Photophysical properties of carborane-containing derivatives of 5,10,15,20-tetra(p-aminophenyl)porphyrin

Absorption, fluorescence emission, fluorescence excitation spectra and fluo rescence decay kinetics of carborane derivatives of 5,10, 15,20-tetra(p-ami nophenyl)porphyrin have been investigated. Carborane derivatives are prepar ed by acylation of the amino groups of 5, 10,15,20-tetra(p-aminophenyl)porp hyrin by 9-carboranyl acetyl chloride. From the analysis of the absorption and fluorescence spectra, it is concluded that covalent linking of carboran e molecules to the tetraphenylporphyrin molecule significantly changes the self-conjugated rr-system of the porphyrin macrocycle: positions of maxima of absorption and fluorescence spectra shift to the red region by 3-8 nm; t he halfwidths of these bands an broadened by 2.5-5.0 nm; the relative inten sity of the bands I-IV also changes. The fluorescence decay kinetics of the carborane derivatives are biexponential. According to the experimental dat a and model simulation, it is concluded that the intramolecular electron tr ansfer proceeds from the porphyrin excited part of the molecule to carboran yls with a rate constant of 415 ps(-1) and efficiency of 0.16-0.8. Recombin ation of separated charges occurs within 1.4 ns. (C) 2000 Elsevier Science S.A. All rights reserved.