N-Salicylideneaminopyridine (SAP) is a derivative of the common organic photochromic compound, N-salicylideneaniline (SA), whose crystal changes colors from orange to red upon UV irradiation. Interestingly, the photochromic property of the crystal depends on the crystal structure. In this study, SAP derivatives and their co-crystals were synthesized, and their crystal structures were analyzed to determine the relationship between their structures and photochromic properties. The photochromic property was found to be closely related to the molecular conformation and the packing efficiency in the crystal. In general, crystals with large dihedral angles were photochromic, while those with small dihedral angles were non-photochromic. However, even for crystals with large dihedral angles, small free available spaces in the crystal structure led to non-photochromic properties. This study demonstrates the importance of a combination of structural factors to elucidate the photochromic property of SAP derivatives.

中文翻译：

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N-水杨基亚氨基吡啶吡啶衍生物的 晶体结构与光致变色特性之间的关系†

N-水杨基亚氨基吡啶（SAP）是常见的有机光致变色化合物N的衍生物-水杨基苯胺（SA），其晶体在紫外线照射下从橙色变为红色。有趣的是，晶体的光致变色特性取决于晶体结构。在这项研究中，合成了SAP衍生物及其共晶体，并对其晶体结构进行了分析，以确定它们的结构与光致变色性质之间的关系。发现光致变色性质与分子构型和晶体中的堆积效率密切相关。通常，具有大二面角的晶体是光致变色的，而具有小二面角的晶体是非光致变色的。然而，即使对于具有大二面角的晶体，晶体结构中小的可用自由空间也会导致非光致变色特性。