A pair of optically pure triptycene derivatives ((R,R)- and (S,S)-3) containing fluorescent pyrene-based π-conjugated pendant groups attached through amide spacers were prepared via a resolution step using chiral high-performance liquid chromatography. Their absorption, circular dichroism, photoluminescence and circularly polarized luminescence (CPL) properties were investigated under various solution conditions. (R,R)- and (S,S)-3 exhibited clear solvent- and concentration-dependences of the optical and chiroptical properties as a result of the interconversion between molecularly dispersed and aggregate states. We also observed that (R,R)- and (S,S)-3 emitted left- and right-handed circularly polarized light, respectively, upon UV irradiation under aggregation conditions, and their dissymmetry factors were found to be greater than 1.0 × 10. Based on the contrasting result that almost no CPL signal appeared in the monomeric solution state, the resulting CPL was considered to arise from the supramolecular chirality induced in the hydrogen-bonded aggregate, wherein the pyrenyl pendants of 3 were most likely arranged in a preferred-handed twisting structure.
Chiral fluorescent sensors were designed and synthesized from naturally occurring optically active cellulose, in which a terthienyl moiety was used as a fluorescent signaling unit, and their chiral recognition abilities were investigated on the basis of an enantioselective fluorescence response to aromatic nitro compounds as quenchers. A cellulose phenylcarbamate derivative (Ce-1b) exhibited an apparent enantioselectivity for various types of aromatic nitro compounds containing either central or axial chirality. Considering the fact that a corresponding monosaccharide derivative showed almost no enantioselectivity, the chiral recognition ability of the cellulose-based fluorescence sensor is attributed to its regular higherorder structures, probably a one-handed helical conformation. The resolution ability of Ce-1b as a chiral stationary phase for high-performance liquid chromatography was basically higher than that of the previously reported cellulose tris( phenylcarbamate), revealing that the terthienyl-based pendant provides attractive chiral recognition sites along the helical backbone as well as the fluorescent functionality. † Electronic supplementary information (ESI) available. See
Phenylcarbamate derivatives of amylose and β-cyclodextrin show excellent chiral recognition when used as chiral stationary phases (CSPs) for high-performance liquid chromatography. To open up new possibilities of carbohydrate-based materials, we developed chiral fluorescent sensors based on amylose and β-cyclodextrin (Am-1b and CyD-1b, respectively) by attaching fluorescent π-conjugated units on their side chains. Their recognition abilities toward chiral analytes containing a nitrophenyl unit were evaluated by measuring the enantioselective fluorescence quenching behavior. Both sensors showed the same degree of enantioselective fluorescence response for various aromatic nitro compounds. However, in some cases, their enantioselectivities were different depending on the analytes. The difference in the chiral recognition abilities between Am-1b and CyD-1b seems to be based on the structural difference of their inherent backbones, that is, the one-handed helical structure and cyclic structure, respectively. The study on the resolution ability of the Am-1b-based CSP revealed that the terthienyl-based pendant of Am-1b provides not only a fluorescent functionality but also a different chiral recognition site from that of amylose tris(phenylcarbamate).
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