The Coloring Efficiencies of a Benzospiran Compound in Polymer Matrix by UV Irradiation and Electron Bombardment

Abstract

The coloring efficiency of a photochromic benzospiran (1', 3'-dihydro-1', 3', 3'-trimethy1-6nitrospiro[2H-1-benzopyran-2, 2'-[2H]indole] species (A)) in polystyrene matrix was studied in terms of the initial rate of coloration by photoirradiation (365 nm: UV) and electron bombardment (7 kV) at a low temperature (-30°C) under the pressure of 10^-5 Torr.
On photoirradiation, [A] in polystyrene which was colorless turned to magenta (species [B])and it returned reversibly to [A] by a thermal reaction. On the other hand, by electron bombardment of [A], in addition to [B] another colored species which had a longer life time was formed by a reaction between [B] and component of matrix. Thus the measured absor bance of [B] was greatly influenced by side reactions. Therefore, the values obtained by the extrapolation of [B] divided by exposed time to zero time were considered to be the rate at the inital stage of reaction. The molecular extinction coefficient (ε_max) of [B] in the sample was estimated by that in a non-polar solvent. The influence of matrix was calibrated by the change of e of [A] at 350 nm as a function of [A] contents in the sample. The initial quantum yield (φ) was caluculated by applying the Lambert-Beer rule.
The ε_max. of [B] φ and were influennced by contents of [A] in the sample. The value of φ for photoreaction (φ_p) changed from 0.94 ([A]: 10 wt %) to 0.29 (80 wt %). The yield per a bombarded electron (φ_e) was over a hundred times that of photon. The electron shows different behavior to reactant from the case of photon. The reaction of electron takes place in all of the components of sample and involves various complicated processes. Thus φ_e is more affected by bombarding conditions than φ_p. On the contrary, G value (number of product per 100 eV) is of more practical importance. The measured G value of the formation of [B] changed from 1.44 for 10 wt % sample to 0.52 for 80 wt % one, as in the case of φ_p.