Aromaticity of Kekulene and Physical Mechanism of Photoinduced Charge Transfer

doi:10.12422/j.issn.1006-396X.2024.02.004

Abstract

Abstract:

Aromaticity is one of the important chemical properties of aromatic compounds. Clarifying the aromaticity of a clearly ring?conjugated system is crucial for understanding the chemical reactivity and stability of the system. A detailed study of the aromaticity, one?photon absorption (OPA), two?photon absorption (TPA) spectra, and electron transfer properties of Kekulene was carried out through quantum chemical calculations and wave function analysis. The aromaticity of different benzene rings in the molecule was quantitatively analyzed through multicenter bond indices and AV1245 indices. The aromaticity of Kekulene was studied through various methods such as electron localization function (ELF), localized orbital locator (LOL), magnetic susceptibility current, and isotropic chemical shielding surface (ICSS). The electron transfer processes of OPA and TPA transitions were visualized through charge difference density (CDD) analysis. The results showed that the aromaticity of rings 1 and 2 was significantly stronger than that of rings 3 and 4. The π electrons of ELF and LOL can be highly delocalized on both sides of the first ring and form a loop. The OPA spectrum has excited states with higher transition dipole moments, which are more likely to become intermediate states in the TPA process. The research results can provide effective theoretical methods and application approaches for the aromaticity of different systems.

Key words: Aromatic, Electron delocalization, Magnetically induced current, ICSS, Electronic transition

摘要：

芳香性是芳香族化合物的重要化学性质之一，明确环状共轭体系的芳香性对了解体系的化学反应性能和稳定性至关重要。通过量子化学计算和波函数分析对凯库勒烯（Kekulene）的芳香性、单光子吸收（OPA）和双光子吸收（TPA）光谱及电子转移特性进行了详细的研究；通过多中心键级和AV1245指数对分子中不同苯环的芳香性进行了定量分析；通过电子定域化函数（ELF）、定域化轨道定位函数（LOL）、磁感生电流和等化学屏蔽表面（ICSS）等多种方法，对Kekulene的芳香性进行了研究；通过电荷差分密度（CDD）对OPA和TPA跃迁过程的电子转移进行了可视化分析。结果表明，1、2环的芳香性明显强于3、4环；ELF和LOL的 $π$ 电子可以在1环两侧高度离域并形成回路；OPA光谱具有较高跃迁偶极矩的激发态，更易成为TPA过程中的中间态。研究结果可为不同体系的芳香性提供有效的理论方法和应用途径。

关键词: 芳香性, 电子离域, 磁感应电流, ICSS, 电子跃迁

CLC Number:

TQ012

Weijian FENG, Yi ZOU, Jingang WANG. Aromaticity of Kekulene and Physical Mechanism of Photoinduced Charge Transfer[J]. Journal of Petrochemical Universities, 2024, 37(2): 24-30.

冯伟键, 邹怡, 王金刚. 凯库勒烯芳香性及光诱导电荷转移物理机制研究[J]. 石油化工高等学校学报, 2024, 37(2): 24-30.

Figures/Tables 11

Fig.1 Schematic diagram of the structure of Kekulene

Table 1 The multicenter bond orders and AV1245 indices of the four rings

碳环	多中心键级	AV1245指数
1	0.045 833 311 4	8.649 406 94
2	0.020 306 220 8	3.699 878 60
3	0.000 000 048 2	1.989 401 34
4	0.000 017 223 3	0.912 238 78

Fig.2 Kekulene′s π, σ orbitals and total density of states

Fig.3 STM image of scanning tunnelswith a bias of —2.2 eV

Fig.4 Isosurface and floor plan of ELFπ and ELFσ

Fig.5 Isosurface and floor plan of LOLπ and LOLσ

Fig.6 Magnetic induction current density of Kekulene

Fig.7 Isosurface and floor plan of the isochemical shielding surface of Kekulene

Fig.8 The single?photon absorption spectra and two?photon absorption spectra of Kekulene

Fig.9 The CDD graph of S9/10，S12/13 and the degenerate density states

Fig.10 CDD diagram of two-photon absorption two-step transition

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