Yoshimitsu Itoh

A rational strategy for the realization of chain-growth supramolecular polymerization

Popping open one by one into polymers We rarely board airplanes by joining the back of a single well-ordered line. More often, we jostle around in one of several bulging crowds that merge haphazardly near the gate. Roughly speaking, these processes are analogous to the chain growth and step growth mechanisms of polymer assembly at the molecular level. Kang et al. present a strategy to link molecular building blocks through hydrogen bonding in accord with the well-controlled chain growth model. The molecules start out curled inward, as they engage in internal hydrogen bonding, until an initiator pulls one open; that molecule is then in the right conformation to pull a partner into the growing chain, poising it to pull in yet another, and so forth down the line. Science, this issue p. 646 An initiator directs assembly of monomers by pulling them open to engage in external rather than internal hydrogen bonding. Over the past decade, major progress in supramolecular polymerization has had a substantial effect on the design of functional soft materials. However, despite recent advances, most studies are still based on a preconceived notion that supramolecular polymerization follows a step-growth mechanism, which precludes control over chain length, sequence, and stereochemical structure. Here we report the realization of chain-growth polymerization by designing metastable monomers with a shape-promoted intramolecular hydrogen-bonding network. The monomers are conformationally restricted from spontaneous polymerization at ambient temperatures but begin to polymerize with characteristics typical of a living mechanism upon mixing with tailored initiators. The chain growth occurs stereoselectively and therefore enables optical resolution of a racemic monomer.

Modular synthesis of benzo[b]phosphole derivatives via BuLi-mediated cyclization of (o-alkynylphenyl)phosphine.

Treatment of an (o-alkynylphenyl)phosphine with a stoichiometric amount of BuLi effects a cyclization reaction to produce a 3-lithiobenzo[b]phosphole, which affords a variety of 3-substituted benzophospholes upon reaction with electrophiles. An example is given for the synthesis of a bis-benzo[b]phosphole, which can be further converted to the corresponding benzo[b]phosphole oxide possessing high electron affinity.

Photovoltaic Universal Joints: Ball‐and‐Socket Interfaces in Molecular Photovoltaic Cells

A new approach toward higher efficiency organic photovoltaic devices (OPVs) is described. Complementarity in shape between the donor (contorted hexabenzocoronene, see picture) and acceptor (buckminsterfullerene) molecules results in OPVs that perform surprisingly well. This exploitation of host-guest chemistry at the organic/organic interface demonstrates a new direction for OPV device design.

Columnarly Assembled Liquid-Crystalline Peptidic Macrocycles Unidirectionally Orientable over a Large Area by an Electric Field

Being inspired by naturally occurring peptidic macrocycles, we developed liquid-crystalline (LC) compounds 1 and 2 that are capable of self-assembling into hexagonal columnar mesophases over a wide temperature range that includes room temperature. Their bowl-shaped macrocyclic cores are conformationally robust because of the presence of internal H-bonds, while the columnar assembly is ensured by intermolecular H-bonding interactions involving the exocyclic amide units. When an electric field was applied to their LC films from a direction orthogonal to the film plane, the columns were oriented homeotropically over a large area.

Homochiral supramolecular polymerization of bowl-shaped chiral macrocycles in solution

Chiral monomers 1 and 2, carrying C4- and C3-symmetric bowl-shape peptidic macrocycle cores, respectively, undergo supramolecular polymerization in solution via van der Waals and hydrogen bonding interactions. Size-exclusion chromatographic studies, using UV and CD detectors, on the supramolecular copolymerization of their enantiomers demonstrated that these monomers are the first chiral macrocycles that polymerize enantioselectively with a strong preference for chiral self-sorting.

Cu-catalyzed trifluoromethylation of aryl iodides with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide

Summary The trifluoromethylation of aryl iodides catalyzed by copper(I) salt with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide and Zn dust was accomplished. The catalytic reactions proceeded under mild reaction conditions, providing the corresponding aromatic trifluoromethylated products in moderate to high yields. The advantage of this method is that additives such as metal fluoride (MF), which are indispensable to activate silyl groups for transmetallation in the corresponding reactions catalyzed by copper salt by using the Ruppert–Prakash reagents (CF3SiR3), are not required.

