Ground and excited state dynamics of core-modified normal and expanded porphyrins

Abstract

Singlet and triplet excited state data on two new core-modified expanded porphyrins and their protonated derivatives are reported. Absorption spectral studies indicate a gradual red shift of the absorption bands upon sulfur substitution into the core. The singlet lifetimes for expanded S₃-sapphyrin and S₄-rubyrin decrease steadily relative to STPPH and S₂TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S₃-sapphyrin and S₄-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M^-1 respectively. However, the triplet lifetime for S₃-sapphyrin is longer (58.80 µ s) than for normal thiaporphyrins (STPPH, 37.45 µ s; S₂TPP, 20.96 µ s), suggesting that it could be very well suited for photosensitizing triplet oxygen.