利用hydrostatic pressure调控二辛基取代聚芴的分子间相互作用
Tuning intermolecular interactions in di-octyl substituted polyfluorene via hydrostatic pressure
摘要：
聚芴（PF）是一类独特的聚对苯撑基蓝光聚合物，具有有趣的结构-性能关系。官能化侧链的选择的轻微变化导致PF中链间和链内结构的显著差异。我们目前的光致发光（PL）和拉曼散射研究的体样品和薄膜的二辛基取代的PF（PF 8）在静水压力下。在1.9 GPa下对大块样品进行进一步热退火。样品的光致发光振动电子学以26 meV/GPa的平均速率发生红移。热退火的样品的特征在于在1.1 GPa和4.2 GPa下的至少两个相变，每个相变对于PL振动电子学具有不同的压力系数。黄-里斯因子，电子-声子相互作用的措施，被发现随着压力的增加，信号的电子态的更高的几何弛豫。拉曼峰随着压力的增加而变硬;在1600 cm $^{-1}$处的环内C-C伸缩频率具有7.2 cm $^{-1}$ /GPa的压力系数，并且在更高的压力下表现出不对称的线形，这是强电子-声子相互作用的特征。在高压下的光学性质的PF 8的进一步对比与那些支链侧链取代的PF。
英文摘要：
Polyfluorenes (PFs) represent a unique class of poly para-phenylene based blue-emitting polymers with intriguing structure-property relationships. Slight variations in the choice of functionalizing side chains result in dramatic differences in the inter- and intra-chain structures in PFs. We present photoluminescence (PL) and Raman scattering studies of bulk samples and thin films of dioctyl-substituted PF (PF8) under hydrostatic pressure. The bulk sample was further thermally annealed at 1.9 GPa. The PL vibronics of the as-is sample red-shift at an average rate of 26 meV/GPa. The thermally annealed sample is characterized by at least two phase transitions at 1.1 GPa and 4.2 GPa, each of which has a different pressure coefficient for PL vibronics. The Huang-Rhys factor, a measure of the electron-phonon interaction, is found to increase with increasing pressures signaling a higher geometric relaxation of the electronic states. The Raman peaks harden with increasing pressures; the intra-ring C-C stretch frequency at 1600 cm$^{-1}$ has a pressure coefficient of 7.2 cm$^{-1}$/GPa and exhibits asymmetric line shapes at higher pressures, characteristic of a strong electron-phonon interaction. The optical properties of PF8 under high pressure are further contrasted with those of a branched side chain substituted PF.
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