Polarity effects on the photophysics of dendrimers with an oligophenylenevinylene core and peripheral fullerene units.
Polarity effects on the photophysics of dendrimers with an oligophenylenevinylene core and peripheral fullerene units.
复制标题
极性对具有低聚亚苯基亚乙烯基核心和外围富勒烯单元的树枝状聚合物的光物理学的影响。
DOI：
10.1002/chem.200400157
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
J. Nierengarten
中科院分区：
文献类型：
--
作者：
M. Gutiérrez;G. Accorsi;P. Masson;N. Armaroli;J. Nierengarten
高可溶性的树枝状分支与富勒烯亚基在外围和羧酸功能的焦点已通过收敛的方法制备。它们已被连接到一个oligophenylenevinylene（OPV）的核心轴承两个醇功能产生树枝状聚合物与两个，四个或八个外围C60基团。它们的物理化学性质已在极性增加的溶剂中进行了系统的研究，即甲苯，二氯甲烷和苯甲腈。超快OPV-->C60单线态能量转移发生在整个系列的树枝状聚合物，无论溶剂。热力学允许富勒烯单重态的电子转移在CH 2Cl 2和苯甲腈中进行，但在非极性甲苯中不允许。对于一个给定的溶剂，电子转移的程度，信号的富勒烯荧光猝灭，是不相同的沿着系列，尽管事实上，相同的电子转移伴侣存在。通过增加树枝状聚合物尺寸，由于树枝状分支隔离中心OPV核，电子转移逐渐变得更加困难，这阻碍了溶剂诱导的电荷分离对的稳定化。疏水树枝状聚合物的紧凑结构在较高极性的溶剂中是有利的。这些结构效应也能够合理化单线态氧敏化产率的意外趋势。
Highly soluble dendritic branches with fullerene subunits at the periphery and a carboxylic acid function at the focal point have been prepared by a convergent approach. They have been attached to an oligophenylenevinylene (OPV) core bearing two alcohol functions to yield dendrimers with two, four or eight peripheral C60 groups. Their photophysical properties have been systematically investigated in solvents of increasing polarity; that is, toluene, dichloromethane, and benzonitrile. Ultrafast OPV-->C60 singlet energy transfer takes place for the whole series of dendrimers, whatever the solvent. Electron transfer from the fullerene singlet is thermodynamically allowed in CH2Cl2 and benzonitrile, but not in apolar toluene. For a given solvent, the extent of electron transfer, signaled by the quenching of the fullerene fluorescence, is not the same along the series, despite the fact that identical electron transfer partners are present. By increasing the dendrimer size, electron transfer is progressively more difficult due to isolation of the central OPV core by the dendritic branches, which hampers solvent induced stabilization of charge separated couples. Compact structures of the hydrophobic dendrimers are favored in solvents of higher polarity. These structural effects are also able to rationalize the unexpected trends in singlet oxygen sensitization yields.