Wu Changfeng, McNeill Jason
Department of Chemistry and Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, SC 29634, USA.
Langmuir. 2008 Jun 3;24(11):5855-61. doi: 10.1021/la8000762. Epub 2008 May 7.
Highly fluorescent nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) with distinct phases were prepared, and their photophysical properties were studied by steady state and time-resolved fluorescence spectroscopy. An aqueous suspension of PFO nanoparticles prepared by a reprecipitation method was observed to exhibit spectroscopic characteristics consistent with the glassy phase of the polymer. We demonstrate that controlled addition of organic solvent leads to partial transformation of the disordered polymer chains into the planarized conformation (beta-phase), with the fractions of each component phase dependent on the amount of solvent added. Fluorescence spectroscopy of the PFO nanoparticles containing beta-phase indicates efficient energy transfer from the glassy-phase regions of the nanoparticles to the beta-phase regions. Salient features of the nanoparticles containing beta-phase include narrow, red-shifted fluorescence and increased fluorescence quantum yield as compared to the glassy-phase nanoparticles. Fluorescence lifetime measurements indicate that the increased quantum yield of the beta-phase PFO originates from a decrease in the nonradiative decay rate, with little change in the radiative rate. This decrease is likely due to exciton trapping by the beta-phase, which leads to a reduction in the energy transfer efficiency to quencher species present within the nanoparticle.
制备了具有不同相态的共轭聚合物聚（9,9-二辛基芴）（PFO）的高荧光纳米粒子，并通过稳态和时间分辨荧光光谱研究了它们的光物理性质。通过再沉淀法制备的PFO纳米粒子的水悬浮液表现出与聚合物玻璃态相一致的光谱特征。我们证明，可控地添加有机溶剂会导致无序聚合物链部分转变为平面化构象（β相），各组分相的比例取决于添加的溶剂量。含β相的PFO纳米粒子的荧光光谱表明，能量从纳米粒子的玻璃态区域有效地转移到了β相区域。与玻璃态纳米粒子相比，含β相的纳米粒子的显著特征包括窄的、红移的荧光以及增加的荧光量子产率。荧光寿命测量表明，β相PFO量子产率的增加源于非辐射衰减率的降低，而辐射率变化不大。这种降低可能是由于β相捕获激子，导致纳米粒子内存在的猝灭剂物种的能量转移效率降低。
