Multiconfigurational\nExcitonic Couplings in Homo-\nand Heterodimer Stacks of Azobenzene-Derived Dyes

Molecular excitons play a major role within dye aggregates\nand\nhold significant potential for (opto)electronic and photovoltaic applications.\nNumerous studies have documented alterations in the spectral properties\nof dye homoaggregates, but only limited work has been reported for\nheteroaggregates. In this article, dimeric dye stacks were constructed\nfrom azobenzene-like dyes with identical or distinct structures, and\ntheir excitonic features were computationally investigated. Our results\nshow that strong exciton coupling is not limited to identical chromophores,\nas often assumed, based on a recently made available Frenkel Exciton\nHamiltonian and multiconfigurational plus second-order perturbation\ntheory energetics methodology. Heteroaggregate stacks were found to\nexhibit different absorption features from the corresponding interacting\nmonomers, indicating considerable coupling interactions between units.\nWe analyzed how such coupling may vary according to various aspects,\nsuch as the relative positions of the interacting monomers or the\ndifferences in their energetics. Such qualitative and semiquantitative\nanalyses allow the evaluation of the excitonic behavior of these dye\naggregates to encourage further efforts toward a deeper understanding\nof the excitonic properties of tailored dye heteroaggregate systems.