Near-Infrared Luminescence and Inner Filter Effects of Lanthanide Coordination Polymers with 1,2-Di(4-pyridyl)ethylene

Abstract

A series of 12 lanthanide coordination polymers was synthesized from anhydrous LnCl 3 and 1,2-di(4-pyridyl)ethylene (dpe) under solvothermal conditions in either thiazole (thz) or pyridine (py). The reactions yielded ∞ 1 [Ln 2 Cl 6 (dpe) 2 (thz) 4 ]·dpe with Ln = Ce ( 1 ), Nd ( 2 ), ∞ 1 [LnCl 3 (dpe)(py) 2 ]·(dpe/py) with Ln = Gd ( 3 ), Er ( 4 ), and ∞ 1 [LnCl 3 (dpe) (thz) 2 ](dpe/thz) with Ln = Sm ( 5 ), Gd ( 6 ), Tb ( 7 ), Dy ( 8 ), Er ( 9 ), Yb ( 10 ), as well as ∞ 1 [HoCl 3 (dpe)(thz) 2 ]·thz ( 11 ) and ∞ 2 [La 2 Cl 6 (dpe) 3 (py) 2 ]·dpe ( 12 ). One-dimensional coordination polymers (CPs) and a two-dimensional network of five different constitutions are formed by connection of LnCl 3 units via dpe molecules. As free ligand, dpe shows an excimer effect that is reduced in the coordination polymers. In addition, dipyridylethylene proves to be a suitable sensitizer for the photoluminescence of lanthanides in the near-infrared region (NIR) only. Thereby, dpe differs from the related ligand 1,2-di(4-pyridyl)ethane. For the compounds presented, four different luminescence effects were detected: luminescence based on fluorescence of the linker dpe is observed in the visible region, whereas ligand-sensitized 4f–4f NIR emission is dominating for trivalent Nd, Er, and Yb. The Er-containing CPs show an inner-filter effect of Er 3+, which is based on reabsorption of emission of dpe triggering the erbium NIR emission.