Synthesis, structure, and luminescent properties of oligothiophene-containing metal–organic frameworks

Abstract

Metal–organic frameworks (MOFs) based on Zn and functionalized bithiophene dicarboxylic acids are reported, [Zn₂(L1)₂(DMA)₂·3 DMF]_n (1), [Zn(L2)(DMA)₂]_n (2), [Zn(L3)(bpe)_0.5]_n (3), [Zn(L1)(bpe)·2 DMF]_n (4), and [Zn₃(L2)₃(bpe)₂·4 DMF · H₂O]_n(5) (H₂L1 = 3,3′-diphenyl-2,2′-bithiophene-5,5′-dicarboxylic acid, H₂L2 = 3,3′-dihexyl-2,2′-bithiophene-5,5′-dicarboxylic acid, H₂L3 = 2,2′-bithiophene-5,5′-dicarboxylic acid, DMA = dimethylamine, DMF = N,N-dimethylformamide, bpe = trans-1,2-bis(4-pyridyl)ethylene). MOFs 1, 2, and 4 consist of 2-D 4-connected sheets while 3 and 5 are 3-D interpenetrated networks with pcu and (4,6)-connected seh topology, respectively. The emission spectra and lifetimes of 1–5 have been determined: 4 and 5 exhibit reduced emission relative to 1 and 2, respectively, attributed to energy transfer quenching by the bpe, whereas 3 does not exhibit a reduction in emission intensity. Solid state lifetime measurements of 1–5 show that the emission decays are similar to those of the constituent ligands.