The stilbazolium-based organic salt, DAST, is probably the most well-known commercial organic non-linear optical (NLO) material. Chemical derivatives of DAST have therefore been designed to engender even better performing NLO materials; the DAST-derivative, BP3, is one success in this regard. This paper provides a proof-of-principle in the use of structure factors, $F$, to determine the effects of the crystalline environment on intramolecular charge transfer (ICT), and thus the second-order NLO response of such molecules. A concerted experimental and computational approach is adopted. In particular, the application of the relatively new x-ray wave function refinement method, which tempers theoretical calculations with experimentally derived structure factors to yield an isolated molecule influenced by crystal-field forces, enables the impact of those crystal-field forces on ICT to be established. This study employs high-resolution x-ray diffraction data for its experimental component, this resolution being necessary given the marked challenges that are associated with the complicated interionic interactions within an organic salt. The results presented pinpoint the molecular-scale features that afford BP3 better second-order NLO prospects than DAST, laying the foundations for the molecular engineering of DAST derivatives that are better tailored to optimize NLO function.

中文翻译：

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多相结构模型和超极化性计算解释了噻唑鎓离子的二阶非线性光学性质

基于噻唑鎓的有机盐DAST可能是最著名的商业有机非线性光学（NLO）材料。因此，DAST的化学衍生物被设计成可产生性能更好的NLO材料。DAST衍生物BP3在这方面是成功的。本文提供了使用结构因子的原理证明，$F$，以确定晶体环境对分子内电荷转移（ICT）的影响，从而确定此类分子的二阶NLO响应。采用了协调一致的实验和计算方法。尤其是，使用相对较新的X射线波函数细化方法的应用，该方法利用实验得出的结构因子调整理论计算以产生受晶场力影响的孤立分子，从而使这些晶场力对ICT产生了影响。被建立。这项研究使用高分辨率的X射线衍射数据作为其实验组分，鉴于与有机盐内复杂的离子间相互作用相关的显着挑战，该分辨率是必需的。