5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Covalently Bound to Nano-silica Surface: Preparation, Characterization and Chemosensor Application to Detect TNT

Mesoporous silica is a very suitable carrier for preparation of sensors for detection of explosive compounds with high selectivity and rapid responsiveness by incorporating chemical sensing units into silica films. Three types of porphyrin-doped silica with mesoporous and amorphous structures were prepared. 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin was synthesized in two steps starting from p-methoxycarbonylbenzaldehyde. 5,10,15,20-tetrakis(4-(methoxycarbonyl) phenyl) porphyrin (1a) was hydrolyzed with trifluoroacetic acid (TFA) to produce 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (1b) in 100 % yield. Different kinds of silica such as Hexagonal SBA-15 (SBA-15(Hex)), Spherical SBA-15 (SBA-15(Sp)) and commercial SiO2(SiO2(Ald)) were functionalized using 3-aminopropyltriethoxysilane (3-APS). Porphyrin with carboxylic substituent was reacted with N-hydroxysuccinimide (NHS) and N, N-'-dicyclohexylcarbodiimide (DCC) to produce 5-[4-(succinimidyloxycarbonyl)phenyl]-10,15,20-tri(4-carboxyphenyl)porphyrin (H2SPTCPP) and grafted to the surface of modified silica to obtain porphyrin-doped silica materials. Results suggest that the synthetic route achieves a high content of porphyrin incorporated to the support. The percentage of porphyrin incorporated to the support, which is higher in the case of SBA-15(Sp) with higher surface area and containing a larger number of silanol groups available for grafting, is directly related to the catalytic activity. Time-dependent fluorescence quenching of porphyrin-doped silica films was studied for three different mesostructures and it showed a rapid quenching upon exposure to a trace amount of TNT vapor due to the high surface area and highly ordered structure of silica.