Functionalization of Silica Surface by Tetrahydroxyporphyrin via Si–O Linkages

Abstract

Abstract To construct an interface between a π-conjugated organic molecule and an inorganic/metal surface, 5,10,15,20-tetrakis[4-(5-hydroxypentyloxy)phenyl]porphyrin was chemisorbed on silica gel by refluxing in pyridine. Thermogravimetric analysis confirmed that 1.5–6.3 mg tetrahydroxyporphyrin was adsorbed on 50 mg of silica gel. To functionalize the surface of a silicate glass plate with the porphyrin, a spin-coated film of the porphyrin on the glass plate was heated at 80–296 °C, followed by sonication in pyridine to remove the unreacted porphyrin. Heating above 130 °C gave a monolayer film. The reaction proceeds between two solid phases since the melting point of the porphyrin was 293 °C. The threshold temperature for the reaction to proceed was 90, 160, and 250 °C for 5,10,15,20-tetrakis[4-(5-hydroxypentyloxy)phenyl]porphyrin, 5,10,15,20-tetrakis[4-(5-acetoxypentyloxy)phenyl]porphyrin, and 5,10,15,20-tetrakis(4-hexyloxyphenyl)porphyrin, respectively. The different reactivities of the alcohol, ester, and ether functional groups could be used to construct highly sophisticated organic–inorganic surfaces.