Effect of Fluorination on the Polymorphism and Photomechanical Properties of Cinnamalmalononitrile Crystals
Effect of Fluorination on the Polymorphism and Photomechanical Properties of Cinnamalmalononitrile Crystals
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DOI：
10.1021/acs.cgd.2c00930
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发表时间：
2022-11
期刊：
影响因子：
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通讯作者：
T. J. Gately;C. Cook;Raghad Almuzarie;I. Islam;Zachary S. Gardner;R. Iuliucci;R. Al‐Kaysi;G. Beran;C. Bardeen
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文献类型：
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作者：
T. J. Gately;C. Cook;Raghad Almuzarie;I. Islam;Zachary S. Gardner;R. Iuliucci;R. Al‐Kaysi;G. Beran;C. Bardeen
肉桂丙二腈 (CM) 衍生物已被证明在晶体形式下表现出强烈的光机械响应。在本文中，探讨了氟取代对该类光致变色材料的分子性质、晶体堆积和固态光化学反应性的影响。氟的添加将分子 S0-S1 间隙转移到高达 0.4 eV 的更高能量。氟化还使得一些衍生物能够产生多态性，从而有效地控制它们是否可以进行[2 + 2]光二聚化。根据取代模式，可以获得头对尾（HT，非反应性）或头对头（HH，反应性）晶型。对于某些衍生物，两种多晶型物都可以根据溶剂生长。对这些分子子集的理论计算阐明了 CM 框架的氟化如何改变多晶型景观并改变不同堆积基序的能量。这些CM似乎支持丰富的多晶型景观，其中HH和HT结构在彼此相差几kJ/mol的范围内共存，允许芳香族H原子与F原子的简单交换，从而由于晶体堆积的变化而导致光机械活性完全丧失。实验和计算结果强调了即使对分子结构进行微小的修改也可以改变所得的晶体结构和光机械行为。
Cinnamalmalononitrile (CM) derivatives have been shown to exhibit a strong photomechanical response in the crystal form. In this paper, the effects of fluorine substitution on the molecular properties, crystal packing, and solid-state photochemical reactivity on this family of photochromes are explored. The addition of fluorines shifts the molecular S0– S1gap to a higher energy up to 0.4 eV. Fluorination also enables polymorphism in some of the derivatives that effectively controls whether or not they can undergo the [2 + 2] photodimerization. Depending on the substitution pattern, either the head-to-tail (HT, unreactive) or head-to-head (HH, reactive) crystal forms could be obtained. For some derivatives, both polymorphs could be grown depending on the solvent. Theoretical calculations on a subset of these molecules clarify how the fluorination of theCMframework modifies the polymorph landscape and shifts the energetics of the different packing motifs. TheCMs appear to support a rich polymorph landscape where HH and HT structures coexist within a few kJ/mol of each other, allowing the simple exchange of an aromatic H atom for an F atom to cause a complete loss of photomechanical activity due to changes in crystal packing. The experimental and computational results highlight how even minor modifications to the molecular structure can alter the resulting crystal structures and photomechanical behavior.