Direct evidence for distinct colour origins in ROY polymorphs,Chemical Science

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Direct evidence for distinct colour origins in ROY polymorphs
Chemical Science ( IF 7.6 ) Pub Date : 2021-09-01 , DOI: 10.1039/d1sc04051k
Lisette R Warren ₁ , Evana McGowan ₁ , Margaret Renton ₁ , Carole A Morrison ₁ , Nicholas P Funnell ₂

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ROY is one of the most well-studied families of crystal structures owing to it being the most polymorphic organic material on record. The various red, orange, and yellow colours of its crystal structures are widely-believed to originate from molecular conformation, though the orange needle (ON) polymorph is thought to be an exception. We report high-pressure, single-crystal X-ray measurements which provide direct experimental evidence that the colour origin in ON is intermolecular, revealing that the molecule undergoes minimal deformation but still exhibits a pronounced, reversible, pale orange → dark red colour change between ambient pressure and 4.18 GPa. Our experimental data are rationalised with band structures, calculated using an accurate hybrid DFT approach, where we are able to account for the variation in colour for five polymorphs of ROY. We highlight the outlier behaviour of ON which shows marked π⋯π stacking interactions that are directly modified through application of pressure. Band structure calculations confirm these intermolecular interactions as the origin of the colour change.

中文翻译：

ROY 多晶型物中不同颜色起源的直接证据

ROY 是研究最深入的晶体结构家族之一，因为它是有记录以来多晶型最多的有机材料。人们普遍认为其晶体结构的各种红色、橙色和黄色源于分子构象，但橙色针状 (ON) 多晶型物被认为是一个例外。我们报告了高压、单晶 X 射线测量，这些测量提供了直接的实验证据，证明 ON 的颜色起源是分子间的，揭示了分子经历了最小的变形，但仍然表现出明显的、可逆的、浅橙色→深红色之间的颜色变化。环境压力和 4.18 GPa。我们的实验数据通过能带结构合理化，使用精确的混合 DFT 方法计算，我们能够解释 ROY 的五种多晶型物的颜色变化。我们强调 ON 的异常行为，它显示了明显的 π⋯π 堆积相互作用，这些相互作用通过施加压力直接修改。能带结构计算证实这些分子间相互作用是颜色变化的根源。

更新日期：2021-09-02

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