Spectral and Luminescent Characteristics of a Hexaphenyltetraazachlorin Zinc Complex

Abstract

In continuation of previous studies on the photophysics of phenyl-substituted tetraazachlorins, we determined the spectral and luminescent characteristics of a tetramethylhexaphenyltetraazachlorin zinc complex at 293 and 77 K. Absorption, fl uorescence, and fl uorescence excitation spectra; the fl uorescence quantum yield and lifetime; and the quantum yield for singlet oxygen generation were measured at room temperature. Fluorescence, fl uorescence excitation, and fl uorescence polarization spectra were measured at liquid nitrogen temperature. Fluorescence spectra indicated that the zinc complex rearranged in the excited electronic state S 1 at both temperatures. A high quantum yield for singlet oxygen generation (0.91) was obtained for a toluene solution. Zn-tetramethylhexaphenyl tetraazachlorin was proposed as a photosensitizer for photodynamic therapy because the long-wavelength band at 707 nm was located in the transparent region of biological tissues.Introduction. Phenyl rings substituted onto the pyrrole rings of a tetraazaporphyrin (porphyrazine) macrocycle represent a structural factor capable of affecting considerably and controlling the physicochemical properties of tetrapyrrole macroheterocycles. The photophysics of two tetraazachlorins with aromatic pyrrole rings containing two phenyl rings each were studied before [1]. These were tetramethylhexaphenyltetraazachlorin [2] (H 2 Ph 6 TAC tm , where tm = tetramethyl) and N-methylpyrrolidineoctaphenyltetraazachlorin, the spectral properties of which differed slightly. The zinc complexes were studied in parallel with the free bases in a series of studies [3][4][5] in order to expand information on the properties of the macrocycles. Therefore, it seemed advisable to continue the work [1] by studying the photophysical characteristics of the zinc complex ZnPh 6 TAC tm :