Sandwiched amines: A π‐conjugated polymer with carboxy groups self‐associates to form a racemic double helix. In contrast, with chiral amines it forms a unique one‐handed double helix, in which the strands sandwich pairs of chiral amines through cyclic hydrogen‐bonding networks (see picture). The chiral information of the amines is transferred to the polymer backbones with remarkable amplification of the helical chirality.

Self-recognition and self-discrimination within complex mixtures are of fundamental importance in biological systems, which entirely rely on the preprogrammed monomer sequences and homochirality of biological macromolecules. Here we report artificial chirality- and sequence-selective successive self-sorting of chiral dimeric strands bearing carboxylic acid or amidine groups joined by chiral amide linkers with different sequences through homo- and complementary-duplex formations. A mixture of carboxylic acid dimers linked by racemic-1,2-cyclohexane bis-amides with different amide sequences (NHCO or CONH) self-associate to form homoduplexes in a completely sequence-selective way, the structures of which are different from each other depending on the linker amide sequences. The further addition of an enantiopure amide-linked amidine dimer to a mixture of the racemic carboxylic acid dimers resulted in the formation of a single optically pure complementary duplex with a 100% diastereoselectivity and complete sequence specificity stabilized by the amidinium–carboxylate salt bridges, leading to the perfect chirality- and sequence-selective duplex formation.

Sandwiched amines: A π‐conjugated polymer with carboxy groups self‐associates to form a racemic double helix. In contrast, with chiral amines it forms a unique one‐handed double helix, in which the strands sandwich pairs of chiral amines through cyclic hydrogen‐bonding networks (see picture). The chiral information of the amines is transferred to the polymer backbones with remarkable amplification of the helical chirality.

An optically active, m-terphenyl-based p-conjugated polymer bearing carboxy groups was synthesized by the copolymerization of the diethynyl monomer bearing a carboxy group with (S,S)-2,5-bis(2-methylbutoxy)-1,4-dibromobenzene using Sonogashira reaction. The copolymer showed a weak circular dichroism (CD) in the main-chain chromophore region due to a homo-double helix formation with an excess helical handedness biased by the chiral alkoxy substituents through self-association. However, upon complexation with achiral amines, such as piperidine, the CD intensity of the polymer significantly increased resulting in the formation of a greater excess one-handed homo-double helix via hydrogen-bonded inclusion complexation with the achiral amines between each strand, leading to the amplification of the helicity. A preferredhanded homo-double helix was also induced in the polymer in the presence of nonracemic amines. The effect of the achiral and chiral amines on the homo-double helix formation was investigated by comparing the CD spectra of the polymer to those of its model dimer. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 990-999

Optically active amidine ((R)‐1) and achiral carboxylic acid (2) dimers with a m‐terphenyl backbone linked by a 1,4‐phenylene diacetylene unit form a double helix, (R)‐1⋅2, through complementary amidinium–carboxylate salt bridges in THF. Upon the addition of poor solvents, such as n‐hexane, the duplex forms an organogel as a result of supramolecular polymerization of the duplex by intermolecular rearrangement of the salt bridges. In sharp contrast, an analogous racemic duplex composed of achiral amidine residues and an optically active duplex linked by a shorter diacetylene unit with a higher binding affinity than that of (R)‐1⋅2 does not show any gelation. The supramolecular fluorescent gels exhibit reversible thermo‐ and chemoresponsive behavior. The chiroptical properties of the gels, the mechanism of gelation, and the amplification of helical chirality during the gelation of (R)‐1⋅2 in the absence and presence of its enantiomeric counterpart, (S)‐1⋅2, and a racemic duplex, consisting of achiral amidine and carboxylic acid dimers, were investigated by following changes in the absorption and circular dichroism spectra.