The nanometer cavity structure of a photochromic naphthopyran

A novel photochromic compound, 3, 3-(2, 4-dimethoxy-phenyl)-3H-naphtho [2, 1-b] pyran (Compound I), was synthesized and the structure was determined by X-ray diffraction and TEM. Introduction of methoxy groups in the 2, 4-position of the phenyl moiety affects the whole arrangement of molecular self-assembly. The structure displays motifs formed by only weak C-H⋯π interactions. The motifs thus generated show cavities, which could serve as hosts for complexation. To our surprise, it was shown that the aperture of the cavity structure is up to nanometer level by TEM, which is rarely seen in organic compound. Moreover, the photochromic properties of the compound I in solid state and polyvinyl butyral film were studied. The results showed compound I exhibited good reversible photochromism.