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首页> 外文期刊>Chemistry: A European journal >Polymorphism Versus Thermochromism:Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes
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Polymorphism Versus Thermochromism:Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

机译：多态性与热致变色：双拥挤的双环芳香烯中颜色和构象的相互关系

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摘要

The nature of the thermo-chromic form of overcrowded bistricy-clic aromatic enes (BAEs) has been controversial for a century.We report the single-crystal X-ray structure analysis of the deep-purple and yellow poly-morphs of 9-(2,7-dimethyl-9H-fluoren-9-ylidene)-9H-xanthene (11),which revealed the molecules in a twisted and a folded conformation,respectively.Therefore,the deeply colored thermo-chromic form B of BAEs is identified as having a twisted conformation and the ambient-temperature form A as having a folded conformation.This relationship between the color and the conformation is further supported by the X-ray structures of the deep-purple crystals of the twisted 9-(9H-fluoren-9-ylidene)-9H-xanthene (10),and of the yellow crystals of the folded 9-(11H-benzo[b]fluoren-11-ylidene)-9H-xan-thene (12).Based on this conclusive crystallographic evidence,eleven previously proposed rationales of thermo-chromism in BAEs are refuted.In the twisted structures,the tricyclic moieties are nearly planar and the central double bond is elongated to 1.40 A and twisted by 42 deg.In the folded structures,the xanthylidene moieties are folded by 45 deg and the fluorenylidene moieties by 18-20 deg.Factors stabilizing the twisted and folded conformations are discussed,including twisting of formal single or double bonds,intramolecular overcrowding,and the significance of a dipolar aromatic "xanthenylium-fluore-nide" push-pull structure.
机译：过度拥挤的双晶-环状芳香烯（BAE）的热致变色形式的性质一直存在一个世纪的争议。我们报道了9-（-）的深紫色和黄色多晶型物的单晶X射线结构分析2,7-二甲基-9H-芴-9-亚甲基）-9H-x吨（11）分别揭示了分子呈扭曲和折叠构象的分子。因此，鉴定出BAE的深色热致变色形式B 9-（9H-荧光）的深紫色晶体的X射线结构进一步支持了颜色和构象之间的这种关系，这是因为它具有扭曲的构象，而环境温度形式A具有折叠的构象。 -9-亚烷基）-9H-an吨（10）和折叠的9-（11H-苯并[b]芴-11-亚基）-9H--吨（12）的黄色晶体。晶体学证据，驳斥了先前提出的BAE中热变色的11个基本原理。在扭曲的结构中，三环部分接近y平面且中心双键延长至1.40 A并扭曲42度。在折叠结构中，亚蒽叉基部分折叠45度，芴二烯部分折叠18-20度。讨论了稳定扭曲和折叠构象的因子包括形式单键或双键的扭曲，分子内的过度拥挤，以及偶极芳族“氧杂蒽酮-氟-氮”推挽结构的意义。

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