Structural Requirements for Producing Solvent-Free Room Temperature Liquid Fullerenes

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• 作者：Tsuyoshi Michinobu ; Kensuke Okoshi ; Yoshihiko Murakami ; Kiyotaka Shigehara ; Katsuhiko Ariga ; Takashi Nakanishi
• 刊名：Langmuir
• 出版年：2013
• 出版时间：April 30, 2013
• 年：2013
• 卷：29
• 期：17
• 页码：5337-5344
• 全文大小：457K
• 年卷期：v.29,no.17(April 30, 2013)
• ISSN：1520-5827

文摘

A new class of solvent-free room temperature liquid fullerenes was synthesized by attaching a single substituent of 1,3,5-tris(alkyloxy)benzene unit to C₆₀ or C₇₀ under the Prato conditions. Although the C₆₀ monoadducts were single components after chromatographic purification, the C₇₀ monoadducts were isomeric mixtures due to the prolate spheroidal 蟺-chromophore. The alkyl chain length of the substituents significantly affected both melting points and rheological behavior of the fullerene derivatives. When the alkyl chains were short, the intermolecular 蟺鈥撓€ interactions of adjacent fullerene cores led to a melting point higher than room temperature. In contrast, in the case of exceedingly long alkyl chains, such as eicosyl (鈭扖₂₀H₄₁) and docosanyl (鈭扖₂₂H₄₅) groups, the van der Waals interactions among neighboring alkyl chains became dominant. Accordingly, only medium alkyl chain lengths could provide solvent-free fluidic fullerenes with low melting points. The rheological measurements of the liquid fullerenes at 25 掳C revealed their unique liquid characteristics; molecular-level friction (or viscosity) and nanometer-scale clustering were noticed. It is generally thought that alkyl chains serve as a stabilizer of the fullerene core units. Thus, a longer chain or higher plasticity of the stabilizers would promote the disturbance of the core鈥揷ore interactions. It was indeed shown that longer alkyl chains resulted in a lower fluid viscosity. It was also found that metastable solid phases were produced by the noticeable van der Waals interaction between the long alkyl chains especially when a symmetric C₆₀ core was adopted. This interesting finding enabled the comparison of electrochemical activities of the C₆₀ unit between the solvent-free liquid and metastable solid form, which revealed a superior electrochemical activity in the liquid state.