Influence of cyclodextrin size on fluorescence quenching in conjugated polyrotaxanes by methyl viologen in aqueous solution
作者:Francine E. Oddy、Sergio Brovelli、Matthew T. Stone、Eric J. F. Klotz、Franco Cacialli、Harry L. Anderson
DOI:10.1039/b821950h
日期:——
Poly(4,4′-diphenylenevinylene) rotaxanes and [2]rotaxanes with α-, β-, γ-cyclodextrin macrocycles were synthesised and their sensitivities to fluorescence quenching by methyl viologen in aqueous solution were determined, relative to uninsulated analogues. Stern–Volmer analysis revealed that the fluorescence quenching response of polyrotaxanes is strongly dependent on the diameter of the cyclodextrins. Polyrotaxanes, composed of the smaller diameter α- or β-cyclodextrins, are the least easily quenched, with Stern–Volmer constants about two orders of magnitude smaller than from the wider γ-cyclodextrin polyrotaxane and the uninsulated polymer. Time-resolved photoluminescence results demonstrate the crucial role of interchain aggregation on the sensitivity to fluorescence quenchers. The materials with the highest Stern–Volmer constants exhibit the most biexponential photoluminescence decay, which is indicative of aggregation, and the emission spectra of solutions containing methyl viologen resemble the early-time emission spectra (0–3 ns after excitation) of the unquenched samples. The results show that the threaded α-cyclodextrin is effective in preventing aggregation, and in hindering fluorescence quenching, even when only a small fraction of the conjugated polymer is encapsulated. This conclusion is relevant to the application of these materials in optoelectonic devices, such as light-emitting diodes, where it is essential to prevent luminescence quenching without hindering charge transport.
合成了具有 α-、β-、γ- 环糊精大环的聚(4,4′-二苯基乙烯)轮烷和[2]轮烷,并测定了它们相对于未绝缘类似物在水溶液中被甲基紫罗兰烯淬灭荧光的灵敏度。斯特恩-伏尔默分析表明,聚二十二烷的荧光淬灭响应与环糊精的直径密切相关。由直径较小的α-或β-环糊精组成的聚二十二烷最不容易淬灭,其斯特恩-沃尔默常数比直径较大的γ-环糊精聚二十二烷和未绝缘聚合物的斯特恩-沃尔默常数小两个数量级。时间分辨光致发光结果表明,链间聚集对荧光淬灭剂的敏感性起着至关重要的作用。具有最高斯特恩-伏尔默常数的材料表现出最多的双指数光致发光衰减,这表明存在聚集现象,而含有甲基紫精的溶液的发射光谱与未淬灭样品的早期发射光谱(激发后 0-3 毫微秒)相似。结果表明,即使只封装了一小部分共轭聚合物,带螺纹的 α-环糊精也能有效防止聚集和阻碍荧光淬灭。这一结论与这些材料在发光二极管等光电设备中的应用有关,在这些设备中,必须在不妨碍电荷传输的情况下防止发光淬灭。