Effect of axial ligands on the photophysical properties of new silicon(IV) phthalocyanines

A series of axial di-substituted silicon(IV) phthalocyanines with electron-donating and electron-withdrawing properties were synthesized. The compounds were characterized by elemental analysis, ¹H NMR, IR, and ESI-MS. The effect of axial ligands on the photophysical properties of silicon phthalocyanines was studied by UV/Vis, steady-state and time-resolved fluorescence spectroscopic analyses. Compared with silicon phthalocyanines with electron-donating properties, silicon phthalocyanines with electron-withdrawing properties could expand the π-conjugation in the dyes, resulting in a redshift of Q bands, lower fluorescence emission intensity and fluorescence quantum yields, but increasing fluorescence lifetimes. These results strongly suggest that the molecular design of phthalocyanines is essential for construction of photoactive materials.