Photochemical Synthesis of Water-Soluble Gold Nanorods: the Role of Silver in Assisting Anisotropic Growth

The optical gas recognition capability of a covalently self-assembled monolayer of 5,10,15-tri-{p- dodecanoxyphenyl}-20-(p-hydroxyphenyl) porphyrin molecules on silica substrates was studied. The following analytes have been investigated: NO2, CO, CH4,H2,NH3, HCl, CHCl3,C2H5OH, CH3OH, pyridine, tetrahydrofurane, triethylamine, and dimethylformamide. The self-assembled porphyrin monolayer appears highly sensitive to 1 ppm of NO2 in both anhydrous and humid conditions. The selectivity of the self-assembled porphyrin monolayer with respect to other analytes was also examined and present data show that the presence of CO, CH4,H2, and NH3 does not influence its UV vis spectrum. Many common solvents slowly affect the position of the Soret band. The presence of HCl vapors results in a broad band extending over the entire 440 500 nm range while the starting Soret disappears. UV vis measurements on a n-hexane 1.0 10 5 solution of the 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine, that does not contain phenyl substituents in the meso positions, show no changes in the optical spectrum upon NO2 interaction. It emerges that aromatic substituents in the meso positions play a crucial role in determining the optical sensing properties.