Supramolecular Control On Optoelectronic Properties Of Meta-Polyfluorene And Its Derivatives

Films of π-conjugated polymers have received widespread attention for broad application in optoelectronic devices. Optoelectronic properties of conjugated polymer in the film, such as spectral shape, luminescence efficiency and carrier mobility, are mainly determined by the single molecule state and aggregation structure. The aggregation structure is relatively complicated, for it depends not only on molecular structure but also on processing of film fabrication. In this thesis, basing on the classic polyfluorene and its derivatives, we study the influence of supramolecular interaction on the aggregation structure and optoelectronic properties.Firstly, we begin with the origin of low-energy emission in meta-linked polymer poly(9,9’-spirobifluorene-3,6-diyl)(Ps F36). Because the spirobifluorene structure eliminates the fluorenone induced low-energy emission, and its spectra characteristics are consistent with the spectral characteristics of excimer which indicates low-energy emission in Ps F36 comes from excimer. Compare with para-linked polymers and its monomer, we find that meta-linkage and cis-conformation have amplification effect on excimer formation. Furthermore, we have found poor solvent induced the chain assemblies of Ps F36, where the excimer is effectively restrained.In meta-linked and para-linked copolymers, we achieved enhancement of carrier mobility and luminescence efficiency through supramolecular control. It is common law that organic conjugated polymers structure tends to be flat under the excited state and the charged state based on the repeating units for organic conjugated polymers are connected by a single bond. The flatter molecule structure could reduce energy dissipation when molecule adjusts its conformation under excited state and reorganization energy when charge transited. Basing on the theory above, we could achieve enhancement of both carrier mobility and luminescence efficiency. In meta-polyfluorene, we achieved enhanced pure violet emission when added with poor solvent. In meta-linked and para-linked copolymers, the significant redshift occurred in UV-vis spectra not in fluorescence spectra when added with poor solvent, which indicated molecular conformations are the same in the state after the poor solvent added and under excited. The hole mobility is enhanced by nearly an order in the corresponding hole-only devices.