Highly Efficient White-Light Emission and UV–Visible/NIR Luminescence Sensing of Lanthanide Metal–Organic Frameworks

A series of new isostructural lanthanide metal–organic frameworks (Ln-MOFs), [Ln2(L)2(DMAC)2]·nH2O [Ln = La (1), Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), Tb (7), and Tm (8); H4L = 5-(bis(4-carboxybenzyl)amino)-isophthalic acid, DMAC = N,N′-dimethylacetamide], have been isolated. Single-crystal X-ray diffraction analysis reveals that all complexes exhibit a rare (4,8)-connected alb-4,8-P topology with binuclear [Eu2(COO)8]n secondary building units as 8-connected nodes and H4L ligands as 4-connected nodes. Two mixed-lanthanide analogues of single-lanthanide MOFs were designed and prepared [Ln = La0.93Eu0.02Tb0.05 (9) and Tm0.47Eu0.18Tb0.35 (10)] by way of careful regulation of the relative concentration of lanthanide ions which are able to emit pure white light. Luminescent sensing of complexes 3 and 5 has been investigated. Strikingly, complex 5 exhibits an excellent luminescent sensing to TNP with a high Ksv value of 3.58 × 104 M–1 and a low detection limit of 4.66 × 10–4 mM. Complex 3 reveals high selectivity and sensitivity toward benzaldehyde (Ksv of 4.9 × 104 M–1; detection limit of 3.4 × 10–4 mM). It represents the first example of an NIR luminescent MOF for sensing of benzaldehyde.