RT-variation of the photochromic properties of spirooxazine trapped in organic-inorganic hybrid matrices in the course of the sol-wetgel-xerogel transformation

Abstract

In a photochromic system host matrices significantly affect the photochromic properties of the encapsulated organic dye. They must be prepared at temperatures considerably below the decomposition point of the dye, and they should have sufficient free volume for the structural rearangement to take place. The low-temperature, wet-chemical characteristics of sol-gel process and the pore structure of the gels make these requirements excellently satisfied. In this work, organically modified silanes, ethyltrimethoxysilane (ETMS) and 3-glycidyloxypropyltrimehtosysilane (GPTMS) are used as starting materials to prepare gels doped with spirooxazine. Room temperature (RT)-variation of the photochromic properties in the organic-inorganic hybrid matrices (OIHM) containing NaF or bisphenol-A (BPA) is monitored during the sol-wet gel-xerogel transfromation process. Without the addition of BPA, both the photochromic intensity (DeltaAo) and the half-life time(t 0.5) decrease and level off in the wetgel-xerogel stage, while with the addition of BPA they increase and level off in the wetgel-xerogel stage. These results are discussed in terms of viscosity growth, pore structure formation, increase of polarity and steric hindrance.