N-donor ligands enhancing luminescence properties of seven Zn/Cd(ii) MOFs based on a large rigid π-conjugated carboxylate ligand

Abstract

A series of Zn/Cd(II) coordination polymers, namely, [Zn(IDPA)(H₂O)]_n·n(H₂O) (1), [Cd(IDPA)(bpp)]_n·n(H₂O) (2), [Cd(IDPA)(4,4′-bpy)_1/2]_n (3), [Zn(IDPA)(4,4′-bpy)_1/2]_n (4), [Zn₄(IDPA)₄(phen)₂·(H₂O)₂]_n·2n(H₂O) (5), [Zn(IDPA)(phen)·(H₂O)]_n·n(H₂O) (6) and [Zn(IDPA)(2,2′-bpy)·(H₂O)]_n·n(H₂O) (7), have been prepared on the basis of a bulky 1,3-benzenedicarboxylate derivative ligand, 5-(1-oxoisoindolin-2-yl)isophthalic acid (H₂IDPA), with the help of 1,3-bis(4-pyridyl)propane (bpp), 4,4′-bipyridine (4,4′-bpy), 1,10-phenanthroline (phen) or 2,2′-bipyridine (2,2′-bpy) as a secondary ligand. H₂IDPA is a luminous ligand with a large rigid π-conjugated system, and the solid-state luminescence properties of compounds 1–7 have been comparatively investigated. The results indicate that their luminescence properties have been enhanced compared to those of the free ligand, especially for compounds 2–7 which have been further regulated by N-donor ligands with a π-conjugated system. Compound 2 is a 2D layer structure, and its quantum yield (QY) is 39.80%, which is much higher than those of the H₂IDPA ligand (QY = 4.41%) and compound 1 (QY = 6.32%). From the viewpoint of crystal structure diversity and comparison, our results further demonstrate that ligands with a large π-conjugated system have a promotional effect on luminescence properties of coordination polymers.