Intramolecular Repulsive Interactions Enable High Efficiency of NIR-II Aggregation-Induced Emission Luminogens for...

Strategies to acquire high-efficiency luminogens that emit in the second near-infrared (NIR-II, 1000-1700 nm) range are still rare due to the impediment of the energy gap law. Herein, a feasible strategy is pioneered by installing large-volume encumbrances in a confined space to intensify the repulsive interactions arising from overlapping electron densities. The experimental results, including smaller coordinate displacement, reduced reorganization energy, and suppressed internal conversion, demonstrate that the repulsive interactions assist in the inhibition of radiationless deactivation. Meanwhile, the configuration and hybridization form of the donor units are transformed along with the repulsive interactions, bringing about improved oscillator strength. A 3.8-fold higher luminescence efficiency is realized via the synergistic effect. Furthermore, the repulsive interactions endow the NIR-II fluorophores with a highly twisted conformation, superior AIE activity, and cascaded improvement of fluorescence emission from isolated molecules to aggregates. By utilizing a brain-targeting peptide to functionalize the NIR-II nanoparticles, accurate detection and high-contrast imaging of orthotopic glioblastoma are realized. This work not only explores a fundamental principle to handle the intractable energy gap law but also provides potential applications of NIR-II luminogens in high-contrast bioimaging and glioblastoma detection.