Ultralong Organic Phosphorescent Nanocrystals with Long-Lived Triplet Excited States for Afterglow Imaging and Photodynamic Therapy.

The development of novel applications of ultralong organic phosphorescent (UOP) materials is highly desired. Herein, a series of UOP materials (EDCz, E = O, S, Se, and Te) for bacterial afterglow imaging and photodynamic therapy (PDT) is reported. By structurally bonding with the chalcogen atoms with π-conjugated scaffolds, EDCz not only absorbs visible light but also emits UOP with an efficiency of ca. 0.01-6.8% and a long lifetime of 0.08-0.318 s under ambient conditions. Benefiting from the long-lived triplet excited states, the SeDCz nanocrystals (NCs) possessed the best optical properties in the series, generating 1O2 under white light irradiation and performing as an agent for Staphylococcus aureus afterglow imaging and PDT at a low concentration (98 ng mL-1). The SeDCz NCs are also utilized as real-time UOP imaging agents and promoted healing of infected wounds in living mice. To the best of our knowledge, this study presents the first example of UOP-based bacterial photodynamic theranostic agents and creates a platform for the next-generation efficient UOP-based photosensitizers for bioimaging and skin regeneration.