Water-soluble cationic poly(p-phenyleneethynylene)s (PPEs):: Effects of acidity and ionic strength on optical behaviour
Water-soluble cationic poly(p-phenyleneethynylene)s (PPEs):: Effects of acidity and ionic strength on optical behaviour
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DOI：
10.1021/ma048717k
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发表时间：
2005-04-05
期刊：
影响因子：
5.5
通讯作者：
Huang, W
中科院分区：
文献类型：
--
作者：
Fan, QL;Zhou, Y;Huang, W
通过季铵化反应得到了三种阳离子聚芳醚类阳离子聚合物P1 '-P3 '，它们的侧链上分别带有叔氨基（P1）、叔氨基和三乙二醇甲基醚基交替存在（P2）和叔氨基和十二烷氧基交替存在（P3）。P1 '的季铵化度仅为45%，但仍表现出固有的水溶性。在pH < 13的酸性环境中，紫外-可见吸收最大值轻微蓝移（最大Δ λ（max）约为3 nm），在碱性环境中，吸收最大值明显红移（最大Δ λ（max）约为30 nm），发射最大值（最大Δ λ（max）约为20 nm），这是由于pH诱导共轭骨架平面化所致。当pH升高到14时，在较红的区域出现了一个新的吸收峰（λ（max）约为478 nm）和发射峰（λ（max）约为495 nm），荧光强度进一步显著降低，表明共轭主链发生了从平面化到链间聚集的构象变化。P1 '在酸性环境中的荧光增强和在碱性环境中的荧光减弱归因于侧链上未季铵化的叔氨基的氮原子上的非键合电子对的pH影响的猝灭能力和链间聚集。这种受pH影响的荧光强度可以通过加入pH < 10的盐来有效缓冲。虽然在中性环境中添加盐仅产生PPE共轭主链的平面化，但在碱性环境中添加盐显著促进链间聚集的形成。观察到阴离子猝灭剂Fe（CN）（6）（4-）对P1 '的放大猝灭，并且其K-sv在添加盐或将pH增加至14后显著增加，例如当[NaCl] = 0.1 M时，K-sv从pH = 7时的9.6 × 10（5）M-1增加至pH = 10时的7.7 × 10（6）M-1，这是由于形成延长的π-缀合。
Three cationic PPEs P1 '-P3 ' were obtained through quaternization of their neutral polymers, of which all side chains were respectively featured with a tertiary amino group (P1), an alternative tertiary amino and tri(ethylene glycol)methyl ether group (P2), and an alternative tertiary amino and dodecyloxy group (P3). P1 ' showed intrinsic water-solubility although its quaternization degree was only 45%. Slightly blue-shifted UV-vis absorption maxima in an acidic environment (maximal Delta lambda(max) approximate to 3 nm) and obvious red-shifted absorption (maximal Delta lambda(max) approximate to 30 nm) and emission maxima (maximal Delta lambda(max) approximate to 20 nm) in an alkaline environment at pH < 13 are explained in terms of pH-induced planarization of the conjugated backbone. After the pH was increased to 14, a new absorption (lambda(max) approximate to 478 nm) and emission (lambda(max) approximate to 495 nm) peak appeared in the redder region and the fluorescence intensity further dramatically decreased, implying the occurrence of the conformational change from the planarization of conjugated backbone to the interchain aggregation. The fluorescence enhancement of P1 ' in an acidic environment and the fluorescence decrease of P1 ' in an alkaline environment are attributed to the pH-influenced quenching ability of the nonbonding electron pair on the nitrogen atom, which belongs to the unquaternized tertiary amino group on the side chain, and the interchain aggregation. Such pH-influenced fluorescence intensity can be efficiently buffered by adding salts at pH < 10. Although adding salts in a neutral environment only creates the planarization of PPE conjugated backbone, adding salts in an alkaline environment significantly promotes the formation of interchain aggregation. Amplified quenching of P1 ' by anionic quencher Fe(CN)(6)(4-) was observed and its K-sv increased significantly after adding salts or increasing pH to 14, for example from K-sv = 9.6 x 10(5) M-1 at pH = 7 to 7.7 x 10(6) M-1 at pH = 10 when [NaCl] = 0.1 M, due to the formation of elongated pi-conjugation.