Protonation-induced rearrangements in Langmuir films and redox properties of Langmuir–Blodgett films of 2-(n-alkyl)fulleropyrrolidines

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• 作者：Noworyta ; Krzysztof ; Kutner ; Wlodzimierz ; Deviprasad ; Gollapalli R. ; D’ ; Souza ; Francis
• 关键词：2-(n-Alkyl)fulleropyrrolidines ; Langmuir films ; Langmuir&ndash ; Blodgett films ; Protonation equilibria ; Orientation change in film ; Electrochemical quartz crystal microbalance ; Simultaneous voltammetry and piezoelectric microgravimetry ; Redox properties of
• 刊名：Synthetic Metals
• 出版年：2002
• 出版时间：October 20, 2002
• 年：2002
• 卷：130
• 期：3
• 页码：221-227
• 全文大小：219 K

文摘

The effect of protonation of the pyrrolidine ring nitrogen of 2-(n-alkyl)fulleropyrrolidines, C₆₀pyr–C_m (m=4, 6, 8, 10 and 12), on the properties of the Langmuir and Langmuir–Blodgett (LB) films was investigated. The isotherms of both surface pressure (π) and surface potential change (ΔV) versus area per molecule (A) for the Langmuir films of C₆₀pyr–C_m were determined simultaneously. It was found that the longer the alkyl chain of the fulleropyrrolidine the larger is the film compressibility, κ, i.e., κ(C₆₀pyr–C₄)=(2.1±0.4)×10⁻²mmN⁻¹, κ(C₆₀pyr–C₈)=(3.5±0.4)×10⁻²mmN⁻¹ and κ(C₆₀pyr–C₁₂)=(4.1±0.5)×10⁻²mmN⁻¹, as expected for the liquid surface films. The values of surface area at zero surface pressure (A₁) differ in the range 0.6nm²molecule⁻¹ (for m=4–8) to 1.4nm²molecule⁻¹ (for m=10–12), indicating that all 2-(n-alkyl)fulleropyrrolidines form multilayer or aggregated films on neutral water subphase. However, acidification of the water subphase increases the A₁ values for all investigated fulleropyrrolidines up to ca. 1.9nm²molecule⁻¹, i.e., the value corresponding to maximum area occupied by a fulleropyrrolidine at horizontal orientation in a monolayer film. Apparently, 2-(n-alkyl)fulleropyrrolidinium cations formed at low pH are markedly de-aggregated in the films and their orientation is changed due to protonation of the pyrrolidine nitrogen. Similarly, however, less pronounced effects are observed if ionic strength of the subphase solution, I, is increased in the range 0≤I≤1.0moldm⁻³ NaCl. The Langmuir films formed on a water subphase were the most stable with respect to the LB transfer onto 5MHz Au–quartz crystal vibrators. Simultaneous cyclic voltammetry and piezoelectric microgravimetry at an electrochemical quartz crystal microbalance of these films showed at least two electroreductions where the fulleropyrrolidine mono anions were stable with respect to dissolution.