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

Metal-organic frameworks (MOFs) based on Zn and functionalized bithiophene dicarboxylic acids are reported, [Zn-2(L1)(2)(DMA)(2)center dot 3 DMF](n) (1), [Zn(L2)(DMA)(2)](n) (2), [Zn(L3)(bpe)(0.5)](n) (3), [Zn(L1)(bpe)center dot 2 DMF](n) (4), and [Zn-3(L2)(3)(bpe)(2)center dot 4 DMF center dot H2O](n)(5) (H(2)L1 = 3,3'-diphenyl-2,2'-bithiophene-5,5'-dicarboxylic acid, H(2)L2 = 3,3'-dihexyl-2,2'-bithiophene-5,5'-dicarboxylic acid, H(2)L3 = 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.