Time-resolved resonance Raman and transient absorption studies on water-soluble copper(II) porphyrins

Transient Raman and absorption spectroscopic investigations were carried out on copper(II) tetrakis(p-sulfonatophenyl)porphyrin ((CuTSPP)-T-II) and copper(II) tetrakis(4-N-methylpyridyl)porphyrin (Cu-II(TMpy-P4)) in water, dioxane, and the mixed solvents to examine the exciplex formation of these water-soluble porphyrins with the solvents. We explained the nature of exciplex in terms of a photoinduced axial ligation with the solvent molecules. We demonstrated that the excited state lifetimes of copper(II) porphyrins are predominantly responsible for the observation of new transient Raman bands corresponding to the exciplex formation with the solvent molecules in the nanosecond transient Raman spectra. The addition of oxygen-containing solvents such as dioxane and tetrahydrofuran to the aqueous copper(II) porphyrin solutions induces an increase in the lifetimes of the transient species and consequently results in the observation of the transient Raman bands contributed by these exciplex species in the nanosecond transient Raman spectra. On the basis of a photokinetic scheme for the excited water-soluble copper(II) porphyrins in the water/dioxane mixed solvents, we have tried to provide further information on the ligand binding affinity of photoexcited water-soluble copper(II) porphyrins in the water/dioxane mixed solvents.