8,17,18-TETRABROMO-5,10,15,20-TETRAPHENYLPORPHYRIN AND ITS METAL DERIVATIVES PHOTOPHYSICAL PROPERTIES AND ELECTRONIC-STRUCTURE

The absorption and emission spectral properties of 8,17,18-tetrabromo- 5,10,15,20-tetraphenylporphyrin and its metal derivatives are presente d. Substitution with the electron-withdrawing bromine groups at the py rrole carbons produces remarkable red shifts in their absorption and e mission bands, which are influenced by the number of electron-withdraw ing substituents. These results are rationalized by using four-orbital approach. The decrease in the fluorescence quantum yields and lifetim es for MTPPBr4 (M = H-2, Zn) are attributed to increased rate of inter system-crossing. (C) 1997 Elsevier Science B.V.