Synthetic Chemical Systems Involving Self‐Catalytic Reactions of Helicene Oligomer Foldamers

Sawato, Tsukasa; Yamaguchi, Masahiko

doi:10.1002/cplu.202000489

Cited by 10 publications

(14 citation statements)

References 112 publications

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“…Thermal hysteresis in our previous studies generally started from high temperatures, in which the thermal hysteresis curve and equilibrium curve overlapped. [3][4][5] We have shown herein that middle-range stable thermal hysteresis can occur, which starts from intermediate states in the equilibrium curve (Figure 1a, red lines). The observation of middle-range thermal hysteresis significantly broadens the scope of thermal hysteresis.…”

Section: An Equilibrium Curve Was Determined In Different Experimentsmentioning

confidence: 64%

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Unstable and Stable Thermal Hysteresis Under Thermal Triangle Waves

2021

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A 1 : 1 mixture of aminomethylenehelicene (P)-tetramer with C 16 alkyl groups (P)-1-C 16 and (M)-pentamer (M)-2 in fluorobenzene forms hetero-double-helices, and the processes of formation and dissociation exhibit thermal hysteresis on cooling and heating. When thermal triangle waves with repeated cooling and heating cycles are applied, unstable thermal hysteresis appears, which becomes a stable thermal hysteresis after sufficient numbers of cycles. The phenomenon of middle-range stable thermal hysteresis is observed in this case. Properties of unstable and stable thermal hysteresis are examined under various thermal triangle waves.

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Section: An Equilibrium Curve Was Determined In Different Experimentsmentioning

confidence: 64%

“…Diverse mechanisms of thermal hysteresis can be considered. [3][4][5] For example, a reversible chemical reaction involving self-catalysis can exhibit thermal hysteresis, when the acceleration of reaction occurs during cooling or heating.…”

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confidence: 99%

Unstable and Stable Thermal Hysteresis Under Thermal Triangle Waves

2021

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“…Another type of thermal hysteresis involving reversible self-catalytic reaction 2 A + B 2 B , in which B catalyzes the reaction of 2 A to become B , can be considered . As the reaction proceeds, the concentration of B , which is a catalyst, increases and the reaction rate increases (Figure ).…”

Section: Thermal Hysteresis Involving Reversible Self-catalytic React...mentioning

confidence: 99%

Thermal Hysteresis Involving Reversible Self-Catalytic Reactions

Yamaguchi

2021

Acc. Chem. Res.

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Conspectus Hysteresis is ubiquitous in nature and biology. It appears in ferromagnetism, ferroelectrism, traffic congestion, river sedimentation, electronics, thermoresponses, cell division, differentiation, and apoptosis. Hysteresis phenomena are beyond equilibrium and involve nonlinear, bistable, time delay, and memory events, which are described in input/output profiles by different outputs during continuous decreases and increases in input intensity. Although hysteresis profiles in these phenomena appear similar, the mechanisms underlying them are complex, and their basic understanding is desired. In this Account, I describe thermal hysteresis caused by molecules dispersed in dilute solutions containing optically active helicene oligomers, which form homo- and heterodouble helices, the cooling and heating processes of which cause different structural changes with regard to their relative concentrations. Reversible self-catalytic reactions are involved in the formation of a double helix, which catalyzes its own formation. The reactions accelerate as they progress, in contrast to ordinary reactions, which exhibit monotonic retardation as they progress. Thermal hysteresis involving reversible self-catalytic reactions exhibits notable phenomena, when various cooling/heating inputs are applied during the reaction; these phenomena are shown herein with profiles of experimental results of Δε outputs obtained by circular dichroism (CD) plotted against temperature inputs. Thermal hysteresis is discussed in terms of (1) two states of the homodouble helix and a random coil involving one reversible self-catalytic reaction and (2) three states of enantiomeric heterodouble helices and a random coil involving two reversible self-catalytic reactions. Repeated cooling and heating processes provide the same stable thermal hysteresis loops, when the initial and final high-temperature states are under equilibrium, and nonloop and unstable thermal hysteresis appears when whole the systems are beyond equilibrium. Diverse thermal hysteresis loops are obtained under different temperature change conditions for different oligomers. The mechanism of thermal hysteresis involves different macroscopic mechanisms at a fixed temperature, when the relative concentrations of substrates/products and the reaction direction differ. Microscopic mechanisms, which are shown by energy diagrams, are fixed at a temperature irrespective of cooling or heating. A comparison of thermal hysteresis loops and equilibrium curves provides distances to the metastable states on the loops from equilibrium, and reactions occur from the metastable states toward equilibrium. Notable phenomena described herein include bistability, high sensitivity to small concentration changes, equilibrium crossing, three-state one-directional structural change caused by a single heating procedure, reaction shortcuts, the memory effect on thermal history, figure-eight thermal hysteresis, chemical oscillation, stable and unstable thermal hysteresis, double-helix formation only under ...

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“…Helicenes are a typical class of nonplanar PAHs with a helically twisted π-conjugated framework that consist of angularly fused aromatic units. [11][12][13][14][15][16] To date, a vast variety of helicenes 17,18 and multiple helicenes, [19][20][21][22][23] in which plural helicene moieties are fused together, and their analogues [24][25][26][27][28][29] have been prepared with great interest and applied to organic semiconducting materials, 14,15 spin filters, [30][31][32][33] and chiral functional materials for chiral recognition, 34,35 chiroptical switches, 36 asymmetric catalysis, [37][38][39][40] and circularly polarized luminescence (CPL). 41,42 In 2017, Tilley and coworkers reported a series of spiral-shaped PAHs with a helical cavity consisting of alternating angularly and linearly fused aromatic units arranged in a helical manner and classified them as "expanded helicenes" (I in Figure 1a).…”

Section: Introductionmentioning

confidence: 99%

Consecutively fused single‐, double‐, and triple‐expanded helicenes

et al. 2022

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We report the quantitative, chemoselective, and diastereospecific formation of the defect-free C-shaped single and S-and M-shaped consecutively fused doubleand triple-expanded homochiral helicenes (all-right (P) or all-left (M) handed), in which two and three expanded helicene subunits were exclusively fused together in a helically winding manner, respectively, through the trifluoroacetic acid-promoted intramolecular multistep cascade alkyne benzannulations of anthracene-based cyclization precursors composed of a large number of complicated dynamic stereoisomers due to axial chirality. The resulting racemic expanded helicenes were all separated into enantiomers by chiral chromatography and showed intense circular dichroism and circularly polarized luminescence (CPL) with the absorption and luminescence dissymmetry factors of up to 1.5 × 10 −2 and 0.94 × 10 −2 , respectively. Moreover, the triple-expanded helicene showed the highest CPL brightness (255 M −1 ⋅cm −1 ) among all the reported CPL-active carbo-and heterohelicenes and -helicenoids. The helicity inversion barriers remarkably increased with the increasing number of incorporated helicene subunits, and the racemization of the triple-expanded helicene was completely suppressed even at 80 • C, providing the first example of an optically active expanded helicene with a static helical chirality.

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Synthetic Chemical Systems Involving Self‐Catalytic Reactions of Helicene Oligomer Foldamers

Cited by 10 publications

References 112 publications

Unstable and Stable Thermal Hysteresis Under Thermal Triangle Waves

Unstable and Stable Thermal Hysteresis Under Thermal Triangle Waves

Thermal Hysteresis Involving Reversible Self-Catalytic Reactions

Consecutively fused single‐, double‐, and triple‐expanded helicenes

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