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

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 S-3-sapphyrin and S-4-rubyrin decrease steadily relative to STPPH and S2TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S-3-sapphyrin and S-4-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M-1 respectively. However, the triplet lifetime for S-3-sapphyrin is longer (58.80 mu s) than for normal thiaporphyrins (STPPR 37.45 mu s; S2TPP 20.96 mu s), suggesting that it could be very well suited for photosensitizing triplet oxygen. (C) 1998 John Wiley & Sons, Ltd.