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

The ingenious manipulation of electron donor/acceptor (D/A) has long been the major trend for advanced optoelectronic materials. In this context, benefitting from the diversity of electron donor species, donor engineering studies have ob-tained vigorous explorations, whereas the research on acceptor engineering received a snub by contrast. By learning from the philosophical idea of “more is different”, two types of compounds with the molecular structures of D−D−A−D−D (abbreviated as 1A system) and D−D−A−A−D−D (abbreviated as 2A system) based on acceptor engineering were un-precedentedly designed and studied. It was demonstrated that the compounds in 1A system presented an alteration from weak aggregation-induced emission (AIE) tendency to aggregation-caused quenching (ACQ) phenomenon along with the enhancement of electron-withdrawing capacity of the acceptors. Interestingly, the 2A system exhibited an opposite change of ACQ-to-AIE transformation when more electron-deficient acceptors were employed, manifesting that the in-troduction of an extra acceptor could largely contribute to the AIE feature. Thanks to the second near-infrared (NIR-II) window emission, superior AIE effect, favorable reactive oxygen species production ability and excellent photothermal conversion efficiency, 2TT-2BBTD (a member of 2A system) nanoparticles were proved to be handily competent in fluo-rescence-photoacoustic-photothermal multimodal imaging-guided photodynamic and photothermal therapy for eliminat-ing the orthotopic 4T1 mouse breast carcinoma. This work provides a fascinating molecular design philosophy for devel-oping versatile phototheranostic agent with a higher molar absorptivity, superb aggregation-intensified NIR-II fluorescent emission, and improved heat generation capacity.