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

Masahiko Iyoda*, Keita Tanaka, Hideyuki Shimizu, Masashi Hasegawa, Tohru Nishinaga, Tomohiko Nishiuchi, Yoshihito Kunugi, Takayuki Ishida, Hiroyuki Otani, Hiroyasu Sato, Koji Inukai, Kazukuni Tahara, Tobe Yoshito

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

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 12+, 2•+ and 22+, and 4•+ and 42+, 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, 12+, which has 34π-electrons, exhibited a large diatropic ring current effect, whereas 34π dication 42+ only showed a medium diatropic ring current effect. In contrast to 12+ and 42+, 52π dication 22+ 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.

Original languageEnglish
Pages (from-to)2389-2396
Number of pages8
JournalJournal of the American Chemical Society
Volume136
Issue number6
DOIs
StatePublished - 12 Feb 2014

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