Rigid‐Flexible Molecular Engineering of Glass‐Forming Copper(I) TADF Scintillators for Underwater X‐Ray Videography

ABSTRACT Thermally activated delayed fluorescence (TADF) metal‐organic complexes offer near‐unity exciton utilization and strong X‐ray absorption, yet achieving transparent glassy TADF materials that simultaneously maintain high radioluminescence efficiency and structural stability remains challenging. Herein, we introduce an “intramolecular‐rigidity intermolecular‐flexibility” design strategy that enables glass formation while preserving TADF characteristics in Copper(I) halide complexes. A rigid diphenyl‐2‐pyridylphosphine (dppy) anchors the [Cu 2 I 2 ] core, suppressing geometrical distortion in the amorphous state, whereas functionalized triphenylphosphine ligands (R‐PPh 3 , R = H, F, Me, OMe) tune intermolecular interactions and promote vitrification, yielding a family of Cu(I)‐based TADF glasses (CuR‐G). The coordination‐stabilized molecular framework sustains efficient TADF in the glassy state, affording relative light yields exceeding 50 000 photons MeV −1 . Among them, CuOMe‐G exhibits weakened intermolecular coupling, enabling low‐temperature vitrification, high optical transparency, and high‐resolution static X‐ray imaging up to 28.5 lp mm −1 . Notably, the exceptional aqueous stability of CuOMe‐G—retaining nearly constant radioluminescence after 10 days of immersion—allows real‐time underwater X‐ray imaging of living organisms under low‐dose conditions, establishing a rare scintillator platform that integrates glass‐state TADF, environmental resilience, and dynamic imaging capability. This work provides a generalizable molecular‐locking approach for developing high‐performance amorphous scintillators.