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

N-[4-(4-n-Alkoxybenzoyloxy)-2-hydroxybenzylidene]chloroanilines [n AHm Cl ( 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 irradiat ion. In 1AH2Cl, the fresh solid species as prepared by crystallization from ethanol solution was highly photochromic, more so than any of the other co mpounds studied. The solid species derived from the melt was hardly photoch romic but was thermochromic, The species became photochromic on annealing a t about 100 degrees C, The annealed species exhibited both photochromism an d thermochromism, Through the measurement of Raman spectra, the behavior wa s explained by the change in the twist angle of the aniline ring to the sal icylaldimino 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 reliabl e indication of the photochromic form's identity. Copyright (C) 1999 John W iley & Sons, Ltd.