Excitons: Energetics and spatio-temporal dynamics

TL;DR

This article surveys the evolving landscape of exciton research in complex chemical systems and nanostructured solids, arguing that simple Wannier or Frenkel pictures are insufficient due to vibronic coupling, CT contributions, spin dynamics, and electronic correlation. It synthesizes experimental tools (including 2D and time-resolved spectroscopy) with first-principles electronic structure approaches and advanced quantum-dynamics methods (such as HEOM and ML-MCTDH) to address exciton energetics and spatio-temporal dynamics across diverse nanostructures. Key themes include the construction of diabatic, ab initio exciton Hamiltonians, beyond-F"orster transfer mechanisms, and the role of light–matter coupling in polaritons and quantum-light experiments. The collection highlights progress and persistent challenges in achieving quantitative agreement between theory and experiment, and underscores the necessity of integrating spectroscopy, computation, and theory to guide the design of materials for solar energy conversion, displays, and quantum information applications.

Abstract

The concept of an exciton as a quasiparticle that represents collective excited states was originally adapted from solid-state physics and has been successfully applied to molecular aggregates by relying on the well-established limits of the Wannier exciton and the Frenkel exciton. However, the study of excitons in more complex chemical systems and solid materials over the past two decades has made it clear that simple concepts based on Wannier or Frenkel excitons are not sufficient to describe detailed excitonic behavior, especially in nano-structured solid materials, multichromophoric macromolecules, and complex molecular aggregates. In addition, important effects such as vibronic coupling, the influence of charge-transfer (CT) components, spin-state interconversion, and electronic correlation, which had long been studied but not fully understood, have turned out to play a central role in many systems. This has motivated new experimental approaches and theoretical studies of increasing sophistication. This article provides an overview of works addressing these issues that were published for A Special Topic of the Journal of Chemical Physics on "Excitons: Energetics and spatio-temporal dynamics" and discusses their implications.