On-Demand Photoprotection by UV-Transparent Small Molecules via Aggregation-Induced Absorption: The Origin and Modern Application.

A central challenge across modern chemistry, biology, materials science, and origins-of-life research is obtaining a balance between harnessing beneficial photoreactions and minimizing detrimental photodamage. Here, we have discovered an aggregation-induced photoprotection pathway provided by nonconjugated small molecules. Although conventionally classified as UV-transparent due to the lack of chromophores, these molecules are found to form supramolecular assemblies at elevated concentrations and develop emergent UV-absorbing properties, likely via slip-stacked J-aggregation, as confirmed by multiple spectroscopic characterizations. Density functional theory calculations further elucidated the mechanism of the observed concentration-dependent absorption. A predictive structure-property relationship has been proposed. Regulated by concentration, this effect can smartly allow necessary photoreactions while shielding critical biomolecules from excessive UV radiation. It also suggests that self-photoprotection of the aggregatable molecules could have enabled their prebiotic survival and enduring presence under harsh UV conditions. Furthermore, these findings prompted us to develop a convenient and noninvasive photoprotection strategy for contemporary plastic materials using inexpensive and environmentally friendly small agents.