双芘环荧光体Pyrene-diIL-Pyrene荧光特性的分子动力学研究

Molecular dynamics study on microstructure related optical properties of a pyrene-dilL-pyrene phosphor

采用分子动力学模拟方法研究双芘环荧光体Pyrene-diIL-Pyrene(PDP)在水和甲醇中荧光改变的机制。结果表明,平衡时(1)该荧光体当分子中的芘环中心间距小于6A时,芘环在甲醇中比在水中的排列无序;(2)最近邻芘环中心间距从约4.1A处移到了6.0A处,降低了芘分子形成芘激子的概率,进而表明该荧光体的激子辐射强度下降,该结果与实验结果完全吻合。为了进一步研究三硝基甲苯(TNT)对该荧光体在水和甲醇中光物理行为变化的影响,我们又模拟了当存在TNT时,该荧光体分别在水和甲醇中的情况。模拟表明,平衡时(1)由于分子的极性,致使TNT分子在水中的分布要比在甲醇中集中一些;(2)引入的TNT分子破坏了适合形成芘激子的距离,大多数芘分子趋向于和TNT分子发生作用而形成不发光的TNT-pyrene复合体,从而表明该荧光体的激子辐射在水中很快下降。分子动力学模拟结果与实验结果完全一致,即将TNT分别加入水和甲醇中时,该荧光体在水中的猝灭效率明显比甲醇中高。

Molecular dynamics（MD） simulations of fluorescent properties on pyrene-dilL-pyrene（PDP） phosphor in water and in methanol are carried out in this paper.The simulations show that,at equilibrium state,（1） the pyrene rings of the PDP phosphor molecules in methanol are more disordered within a ring-to-ring distance of 6 A than that in water;（2） the center-to-center distance of the neighboring pyrene ring pairs shifts from～4.1 A to～6.0 A clearly indicates a population decrease of pyrene excimers and thus reduces the excimer emission of the phosphor, which greatly supports our experimental results.By introducing nine trinitrotoluene（TNT） molecules in water and in methanol respectively, MD simulations reveal that（1） the concentration of TNT in water is higher than that in methanol due to its molecular polarization;（2） the inserting TNT molecules destroy the distance that is suitable for the formation of the pyrene excimer,and tend to form a TNT-pyrene complex with pyrene molecules.The dynamics results suggest a greater decrease of excimer emission of phosphor in water than that in methanol.The MD simulations are very consistent with our experimental observations that,after adding TNT into these two systems,the fluorescent quenching efficiency in water is much higher than that in the methanol.