Photophysics of aminobenzazole dyes in silica-based hybrid materials

In this work two aminobenzazole derivatives (5-AHBT and 5-AHBI) were dispersed in silica-based hybrid materials with different surface hydrophobicity, which were obtained by the sol–gel process using tetraethylorthosilicate as inorganic precursor and dimethyldimethoxysilane as organic precursor, with a molar percent of organic precursor changing from 0 to 50%. The photophysics of the obtained doped silica hybrid materials was investigated by means ultraviolet–visible diffuse reflectance and steady-state fluorescence emission spectroscopy in the solid state. The materials present absorption maxima located around 353 and 318 nm when doped with 5-AHBT and 5-AHBI, respectively. The red shifted absorption maxima of the 5-AHBT can be explained by the better electron delocalization allowed by the sulfur atom in relation to the nitrogen. The fluorescence emission spectra are located in the blue-green regions and the high Stokes shift indicates that the ESIPT mechanism occurs in the excited state for both dyes. The photophysical behavior of 5-AHBT shows that this dye is more affected by the matrix polarity due to specific interactions that take place in the ground state.