Steric-Hindrance-Driven Near-Unity Luminescence in Mn(II) Halides for X-ray Imaging

Abstract Organic–inorganic hybrid scintillators have attracted considerable interests for high-resolution X-ray imaging. Herein, two monodentate Mn(II) halide complexes, namely, TPPOMn and TTPOMn, are prepared through nearly quantitative coordination between phosphine oxide and MnBr2, respectively. Both Mn(II) halides exhibit green luminescence, originating from the radiative transition 4T1 → 6A1 of the Mn(II) center. Intriguingly, the introduction of steric hindrance in TTPOMn not only dramatically enhances the emission efficiency but also significantly slows down temperature-dependent luminescence quenching. The underlying mechanism can be attributed to steric-hindrance-induced structural rigidity, as further verified by structural analysis and theoretical simulations. Thanks to the excellent emission and strong X-ray absorption, TTPOMn delivers outstanding scintillation performance with a low detection limit of 25.4 nGy/s and a high spatial resolution of 21 lp/mm. This study establishes a promising steric-hindrance strategy to boost luminescence for superior scintillation.