More Is Better: Acceptor Engineering for Constructing NIR-II AIEgens to Boost Multimodal Phototheranostics

The manipulation of electron donor/acceptor (D/A) shows endless impetus for innovating optoelectronic materials. Because of the diversity of electron-donating species, the study on donor engineering has explored systematically, whereas the research on electron acceptor engineering received a snub by contrast. Inspired by the philosophical idea of “more is different”, two systems with D'−D−A−D−D' (1A system) and D'−D−A−A−D−D' (2A system) structures based on the acceptor engineering are ingeniously designed and studied. It is demonstrated that the 1A system presents a weak aggregation-induced emission (AIE) to aggregation-caused quenching (ACQ) phenomenon along with the increased acceptor electrophilicity. Interestingly, the 2A system exhibits an opposite ACQ-to-AIE transformation, manifesting the dual-acceptor tactic could facilitate AIE activity. Thanks to the highest molar absorptivity, near-infrared-II (NIR-II, 1000–1700 nm) emission, superior AIE effect, favorable reactive oxygen species generation and high photothermal conversion efficiency, a representative member of 2A system handily perform in fluorescence-photoacoustic-photothermal multimodal imaging-guided photodynamic-photothermal synergetic therapy for efficient tumor elimination. Meanwhile, NIR-II fluorescence imaging of blood vessels and lymph nodes in living mice are also accomplished. This work provides a fascinating molecular design philosophy for developing versatile phototheranostic agent with a higher molar absorptivity, superb aggregation-intensified NIR-II fluorescent emission, and improved heat generation capacity.