PHOTOCHROMISM OF SPIROPYRAN AND DIARYLETHENE-DOPED SILICA-GELS PREPARED BY THE SOL-GEL PROCESS

Spiropyran and diarylethene were doped in silica gels which were prepared from Si(OCH3)(4) and Si(OC2H5)(4), respectively, and their photochromic properties were compared. In the gels, both organics are incorporated with open modifications and show the photochromism between red and colourless modifications. The closed form of spiropyran, which is converted from the open one by irradiation with light, is thermally backed into the open form after the light is blocked. The activation energy of thermochemical reaction is 0.86 eV. Diarylethene shows no thermochemical reaction below 140 degrees C, but shows a photochemically reversible change on alternate irradiation by light of 436.5 and 578 nm.