Salicylideneaniline derivative

S. Takeda, H. Chihara, T. Inabe, T. Mitani, and Y. Mamyama, NMR study of proton dynamics in the hydrogen bonds in the thermochromic crystals of iV-salicylideneaniline derivatives, Mol. Cryst. liq. Cryst. Sci. Technol., Sect. A 216, 235-240 (1992). 

The first example is the structure of the metastable red species of a salicylideneaniline derivative, A-3,5-di-rert-butylsalicylidene-3-nitroaniline, which, when the pale yellow crystal is irradiated with a mercury lamp, shows photochromism with the largest lifetime among various salicylideneaniline derivatives [9]. Much research on this subject has been undertaken but the structure of the photo-coloured red species remains controversial [10]. 

A particular effect of an intramolecular hydrogen bond occurs in iV-salicylideneaniline derivatives 1 and anils of hydroxynaphthaldehydes, and their tautomerism (shown... 

Keywords Pyridine derivatives Salicylideneaniline derivatives Structure of excited molecule Structure of lophyl radical Unstable species of photochromism... 

This section describes the characteristics of the photo- and thermochromism derived from proton tautomerization in crystals, using the photo- and thermochromic behaviour of 2-alkylisophthalaldehydes, salicylideneanilines, and dinitrobenzylpyridines as typical examples. 

Salicylideneaniline [32] and its derivatives are known to exhibit photochromic behaviour. The colour of the crystal of salicylideneaniline changes from pale yellow to red, and the red colour changes back to the original one in a thermal process. On the other hand, other derivatives of salicylideneaniline show only thermochromic behaviour. It is usually the case that a photochromic crystal never exhibits thermochromism, and vice versa. 

R. S. Becker, C. Lenoble, and A. Zein, Photophysics and photochemistry ofthe nitro derivatives of salicylideneaniline and 2-(2 -hydroxyphenyl)benzothiazole and solvent effects, J. Phys. Chem. 91, 3517-3524(1987). 

A 13C-NMR spectroscopic study in solution of the tautomers of several anils derived from salicylaldehyde and from 2-hydroxynaphthalene-l-carbaldehyde having the same amino part (141-145, Scheme 17) has been reported.82 Variable-temperature NMR spectroscopy and comparison with appropriate models show that while salicylideneanilines exist as phenolic tautomers, naphthylidene-anilines exist as equilibrium mixtures containing appreciable amounts ofboth enol and keto tautomers, the latter being slightly predominant (Table 9). In fact, there is a negligible shift in the equilibrium on changing the electronic effect of the R substituent. 

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