F Dos Santos Luan G, Chagas Julio C V, Nieman Reed, Aquino Adelia J A, Machado Francisco B C, Lischka Hans
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, USA.
Departamento de Química, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
Phys Chem Chem Phys. 2025 Jun 5;27(22):11558-11569. doi: 10.1039/d5cp00618j.
Polycyclic aromatic hydrocarbons (PAHs) have attracted significant attention in scientific research due to their unique electronic properties and potential applications in various fields such as photovoltaics and photocatalysis. In this study, the excited states and intramolecular charge transfer mechanisms within boron/nitrogen (B/N) doped PAHs using a 5-armchair,5-zig-zag periacene as model were investigated. Starting with a pristine periacene sheet, twelve chemically modified structures were explored, with different topologies of boron and nitrogen doping. Geometry optimization calculations in the ground state were performed at the ωB97XD/def2-SV(P) level, followed by single-point calculations of the low-lying singlet excited states using multireference MR-CISD and SC-NEVPT2 methods and single reference (SR) ADC(2) and TD-DFT theories for comparison. The analysis of energy spectra and charge transfer (CT) character were conducted using the one particle density matrices, analyzing the involved natural transition orbitals (NTOs) and through the decomposition of the states into contributions of local excitations (LE), charge transfer (CT) or double excitations (2-el.) A S CT state was characterized for three of the suggested doped PAHs. Interestingly, in one of these cases, the CT state was dominated by a double excitation character. Beyond this case, it turned out that most of the other excitations also have a strong double excitation component. This fact makes MR calculations highly desirable for accurate investigations, as SR methods such as ADC(2) and TD-DFT become questionable in many cases.
多环芳烃（PAHs）因其独特的电子性质以及在光伏和光催化等各个领域的潜在应用，在科学研究中备受关注。在本研究中，以一个5扶手椅型、5锯齿型并四苯为模型，研究了硼/氮（B/N）掺杂多环芳烃的激发态和分子内电荷转移机制。从原始的并四苯薄片开始，探索了十二种化学修饰结构，具有不同的硼和氮掺杂拓扑结构。在ωB97XD/def2-SV(P)水平上进行基态的几何优化计算，随后使用多参考MR-CISD和SC-NEVPT2方法以及单参考（SR）ADC(2)和TD-DFT理论对低激发单重态进行单点计算以作比较。使用单粒子密度矩阵分析能谱和电荷转移（CT）特征，分析涉及的自然跃迁轨道（NTOs），并通过将态分解为局域激发（LE）、电荷转移（CT）或双激发（2-el.）的贡献。对三种建议的掺杂多环芳烃表征出了一种S CT态。有趣的是，在其中一种情况下，CT态以双激发特征为主。除此之外，结果表明大多数其他激发也具有很强的双激发成分。这一事实使得对于精确研究而言，多参考计算非常必要，因为在许多情况下，诸如ADC(2)和TD-DFT等单参考方法变得不可靠。
