Benzene Excimer and Excited Multimers: Electronic Character, Interaction Nature, and Aromaticity

In this Letter we analyze the forces involved in the formation of the benzene excimer and its electron structure, and (anti)aromatic character. We extend our study to excited states in molecular aggregates, the triplet excimer and the benzene-tricyanobenzene exciplex. Electronic wave functions are decomposed in terms of localized excitations and ion-pair configurations through diabatization, and we show that excimer (anti)aromaticity can be described as the linear combination of ground, excited, and ionic molecular states. Our analysis concludes that the benzene excimer must be characterized as antiaromatic, with weaker antiaromaticity than the molecular excited singlet. Moreover, we define a model electronic Hamiltonian for the excimer state and we use it as a building block for the extrapolation of electronic Hamiltonians in molecular aggregates. Benzene multimers present a nonuniform (anti)aromatic character, with the center of the column being antiaromatic and the edges behaving as aromatic. The implications of this work go beyond the study of the excimer, providing a general framework for the calculation and characterization of excited states in aggregates.

Automated summary

This study analyzes the forces involved in the formation of benzene excimer, its electron structure, and (anti)aromatic character. The research extends to excited states in molecular aggregates, including triplet excimer and benzene-tricyanobenzene exciplex. The study concludes that the benzene excimer should be characterized as antiaromatic and provides a model electronic Hamiltonian for the excimer state, serving as a building block for extrapolating electronic Hamiltonians in molecular aggregates. Benzene multimers exhibit a nonuniform (anti)aromatic character, with the center being antiaromatic and the edges behaving as aromatic. The implications of this work go beyond the excimer study, offering a general framework for calculating and characterizing excited states in aggregates.