Preparation and optical properties of amorphous silica doped with porphins of free-base by the two-step sol-gel process

Abstract

Tetraphenylporphinetetrasulfonic acid (TPPS), which is known as a photo-chemical holeburning (PHB) dye, was incorporated in silica gels obtained by the sol-gel process from tetraethoxysilane (TEOS). The form of TPPS must be free-base (H 2 P), which exists in basic condition, to be active in PHB. In this study to obtain transparent and dense silica gels doped with free-base TPPS, a two-step hydrolysis process using solutions containing NaOH or using ammonia were developed. In the first step we used acidic catalyst to get denser and transparent gels and in the second step basic catalyst was adopted to obtain free-base TPPS. Monolithic silica gels can be obtained by this two-step process from the hydrolysis of TEOS. By the spectroscopic analysis of TPPS incorporated in the gels, it is found that the free base form of TPPS is retained at the molar ratio of NaOH/TEOS above 10 -3 . The spectra of monocation are observed at the molar ratio of NaOH/TEOS below 10 -3 . And the dimerization of TPPS incorporated in the TEOS gels does not occur at higher NaOH concentration than that in the TMOS gels.