Preparation And Self-Assembly Of Novel Fluorene-Based Conjugated Polymers And Nanoscale Luminescent Microspheres

Light-emitting polymers have received remarkable scientific and industrial attention in recent years, due to their merits such as low-cost solution processing, good thermal stability, flexibility, and so on. Their potential applications in large-area flat-panel displays have been widely recognized. Among these polymers, fluorene-based polymers are one kind of most promising blue-light-emitting materials for commercial applications due to their excellent properties such as high photoluminescence efficiency, good processability and thermal stability. In this work, a series of novel luminescent conjugated polymers based on fluorene and carbazole were thus designed and successfully synthesized. And the structures and photophysical properties of these polymers were investigated in detail by using various characterization techniques.Polyfluorene homopolymer (P1) and its carbazole derivatives (P2-P4) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography (GPC), ¹H NMR, ¹³C NMR, elemental analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA), UV-vis absorption, photoluminescence (PL) and cyclic voltammetry (CV) methods. The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties of the synthesized polymers has been investigated. The introduction of both carbazole and the hyperbranched structure increases the thermal and photoluminescence stability. The cyclic voltammetry shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer (P1). The electroluminescence (EL) devices fabricated by these polymers exhibit pure blue light-emitting with negligible low-energy emission bands, indicating that the presence of hyperbranched structure has a strong effect on the PLED performance. Thus, incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue-light-emitting conjugated polymers. And it is also possible to adjust the photophysical and other properties of light-emitting polymers by tailoring the amount of carbazole derivative incorporated into the polymers.Luminescent nanoparticles are widely used in biotechnology areas. And much research is mainly focused on the compounds of inorganic nanocrystals and polymers. But the toxicity of nanocrystals, which are usually the compounds of heavy metals, greatly limits their applications. Specified to conjugated polymers, more efforts have been paid to their applications in PLED devices, and their potential applications in other areas are surprisingly much scarce. In this work, the luminescent nanospheres based on conjugated polymers, polyfluorene, have been created and studied.A series of novel well-defined polyfluorene-based hybrid copolymers were prepared by using polyfluorene macroinitiators to initiate atom transfer radical polymerization (ATRP) ofγ-methacryloxypropyltrimethoxysilane (MPS). The chemical structures of the hydroxy-functionalized PF (PF-OH), PF macroinitiators (PF-Br) and polyfluorene-b-poly(γ-methacryloxypropyltrimethoxysilane) (PF-b-PMPS) block copolymers were confirmed by ¹H NMR. In aqueous solution, amphiphilic PF-b-PMPS block copolymers can self-assemble into micelles with PMPS as the core and PF as the shell. Base-catalyzed sol-gel process inside the PMPS cores results in the formation of PF-encapsulated silica hybrid core-shell nanospheres. Transmission electron microscopy (TEM) studies reveal the formation and morphologies of the densely grafted PF at the surfaces of silica cores. The effect of core-shell structure on the optical and electrochemical properties was also investigated in detail. It has been found that the luminescent properties of the original polymer (polyfluorene) are still remained in the core-shell microspheres. These kinds of luminescent nanoscale microspheres may find potential applications in bioanalysis, biomedical and light-emitting devices.The nanospheres of conjugated polymers were synthesized by emulsion polymerization based on Suzuki coupling reaction using Tween80 as surfactant. The formation of nanospheres with regular sphere shape prepared by this new method was confirmed by TEM observations. And most importantly, the optical studies indicated that these nanospheres still keep good luminescent properties of the original polymer (polyfluorene). This method to prepare polymer-based luminescent microspheres is suitable not only for homopolymer systems, but also for copolymer ones. That is, different kinds of monomers can be used to adjust the wavelength of luminescent nanospheres. Therefore, this is a simple and novel method to prepare luminescent nanospheres with conjugated polymers for wide and potential applications.