Luminescent open metal sites within a microporous Eu(BTC) (see figure, BTC = benzene-1,3,5-tricarboxylate) metal-organic framework are used for binding and sensing small molecules. The small molecules, such as dimethyl formamide, acetone, and ethanol exhibit different enhancing and quenching effects on the luminescence intensity of Eu(BTC). These specific properties may allow the use of such frameworks as sensors for small molecules.