Excitons in confined molecular aggregates

Abstract Organic optoelectronic materials have attracted extensive attention in the past decades due to their wide applications in organic light‐emitting diodes (OLEDs), organic photovoltaics (OPVs), photocatalysis, etc. Significant advancements have been obtained in the material designs based on the insight into the fundamental physics of exciton related to molecular stacking patterns in solid/condensed states. The exciton characteristics and behaviors are not only a starting point for studying photophysical and photochemical processes on a microscopic level, but also a crucial point in determining the optoelectronic properties of macroscopic aggregates. This review summarizes the historic development of exciton models, accompanied by the discoveries of special molecular stacking patterns (H‐/J‐/X‐/M‐aggregates), and the competitive de‐excitation pathways of excitons including fluorescence, energy transfer, singlet fission, excimer formation and symmetry‐breaking charge separation in the confined aggregate structures. Additionally, it highlights the capabilities of a correlation between molecular stacking modes and exciton behaviors, which provides new insights and perspectives for optimizing exciton character and behavior through the modulation of molecular arrangement in aggregate states, thereby enhancing the performance of optoelectronic materials.