Hydrogen-Bonded Aggregates Featuring n → π* Electronic Transition for Efficient Visible-Light-Responsive Photocatalysis

The generation of stable photocatalysts for solar energy conversion is currently one of the urgent missions of photocatalytic science. Herein, we reported a discovery that the hydrogen-bonded trithiocyanuric acid (TA) aggregates can function as a photocatalyst. The weak conjugation between n electrons from the sulfur atoms and the triazine moiety in the aggregated TA (denoted as ATA) was found to be the origin of visible-light harvesting ability. Simultaneously, the weak entanglement of hydrogen-bonded aggregates was favorable for the charge delocalization, thereby prolonging the charge lifetime of ATA up to 1241.7 ns. Consequently, the ATA exhibited high photocatalytic hydrogen production activity, comparable to the existing photocatalysts. More significantly, similar n → π* electronic transition and photocatalytic functions were found in a series of sulfur/oxygen/nitrogen-containing non-covalent aggregates (8 examples), suggesting a general principle of the aggregation-induced photocatalysis. Moreover, combining theoretical calculation, more than 80 chemical compounds with n → π* electronic transition that in principle can act as potential photocatalysts after aggregation. Our discovery together with the insightful results represents a step-change in photosynthesis where non-covalent aggregates are identified as a class of metal-free photocatalysts.