Preparation and characterization of porphyrin chromophores immobilized on micro-silica gel beads

Micro-silica gel beads (1a–c) immobilizing dihydroxoantimony(V) tetraphenylporphyrin (SbTpp), free base tetraphenylporphyrin (H2Tpp), and zinc(II) tetraphenylporphyrin (ZnTpp) chromophores were prepared by the reactions of 3-aminopropyl silica gel (SiO2-NH2) with the dihydroxoantimony(V) complex (2a), the free base (2b), and the zinc complex (2c) of 5-[4-(succinimidyloxycarbonyl)phenyl]-10,15,20-triphenylporphyrin, respectively. Absorption spectrophotometry was performed on 1a–c using a confocal laser scanning microscope (CLSM) and determined that the yields for the immobilization of SbTpp, H2Tpp, and ZnTpp on SiO2-NH2 were 31.7, 95.9, and 45.1%, respectively. Moreover, 1a was converted into its acetyl analog (1a’) by the acetylation of the axial hydroxo ligands and aminopropyl of 1a with Ac2O, since the interactions of the SbTpp chromophore with the residual amino group on SiO2 was observed by spectroscopic analysis using CLSM. In micro-channel reactors (MCR), the photoreaction of 1a’ with Et2NH induced demetallation to produce 1b immobilizing H2Tpp chromophore. Moreover, the reaction of 1b with Zn(OAc)2 produced 1c immobilizing ZnTpp chromophore. Thus, micro-silica gel beads (1a) were transformed into 1c in a micro-region of a silica gel surface by way of photochemical reaction with Et2NH and subsequent metallation with Zn(OAc)2.