Giant macrocycles composed of thiophene, acetylene, and ethylene units

Controllable synthesis of conjugated thio-phenylethyne-based compounds with different chain lengths

A series of compounds consisting of alternating thiophene and acetylene units were designed and synthesized. Some were applied as the semiconductor in FETs to show excellent performance. 2D-GIXRD was employed to study the molecular orientations.

Synthesis, structures, and photophysical properties of π-expanded oligothiophene 8-mers and their Saturn-like C₆₀ complexes

Two isomers of a multifunctional π-expanded macrocyclic oligothiophene 8-mer, E,E-1 and Z,Z-1, were synthesized using a McMurry coupling of a dialdehyde composed of four 2,5-thienylene and three ethynylene units under high dilution conditions. On the other hand, cyclo[8](2,5-thienylene-ethynylene) 2 was synthesized by intramolecular Sonogashira cyclization of ethynyl bromide 5. From STM measurements, both E,E-1 and Z,Z-1 formed self-assembled monolayers at the solid-liquid interface to produce porous networks, and from X-ray analyses of E,E-1 and 2, both compounds had a round shape with a honeycomb stacked structure. E,E-1 formed various fibrous polymorphs due to nanophase separation of the macrorings. E,E-1 and Z,Z-1 in solution exhibited photochromism upon irradiation with visible and UV light, respectively, and this photoisomerization was confirmed by using STM. Furthermore, amorphous films of Z,Z-1 and E,E-1 showed photoisomerization, although single crystals, fibers, and square tubes of E,E-1 remained unchanged under similar conditions. E,E-1 with a 12.5-14.7 Å inner cavity incorporated fullerene C60 in the cavity in solution and the solid state to produce a Saturn-like complex, whose structure was determined by X-ray analysis. 2 also formed a Saturn-like complex with C60 in the solid state. These Saturn-like complexes are stabilized by van der Waals interactions between the sulfur atoms of 8-mer and C60. The complexes exhibited charge-transfer interactions in the solid state. Like E,E-1, Saturn-like complex E,E-1⊃C60 formed small cube and fiber structures depending on the solvent used, whereas those of Saturn-like complex 2⊃C60 were limited due to the rigidity of the macroring of 2.

Multifunctional π-expanded macrocyclic oligothiophene 6-mers and related macrocyclic oligomers

Multifunctional π-expanded macrocyclic oligothiophene 6-mer 1, as well as 9- (2) and 12-mers (3), was synthesized using a McMurry coupling reaction as the key step. The 6-mer 1 was converted to cyclo[6](2,5-thienylene-ethynylene) (4) by using a bromination-dehydrobromination procedure. From X-ray analysis, the crystal structures of nonplanar 1 and round-shaped 2 and 4 were elucidated. STM showed that 4 formed a self-assembled monolayer at the liquid/solid interface to produce a hexagonal porous network. Chemical oxidation of 1, 2, and 4 with 1 and 2 equiv of Fe(ClO4)3 produced 1(•+) and 1(2+), 2(•+) and 2(2+), and 4(•+) and 4(2+), respectively. Although oligothiophene radical cations containing β,β-disubstituted thiophenes usually do not form π-dimers, 4(•+) clearly formed a π-dimer owing to its planar, round shape. As for the dications of 1, 2, and 4, 1(2+), which has 34π-electrons, exhibited a large diatropic ring current effect, whereas 34π dication 4(2+) only showed a medium diatropic ring current effect. In contrast to 1(2+) and 4(2+), 52π dication 2(2+) had biradical cationic character instead of Hückel-type cyclic conjugation. Interestingly, 6-mer 1 showed polymorphism and unusual melting point behavior due to the number of stable conformations in the solid state. Single crystals of 1 melted at 176 °C, whereas an amorphous film of 1 crystallized in the temperature range of 80-83 °C to form a lamellarly stacked microcrystalline film, which melted at 139 °C. The polymorphism of 1 was applied to either fluorescence switching or switching of field effect transistor (FET) activity and electrical conductivity.

Liquid crystalline and antinematic behavior of shape-persistent macrocycles from molecular-dynamics simulations

In this work we present a molecular-dynamics study of a coarse-grained (CG) model for a system of planar shape-persistent macrocycles (SPMs). SPMs are synthetic organic rigid macromolecules typically comprised of meta- and para-aromatics groups connected by acetylene and/or diacetylene units. In the CG model, each SPM is represented as a rigid hexagonal arrangement of 24 soft-repulsive spheres, resembling a large ring or hoop. The supramolecular arrangement of these macrocycles at high pressures is studied using N-P-T molecular-dynamics simulation both by expansion of an initial hexagonal lattice structure and also by compression of an isotropic phase. In both cases, systems under consideration exhibit an isotropic-smectic-A phase transition, which is detected by monitoring relevant order parameters and analyzing snapshots of equilibrium configurations. The smectic-A phase is unique; although the molecules form layers, the system presents antinematic order where the orientation of the molecular axes is perpendicular to the direction of the layers themselves. Due to their planar geometry, the SPM molecules would be expected to form columnar or nematic phases. On the contrary, these phases seem suppressed by a novel smectic-A phase, formed by the mutual interpenetration of the cycles. These results are a unique example of how molecular nonconvexity can, by itself, induce mesomorphism in anisotropic systems.