Three new macrocyclic π‐extended thiophene hexamers composed of four thienylene‐ethynylene and two thienylene‐vinylene units with or without four alkyl substituents have been synthesized. Despite similar shape‐persistent structures in solution, the alkyl substituents control the solid‐state structures and morphologies. The unsubstituted hexamer exhibited a planar conformation with a theoretically predicted structure in the solid state; however, the planar hexamer with four ethyl substituents formed a closely stacked columnar crystal structure to exhibit π‐π interactions. Interestingly, the hexamer with four butyl substituents adopted both planar and twisted conformations in the solid state, exhibiting polymorphism based on induced‐fit stacking of molecules. Thus, the butyl‐substituted hexamer produces a mixture of yellow, orange, and red single crystals from toluene/acetone, and X‐ray analysis revealed six different conformations. Consequently, the small structural difference in the macrocycles causes a key effect on their functional properties in the solid state, and their morphology governs electrical conductivity and organic field‐effect‐transistor activity. The polymorphism of the hexamers was applied to the switching of film morphology.

McMurry coupling is one of the most useful and convenient tools for the preparation of π-conjugated molecules. However, for the synthesis of strained macrocycles containing ethynylene linkages, reduction of ethynylene to vinylene linkage sometimes took place. Especially, for the synthesis of macrocyclic π-extended thiophene hexamers using McMurry coupling of dialdehyde 1 composed of three thienylene, two ethynylene, and two formyl groups, reduction of ethynylenes to vinylenes often takes place to produce unique products in a one-pot procedure, depending on very small steric and electronic effects such as reaction temperature, amounts of titanium reagent, and substituents of thiophene hexamers. The attractive structures and functional properties of reduced thiophene hexamers have been determined using X-ray analysis and OFET measurements.

A phenyl-substituted macrocyclic π-extended thiophene hexamer 1, composed of four thienylene-ethynylene and two thienylene-vinylene units, has a solid-state structure in which π−π, CH−π, and van der Waals interactions occur. Slow addition of acetone to a solution of 1 in CS 2 produces a yellow nanostructured fiber 1-A containing a 1:1.5:1 ratio of 1, acetone, and CS 2 . Over a 2 min period at 25 °C, 1-A gradually changes to an orange fiber 1-B containing a 1:0.5:1 ratio of 1, acetone, and CS 2 . On exposure to acetone vapor, 1-B regenerates 1-A (vapochromism), and removal of all solvents from 1-A and 1-B generates a red-orange fiber 1-C, which upon brief immersion in acetone/CS 2 produces 1-A. Furthermore, 1-C is converted to orange yellow fiber 1-D upon exposure to acetone vapor for 1 s at 25 °C. Analysis of the horizontal and vertical profiles of the X-ray diffraction (XRD) patterns shows that removal of solvent from 1-A reversibly creates 1-B in conjunction with a shape and size change along with arching.

Macrocyclic 10-mesityl-1,8-diphenylanthracene dimer 4 was synthesized by using the electron-transfer oxidation of Lipshutz cuprate derived from 1,8-bis(4-bromophenyl)-10-mesityl-anthracene 7 in moderate yield. This dimer 4 is a considerably fluorescent molecule (Φ 0.40) with high thermal, photo, and air stability. The X-ray analysis of 4 revealed a unique structure with a small inner cavity which can incorporate a small molecule or atom. H NMR spectra in solution and emission spectra of 4 in the solid state showed that copper(I) ion was incorporated to form a 1:1 complex 4·CuOTf, whereas silver(I) ion only weakly interacted with 4 under similar conditions.

The cover feature shows the columnar stacking of a macrocyclic π‐extended thiophene hexamer bearing four butyl groups. The red‐orange and yellow stools represent how this macrocycle adopts different conformations in the solid state and forms crystal polymorphs with varying colors that arise from the induced‐fit stacking of macrocycles. More details can be found in the Full Paper by M. Iyoda, M. Hasegawa, H. Otani, and co‐workers on page 694 in Issue 6, 2019 (DOI: 10.1002/cplu.201900062).

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