Efficient X-ray scintillating lead(ii)-based MOFs derived from rigid luminescent naphthalene motifs

Solid-state X-ray scintillators are widely applied in medical imaging and space exploration. However, it is still a great challenge to probe into the intrinsic nature of scintillating behaviour due to the ambiguous structure-function relationship. Herein, four structure-defined X-ray scintillating Pb(ii)-based metal-organic frameworks (SMOFs) were successfully obtained under solvothermal conditions, [Pb(1,4-ndc)(DMF)]_n (SMOF-1), [Pb(1,4-ndc)(DMA)]_n (SMOF-2), [Pb₂(2,6-ndc)₂(H₂O)]_n·nDMF (SMOF-3) and [Pb₄(2,6-ndc)₃Cl₂]_n (SMOF-4), where 1,4-H₂ndc = 1,4-naphthalene dicarboxylate, 2,6-H₂ndc = 2,6-naphthalene dicarboxylate, DMF = N,N-dimethylformamide, and DMA = N,N-dimethylacetamide. SMOFs 1-4 show scintillating signals under X-rays triggered by a highly purified tungsten target. Compared with SMOFs 1-3, SMOF-4 exhibits excellent scintillating performance owing to its solvent-free and denser structure, which favours more efficient conversion ability of X-rays to visible light. X-ray stimulated luminescence (XSL) spectra present multiple emission peaks, which is further confirmed by wavelength-dependent luminescence spectra under UV-Vis light, and density of state and DFT calculations. The synergistic effects of heavy metal Pb(ii) centres as effective X-ray absorbers and organic ligands as luminescent motifs endow these Pb(ii)-based MOFs with application prospects in X-ray detection.