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 ionpair 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.

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The violation of the Kasha photoemission rule in organic molecules has intrigued chemists since their discovery, being always of relevance given its connection with unique electronic properties of molecules. However,...

Excited state aromaticity is a stimulating area of research, widely used as a probe to describe and rationalize many photochemical phenomena. Herein, we review some of the recent findings of unprecedented aromatic stabilization in spin singlet excimer and through-space aromatic character in triplet excimers of a series of linear [n]acenes, as paramount examples of polycyclic aromatic hydrocarbons (PAHs). This review also provides insights on the

The search for efficient heavy atom free photosensitizers (PS) for photodynamic therapy (PDT) is a very active field. We describe herein a simple and easily accessible molecular design based on...