Julio C. de Paula of Haverford College is supported by the Experimental Physical Chemistry Program to investigate the nature of excited states of metalloporphyrins using time-resolved resonance Raman spectroscopy. The focus of his studies will be (a) to investigate equilibrium dynamics between conformers of tetraphenylporphyrins in triplet excited states, (b) to distinguish between charge-transfer and metal-centered excited states by varying the substituents on ruthenium and nickel ion complexes, and (c) to assign the time-resolved resonance Raman spectra of the cupric tetraphenylporphyrins. Metalloporphyrins have a rich photochemistry that may be applied to artificial photosynthesis, molecular electronics, and photodynamic cancer therapy. For example, free-base zinc and cupric porphyrins are known to sensitize tumor necrosis in vitro. Further, polymers of ruthenium porphyrins are photoconductive and can act as molecular wires. Non-planar metalloporphyrins are emerging as important compounds for a number of these applications, because distortions of the porphyrin ring modulate electrochemical and photochemical properties. These studies of the excited electronic states of metalloporphyrins will lead to a better understanding of their photochemical activity.
