Syntheses and Photophysical Behavior of Porphyrin Isomer Sn(IV) Complexes

Abstract

2,3,6,7,12,13,16,17-Octaethylhemiporphycenato Sn(IV) chloride, [Sn(IV)(OEHPc)Cl(2)], and 2,3,6,7,12,13,16,17-octaethylporphycenato Sn(IV) chloride, [Sn(IV)(OEPc)Cl(2)], were synthesized in high yields and fully characterized by various spectroscopic methods. The X-ray crystal structures of the Sn(IV) complexes with porphycene and hemiporphycene were determined for the first time. The photophysical and photochemical properties of the singlet state of the Sn(IV) porphycene and hemiporphycene complexes, structural isomers of porphyrin, have been investigated by fluorescence and phosphorescence spectroscopies. The relatively strong emission and long fluorescence lifetime of the Sn(IV) porphycene complexes indicated by the fluorescence quantum yield and lifetime measurement were observed in the case of the Sn(IV) porphycene ([Sn(IV)(OEPc)Cl(2)], Phi(F) = 0.125, tau(s) = 2681 ps; [Sn(IV)(OEP)Cl(2)], Phi(F) = 0.010, tau(s) = 438 ps; [Sn(IV)(OEHPc)Cl(2)], Phi(F) = 0.027, tau(s) = 733 ps). The triplet state of the Sn(IV) complexes was investigated by transient absorption spectroscopy. It became clear that the triplet lifetime of the Sn(IV) porphycene (tau(T) = 49.9 mus) was longer when compared to those of the Sn(IV) porphyrin (tau(T) = 32.6 mus) and hemiporphycene complexes (tau(T) = 28.3 mus). These porphyrin isomer Sn(IV) complexes showed the high singlet oxygen generating ability, and the photo-oxidation of the 1,5-hydroxynaphthalene mediated by the Sn(IV) porphycene was the most effective among the complexes. This result is due to its more effective light absorption in the visible region and indicated that the porphycene is an excellent candidate as a photosensitizer.