Modular Amphiphilic Design Enables Control of Oblique vs J‐Type Exciton Coupling in Aqueous Self‐Assembly

Molecular design strategies are essential for rationalizing the aqueous self‐assembly behavior of π ‐conjugated amphiphilic molecules and for clarifying the relationship between their photophysical properties and nanostructure morphology. Despite notable advances in understanding structure–property relationships that enable the selective formation of face‐to‐face (H‐type) and slipped (J‐type) aggregates in water, accurately predicting self‐assembly outcomes and resulting functions remains challenging. This is partly because the molecular requirements governing other exciton coupling modes, such as oblique‐type interactions, and their effects on aggregate morphology are still poorly understood. Herein, a molecular design strategy employing amphiphilic aza‐BODIPY dyes that enables precise tuning of exciton coupling (J‐type vs oblique) and nanoscale morphology in aqueous environments is presented. By systematically varying both the number and positioning of hydrophilic triethylene glycol chains and the length of hydrophobic alkyl substituents, the structure–property relationships that govern self‐assembly behavior, employing a combination of theoretical, spectroscopic, and microscopic methods are elucidated. This work advances the understanding of exciton coupling beyond the well‐studied H‐ and J‐type aggregates and provides new design principles for engineering functional materials through supramolecular self‐assembly.