Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

被引:16
作者
Paudel, K. [1 ]
Knoll, H. [1 ]
Chandrasekhar, M. [1 ]
Guha, S. [1 ]
机构
[1] Univ Missouri, Dept Phys & Astron, Columbia, MO 65211 USA
基金
美国国家科学基金会;
关键词
CONJUGATED MOLECULES; OPTICAL-PROPERTIES; MORPHOLOGY; PHOTOPHYSICS; BEHAVIOR; CHAINS;
D O I
10.1021/jp911778r
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
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 intrachain structures in PFs. Dioctyl-substituted PF (PF8) is characterized by different backbone conformations that depend upon the torsion angle between the monomers. 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 and studied as a function of pressure. The PL energies of the as-is and thermally annealed samples both red shift but at very different rates, and the difference between their pressure coefficients elucidates the role of the backbone torsional angle. This is further corroborated by density functional theoretical calculations of a fluorene oligomer, where the energy gap is calculated as a function of both the torsion angle as well as compression. The Raman peaks harden with increasing pressures; the intraring 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.
引用
收藏
页码:4680 / 4688
页数:9
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