Photophysics of supported dyes: phthalocyanine on silanized silica

Abstract

Aluminum tetracarboxyphthalocyanine is adsorbed onto silanized silica particles at different dye to particle ratios. Diffuse reflectance spectra are measured and the equilibrium between dye monomers and aggregates is studied. Between 4.0 × 10⁻⁸ and 2.0 × 10⁻⁶ mol of dye g⁻¹ of support, a simple dimerization equilibrium explains experimental results. Fluorescence spectra and quantum yields are calculated and corrected for light absorption by non-fluorescent dimers and reabsorption of emitted radiation. Once corrected, fluorescence quantum yields are of the same order of magnitude than in solution. Absorption spectra are also obtained for suspensions of the same materials in water. The hydrophilic environment enhances aggregation dramatically. Singlet oxygen quantum yields measured in suspension are lower than those found for the same phthalocyanine in solution of DMSO. Results are compared with those previously obtained for similar materials.