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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。
The experimental results show that the fluorescence of pyrene-functionalized monolayer fluorescent film is significantly quenched by nitrobenzene in solution. In order to find out the root cause of quenching, the molecular dynamics simulation method is used to study the quenching mechanism. The simulation results show that the distance between a pair of pyrene rings in a vacuum environment is between (4 ~ 10) Å and mainly around 5.3 (Å), which is suitable for the formation of pyrene excitons . When nitrobenzene molecules were added to the film, we found that the distribution of pyrene molecules at this distance decreased, indicating that the addition of nitrobenzene reduced the number of pyrene excitons and thus impaired fluorescence of exciton radiation . In addition, the pyrene ring tends to form a quasi-coplanar structure in a vacuum environment of the film, but this quasi-coplanar structure is destroyed when nitrobenzene is added. Further studies showed that the structure of the pyrene molecule is mainly due to the insertion of nitrobenzene molecules into the previously formed coplanar pyrene rings. Finally, we also analyze the length and direction of the chain changes, the results show that the addition of nitrobenzene molecules not only reduces the flexibility of the chain but also reduces the degree of orderly arrangement of long chains. Therefore, pyrene-functionalized monolayer fluorescent film in the pyrene molecular structure change is the main reason leading to fluorescence quenching.