Photophysical behavior of a phthalocyanine adsorbed on silica. Comparison with a chemically linked system

A. IRIEL, M.G. LAGORIO, L.E. DICELIO Y E. SAN ROMÁN

Ascochinga, Argentina

Congreso; XXII th Inter-American Photochemical Society Conference; 2001

As a result of previous studies it was demonstrated that hydroxoaluminum tricarboxymonoamidephthalocyanine (AlTCPc) is an efficient singlet oxygen photosensitizer when covalently bound to silanizated silica. However, a full characterization of the system could not achieved because of the following reasons, inherent to the study of solid photosensitizers: a) the amount of dye effectively incorporated was difficult to quantify and b) the state of aggregation of the dye on the surface could not be ascertained without a systematic variation of the surface concentration. Both factors are relevant to rationalize measured fluorescence and singlet owygen quantum yields. In this work bound ALTCPc is compared with a series of samples with a variable amount of the dye (2 x 10-8 to 4   x 10-6 mol/g) adsorbed on the same supporting material. Samples were characterized by diffuse reflectance and emission spectroscopy, whereas fluorescence and singlet oxygen quantum yields were measured as a function of the concentration of the dye. Fluorescence was measured using as a reference Rhodamine 101 (R101) adsorbed on different supports. Singlet oxygen was followed by its reaction with imidazol / N,N-diethyl-p-nitrosoaniline using Methylene Blue as a reference. At similar concentrations of the dye, covalently linked AlTCPc shows higher fluorescence and singlet oxygen quantum yields than samples prepared by adsorption. In the last case, however, both yields have only a slight dependency on the concentration of the dye and aggregation is not a determinant factor of the low values obtained. To validate the usage of R101 adsorbed on different substrates as fluorescence standar in the solid state, a detailed analysis on the effect of the matrix on the emission of this dye was also performed.