Small Structural Changes in the Alkyl Substituents of Macrocyclic π‐Extended Thiophene Oligomers Causes a Key Effect on Their Stacking and Functional Properties

Abstract

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.

Reduction of Ethynylenes to Vinylenes in a Macrocyclic π-Extended Thiophene Skeleton Under McMurry Coupling Conditions

“…As reported previously, dialdehyde 1 composed of three thienylene, two ethynylene, and two formyl groups was prepared by the Sonogashira coupling of 2,5-diiodothiophene with two equiv of 2-ethynylthiophene, followed by successive treatments with LDA and DMF . For the McMurry coupling, the reagent was prepared by treatment of TiCl 4 with activated zinc in THF at 0 °C, followed by heating under reflux.…”

“…To the suspension of the McMurry reagent (5 molar equiv to 1 ) was slowly added a solution of 1 in THF containing a small amount of pyridine at 63 °C to afford the dimeric product 5 in 16% yield with the corresponding trimeric product 6 in 1.3% yield (eq 1 in Scheme and entry 1 in Table ). Under similar reaction conditions with 10 equiv of the reagent at 66 °C, 7 produced 8 (35%) with higher cyclic oligomers 9 [ n = 1 (5.5%) and 2 (1.5%)] (eq 1 in Scheme and entry 2 in Table ). In contrast, the reaction of 1 with the reagent (10 equiv) at 66 °C led to 5 (12%), 2 (6%), and 3 (2%) with a trace amount of 6 (entry 3 in Table ).…”

“… a To TiCl 4 in THF was added activated zinc (2 equiv) at 0 °C, followed by heating under reflux. b ref . c ref . d 9 ( n = 1, 5.5%; n = 2, 1.5%). e With a trace amount of 6 . …”

“…As reported previously, macrocyclic π-extended thiophene hexamers composed of four thienylene–ethynylene and two thienylene–vinylene units exhibited multifunctional properties and changeable morphologies owing to nanophase separation between their inner and outer domains. , Therefore, 2–4 composed of two thienylene–ethynylene and four thienylene–vinylene units can be expected to show morphological changes along with variable functional properties. It is well known that OFET properties are dependent on the film morphology of the organic π-electron system . Therefore, we measured morphological changes and OFET behavior of films of 2–4 .…”

Suitability of alkyne donor-π-donor-π-donor scaffolds for electrofluorochromic and electrochromic use

“…The distance for the identical intermolecular hetereoatomic contact of thiophene-alkyne counterparts of 1 was on average 3.58(3) Å. [52][53][54] The thiophenes formed columns along the a axis (Fig. 3C) owing to the supramolecular contacts.…”