Interaction between azobenzene-containing molecules in supramolecular structures or self-assembled monolayers (SAMs) results in the formation of molecular exciton states. These states determine photophysical and photochemical processes in such assemblies. Here, using first-principles quantum chemical calculations, optical spectra and exciton delocalization of the exciton states in model clusters of azobenzene molecules are studied. Specifically, 1D linear chains and 2D SAM-like arrangements are considered, and the exciton states are computed by means of time-dependent long-range corrected density functional theory (TD-lc-DFT) and ab initio configuration interaction singles (CIS), for clusters including up to 18 azobenzene molecules. The nature of the exciton states is analyzed using transition density matrix analysis. In addition, a connection to periodic systems is made applying the Bethe–Salpeter equation (BSE)/Green's function many-body perturbation theory ($GW$) approach to a selected system. It is found that the brightest excitons are dominated by local excitations. The energetic location of charge transfer states in the electronic spectra of aggregates depends to a large extent on a given method and distance between nearest neighbors. Furthermore, it is analized how an excitonic delocalization pattern changes with varying molecular orientation in the unit cell of SAMs.

中文翻译：

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偶氮苯聚集体的激子态：第一性原理研究

超分子结构或自组装单分子层 (SAM) 中含偶氮苯的分子之间的相互作用导致分子激子态的形成。这些状态决定了此类组件中的光物理和光化学过程。在这里，使用第一性原理量子化学计算，研究了偶氮苯分子模型簇中激子态的光谱和激子离域。具体来说，考虑了一维线性链和二维 SAM 类排列，并通过时间相关的长程校正密度泛函理论 (TD-lc-DFT) 和从头算配置相互作用单曲 (CIS) 计算激子态，对于包含多达 18 个偶氮苯分子的簇。使用跃迁密度矩阵分析来分析激子态的性质。此外，$GW$) 选择系统的方法。发现最亮的激子受局部激发支配。聚集体电子光谱中电荷转移态的能量位置在很大程度上取决于给定的方法和最近邻之间的距离。此外，分析了激子离域模式如何随着 SAM 晶胞中分子取向的变化而变化。