Supramolecular Strategies for Modulating Excited-State Properties of Photosensitizers in Photodynamic Therapy

The performance of photosensitizers (PSs) in photodynamic therapy (PDT) is determined not only by their intrinsic molecular structures but also by their spatial organization and environmental interactions. Supramolecular assembly enables precise control over molecular packing, local microenvironments, and intermolecular electronic coupling without altering the chromophore scaffold, thereby offering a versatile approach to modulate the photophysical and photochemical behavior of PSs through noncovalent interactions. In this Minireview, we summarize recent advances in supramolecular strategies for modulating the excited-state properties of PSs in PDT. We focus on two central aspects: promoting intersystem crossing to enhance triplet-state formation, and modulating excited-state deactivation pathways to regulate ROS generation and bias Type-I or Type-II photodynamic processes. Representative examples are discussed to illustrate how supramolecular assembly can reduce singlet-triplet energy gaps, introduce charge-transfer (CT) mediators, suppress nonproductive decay, and facilitate electron or hydrogen atom transfer (HAT) reactions. Finally, we highlight the remaining challenges in mechanistic understanding, structural stability, and translational implementation, and outline future opportunities in bioadaptive assembly, simplified system design, and mechanism-guided development of next-generation supramolecular PSs.