Multifunctional π-Expanded Macrocyclic Oligothiophene 6-Mers and Related Macrocyclic Oligomers

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• 作者：Masahiko Iyoda ; Keita Tanaka ; Hideyuki Shimizu ; Masashi Hasegawa ; Tohru Nishinaga ; Tomohiko Nishiuchi ; Yoshihito Kunugi ; Takayuki Ishida ; Hiroyuki Otani ; Hiroyasu Sato ; Koji Inukai ; Kazukuni Tahara ; Yoshito Tobe
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：February 12, 2014
• 年：2014
• 卷：136
• 期：6
• 页码：2389-2396
• 全文大小：509K
• ISSN：1520-5126

文摘

Multifunctional 蟺-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鈥揹ehydrobromination 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^鈥? and 1²⁺, 2^鈥? and 2²⁺, and 4^鈥? and 4²⁺, respectively. Although oligothiophene radical cations containing 尾,尾-disubstituted thiophenes usually do not form 蟺-dimers, 4^鈥? clearly formed a 蟺-dimer owing to its planar, round shape. As for the dications of 1, 2, and 4, 1²⁺, which has 34蟺-electrons, exhibited a large diatropic ring current effect, whereas 34蟺 dication 4²⁺ only showed a medium diatropic ring current effect. In contrast to 1²⁺ and 4²⁺, 52蟺 dication 2²⁺ had biradical cationic character instead of H眉ckel-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 掳C, whereas an amorphous film of 1 crystallized in the temperature range of 80鈥?3 掳C to form a lamellarly stacked microcrystalline film, which melted at 139 掳C. The polymorphism of 1 was applied to either fluorescence switching or switching of field effect transistor (FET) activity and electrical conductivity.