Spectroscopic study on the photophysical properties of chlorine substituted tetraphenylporphyrin-histidine and its zinc (II) complexes

Abstract

The photophysical properties ofortho- CI,meta-CI andpara-CI substituted tetraphenylporphyrin-histidine and their zinc (II) complexes have been studied by means of steady-state absorption and fluorescence spectroscopies, as well as time-resolved fluorescence spectroscopy. For the cases of both free-base and zinc complexes, it was found that theortho-chlorine substitution onto the phenyl rings significantly altered the fluorescence quantum yield, the fluorescence lifetime and the ratio between radiative and nonradiative deactivation rates of the porphyrin chromophore, i.e. the photophysical parameters were quite different from those ofmeta- andpara-substituted compounds. On the other hand, however, the introduction of covalently-linked histidine did not exert much effects on the photophysical behavior of the porphyrin chromophore. The results are interpreted in terms of the steric effect and the heavy-atom effect from the chlorine atoms substituted onto the phenyl rings.