Photosensitization of Colloidal TiO2 Semiconductor with Zinc Phthalocynine

Abstract

Zinc-phtalocyanine with tyrosine substituents (ZnPcTyr) was attached to the surface of the colloidal nanocrystalline TiO₂ via carboxylic acid group. The interaction of ZnPctyro with colloidal was studied by absorption and fluorescence spectroscopy. The apparent association constant for the association between ZnPcTyr and TiO₂ is about 4.5 × 10⁴ M^-1 with a degree of association up to 90%. Presence of the tyrosine group in ZnPcTyr enhances the solubility of the dye in ethanol and decrease the aggregation behavior. Anchoring of the dye complex to the nanocrystalline TiO₂ enables ultrafast injection of electrons from the excited state into the conduction band of TiO₂ (completed in ca. 500 fs) which results in strong quenching of the singlet state of the ZnPcTyr and a maximum of incident photon to current efficiency (IPCE) is ca. 24% at 690 nm, the low IPCE is due to the surface aggregation and fast charge recombination. Photophysical properties of the zinc phthalocyanine and the transient spectra were also determined.