Theoretical Study on the Regioselectivity of Baeyer–Villiger Reaction of α-Me-, -F-, -CF3-Cyclohexanones

The origin of the regioselectivity of the Baeyer-Villiger reaction of α-Me-, -F-, and -CF(3)-cyclohexanones was investigated theoretically (MPWB1K/6-311++G**-PCM(CH(2)Cl(2))//MPWB1K/6-311G**-Onsager(CH(2)Cl(2))). Investigation of the energy profiles of the rearrangement step revealed the reality of the importance of conventional migratory aptitude based on the stabilization capability of partial positive charge generated during the migration step. We have divided the origin of the regioselectivity into two factors: (1) structural stability (steric repulsion, dipole interaction, etc.) and kinetic reactivity (energy barrier from the intermediate, i.e., cation stabilization capability). For α-CF(3)-cyclohexanone, the migration tendency was mostly dependent on the kinetic reactivity; CF(3) substitution greatly increased the energy barrier. Noteworthy is the orientation of the CF(3) group at the transition state. The CF(3) group possessed the axial orientation overcoming the 1,3-diaxial repulsion, probably because of the strong dipole interaction between the CF(3) group and the leaving acid moiety. Striking results in the case of α-F- and -Me-cyclohexanone were that no difference in the energy barriers by the substituents could be observed. Especially in the case of α-Me substitution, structural stability operates in determining the most stable transition state, which is in contrast to the conventional understanding of the migratory aptitude based on the ability to stabilize partial positive charge.

Electrophoretic Deposition for Cholesteric Liquid-Crystalline Devices with Memory and Modulation of Reflection Colors.

The first design strategy that allows both memorization and modulation of the liquid-crystalline reflection color is reported. Electrophoretic deposition of a tailored ionic chiral dopant is key to realizing this unprecedented function, which may pave the way for the development of full-color e-paper that can operate without the need of color filters.

Energetics of Baird aromaticity supported by inversion of photoexcited chiral [4n]annulene derivatives

For the concept of aromaticity, energetic quantification is crucial. However, this has been elusive for excited-state (Baird) aromaticity. Here we report our serendipitous discovery of two nonplanar thiophene-fused chiral [4n]annulenes Th4COTSaddle and Th6CDHScrew, which by computational analysis turned out to be a pair of molecules suitable for energetic quantification of Baird aromaticity. Their enantiomers were separable chromatographically but racemized thermally, enabling investigation of the ring inversion kinetics. In contrast to Th6CDHScrew, which inverts through a nonplanar transition state, the inversion of Th4COTSaddle, progressing through a planar transition state, was remarkably accelerated upon photoexcitation. As predicted by Baird’s theory, the planar conformation of Th4COTSaddle is stabilized in the photoexcited state, thereby enabling lower activation enthalpy than that in the ground state. The lowering of the activation enthalpy, i.e., the energetic impact of excited-state aromaticity, was quantified experimentally to be as high as 21–22 kcal mol–1.Baird’s rule applies to cyclic π-conjugated molecules in their excited state, yet a quantification of the involved energetics is elusive. Here, the authors show the ring inversion kinetics of two nonplanar and chiral [4n]annulenes to support Baird’s rule from an energetic point of view.

Exceptionally High Electric Double Layer Capacitances of Oligomeric Ionic Liquids

Electric double layer (EDL) capacitors are promising as next-generation energy accumulators if their capacitances and operation voltages are both high. However, only few electrolytes can simultaneously fulfill these two requisites. Here we report that an oligomeric ionic liquid such as IL4TFSI with four imidazolium ion units in its structure provides a wide electrochemical window of ∼5.0 V, similar to monomeric ionic liquids. Furthermore, electrochemical impedance measurements using Au working electrodes demonstrated that IL4TFSI exhibits an exceptionally high EDL capacitance of ∼66 μF/cm2, which is ∼6 times as high as those of monomeric ionic liquids so far reported. We also found that an EDL-based field effect transistor (FET) using IL4TFSI as a gate dielectric material and SrTiO3 as a channel material displays a very sharp transfer curve with an enhanced carrier accumulation capability of ∼64 μF/cm2, as determined by Hall-effect measurements.