Stabilizing Delocalized Charge-Transfer State in Anthraquinone-Centered TADF Emitters for Enhanced Reactive Oxygen Species Production

This study explores the physical mechanism underlying thermally activated delayed fluorescence (TADF) emitters as metal-free photosensitizers for reactive oxygen species (ROS) production. Through a comparative investigation of anthraquinone-based D–A-type emitter, AQ(PhDPA), with D–A–D-type emitter, AQ(PhDPA)2, we demonstrate that the multidonor architecture markedly enhances TADF properties and ROS generation efficiency. Combined theoretical and transient spectroscopic analyses reveal that AQ(PhDPA)2 possesses a more stabilized charge-transfer state with suppressed conformational relaxation relative to its D–A counterpart, leading to improved performance, including a higher delayed fluorescence quantum yield, an increased radiative transition rate, and inhibited nonradiative decay of triplet states. When incorporated into water-dispersible nanoparticles, both anthraquinone-based D–A-type emitters predominantly generate superoxide radicals (O2•–), but AQ(PhDPA)2 shows superior ROS production capability relative to that of AQ(PhDPA). These findings establish symmetric multidonor molecular design as an effective strategy for developing efficient type-I photosensitizers with potential applications in hypoxia-tolerant cancer therapy.