Host-Guest Strategy for Organic Phosphorescence to Generate Oxygen Radical over Singlet Oxygen

Exciton dynamics exert a pivotal role in the photodynamic efficiency of photosensitizers, however, strategies for modulating exciton dynamics to motivate electron transfer in exciton-involved photoreactions remain largely unexplored. Herein, we employed a cutting-edge microfluidic platform combined with computational fluid dynamics to encapsulate a commercial type II PS [rose Bengal (RB)] within a rigid host matrix. This encapsulation yielded host/RB nanoparticles (NPs) with a uniform structure and controllable size. The photoexcited dynamics of these host/RB NPs were characterized using time-resolved spectroscopy, and the results revealed that encapsulation not only extended the triplet exciton lifetime of RB, but also created an optimized environment to motivate electron transfer between RB molecules. These findings rationalize the observed remarkable 20-fold reduction in type II photoreaction and a 3-fold promotion in type I photoreaction for host/RB NPs. Due to the dramatic generation of HO^• and O₂^•-, host/RB NPs demonstrated excellent ability for the in vitro eradication of Staphylococcus aureus and Escherichia coli biofilms and the in vivo treatment of S. aureus-infected wounds under hypoxia, with a minimum killing concentration of 10^-7 M. This work sheds light on the motivation of exciton transfer to develop type I PS with enhanced photodynamic properties.