Dynamic Through-Space Interactions: A Unifying Framework for Aggregation-Induced Photocatalysis

Conspectus The design of organic photocatalysts has long been guided by the assumption that molecular aggregation is detrimental to the performance. This Account presents our laboratory’s systematic development of a fundamentally different paradigm, aggregation-induced photocatalysis (AIP). We demonstrate that the noncovalent assembly of molecules can become the very source of photocatalytic function, a principle that operates in parallel with the well-established paradigm of aggregation-induced emission (AIE), yet pursues a fundamentally different goal. The central mechanistic insight, which we term dynamic through-space interactions (DTSI), rests on two synergistic pillars. Through-space orbital interactions between closely packed molecules create delocalized collective electronic states that dramatically extend light absorption into the red and near-infrared (NIR) regions. Concurrently, the inherent dynamic behavior of noncovalent interactions induces asymmetric molecular packing, generating large dipole moments and built-in electric fields that drive efficient charge separation. We demonstrate the generality of this framework across three distinct material categories. In π-electron aggregation systems, aggregates of organic dyes achieve outstanding hydrogen evolution with a quantum yield (QY) reaching 76% at 600 nm, while carbon nitride nanosheet aggregates set a QY of 76.4% at 420 nm. In lone-pair@π-electron aggregation systems, hydrogen-bonded assemblies activate otherwise forbidden n → π* electronic transition in nonconjugated small molecules, transforming them into visible-light-active photocatalysts. In lone-pair aggregation systems, we challenge the long-held assumption that π-conjugation is a prerequisite for semiconductor photocatalysis by demonstrating that nonaromatic biomass such as glucan and chitosan generates photocatalytic activity solely through through-space electron couplings of lone-pair electrons. A deeper design principle emerges from these studies, which we term the dynamic order–disorder interactions. Optimal function arises not from static perfection but from the interplay between the structural order that enables through-space orbital interactions and the dynamic disorder that sustains the built-in electric field. This Account provides a unifying framework for understanding and designing aggregate-based photocatalysts with implications that extend from solar fuel production to emission phenomena and beyond.