PH Control of photoreactivity of ruthenium(II) pyridyltriazole complexes: photoinduced linkage isomerism and photoanation

Abstract

The photophysical and photochemical behavior of mixed ligand complexes of Ru(II) with 3-(pyridin-2-yl)-1,2,4-triazole (HPTN) have been examined in solutions of varying acidity. Protonation of both the N-2 bound (HPTN-2) and the N-4 bound (HPTN-4) isomers of [(bpy){sub 2}Ru(HPTN)]{sup +} results in a decrease in the luminescence lifetime in solution and an increase in reactivity upon photolysis in CH{sub 2}Cl{sub 2}. The excited state of the deprotonated form of both complexes decays by a single exponential at pHs above 3; the data were fit to a general expression for excited-state decay involving protonation of the excited complex. Results of temperature-dependent luminescence decays suggest the protonated complexes decay via population of a metal-centered excited state, while the deprotonated complexes do not efficiently populate this state at temperatures at or below room temperature. Photolysis of either protonated isomer in CH{sub 2}Cl{sub 2} results in linkage isomerism; equilibrium is established for photolysis at 4:1 [(bpy){sub 2}Ru(HPTN-4)]{sup 2+} to [(bpy){sub 2}Ru(HPTN-2)]{sup 2+}. In the presence of coordinating counterions photoanation occurs to yield the cis-anion complex with loss of pyridyltriazole. The deprotonated form of both isomers is inert to photosubstitution in CH{sub 2}Cl{sub 2} at room temperature. Thus, the substitutional photolability can be controlled by controllingmore » protonation of the ground state of the complex. 41 refs., 9 figs., 3 tabs.« less