Photochromic Behavior of Spiropyrans: The Effect of Substituent

Abstract

Spiropyrans are among the most promising organic photochromic dyes. However, spiropyrans are very sensitive dyes and there are many independent factors that can affect the performance of these dyes. The effect of substituent on the optical absorption spectra, fading kinetic, and also the dye stability of spiropyrans in diphenyl ether by UV irradiation has been investigated. The 6-nitro BIPS displayed greater absorbance intensity of 0.740% at 600nm compared to 8-ethoxy-6-nitro BIPS of 0.651% at 620nm. Furthermore, 6-nitro BIPS is less stable as it has higher rate constant of 0.1003s-1and thus lower half-life time (50% decay of the photochromic effect) of 6.9s, in contrast to 8-ethoxy-6-nitro BIPS of 0.0594s-1and 11.7s respectively.