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Tetraarylated quinodimethanes, which are one of the overcrowded ethylenes, can adopt multiple conformations, such as folded, twisted, and other forms. However, it is difficult to obtain all of these conformations due to energy differences among them. To tackle this issue, we designed flexible polyaryl-substituted tetraazaanthraquinodimethanes (N(4)AQDs), in which a steric hindrance in the overcrowded fjord region was moderately reduced. As a result, X-ray analyses revealed that N(4)AQDs could adopt not only folded and twisted forms but also intermediate structures, e.g., planar and twisted-folded forms, in pseudopolymorphs. Since there is a large difference in the electronic configuration among conformers, the colour tone of crystals varied from yellow to red depending on the conformation of overcrowded N(4)AQDs. Notably, red to near-infrared emission was observed for the crystal containing twisted conformers. This is the first example of exceptionally flexible quinodimethanes with tunable photophysical properties and multi-chromic behaviour based on multiple conformations.

Tetraarylated quinodimethanes, which are one of the overcrowded ethylenes, can adopt multiple conformations, such as folded, twisted, and other forms. However, it is difficult to obtain all of these conformations due to energy differences among them. To tackle this issue, we designed flexible polyaryl-substituted tetraazaanthraquinodimethanes (N(4)AQDs), in which a steric hindrance in the overcrowded fjord region was moderately reduced. As a result, X-ray analyses revealed that N(4)AQDs could adopt not only folded and twisted forms but also intermediate structures, e.g., planar and twisted-folded forms, in pseudopolymorphs. Since there is a large difference in the electronic configuration among conformers, the colour tone of crystals varied from yellow to red depending on the conformation of overcrowded N(4)AQDs. Notably, red to near-infrared emission was observed for the crystal containing twisted conformers. This is the first example of exceptionally flexible quinodimethanes with tunable photophysical properties and multi-chromic behaviour based on multiple conformations.

Thermally switchable redox properties have been reported to be due to a change in the spin state of newly designed overcrowded ethylenes, which can adopt closed-shell folded and open-shell twisted forms. In this study, tetrathienylanthraquinodimethane derivatives were designed to be in thermal equilibrium between a more stable folded form and less stable but more donating twisted diradical in solution, so that the oxidation potential can be controlled by heating/cooling. This is the first example of a switching of redox properties based on a thermally equilibrated twisted diradical, which can be more readily oxidized to the twisted dication.

We demonstrated dynamic chirality based on assemblies of three achiral rods with a twisted macrocycle. The three-fold twisting of a macrocycle can lead to two different chiral forms with C-2- or D-3-symmetry. Through a transmission of chirality to each dynamic chiral form, a helical-sense preference was successfully induced.

We demonstrate so-called “chiral diversification”, which is a design strategy to create multiple chiral molecules through the assembly and double-bridging of achiral components. We used phenylacetylene macrocycles (PAMs) as an achiral element. In a molecule, two achiral rings of [6]PAM are stacked one above the other, or bound to each other mechanically. As an alternative, a single enlarged ring of [12] PAM was also assumed to be a doubled form of [6]PAM. In any case, one or two ring(s) are doublybridged by covalent bonds to exert chirality. Through intramolecular two-bond formation, these multiple chiral molecules were obtained as a set of products in one reaction. The dynamic chirality generated in molecules with either two helically-stacked rings of [6]PAM or a single helically-folded ring of [12]PAM was characterized by induced Cotton effects with the aid of an external chiral source. Thus, a chiral structure based on [12]PAM could be demonstrated as the first success. Alternatively, enantiomeric separation was achieved for molecules with two interlocked rings of [6]PAM to show remarkable chiroptical properties.

We synthesized molecular assemblies of a ring and rod that were covalently bound in a molecule. The bridged components were helically arranged in a threaded or unthreaded form to show unique chiroptical properties based on shape-persistent m-phenylacetylene rings with six, five and four units and phenylene-ethynylene rods.

On the basis of the intramolecular “core-shell strategy,” we designed dihydropyracylene with two spiro(dibenzocycloheptatriene) units, for which theoretical calculations predicted a very weak C–C bond with a bond length around 1.8 Å. This bond is expanded by the forced adoption of an eclipsed conformation and by angle strain through a “scissor effect.” The highly strained hydrocarbon was isolated as a thermally stable compound with no signs of diradical contribution because the weak C–C bond (core) is protected by the shape-persistent fused-ring structure (shell). A Raman shift corresponding to the C–C stretching vibration (587 cm−1) was very different from that for ethane (993 cm−1). The bond length determined by X-ray (1.806(2) Å) was greater than the shortest non-bonded intramolecular C…C contact (1.80(2) Å). The assumed limit for a C–C bond (1.803 Å) by supposing linear correlation between bond length and bond-dissociation energy for covalent bonding was proven to be invalid.

When two planes stacked one above the other are twisted, they provide a dynamic pair of helical conformations with (M)- or (P)-helicity. We designed a three-layer cyclophane that consists of two such dynamic pairs: the top and middle planes, and the middle and bottom planes. Hence, several global conformations could be created for the overall molecule, e.g., double-helical forms with a pair with the same helicity [(M, M) or (P, P)], and a meso-like form with a pair with a different helicity (M, P). These conformations dynamically interconvert to each other in solution. Chiroptical properties were given by the helical-sense preference of the double-helical forms, which was brought about through complexation with a chiral hydrogen-bonding guest. In terms of the conformational energy in a complexed state, when a desirable relationship between double-helical and meso-like forms was attained, complexation-induced circular dichroism was enhanced at elevated temperatures and decreased at lowered temperatures.

A tristerephthalamide host exhibited two helical geometries with (M)- and (P)- helicity, respectively, in terms of the twisting direction of a two-layer structure, and the helical preference switched upon complexation with a ditopic guest. In both uncomplexed and complexed states, the intramolecular transmission of chirality was responsible for the control of helicity.

A method for the stereoselective construction of the C8′–O–C6″ ether of nigricanoside-A, an antimitotic natural product from the green alga Avrainvillea nigricans, has been developed based on chirality-transferring Ireland–Claisen rearrangement. The method was successfully applied to the synthesis of simple models for the C20 lipid chain/galactosyl glycerol segment of the natural product.