Synthesis of tin(IV) complexes of chlorophyll-a derivatives with two halides as axial ligands and their optical properties in solution

Abstract

Methyl pyropheophorbides prepared from naturally occurring chlorophyll-a were reacted with tin(II) dihalide in aerated solvents to give their tin(IV) complexes with two halides as the axial ligands. The tin(II)-insertion into the central position and the successive air-oxidation of tin(II) to tin(IV) proceeded cleanly for the 3-ethyl-, vinyl-, acetyl-, and formyl-chlorins. Their visible absorption and fluorescence emission maxima in dichloromethane were shifted to longer wavelengths in the order of F < Cl < Br as the axial ligand and CH2CH3 < CH = CH2 < COCH3 < CHO as the 3-substituent. The heavy atom effect was observed for their fluorescence emission quantum yields and lifetimes, which were suppressed in the order of H2 (free base) > SnF2 > SnCl2 > SnBr2 at the central position.