Dual-Emission from a Single-Phase Eu–Ag Metal–Organic Framework: An Alternative Way to Get White-Light Phosphor

A new bifunctional NTB (tris(benzimidazol-2-ylmethyl)amine)-type ligand incorporating coordination discriminable tripodal benzimidazolyl and monodentate pyridyl groups, tris((pyridin-3-ylmethyl)benzoimidazol-2-ylmethyl)amine (3-TPyMNTB), has been prepared to assemble 4d–4f heterometallic three-dimensional metal–organic frameworks (MOFs) in a stepwise route: (1) direct reaction of 3-TPyMNTB with Ln(ClO4)3 affords monomeric complexes [Eu(3-TPyMNTB)2](ClO4)3·2.5MeCN (1-Eu) and [Gd(3-TPyMNTB)2](ClO4)3·2MeCN·2CHCl3 (1-Gd), and (2) assembly of the precursors 1-Eu and 1-Gd with AgClO4 gives rise to infinite MOFs [EuAg3(3-TPyMNTB)2(H2O)(MeCN)](ClO4)6·4MeCN (2-Eu-Ag) and [GdAg3(3-TPyMNTB)2(H2O)(MeCN)](ClO4)6·4MeCN (2-Gd-Ag), respectively. In monomer 1-Eu, the ligand shows an antenna effect to transfer absorbed energy to Eu3+ center to emit characteristic red luminescence, while in 4d–4f heterometallic MOF 2-Eu-Ag, the ligand centered emission is resensitized by Ag+ ions to generate dual emissions, coming up with the direct white-light emission from a single crystal. The detailed photoluminescent study has been carried out in both solid state and solution to elucidate the emission nature.