Synthesis and characterization of polymerizable photochromic liquid crystals containing a spiro-oxazine group

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Abstract
Novel polymerizable photochromic liquid crystal materials containing either the 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]naphth[2,1-b][1,4]oxazine] group or the 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]pyrido[3,2-f][1,4]benzoxazine] group as the photochromic moiety, and the biphenylene unit as the mesogenic moiety, were synthesized. Thermal and physical properties of the compounds were examined using differential scanning calorimetry, optical polarizing microscopy, wide-angle X-ray diffractometry and UV-visible spectrophotometry. The photochromic compounds containing both photochromic and mesogenic moieties showed metastable mesophases; These tended to crystallize with time and on heating. The crystallization behaviours were strongly dependent on the structure of the terminal group of alkylene spacer and the position of the spiro-oxazine bound to the mesogen.