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

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.