The Research On The Energy Transfer Properties In Single Conjugated Polymer Molecules

Conjugated polymers represent a class of new organic materials with optical and electrical properties.It is similar to inorganic semiconductors and have the advantages of high photoelectric conversion efficiency,excellent electrical transport properties and plasticity.Conjugated polymers have become a research of interest in physics,chemistry and material science and have broad application in organic optoelectronic devices particularly.The study of the effect of conformation of conjugated polymer on its energy transfer properties is of great significance for the application of polymers in organic photoelectric devices.The photophysical properties of conjugated polymer depend on the conjugated units it contains.Each unit appears as a single chromophore due to the delocalization of the ? electrons in the conjugated unit.Due to the disorder of the structure of the conjugated polymer material,the microscopic photophysical properties of polymers are extremely complicated.The traditional ensemble level measurement only yields average information,which immerges the role of conformation of conjugated polymers on their energy transfer dynamics in the micro-environment.The study of conformation and energy transfer properties of conjugated polymers at the single molecule level has become an important research area in materials science.Single-molecule optical detection eliminates the ensemble averaging.The measurement of the photophysical properties of individual conjugated polymer molecules reveals the conformational change and energy transfer characteristics of the polymer in the micro-environment,providing important insights into the photoelectric properties of conjugated polymers and their applications.In this thesis,we used single molecule spectroscopy to measure the photophysical properties and energy transfer dynamics of single conjugated polymers with different conformations.The main contents of this paper include:(1)The basic photophysical properties of single conjugated polymer molecules including fluorescence spectra,photoblinking,fluorescence polarization and fluorescence lifetime were measured by using confocal scanning microscopy and time-resolved single-photon counting techniques.(2)Single conjugated polymer molecule samples were prepared using different solvents and verified by using atomic force microscopy.Then the fluorescence trajectories of single conjugated polymer molecules with different conformations were measured based on confocal scanning microscopy.A model for the effect of conformation on the photoproperties of single conjugated polymer molecules was proposed.(3)The three-dimensional orientation characteristics of the transition dipole moment of single conjugated polymer molecules were obtained based on wide-field defocused imaging.By comparing the change of the transition dipole moment and fluorescence trajectories of single conjugated polymer molecules with different conformation,the spectroscopic units on single conjugated polymers chain were identified.The effect of the conformation of a single conjugated polymer chain on its photophysical properties and energy transfer properties were studied.It is found that intrachain energy transfer plays an important role in single conjugated polymer molecules with extended conformation,while interchain energy transfer is dominant in folded conformation.Statistical results show that about 35% of single conjugated polymer molecules with folded conformation have one emitting chromophore before photobleaching,while others have two or more.The innovation of this work lies in the use of defocused imaging for threedimensional tracking of the transition dipole moment of single conjugated polymer molecule,realizing the spectroscopic units of conjugated polymer chain and then analyzing the effect of the conformation on the energy transfer dynamics of single conjugated polymer molecules.