Raman spectroscopic study of photochromicN-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]chloroanilines

Abstract

N -[4-(4-n-Alkoxybenzoyloxy)-2-hydroxybenzylidene]chloroanilines [nAHmCl (n = 1-8; m = 2, -ortho; m = 3, -meta; m = 4, -para)] were newly synthesized. Some of them exhibited a photochromic color state on ultraviolet irradiation. In 1AH2Cl, the fresh solid species as prepared by crystallization from ethanol solution was highly photochromic, more so than any of the other compounds studied. The solid species derived from the melt was hardly photochromic but was thermochromic. The species became photochromic on annealing at about 100 • C. The annealed species exhibited both photochromism and thermochromism. Through the measurement of Raman spectra, the behavior was explained by the change in the twist angle of the aniline ring to the salicylaldimino part of the molecule. It was found that the band at 999 cm −1 ascribed to the CH out-of-plane vibration of the aniline ring is a reliable indication of the photochromic form's identity.

Liquid Crystalline Properties and Photochromism of 4-Cyano- and 4-Nitro-N-(4-Alkoxysalicylidene) Anilines

“…Potashnik and Ottolenghi have suggested that the molecular rearrangement is the cis-trans isomerization due to rotation about the bond including the benzene ring [4]. It has also been suggested by means of Raman spectra that the photochromic behavior can be explained by a change in the twist angle of the aniline ring to the salicylidene part of the molecule [16]. Recently, it has been shown by use of X-ray diffraction analysis that an interconversion between the enol and trans-keto form is responsible for the color change [17].…”