Regulating the Twisted Intramolecular Charge Transfer and Anti-heavy Atom Effect at Supramolecular Level for Favorable Photosensitizing Activity in Water

Photosensitizing assemblies based on twisted intramolecular charge transfer (TICT) active donor-acceptor-donor (D-A-D) system BrTPA-Qx having bromine atoms at the periphery have been developed. Through strategic incorporation of bromine atoms at the para-position to the nitrogen-carbon bonds of phenyl rings at the periphery, halogen-halogen interactions are induced in BrTPA-Qx nanoassemblies in H₂O:DMSO (99:1) solution. Hence, the anti-heavy atom effect is induced, and the limitations of TICT (dark excited state) and heavy atom effect (triplet deactivation via radiative decay) could be overcome. Because of TICT and anti-heavy atom effect, supramolecular BrTPA-Qx nanoassemblies demonstrate high efficiency in promoting activation of aerial oxygen via electron and energy transfer pathways in aqueous media. The significant influence of the stabilized TICT state and anti-heavy-atom effect in controlling the ROS generation was validated through in-depth solvent-dependent photophysical studies and investigations of the structure-activity relationship in several model compounds. The notable photosensitizing activity of BrTPA-Qx nanoassemblies is manifested in their ability to efficiently catalyze the oxidative coupling of benzylamine (via type I and type II mechanisms), Knoevenagel condensation of aromatic aldehydes (type II), and oxidative hydroxylation of arylboronic acids (type I) under mild conditions.