N-取代苯并菲烯基中关联驱动的单重态-三重态反转与光学光谱：来自PPP-FCI和TDDFT的见解

中文摘要 AI 辅助

多位研究者已报道在氮取代的平面碳氢化合物中，最低单重态（$S_{1}$）和三重态（$T_{1}$）激发态存在非典型的反转。与洪德最大多重度规则相反，苯并菲烯基的多氮杂衍生物（如环嗪和庚嗪）长期以来被认为具有负的单重态-三重态能隙，$\Delta E_{ST}=E(S_{1})-E(T_{1})$。利用著名的Pariser-Parr-Pople（PPP）模型（一种用于关联$\pi$电子的半经验、基于波函数的哈密顿量），我们研究了十种N-取代苯并菲烯基 motifs 中的单重态-三重态能隙。考虑了两种长程库仑相互作用方案，并系统调谐了关键参数，包括格点轨道能、Hubbard U和跳跃积分，以基准化该模型，从而可靠地估计负的单重态-三重态能隙。采用全组态相互作用（FCI）方法来纳入电子关联效应。随后，使用最能再现现有实验数据的优化PPP参数计算了基态和$T_{1}$吸收光谱。为验证起见，还使用各种交换-关联泛函进行了第一性原理TDDFT计算。传统的绝热TDDFT无法再现反转的（$S_{1}-T_{1}$）排序，表明纳入关联驱动的多组态效应对于描述该现象至关重要。我们发现，单重态TDDFT基态吸收光谱再现了PPP-FCI光谱的几个定性特征，尽管TDDFT激发能量系统性偏高。对基态和$T_{1}$吸收光谱的详细分析揭示了显著的组态混合，为所研究的N-取代苯并菲烯基衍生物的光学响应提供了全面的表征。

英文摘要

Several researchers have reported an atypical inversion of the lowest singlet ($S_{1}$) and triplet ($T_{1}$) excited states in nitrogen-substituted planar hydrocarbons. Contrary to Hund's rule of maximum multiplicity, poly-aza derivatives of phenalenyl, such as cyclazine and heptazine, have long been known to possess a negative singlet-triplet gap, $ΔE_{ST}=E(S_{1})-E(T_{1})$. Using the well-known Pariser-Parr-Pople (PPP) model, a semi-empirical, wave-function-based Hamiltonian for correlated $π$-electrons, we investigate the singlet-triplet gap in ten N-substituted phenalenyl motifs. Two schemes of long-range Coulomb interactions are considered, and key parameters, including the on-site orbital energy, Hubbard U, and hopping integrals, are systematically tuned to benchmark the model for reliably estimating negative singlet-triplet gaps. Full configuration-interaction (FCI) method is employed to incorporate electron-correlation effects. Ground-state and $T_{1}$ absorption spectra are subsequently calculated using the optimized PPP parameters that best reproduce the available experimental data. For validation, first-principles TDDFT calculations using various exchange--correlation functionals are also performed. Conventional adiabatic TDDFT fails to reproduce the inverted ($S_{1}-T_{1}$) ordering, indicating that the inclusion of the correlation driven multiconfigurational effects are essential for describing it. We find that the singlet TDDFT ground-state absorption spectra reproduce several qualitative features of the PPP-FCI spectra, although the TDDFT excitation energies are systematically higher. Detailed analysis of the ground-state and $T_{1}$ absorption spectra reveals significant configuration mixing, providing a comprehensive characterization of the optical response of the N-substituted phenalenyl derivatives studied.

发表机构

• Indian Institute of Technology Bombay（印度理工学院孟买分校）

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