Synthesis and Photochromic Properties of Poly(4-vinylpyridine-co-styrene) with Pendant Spiroxazine Moieties

An ionic polymer with pendant photochromic moieties was prepared by the reaction of poly(4-vinylpyridine-co-styrene) and 1,3,3-trimethyl-6′-bromohexyloxyspiro[2H]-indol-2,3′-[3H]-naphth[2,1-b][1,4]oxazine. The photochromic reaction in question is caused by the reversible heterolytic cleavage of the C(spiro)—O bond under UV irradiation, yielding the colored form that can return to the colorless form by ring closure under visible light irradiation or in dark. The visible range absorption of the corresponding polymer increased gradually by UV irradiation which is ascribed to the generation of the open merocyanine form from the closed spiro form. The ionic conductivity of polymer increased upon UV irradiation, which brought about the generation of zwitterions form, and subsequently decreased in dark, which brought about the generation of closed spiro form. Sufficient reversibility was found in this polymer and this response was completely synchronized with that in the absorbance changes.