Spectral properties of amorphous silica (SiO2) and mesoporous structured silicates (MCM-41 and ITQ-6) functionalized with ESIPT chromophores

2-(2′-Hydroxyphenyl)benzazole (HPB) derivatives, fluorescent by an intramolecular proton-transfer mechanism in the electronically excited state (ESIPT), were synthesized and incorporated by physisorption and covalently bound into amorphous silica (SiO2) and mesoporous structured silicates (MCM-41) and delaminated zeolite (ITQ-6). The new fluorescent hybrid-materials were prepared by one-step implantation of the dyes into the inorganic framework. The photophysical behaviour of the triethoxysilylated benzazoles, which are covalently bounded into inorganic matrices, is quite different from the non-silylated benzazoles, which are physisorped into inorganic matrices. The fluorescence emission spectra of the bounded dyes were found to be dependent on the heteroatom, since the ESIPT emission was more affected for the benzothiazole and benzimidazole derivatives. The mechanism associated with the ESIPT process was not significantly modified for non-silylated benzazoles, except for a benzimidazole derivative which the fluorescence emission spectra in the inorganic matrices are similar to that observed in MeOH, suggesting that the molecules are surrounded by the SiOH groups.