Exciton States of Azobenzene Aggregates: A First‐Principles Study

Abstract

AbstractInteraction 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 () 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.