Hybridized Local and Charge‐Transfer Emitter With a Dual‐Hindered Indoline Donor for Fast and Efficient Red Plastic Scintillators

ABSTRACT Flexible organic red/NIR scintillators that convert ionizing radiation into long‐wavelength photons are intrinsically compatible with silicon photomultiplier (SiPM), offering strong potential for medical imaging and non‐destructive testing. However, their practical development is limited by inadequate radiation absorption, inefficient exciton utilization, and sluggish radioluminescence response. Herein, we report a fast and efficient red organic scintillator based on a hybridized local and charge‐transfer (HLCT) emitter featuring an ultra‐strong dual‐hindered indoline donor. The chair‐shaped indoline donor, incorporating a nonconjugated sterically hindered ring, effectively red‐shifts the radioluminescence to match SiPM sensitivity while affording a large Stokes shift and aggregation‐induced emission characteristics. The introduction of an additional bulky tert ‐butyl group further suppresses nonradiative decay and, unexpectedly, accelerates reverse intersystem crossing from high‐lying excited states, enabling intense radioluminescence with an ultrafast decay lifetime of 3.94 ns—among the fastest reported for red scintillators. The resulting scintillator, c ID‐Bt, achieves efficient triplet exciton harvesting and delivers a high light yield of 24231 photons MeV − 1 (1.8 times the commercial benchmark BC‐430), an ultralow detection limit of 168 nGy s − 1 and a resolution of 16.8 lp mm − 1 . Furthermore, c ID‐Bt–encapsulated plastic scintillators and scintillating fibers demonstrate potential for radiation detection and x‐ray imaging, establishing a viable strategy for next‐generation organic red/NIR scintillators.