Blue light emitting star-shaped oxadiazole and thiadiazoles stabilizing fluid columnar phase.

A low molecular weight organogelator containing 3,5-substituted-1,3,4-oxadiazole and tetrazole units was synthesized and characterized. This compound is only soluble in DMSO and forms a stable gel. The solution and gel exhibit a blue light emission. The gel was characterized by atomic force microscopy, field-emission scanning electron microscopy, ¹H NMR and fluorescence measurements. The gel to solution interconversion was reversible for many cycles of heating and cooling. The compound in solution exhibited a high selectivity for the detection of picric acid, a common explosive and water pollutant. Fluorimetric titration studies with nitro explosive compounds revealed that the emission of the compound was red shifted in response to the addition of picric acid, and exhibited a shifting of fluorescence from blue to green. Theoretical and experimental studies revealed that the sensing is due to the complexation of the picrate anion with the protonated fluorophore. The shifting of emission in response to picric acid in the visible region is ideal for the naked eye detection of explosives and therefore it is promising in comparison to the detection methods based on fluorescence quenching.

Since various helical supramolecular polymers became available, their application to molecular chirality recognition have been anticipated but not extensively studied. So far, only a few examples of chiral reactions have been reported, but none for chiral separation. Here, we report the application of a helical supramolecular polymer to the enantio-separation of chiral guest molecules. The monomer of this supramolecular polymer is the salt-pair of a dendritic carboxylic acid with an enantiopure amino alcohol. In an apolar solvent, this salt-pair stacks via hydrogen bonds to form a helical polymer. In conjunction with this carboxylic acid, various amino alcohols afford supramolecular polymers, whose helical handedness is determined by the stereochemistry of the amino alcohols. When two salts with the same chirality are mixed, they undergo copolymerization, while those with opposite chirality do not. Owing to this stereoselective copolymerizability, the helical supramolecular polymer could bias the enantiomeric composition of chiral amino alcohols.

Effect of the number of flexible peripheral tails on the self-assembly of star-shaped molecules.