Preparation And Application Of New Types Of Alkynyl Fluorene Based Polymers

Polyfluorene is one of the most studied photoelectric materials, which has excellent photoluminescence and electroluminescence properties. Its emission wavelength could be tuned and controlled through the introduction of different types of doped groups in the main chain of polymers. And the emission region could be tuned from the blue region to the near infrared region. Compared with other photoelectric materials, the preparation process of polyfluorene is simple and efficient. And its biological toxicity is small. These features greatly promote the applications of polyfluorene on polymer light-emitting diodes (PLEDs), nonlinear optical (NLO), organic storage (OS), organic laser (OL) and high sensitivity of biological fluorescent probes, etc. Although the preparation and application of polyfluorene have been reported in many literatures, there’s much to be explored in the current research. First of all, stacking/dipole-dipole effect can be induced between chromophores, because this kind of compound is basically aromatic ring as the major structure with rigid backbone, which would lead to seriously fluorescent quenching in the solid film. In the second place, because of the poor photostability and thermostability, and the 9 position of fluorene can easily be oxidized to generate fluorenone in case of high temperature working environment, or longtime exposure to strong light irradiation. Finally, fluorene which could easily be modified donating electron group in the 9 position, and it is considered as a typical p type semiconductor material in that it has good ability of hole-transporting properties. There are few literatures about their electronic transmission performance.In regard to these problems,, a series of new type of alkynyl fluorene based polymers were prepared by Sonogashira or Heck coupling reaction in this work. Through the incorporation of bifunctional polyhedral oligomeric silsesquioxane (POSS) into the main chain of polymers, preparation of Pdots with reprecipitation techniques, and introduction of D-A (Donor-Acceptor) arrangement with cross-linked structure, the thermal stability, light physical-stability, electronic transmission properties, photoluminescence and electroluminescent properties of the polymers could effectively be improved. And then, we applied the as-prepared polymers were applied to fluorescent sensors for nitroaromatic explosive, electron-transporting material and PLEDs. This thesis mainly included three parts as below:(1) Carbazole unit was modified to 9 position of fluorene, and the oligomeric alkynyl fluorene (P1) was obtained from di-bromine fluorene monomer and di-alkynyl fluorene monomer via Sonogashira reaction. And a new regular bead polyfluorene (P2) with high regular structure was synthesized via Heck coupling reaction between P1 and diallyl polyhedral oligomeric silsesquioxanes (diallyl-POSS). The molecular weights and the conjugated lengths of P1 and P2 were well controlled to acquire good solubility and excellent optical property. The bead-type POSS based polymer was characterized by gel permeation chromatography (GPC), FT-IR,’H NMR and photoluminescence (PL) spectra. High Resolution Transmission Electron Microscopy (HRTEM) micrographs showed that most of the diallyl-POSS were uniformly nano-dispersed in the polymer matrix. Compared with P1, the POSS-based polyfluorene P2 exhibited not only a higher thermal stability, but also an improved photophysical property in solution and solid states. The strong stacking/dipole-dipole interaction between fluorescent groups in the polyfluorene could effectively be inhibited by the incorporation of diallyl-POSS. The experimental results indicate that the bi-functional POSS based light-emitting polymers with regular and high symmetrical structure could have great potential in optical materials and devices, such as OPV or PLED, etc.(2) The different emissions of alkynyl fluorene based polymers were acquired by the introduction of different narrow-band-gap benzothiadiazole monomers into the polymer backbones. Polymer quantum dots (Pdots) with the high quantum yields (QYs) and stability in water were obtained via reprecipitation technology and fluorescence resonance energy transfer (FRET). And then, a new rapid, sensitive, selective and portable fluorescence detection method for nitroaromatics based on polymer dots (Pdots), had been successfully developed not only in aqueous media but also in solid state with test strips. The fluorescence quenching rates were proportional to the concentrations of 2,4,6-trinitrophenol (TNP) in the range of 0.2-20.0μg/mL and p-nitrophenol (PNP) in the range of 0.05-6.0 μ g/mL, when Pdots were used as ratiometric fluorescent sensors in the aqueous solution. The 3σ limit of detection of PNP even reached 18.8 ng/mL. Compared with polymer-based detection for nitroaromatics in organic phase, the signal enhancement effect was firstly found when Pdots were used to detect nitroaromatics in aqueous phase. It was worth mentioning that Pdots/fiber fluorescent composite strip could get higher quantum yield than polymer/fiber fluorescent composite strip. It could also overcome the disadvantage of fluorescence quenching, which derived from the strong stacking/dipole-dipole interaction between fluorescent groups. And then, the mechanism of interaction between Pdots and nitroaromatics was revealed as the electron transfer phenomenon from the electron-rich chromophoric probe to the electron deficient nitroaromatics. The results indicated that Pdots-based detection was well suitable for on-site qualitative detection and quantitative analysis of nitroaromatics.(3) A series of new D-A type carbazole-alkynyl fluorene copolymer had been successfully synthesized via incorporation of benzothiazole unit, which was an electron-withdrawing group. At the same time, the uracil was modified on the 9 position of carbazole, and the cross-linked and supramolecular assembly films could be obtained via the self-complementary bonding of uracil between adjacent chains. The microstructures of supramolecular assembly films were further confirm by X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and variable-temperature FT IR absorption spectra. As electronic transmission (ET) materials, the semiconducting conjugated polymers (SCPs) demonstrated superior properties by means of fabricating electron-only devices with the configuration of ITO/ET (SCPs)/Ca/Al. Among them, fluorine-containing SCPs exhibited a much smaller threshold voltage (P4:4.6 V; P5:3.5V) and much higher electron mobilities (P4:1.87×10-4 [cm2 V-1 s-1]; P5:3.55×10-4 [cm2 V-1 s-1]) than Alq3 (6.2V; 1.21 ×10-5 [cm2 V-1 s-1]) based on SCLC measurements at electric field 0.4 MV/cm. Meanwhile, a significant enhancement for their luminescence properties was verified by the photoluminescence (PL) and electroluminescent (EL) spectra of cross-linked type SCPs, compared to non-cross-linked type SCPs. The fabricated polymer light-emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/EML (SCPs)/BCP/LiF/Al were able to emit the color from green to red with moderately low turn-on voltages. These results suggested that cross-linked D-A type SCPs films could become a potential candidate as a kind of multi-functional material applied on the field of electronic and photonic devices.