Facilely Achieving\nNear-Infrared-II J‑Aggregates\nthrough Molecular Bending on a Donor–Acceptor Fluorophore for\nHigh-Performance Tumor Phototheranostics

Constructing J-aggregated organic dyes represents a promising\nstrategy\nfor obtaining biomedical second near-infrared (NIR-II) emissive materials,\nas they exhibit red-shifted spectroscopic properties upon assembly\ninto nanoparticles (NPs) in aqueous environments. However, currently\navailable NIR-II J-aggregates primarily rely on specific molecular\nbackbones with intricate design strategies and are susceptible to\nfluorescence quenching during assembly. A facile approach for constructing\nbright NIR-II J-aggregates using prevalent donor–acceptor (D–A)\nmolecules is still lacking. In this study, we present a facile method\nthat transforms D–A molecules into J-aggregates by simply bending\nthe molecule through introducing a methyl group, enabling high-performance\nNIR-II phototheranostics. The TAA-BT-CN molecule exhibits hypsochromic-shift\nabsorption upon forming H-aggregated NPs, while the designed mTAA-BT-CN\nwith a bent structure demonstrates a bathochromic shift of over 100\nnm in absorption upon forming J-aggregated NPs, leading to much enhanced\nNIR-II emission beyond 1100 nm. With respect to its H-aggregated counterpart\nwith the aggregation-caused quenching (ACQ) phenomenon, the J-aggregated\nmTAA-BT-CN NPs exhibit a 7-fold increase in NIR-II fluorescence owing\nto their aggregation-induced emission (AIE) property as well as efficient\ngeneration of heat and reactive oxygen species under 808 nm light\nexcitation. Finally, the mTAA-BT-CN NPs are employed for whole-body\nblood vessel imaging using NIR-II technology as well as imaging-guided\ntumor phototherapies. This study will facilitate the flourishing advancement\nof J-aggregates based on prevalent D–A-type molecules.