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首页> 外文期刊>Crystal growth & design >Unexpected molecular flip in solid-state photodimerization
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Unexpected molecular flip in solid-state photodimerization

机译：固态光二聚化中的意外分子翻转

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摘要

Three cocrystals of the light-stable compound 1,1,6,6-tetraphenyl-2,4- hexadiyne-1,6-diol (I) with light-sensitive molecules 1,2-dimethyl-2(1H)- pyridinone (a), 6-methyl-2(1H)-pyridinone (b) and 2-methyl-2(1H)-pyridinone (c) were exposed to UV light. It was found that the molecules undergo molecular flip perpendicular to the molecular plane (rotation of ～180). In the first two cocrystals, the light-sensitive molecules are disordered, which means that the space provided for them is larger than needed for ordered molecules. Therefore, rotation can take place. Moreover, in I-b, the flip is temperature dependent and takes place without exposure to UV light. Crystal structures at four different temperatures enable one to estimate the activation energy of the flip to be 9.72 kJ/mol. The kinetics of the reaction of I-c was studied at room temperature and revealed a sigmoidal behavior with Avrami exponent of n = 0.95(6) that could be explained by the JMAK model for crystal growth. It means that the nucleation rate is constant over time and that the reaction is homogeneous with equal probability to occur in any region of the sample. This could be explained by the fact that the voids where the reaction and the flip take place are isolated from each other.
机译：光稳定化合物1,1,6,6-四苯基-2,4-己二炔-1,6-二醇（I）与光敏分子1,2-二甲基-2（1H）-吡啶酮（ a），将6-甲基-2（1H）-吡啶酮（b）和2-甲基-2（1H）-吡啶酮（c）暴露于紫外光。发现分子经历垂直于分子平面的分子翻转（〜180度旋转）。在前两个共晶体中，光敏分子是无序的，这意味着为它们提供的空间大于有序分子所需的空间。因此，可以发生旋转。此外，在I-b中，翻转取决于温度并且在不暴露于UV光的情况下发生。在四个不同温度下的晶体结构使人们能够估计翻转的活化能为9.72 kJ / mol。在室温下研究了I-c反应的动力学，揭示了S型曲线，Avrami指数为n = 0.95（6），可以用JMAK模型进行晶体生长来解释。这意味着成核速率随时间变化是恒定的，并且反应是均匀的，并且在样品的任何区域发生的可能性均等。这可以通过以下事实解释：发生反应和翻转的空隙彼此隔离。

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