the solvent cage. Key words: photochemistry, pentacyanoferrate(II) complexes, solvent effect, wavelength effect.