The molecular design, synthesis and photochromic properties of spirooxazines containing a permanent azo (hydrazone) chromophore

•Photochromic spirooxazines containing a permanent chromophore.•Prediction of photochromic properties by molecular modelling approaches.•Spectral investigation of unique photochromic behaviour.•Isolation and characterisation of a decomposition product.

A range of molecular modelling techniques has been applied to predict optimized geometrical conformations and energies of the ring-closed oxazine form and ring-opened merocyanine forms of three azospirooxazines. A comparison of the relative stabilities of the possible isomers of the merocyanines was carried out by applying molecular mechanics (augmented MM2), while the prediction of the potential for photochromic behaviour was made by comparison of the heats of formation calculated by AM1. Synthetic routes were explored and as a result two azospirooxazines were isolated, one of which showed interesting and unusual photochromic behaviour. The instability of this compound towards purification by chromatography was investigated. The decomposition product was isolated and characterized with the aid of single crystal x-ray crystallography. The correlation between predicted and observed photochromic behaviour is discussed.

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