Shin-ichiro Sakurai

Double-stranded helical polymers consisting of complementary homopolymers.

Two complementary homopolymers of chiral amidines and achiral carboxylic acids with m-terphenyl-based backbones were synthesized by the copolymerization of a p-diiodobenzene derivative with the diethynyl monomers bearing a chiral amidine group and a carboxyl group using the Sonogashira reaction, respectively. Upon mixing in THF, the homopolymer strands assembled into a preferred-handed double helix through interstrand amidinium-carboxylate salt bridges, as evidenced by its absorption, circular dichroism, and IR spectra. In contrast, when mixed in less polar solvents, such as chloroform, the complementary strands kinetically formed an interpolymer complex with an imperfect double helical structure containing a randomly hybridized cross-linked structure, probably because of strong salt bridge formations. This primary complex was rearranged into the fully double helical structure by treatment with a strong acid followed by neutralization with an amine. High-resolution atomic force microscopy revealed the double-stranded helical structure and enabled the determination of the helical sense.

Self-Organizing Surface-Initiated Polymerization: Facile Access to Complex Functional Systems

Facile access to complex systems is crucial to generate the functional materials of the future. Herein, we report self-organizing surface-initiated polymerization (SOSIP) as a user-friendly method to create ordered as well as oriented functional systems on transparent oxide surfaces. In SOSIP, self-organization of monomers and ring-opening disulfide exchange polymerization are combined to ensure the controlled growth of the polymer from the surface. This approach provides rapid access to thick films with smooth, reactivatable surfaces and long-range order with few defects and high precision, including panchromatic photosystems with oriented four-component redox gradients. The activity of SOSIP architectures is clearly better than that of disordered controls.

A Chiral and Colorful Redox Switch: Enhanced π Acidity in Action

Deep blue diving: π Acidities up to a new record of −4.74 eV are made possible with simple sulfur redox chemistry (see scheme). This attractive method is able to generate exceptional electron affinities and anion transport efficiencies for applications in optoelectronic devices, medicinal chemistry, and anion–π catalysis.

Visualization of synthetic helical polymers by high-resolution atomic force microscopy

Direct observations of the helical structures of artificial helical polymers, such as helical polyacetylenes and polyisocyanides, by atomic force microscopy (AFM) are described in this tutorial review. The two-dimensional helix bundle formation of specific helical polymers on substrates under solvent vapor exposure permits us to determine their helical structures, including their helical pitch and handedness, at a molecular level by AFM in the tapping mode. The direct observation of supramolecular helical structures based on stereoregular poly(methyl methacrylate)s is also described.

Hierarchical Amplification of Macromolecular Helicity of Dynamic Helical Poly(phenylacetylene)s Composed of Chiral and Achiral Phenylacetylenes in Dilute Solution, Liquid Crystal, and Two-Dimensional Crystal

Optically active poly(phenylacetylene) copolymers consisting of optically active and achiral phenylacetylenes bearing L-alanine decyl esters (1L) and 2-aminoisobutylic acid decyl esters (Aib) as the pendant groups (poly(1L(m)-co-Aib(n))) with various compositions were synthesized by the copolymerization of the optically active 1L with achiral Aib using a rhodium catalyst, and their chiral amplification of the macromolecular helicity in a dilute solution, a lyotropic liquid crystalline (LC) state, and a two-dimensional (2D) crystal on the substrate was investigated by measuring the circular dichroism of the copolymers, mesoscopic cholesteric twist in the LC state (cholesteric helical pitch), and high-resolution atomic force microscopy (AFM) images of the self-assembled 2D helix-bundles of the copolymer chains. We found that the macromolecular helicity of poly(1L(m)-co-Aib(n))s could be hierarchically amplified in the order of the dilute solution, LC state, and 2D crystal. In sharp contrast, almost no chiral amplification of the macromolecular helicity was observed for the homopolymer mixtures of 1L and Aib in the LC state and 2D crystal on graphite.

Latticelike Smectic Liquid Crystal Phase in a Rigid-Rod Helical Polyisocyanide with Mesogenic Pendants

We report a unique macromolecule consisting of a rodlike helical polyisocyanide backbone with a narrow molecular weight distribution and rigid mesogenic chiral pendants linked via a flexible spacer that exhibits lyotropic nematic and latticelike new smectic (lat-Sm) liquid crystal phases at different concentrations. The unprecedented lat-Sm phase is associated with the smectic ordering of both the stiff polymer backbone and the rigid-rod side groups. A detailed investigation of the films using X-ray scattering and atomic force microscopy revealed a novel tilted smectic layer structure of the polymer backbone aligned perpendicular to the smectic layer of the mesogenic pendants, which arrange in an antiparallel overlapping interdigitated manner.

Toward polymerized artificial photosystems with supramolecular n/p-heterojunctions and antiparallel redox gradients

The evaluation of the importance of both ordered and oriented supramolecular architectures for artificial photosynthesis is a topic of current scientific concern. The objective of this study was to synthesize polymerizable zipper architectures and determine the impact of zipper polymerization on the performance of artificial photosystems. We report the synthesis of negatively and positively charged red naphthalenediimides that are equipped with short and long alkenyl tails and attached along oligophenylethynyl scaffolds. The presence of the short butenyl tails turns out to be tolerated by zipper assembly, whereas those of the longer undecenyl tails are not acceptable. Polymerization of the short-tailed zippers with olefin metathesis, using different catalysts in different solvents, is consistently found to reduce the photocurrent generation. These results suggest that polymerization indeed takes places but disturbs rather than stabilizes supramolecular zipper architectures, i.e., that supramolecular systems perform better than macromolecular architectures, at least in the context of this study. We conclude that constructive covalent capture of artificial photosystems should occur during and not after the self-organization of the artificial photosystems. This important conclusion calls for the invention of self-organizing polymer brushes for the synthesis of advanced organic photosystems.