Luminescent lanthanide MOFs based on conjugated 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate ligand: syntheses, structures and photoluminescent properties

A family of novel lanthanide metal-organic frameworks (MOFs) with formula [Ln(2)(EBTC)(1.5)(CH3OH)4]center dot 6H(2)O [EBTC4- = 1,1'-ethynebenzene-3,3',5,5'-tetracarboxylate, Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8) and Dy (9)], have been synthesized via solvothermal reaction. All compounds are isostructural, crystallized in the monoclinic space group P2(1)/n, and show a three-dimensional (4,6)-connected network with Schlafli symbol of {310}. Photoluminescent measurements indicated that 1 and 7 emit the luminescence originating from the intraligand pi <-pi* transition, 2 shows the broadband emission due to allowed 4f-5d transitions, and 4-9 show the emission of typical lanthanide f-f transition via the ligand antenna effect in the solid state at ambient temperature. Interestingly, compounds 6 and 8 showed microsecond time-scale fluorescence lifetimes with 0.84 ms for 6 and 0.39 ms for 8, respectively. Such unique spectroscopy features may have applications in biomacromolecule research.