Efficient Harvesting of Triplet Excitons via a T ₁ ‐Blocked TADF Mechanism in Series MOFs for Optimal X‐ray Detection and Imaging

Abstract

Abstract Scintillators play vital roles in fields such as medical imaging, high‐energy physics, astronomy, and radiation monitoring. Their operational principle, rooted in the excitation of high‐energy radiation, underscores that luminescence efficiency in scintillators is fundamentally limited by their capacity to harness triplet excitons. In this context, thermally activated delayed fluorescence (TADF) molecules present a promising avenue, enabling the efficient utilization of triplet excitons through thermally activated up‐conversion, thereby advancing the development of superior scintillators. Our investigation reveals a T 1 ‐blocked TADF mechanism in H 4 TCPE, where efficient singlet‐triplet exciton transfer arises from the minimized S 1 ‐T 2 energy gap (0.18 eV). Unlike conventional TADF molecules, H 4 TCPE features carboxylic acid groups that enable heavy metal coordination to enhance X‐ray attenuation. Using tetravalent metals (Zr, Hf, and Th) as nodes and H 4 TCPE as linkers, we fabricated metal‐organic frameworks (MOFs) that synergize H 4 TCPE's TADF properties with metal‐enhanced radiation absorption. The resulting MOFs show X‐ray detection and imaging performances superior to pure H 4 TCPE (20.0 lp mm −1 and 1.15 µGy s −1 for Th‐TCPE vs. <14.3 lp mm −1 and 5.01 µGy s −1 for H 4 TCPE), with efficacy correlating to metal atomic number. This work not only broadens TADF molecular diversity through a new energy transfer mechanism and pioneers TADF‐MOF integration for advanced radiation detection.