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

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. The simulation finds that the structural modification of the pyrene molecules in the film is the main reason for the quenching effects. Result reveals that, in the vacuum environment, the distance between a pair of pyrene ring centers distributes from about 4 Å to 10 Å, and a large number of distances populate at 5.3 Å, which is a suitable distance for excimer emission. The introduction of nitrobenzene results in a decrease of the population of pyrene 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 nitrobenzene is 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 chain are also analyzed. All the expectations from the simulation studies are basically consistent with the experimental observations.