Exploiting radical-pair intersystem crossing for maximizing singlet oxygen quantum yields in pure organic fluorescent photosensitizers

摘要

Fluorescent photosensitizers (PSs) often encounter low singlet oxygen ( ~(1) O _(2) ) quantum yields and fluorescence quenching in the aggregated state, mainly involving the intersystem crossing process. Herein, we successfully realize maximizing ~(1) O _(2) quantum yields of fluorescent PSs through promoting radical-pair intersystem crossing (RP-ISC), which serves as a molecular symmetry-controlling strategy of donor–acceptor (D–A) motifs. The symmetric quadrupolar A–D–A molecule PTP exhibits an excellent ~(1) O _(2) quantum yield of 97.0% with bright near-infrared fluorescence in the aggregated state. Theoretical and ultrafast spectroscopic studies suggested that the RP-ISC mechanism dominated the formation of the triplet for PTP, where effective charge separation and an ultralow singlet–triplet energy gap (0.01 eV) enhanced the ISC process to maximize ~(1) O _(2) generation. Furthermore, in vitro and in vivo experiments demonstrated the dual function of PTP as a fluorescent imaging agent and an anti-cancer therapeutic, with promising potential applications in both diagnosis and theranostics.