Photoexcited triplet ESR studies on thiaporphyrins and their protonated derivatives

Abstract

The photoexcited triplet states of mono- and di-thiaporphyrins and their protonated derivatives are investigated by ESR spectroscopy. A comparison of the magnitude of the zero-field splitting parameters (D and E) of neutral thiaporphyrins with H²TPP indicates no significant alterations in the triplet spin density. However, the protonated derivatives show large decreases in D (30%-40%) and E (40%-50%) values. The electron spin polarization pattern (ESP) indicates dominance of an in-plane spin sub-level with respect to the population and decay process for neutral species, while a redirection of spin sub-level activity is observed for protonated species. The structural change accompanying the protonation process accounts for most of these observations.