Minimizing radiative and nonradiative energy leakage in red-light-absorbing supramolecular nanoassemblies to boost oxidative photocatalytic activity in water†

Harnessing abundant red-light, which constitutes a significant portion of solar radiation, to energize oxidative transformations is an economic and eco-friendly strategy for sustainable chemistry. Given this consideration, red-light-absorbing J-type nanoassemblies based on a donor–acceptor–donor (D–A–D) building block (BrTPA-Py) with 4-bromo-N,N-diphenylaniline as the donor and pyrazino[2,3-b]pyrazine-2,3-dicarbonitrile as the acceptor have been developed in aqueous media. The strategic incorporation of bromine atoms at the periphery enhanced spin–orbit coupling and restricted nonradiative/radiative decay through bromine⋯bromine noncovalent interactions. Due to the synergistic effect of strong charge-transfer characteristics, presence of bromine atoms and restricted inter/intramolecular motion, rapid intersystem crossing (ISC) is facilitated in BrTPA-Py nanoassemblies, enabling the activation of aerial oxygen through type I (electron transfer) and/or type II (energy transfer) pathways upon irradiation by red-light. The remarkable photosensitization potential of BrTPA-Py nanoassemblies has been unveiled to catalyse the oxidation of phosphines and hydroxylation of arylboronic acids under red-light irradiation, which is unprecedented. This investigation presents a simple design strategy to propel advances in sustainable photocatalysis by regulating the dynamics of excited state under low-energy radiation through the incorporation of halogen atoms in the backbone of the building block with strong charge-transfer characteristics.