Montserrat Ricardo, Torres Amanda D, Oliveira Ricardo R, Rocha Alexandre B
Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro 21941-909, Brazil.
Instituto Federal do Paraná, Umuarama, Paraná 87507-014, Brazil.
J Phys Chem A. 2025 Apr 17;129(15):3435-3444. doi: 10.1021/acs.jpca.4c08700. Epub 2025 Apr 9.
The photoabsorption and infrared spectra (IR) of molecular systems are heavily influenced by aggregation. In the electronic spectra, the vibronic coupling effect is of utmost importance. Although treating both effects simultaneously can be challenging, it is often the only way to explain the experimental spectrum of molecular clusters. In this work, we study IR spectra and the vibronic coupling effect in the electronic photoabsorption spectra in molecular systems composed of benzene (monomer, dimers, and crystal). Photoabsorption spectra were generated using the direct vibronic coupling method at the density functional theory (DFT) level. We also simulated the spectra with the Liouville-Lanczos approach by calculating the electronic transitions along the main inducing modes for two forbidden transitions (A → B and A → B). DFT was also applied to simulate IR spectra. For the monomer, vibronic coupling was crucial to induce the first and second forbidden transitions. On the other hand, molecular aggregation was sufficient to induce the first and second forbidden transitions in almost all dimers. However, when the vibronic coupling is evaluated for the clusters, the band in the energy range of the A → B transition is affected both by the aggregation itself and the inducing modes. Moreover, some inducing modes drastically change the allowed A → E transition, depending on the dimer under study due to symmetry breaking. In terms of IR spectra, clear signatures are present. For instance, the intensities of the C-H stretching modes decrease as aggregation increases. This work shows that aggregation impacts the band shapes differently in relation to the benzene aggregate structure and the excitation under analysis.
分子体系的光吸收和红外光谱（IR）会受到聚集的严重影响。在电子光谱中，振动 - 电子耦合效应至关重要。尽管同时处理这两种效应具有挑战性，但这往往是解释分子簇实验光谱的唯一方法。在这项工作中，我们研究了由苯（单体、二聚体和晶体）组成的分子体系中的红外光谱以及电子光吸收光谱中的振动 - 电子耦合效应。使用密度泛函理论（DFT）水平的直接振动 - 电子耦合方法生成光吸收光谱。我们还通过计算两个禁戒跃迁（A → B和A → B）沿主要诱导模式的电子跃迁，用刘维尔 - 兰佐斯方法模拟了光谱。DFT也被用于模拟红外光谱。对于单体，振动 - 电子耦合对于诱导第一和第二禁戒跃迁至关重要。另一方面，分子聚集足以在几乎所有二聚体中诱导第一和第二禁戒跃迁。然而，当对簇进行振动 - 电子耦合评估时，A → B跃迁能量范围内的能带会受到聚集本身和诱导模式的影响。此外，由于对称性破缺，一些诱导模式会极大地改变允许的A → E跃迁，这取决于所研究的二聚体。就红外光谱而言，存在明显的特征。例如，C - H伸缩模式的强度随着聚集增加而降低。这项工作表明，聚集对能带形状的影响因苯聚集结构和所分析的激发不同而有所不同。
