We report the synthesis of a luminescent N-salicylidene aniline derivative, N-salicylidene-4-amino-2-methylbenzotriazole (1), and the study of its polymorphism and photophysical properties. Three phases showing yellow (1-Y), orange (1-O), and red (1-R) fluorescence have been isolated and characterized by thermal and single crystal X-ray analysis. The photoluminescence results from excited-state intramolecular proton transfer process and the quantum yield is strongly dependent on polymorphism (Φ_1-Y = 0.87, Φ_1-O = 0.11, Φ_1-R = 0.028). The poorly emitting 1-R can be easily prepared, converted to the bright 1-Y by grinding, and reverted to 1-R through melting and annealing, giving rise to a luminescence on–off mechano-responsive cycle. The different photophysical properties are explained with the variable π-overlap and molecular conformation changes in the three polymorphs, characterized by a very similar crystal packing. By DFT calculations, the absorption properties were explained as dependent on the torsion angle between the two planar portions of the molecule, which affects the equilibrium between enol and keto forms in the ground state.

中文翻译：

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N-水杨基亚烷基-4-氨基-2-甲基苯并三唑在ESIPT发光的开-关机械响应切换

我们报告了一种发光的N-水杨基苯胺衍生物，N-水杨基-4-氨基-2-甲基苯并三唑（1）的合成，及其多态性和光物理性质的研究。已分离出显示黄色（1-Y），橙色（1-O）和红色（1-R）荧光的三个相，并通过热和单晶X射线分析对其进行了表征。光致发光是由激发态分子内质子转移过程引起的，并且量子产率强烈依赖于多态性（Φ1 _-Y = 0.87，Φ1 _-O = 0.11，Φ1 _-R = 0.028）。发射不良的1-R可以容易地制备，通过研磨将其转换为明亮的1-Y，并通过熔化和退火将其还原为1-R，从而产生发光的开-关机械响应循环。解释了不同的光物理性质，其中三个多晶型物的π重叠可变和分子构象变化，以非常相似的晶体堆积为特征。通过DFT计算，吸收特性被解释为取决于分子两个平面部分之间的扭转角，这会影响基态下烯醇和酮形式之间的平衡。