Topochemistry. Part XXVI. The absorption spectra of some thermochromic N-salicylideneanilines and hydroxynaphthylideneanilines in the crystal

Abstract

Methods have been developed for growing thin polycrystalline films, and oriented polycrystalline films. Experiments with the thin films allow measurement of the absorption spectra of the N-salicylideneanilines well into the ultraviolet, and thus permit comparison of the effects of temperature change on the “thermochromic” band and on the ultraviolet bands. In two anils studied the ultraviolet absorption is practically independent of temperature; the intensity of the thermochromic band is much lower than those of the ultraviolet bands. In N-(5-methoxy-3-nitrosalicylidene)aniline the results suggest a temperature-dependent equilibrium between two absorbing species in the crystal. The experiments with oriented films and polarised light indicate that the thermochromic transition is near in-plane long-axis polarised in the isolated molecule.