Engineering the Unoccupied Electronic Levels in Nanoscale Zr-MOFs by Intrinsic Open-Metal-Site Modulation for Enhanced Luminescence

How to modulate the open metal sites (OMS) for enhancing the luminescence emerges as a significant issue to explore in the exploration of high-performance metal-organic frameworks (MOFs) for photoluminescence (PL) sensing and X-ray detection. Here, by efficiently extending the conjugation of the ligand, nanoscale Zr-ADIP, which has eight OMS per Zr cluster, was first synthesized and demonstrated to have enhanced PL and X-ray excited luminescence (XEL) performance. Furthermore, a modulator tuning strategy was adopted to occupy the OMS, which has been proven to be efficient for engineering the unoccupied electronic levels, promoting the relaxation of the excited electrons, and enhancing the PL efficiency. It is found that with benzoic acid as the modulator, the optimal nanoscale Zr-ADIP-BzOH exhibits superior performance with an X-ray detection limit of 0.53 μGy s^–1, which is 10 times lower than the minimum X-ray dose rate requirement for medical X-ray imaging. The superior XEL performance of Zr-ADIP-BzOH has been further proven to be effective in the tentative monitoring of the morphology of a mature pearl in a clam sample by constructing a condensed film device. We expect that the proposed OMS introduction and modulator tuning strategy would offer insights for the structural design and performance enhancement of luminescent MOFs.