Synthesis, photophysics and photochemistry of novel tetra(quinoxalinyl)phthalocyaninato zinc(II) complexes

Abstract

The syntheses and spectral, photophysical and photochemical properties of some zinc phthalocyanine derivatives - {2, (3)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (beta-ZnPc) and 1, (4)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (alpha-ZnPc)} - are presented. The beta-substituted complex is more fluorescent and exhibits lower tendencies to undergo intersystem crossing than its alpha-substituted counterpart, as judged by the former's higher fluorescence quantum yield (phi(F)) and lower triplet quantum yield (phi(T)) than the latter's in three solvents (DMSO, DMF and toluene). Singlet oxygen quantum yield (phi(Delta)) values show the same trends as phi(T) values. The differences in the spectral and photophysical properties of alpha-ZnPc and beta-ZnPc are partly attributed to greater molecular distortions in the former. Studies of the interaction of the triplet states of alpha-ZnPc and beta-ZnPc with triplet oxygen showed that alpha-ZnPc is more vulnerable to oxygen quenching than beta-ZnPc. Also, the smallest quenching rate constants were observed in DMSO, which is attributed to the higher viscosity of DMSO than DMF and toluene. (C) 2009 Elsevier BY. All rights reserved.