Reversal of the Heavy-Atom Effect Isostructural AIE Metal-Organic Frameworks for Enhanced Radioluminescence and Nuclear Battery Performance

Abstract

Incorporation of high-Z elements into conventional organic fluorophores generally induces severe fluorescence quenching owing to the classic heavy-atom effect. Nevertheless, recent advances in aggregation-induced emission (AIE) systems with through-bond/through-space conjugation (TBSC) have uncovered an anomalous heavy-atom-promoted fluorescence enhancement, which remains confined to covalently substituted organic small molecules with nonmetallic heavy atoms. Herein, we extend this unique principle to periodic metal-organic frameworks (MOFs) with coordination-bonded heavy metal nodes. By adopting an isostructural design strategy, two MOFs (Zr-TCPE and Hf-TCPE) are fabricated using a TBSC-type AIE ligand (H4TCPE). Remarkably, both MOFs exhibit hot-exciton thermally activated delayed fluorescence (TADF) features. Under X-ray excitation, Hf-TCPE exhibits substantially enhanced radioluminescence relative to Zr-TCPE, achieving an ultra-low detection limit of 2.53 μGy s–1. Mechanistic investigations confirm that the higher atomic number of Hf enhances X-ray absorption, while the inherent TBSC and hot-exciton TADF properties enable efficient high-energy reverse intersystem crossing from high-lying triplet states to singlet states, effectively suppressing non-radiative T1 decay. This synergistic mechanism fundamentally reverses the conventional heavy-atom quenching effect into a highly radioluminescence enhancement strategy. As a proof-of-concept, the Hf-TCPE-based radioluminescent nuclear battery delivers a maximum output power of 1.15 μW at a dose rate of 5.6 μGy s–1, which is 17.8% higher than that of the Zr-TCPE counterpart, verifying its promising potential in radiation energy conversion. This work extends the heavy-atom-enhanced luminescence principle to periodic MOF systems, providing a universal strategy for the rational design of high-performance scintillators and radiation energy conversion materials.