Through-space charge transfer provides more flexibilities and possibilities to regulate the properties of organic optoelectronic materials, biotechnology, photochemistry, and so on, by changing spatially the aromatic packing configuration. In this study, a series of [2.2]pCp-based cis (pseudogeminal) and trans (pseudopara) molecules are designed to explore the effect of isomers on the activities quantified by the second-order nonlinear optical (NLO) properties from density functional theory calculations. The results show that the first hyperpolarizability (β_tot) of the trans isomer is larger than that corresponding to cis ones, especially for cis/trans-TPA-TRZ systems. Moreover, the designed molecule trans-TPA-TRZ shows remarkably large β_tot value up to 39.7 × 10^–30 esu, which demonstrates that the activity of a material depends not only on the intrinsic property of the acceptor or donor itself but also on their combination, intramolecular conformation, and conjugate packing mode. Interestingly, visualization of the full hyperpolarizability tensor, termed the unit sphere representation, has been used to provide insight and intuition into the relationship between the hyper-Rayleigh scattering response coefficient and molecular structure. Furthermore, the influence of the solid-state environment on the NLO coefficient is substantial, particularly for the trans-TPA-TRZ molecule, whch increases further to 84.2 × 10^–30 esu according to the polarizable continuum model and optimally tuned range-separated hybrid functional. Our work provides rich insight into designing and developing high-performance second-order NLO materials by tuning the relative configuration and polarizable environment of the [2.2]pCp-based through-space π-extended conjugated systems and might be of potential application in optoelectronics.

中文翻译：

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基于[2.2]环芳烃异构体的二阶非线性光学性质的调谐：相对构型和可极化环境

通过空间上的电荷转移，可以通过在空间上改变芳香族填充结构来提供更多的灵活性和可能性来调节有机光电材料，生物技术，光化学等的特性。在这项研究中，设计了一系列基于[2.2] pCp的顺式（伪神经元）和反式（伪对位）分子，以研究异构体对根据密度泛函理论通过二阶非线性光学（NLO）性质量化的活性的影响。计算。结果表明，反式异构体的第一超极化率（_βtot）大于顺式异构体，特别是对于顺式/反式-TPA-TRZ系统。此外，设计的分子反式-TPA-TRZ_βtot值高达39.7×10 ^–30 esu，显示出显着大的值，这表明材料的活性不仅取决于受体或供体本身的固有性质，还取决于它们的组合，分子内构象和结合​​物堆积模式。有趣的是，完整的超极化张量的可视化（称为单位球面表示）已用于提供对超瑞利散射响应系数与分子结构之间关系的洞察和直觉。此外，固态环境对NLO系数的影响很大，特别是对于反式-TPA-TRZ分子，其进一步增加至84.2×10 ^–30esu根据可极化连续体模型和优化调整的范围分隔的混合函数。我们的工作通过调整基于[2.2] pCp的通孔π扩展共轭系统的相对配置和可极化环境，为设计和开发高性能二阶NLO材料提供了丰富的见识，并且可能在光电子学中具有潜在的应用。