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The Influence of Alkyl-Chain Length on Beta-Phase Formation in Polyfluorenes

机译：烷基链长度对聚芴中β相形成的影响

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摘要

Di-n-alkyl substituted polyfluorenes with aikyl chain lengths of 6, 7, 8, 9, and 10 carbon atoms (PF6, PF7, PF8, PF9, and PF10) are studied in dilute solution in MCH using optical spectroscopy. Beta-phase is formed upon cooling in solutions (～ 7 μg mL~(-1)) of PF7, PF8, and PF9 only, which is observed as an equilibrium absorption peak at ～ 437 nm and strong changes in the emission spectra. Beta-phase is formed upon thermal cycling to low temperature in solutions (～7 μg mL~(-1)) of PF7, PF8, and PF9, which is observed as an equilibrium absorption peak at ～ 437 nm and strong changes in the emission spectra. Beta phase is found to occur more favorably in PF8 than in PF7 or PF9, which is attributed to a balance between two factors. The first is the dimer/aggregate formation efficiency, which is poorer for longer (more disordered) alkyl chain lengths, and the second is the Van der Waals bond energy available to overcome the steric repulsion and planarize the conjugated backbone, which is insufficient in the PF6 with a shorter alkyl chain. Beta phase formation is shown to be a result of aggregation, not a precursor to it. A tentative value of the energy required to planarize the fluorene backbone of (15.6 ±2.5) kJ mol~(-1) monomer is suggested. Excitation spectra of PF6, PF7, PF8, and PF9 in extremely dilute (～ 10 ng mL~(-1) solution show that beta phase can form reversibly in dilute solutions of PF7, PF8 and PF9, which is believed to be a result of chain collapse or well dispersed aggregates being present in solution from dilution of more concentrated solutions. PF7, PF8, and PF9 also form beta phase in thermally cycled solid films spin-cast from MCH. However, in the films the PF7 formed a larger fraction of beta phase than the PF9, in contrast to the case in solutions, because it is less likely that the close-packed chains in the solid state will allow the formation of planarized chains with the longer PF9 side chains.
机译：在MCH的稀溶液中，使用光谱学研究了烷基链长度为6、7、8、9和10个碳原子的二正烷基取代的聚芴（PF6，PF7，PF8，PF9和PF10）。仅在PF7，PF8和PF9的溶液（〜7μgmL〜（-1））中冷却时形成β相，观察到它是〜437 nm处的平衡吸收峰，并且发射光谱变化很大。在PF7，PF8和PF9的溶液（〜7μgmL〜（-1））中进行低温热循环后，形成β相，观察到它是〜437 nm处的平衡吸收峰，并且发射强度发生了强烈变化光谱。发现PF8中的β相比PF7或PF9中的β相更有利，这归因于两个因素之间的平衡。第一个是二聚体/聚集体的形成效率，对于更长的（更无序的）烷基链长度来说较差，第二个是可用来克服空间排斥力并使共轭主链平面化的范德华键能量，这在分子结构中是不够的。 PF6具有较短的烷基链。 Beta相的形成被证明是聚集的结果，而不是其先兆。建议将（15.6±2.5）kJ mol〜（-1）单体的芴骨架平面化所需的能量的暂定值。 PF6，PF7，PF8和PF9在极稀（〜10 ng mL〜（-1）溶液中）的激发光谱表明，在PF7，PF8和PF9稀溶液中，β相可以可逆地形成。稀释更浓的溶液导致溶液中出现链塌陷或分散良好的聚集体，PF7，PF8和PF9在由MCH旋铸的热循环固体薄膜中也形成β相，但在薄膜中PF7形成了较大比例的与溶液中的情况相反，β相比PF9中的相大，因为固态的紧密堆积链不太可能形成带有较长PF9侧链的平面化链。

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  • 来源
    《Advanced Functional Materials》 |2009年第1期|67-73|共7页
  • 作者

    Daniel W. Bright; Fernando B. Dias; Frank Galbrecht; Ulli Scherf; Andrew P. Monkman;

  • 作者单位

    Organic Electroactive Materials Group Department of Physics, University of Durham South Road, Durham, DH1 3LE (UK);

    Organic Electroactive Materials Group Department of Physics, University of Durham South Road, Durham, DH1 3LE (UK);

    Bergische Universitaet Wuppertal Institut fuer Polymertechnologie Makromolekulare Chemie Gauss-Str. 20, 42097 Wuppertal (Germany);

    Bergische Universitaet Wuppertal Institut fuer Polymertechnologie Makromolekulare Chemie Gauss-Str. 20, 42097 Wuppertal (Germany);

    Organic Electroactive Materials Group Department of Physics, University of Durham South Road, Durham, DH1 3LE (UK);

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