TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY OF TRIPLET-STATE METALATED AND FREE-BASE TETRAARYLPORPHYRINS

Resonance Raman spectra of the T-1 excited states of Zn and free-base tetra-4-sulfonatophenylporphyrin (TPPS) have been recorded at room temperature in aqueous solution using two-colour time-resolved methods. The spectra of both sulfonated molecules are very similar to their tetraphenylporphyrin (TPP) analogues, which have been recorded in THF solution using the same pump-probe conditions, but they have higher signal-to-noise ratios because interference from strong solvent bands is reduced. Although two different T-1 spectra of Zn(TPP) have been reported these spectra differ slightly from each other and from the spectrum reported here, which has band positions very close (+/-6 cm(-1)) to those of Zn(TPPS). The high S/N ratios obtainable for the water-soluble porphyrins have allowed reliable polarization data to be recorded for their S-0 and T-1 states. This data set allows a realistic comparison of the changes in bonding associated with excitation of both free-base and Zn tetraarylporphyrins to the T-1 state.