We explored the possibility of nanoscale mechanical manipulation and control of photophysical properties of conjugated polymer nanoparticles. We carried out a simultaneous atomic force microscopy (AFM) and fluorescence microspectroscopy study on single nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene). The nanoparticles are prepared by a reprecipitation method and have an average height of 27 nm, and their emission is dominated by the well-ordered β-phase conformation. Fluorescence polarization anisotropy and numerical simulations show that each particle contains at least three partly oriented straight β-phase segments surrounded by amorphous glass-phase polyfluorene chains. In the simultaneous experiments, an AFM tip was used to apply external force on a single nanoparticle, and a confocal fluorescence microscope was used to monitor in real time the resulting changes in the fluorescence intensity and spectra. In a nitrogen atmosphere, weak to moderate force of up to 1 μN acts mainly on the glass-phase polyfluorene chains by forming quenchers that cause an efficient and reversible fluorescence decrease, whereas the β-phase segments stay unaffected. A higher force of 5 μN, on the contrary, breaks the β-phase segments into multiple glass-phase segments, causing a net increase in fluorescence intensity. Under ambient air conditions, even a moderate force of 1 μN strongly accelerates the degradation of the nanoparticle by preferably photobleaching the β-phase and partially transforming it into the glass phase. These results will contribute to the fundamental knowledge on the relationship between photophysical and structural properties of polyfluorene nanostructures, and will also provide important feedback for potential applications of such nanostructures in flexible optoelectronic devices.

中文翻译：

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机械诱导的共轭聚合物聚（9,9-二辛基芴）的单个纳米粒子中的构象变化，荧光调制和机械辅助的光降解。

我们探索了纳米级机械操作和控制共轭聚合物纳米粒子光物理性质的可能性。我们对共轭聚合物聚（9,9-二辛基芴）的单个纳米粒子进行了同时原子力显微镜（AFM）和荧光显微镜研究。纳米颗粒通过再沉淀方法制备，平均高度为27 nm，且其发射主要由排列良好的β相构象控制。荧光偏振各向异性和数值模拟表明，每个粒子包含至少三个部分定向的无定形玻璃相聚芴链包围的直β相链段。在同步实验中，使用AFM尖端对单个纳米颗粒施加外力，使用共聚焦荧光显微镜实时监测荧光强度和光谱的变化。在氮气氛中，高达1μN的弱到中度力主要通过形成淬灭剂作用在玻璃相聚芴链上，该淬灭剂引起有效和可逆的荧光降低，而β相链段则不受影响。相反，更高的5μN的力会将β相片段分裂成多个玻璃相片段，从而导致荧光强度净增加。在环境空气条件下，即使适度的1μN力也可以通过优选地对β相进行光漂白并将其部分转化为玻璃相而大大加速纳米颗粒的降解。