Dual-Functional Noncovalent Dimers: Amplifying ROS Generation and Fluorescence for Enhanced Photodynamic Therapy and Aerobic Photocatalysis

The conflicting demands of enhancing reactive oxygen species (ROS) generation and fluorescence emission, two photophysical processes competing for excited-state energy, constitute a fundamental barrier in developing multifunctional photosensitizers (PSs). Herein, we present a noncovalent dimerization strategy using cucurbit[8]uril (CB[8]) to address this dual requirement in A-D-A-structured photosensitizers PS1 and PS2. Host–guest complexation leads to the formation of noncovalent dimers, PS1@CB[8] and PS2@CB[8]. Compared to their monomeric forms, PS1@CB[8] and PS2@CB[8] show a 34.6-fold and 39.5-fold enhancement in fluorescence intensity, respectively, accompanied by redshifts over 41 nm, indicating tailored photophysical properties achieved through noncovalent dimerization. Theoretical calculations suggest that the ordered dimeric arrangement within CB[8] significantly reduces the energy gap (ΔEST) between the singlet and triplet excited states of the PSs. Furthermore, the conical intersection between the S1 and S0 states of PS1 and its dimer demonstrates that the dimerization can simultaneously inhibit S1 → S0 nonradiative relaxation. These findings facilitate ISC processes and radiative decay, thereby amplifying ROS generation and fluorescence emission. As a proof of concept, PS1@CB[8] was successfully employed in photodynamic antibacterial therapy and fluorescence imaging using confocal laser scanning microscopy. Meanwhile, PS2@CB[8] demonstrated superior catalytic performance in thioether oxidation (0.05 mM, 2 h, conv. ≥ 95%) and in the value-added conversion of 5-hydroxymethylfurfural (0.05 mM, 8 h, conv. > 99%). This study presents a straightforward supramolecular strategy for the photophysical modulation of PSs, offering promising avenues to address the challenges in optimizing ROS production and fluorescence emission.