In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density functional theory (DFT), a spin-flip time-dependent DFT approach, and the multireference CASSCF/NEVPT2 method have been applied to correlate the diradical character with the energetic trends (i.e., singlet–triplet energy gaps). In addition, the nucleus-independent chemical shift together with ACID plots and Raman intensity calculations were used to strengthen the relationship between the diradical character and (anti)aromaticity. Our study reveals that the substitution pattern and structural isomerism represent a very effective way to tune the diradical properties in ICz-based systems with meta-substituted systems with a V-shaped structure displaying the largest diradical character. Thus, this work contributes to the elucidation of the challenging chemical reactivity and physical properties of diradicaloid systems, guiding experimental chemists to produce new molecules with desirable properties.

中文翻译：

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调整吲哚并咔唑的双自由基特征：结构异构和取代位置的影响


在这项研究中，通过计算研究了一组 10 个位置的吲哚并咔唑 (ICz) 异构体，这些异构体被通过对位或间位连接的二氰亚甲基取代，目的是探索结构异构和取代位置在控制其光学和电子性质方面的效率。无限制密度泛函理论 (DFT)、自旋翻转时间相关 DFT 方法和多参考 CASSCF/NEVPT2 方法已被应用于将双自由基特征与能量趋势（即单重态-三重态能隙）关联起来。此外，与核无关的化学位移与酸图和拉曼强度计算一起用于加强双自由基特征和（反）芳香性之间的关系。我们的研究表明，取代模式和结构异构现象代表了一种非常有效的方法来调整基于 ICz 的系统的双自由基性质，其中间位取代系统的 V 形结构显示出最大的双自由基特征。因此，这项工作有助于阐明双自由基系统具有挑战性的化学反应性和物理性质，指导实验化学家生产具有所需性质的新分子。