芘功能化单分子层荧光薄膜荧光猝灭机理的分子动力学研究

Molecular dynamics study on the reason of fluorescence quenching of a pyrene-functionalized fluorescent film

实验证明,芘功能化单分子层荧光薄膜的荧光能被溶液中的硝基苯显著猝灭,为了找到猝灭的根本原因,本文采用分子动力学模拟方法来研究猝灭的机理。模拟结果表明,该薄膜在真空环境中,一对芘环中心的距离分布在(4～10)(?)之间,且主要是在5.3(?)左右,该距离正适合于形成芘激子。当把硝基苯分子加入到该薄膜中时,我们发现芘分子在这一距离处的分布有所下降,表明硝基苯的加入减少了芘激子的数目,从而削弱了荧光的激子辐射。另外,该薄膜在真空的环境中,芘环趋于形成准共面结构,但是当加入硝基苯之后,这一准共面结构遭到破坏。进一步的研究表明,芘分子这一结构的改变主要是由于硝基苯分子插到了之前形成的共面的芘环之间。最后我们还分析了链的长度和方向的变化,结果表明硝基苯分子的加入不仅降低了链的弹性而且降低了长链排列的有序度。因此,芘功能化单分子层荧光薄膜中芘分子结构的改变是导致荧光猝灭的主要原因。

Experimentally, the fluorescent intensity of the pyrene-functionalized fluorescent film is reduced by introducing nitrobenzene, in order to fulfill the functional reason of this quenching effect, a molecular dynamics simulation is adopted in this paper. Result reveals that, in the vacuum environment, the distance between a pair of pyrene ring centers distributes from about 4 A to 10 A, and a large number of distances populate at 5.3 A, which is a suitable distance for excimer emission. The introduction of nitrobenzenes results in a decrease of the population ofpyrene molecules within that distance, indicating a decrease of excimer emission of the film. In addition, the pyrene molecule rings in the film prone to adopt quasi-coplanar structure in the vacuum, but less likely arrange into a coplanar structure when nitrobenzenes are introduced. Study clearly indicates that the structural changes are all caused by the insertion of the incoming nitrobenzene molecules into the previously coplanar pyrene rings. Finally, length and orientation of chains are also analysed. Results shows that the flexibility and order of chains are declined when nitrobenzenes are introduced. Therefore. the structural modification of the ovrene molecules in the film is the main reason for the auenching effect.