The photophysical properties of a julolidene-based molecular rotor
The photophysical properties of a julolidene-based molecular rotor
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DOI：
10.1039/b507165h
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发表时间：
2005-01-01
影响因子：
3.3
通讯作者：
Yu, CF
中科院分区：
文献类型：
--
作者：
Allen, BD;Benniston, AC;Yu, CF
9-二氰基乙烯基久洛尼定的物理性质对溶剂粘度敏感，但受极性变化的影响很小。在流体溶液中，第一激发单重态的寿命很短，三重态的形成不能用激光探测。灰光分解在77 K时，激发单重态的衰变被强烈激活，在玻璃基质中可以观察到微弱的磷光。变温H-1 NMR研究表明，该分子在溶液中发生缓慢的内旋转，其活化能约为1.25。35 kJ mol（-1）。这个过程不太可能解释流体溶液中发现的差的荧光量子产率。相反，认为目标化合物从激发单重态围绕二氰基乙烯基双键经历快速旋转。在室温下，在一系列线性醇中，旋转速率弱地取决于溶剂的粘度。这可能代表转子相对较小并且可以装入溶剂结构中的空腔中的事实。在甘油中，旋转速率对粘度影响更敏感，但在乙醇中观察到相当复杂的温度依赖性。在这里，该速率在高温下在玻璃基质和流体溶液中几乎是无活化的，但在中间温度下强烈活化。
The photophysical properties of 9-dicyanovinyljulolidine are sensitive to solvent viscosity but are little affected by changes in polarity. In fluid solution, the lifetime of the first-excited singlet state is very short and triplet state formation cannot be detected by laser. ash photolysis. Decay of the excited singlet state is strongly activated and weak phosphorescence can be observed in a glassy matrix at 77 K. Temperature dependent H-1 NMR studies indicate that the molecule undergoes slow internal rotation in solution, for which the activation energy has a value of ca. 35 kJ mol(-1). This process is unlikely to account for the poor fluorescence quantum yield found in fluid solution. Instead, it is considered that the target compound undergoes rapid rotation around the dicyanovinyl double bond from the excited singlet state. The rate of rotation depends weakly on the viscosity of the solvent in a range of linear alcohols at room temperature. This might represent the fact that the rotor is relatively small and can pack into cavities in the solvent structure. In glycerol, the rate of rotation is more sensitive to viscosity effects but a quite complex temperature dependence is observed in ethanol. Here, the rate is almost activationless in a glassy matrix and in fluid solution at high temperature but strongly activated at intermediate temperatures.