Spectral Properties and Photochromic Characteristics of Spiropyran Dyes

A bis-benzospiropyran(BBSP) and nitro-substituted indoline spirobenzopyrans(SBP) were prepared by following a simple procedure. The reaction mechanism of synthesizing bis-benzospiropyran is discussed. A comparative analysis of the spectral and photochromic properties between SBP and BBSP was carried out with the aid of a PMMA film. The results indicate that chemical structures and UV irradiation played an important role in the spectral and photochromic properties of SBP and BBSP, which would readily affect λ_ max of the colored forms and the reversibility. The IR spectra and ~1H NMR spectra of these compounds are used to interpret the photochromic phenomena under different UV irradiation and determine the configurations of SBP and BBSP.