The Influence of Alkyl-Chain Length on Beta-Phase Formation in Polyfluorenes
The Influence of Alkyl-Chain Length on Beta-Phase Formation in Polyfluorenes
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DOI：
10.1002/adfm.200800313
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发表时间：
2009-01-09
影响因子：
19
通讯作者：
Monkman, Andrew P.
中科院分区：
文献类型：
--
作者：
Bright, Daniel W.;Dias, Fernando B.;Monkman, Andrew P.
使用光谱法在 MCH 稀溶液中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（类似于 7 μg mL(-1)）中冷却后形成 β 相，观察到在类似于 437 nm 的平衡吸收峰和发射光谱的强烈变化。 PF7、PF8和PF9的溶液（约7μg·mL(-1)）热循环至低温时形成β相，在约437 nm处观察到平衡吸收峰，发射光谱发生强烈变化。发现 PF8 中的 Beta 相比 PF7 或 PF9 中更容易发生，这是由于两个因素之间的平衡。第一个是二聚体形成效率，对于较长（更无序）的烷基链长度而言，该效率较差；第二个是可用于克服空间排斥并使共轭主链平坦化的范德华键能，这在具有较短烷基链的PF6中是不够的。 β 相的形成被证明是聚集的结果，而不是聚集的前体。建议平坦化 (15.6 +/- 2.5) kJ mol(-1) 单体的芴主链所需的能量暂定值。 PF6、PF7、PF8 和 PF9 在极稀溶液（类似于 10 ng mL(-1)）中的激发光谱表明，β 相在 PF7、PF8 和 PF9 的稀溶液中可逆形成，这被认为是由于稀释较浓溶液而导致链塌陷或溶液中存在良好分散的聚集体的结果。 PF7、PF8 和 PF9 也在 MCH 旋铸的热循环固体薄膜中形成 β 相。然而，与溶液中的情况相比，在薄膜中，PF7 形成的 β 相比例高于 PF9，因为固态的密堆积链不太可能形成具有较长 PF9 侧链的平面化链。
Di-n-alkyl substituted polyfluorenes with alkyl 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 (similar to 7 mu g mL(-1)) of PF7, PF8, and PF9 only, which is observed as an equilibrium absorption peak at similar to 437 nm and strong changes in the emission spectra. Beta-phase is formed upon thermal cycling to low temperature in solutions (similar to 7 mu g mL(-1)) of PF7, PF8, and PF9, which is observed as an equilibrium absorption peak at similar to 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 a re ate 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 (similar to 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.