The Synthesis Of Fluorene-based Polymer Containing Hydroxyethyl And Optical Characterization

Conjugated polymer generally refers to the polymer that having a conjugated πbond of a long-chain structure,this type of materials has excellent optical properties.In recent years, conjugated polymers has attracted widespread attention because oftheir potential applications in the field of organic electroluminescent devices,chemical and biological sensors, while polyfluorene and its derivatives have a highthermal and chemical stability and high fluorescence quantum yields in solution andsolid-state, therefore such materials have broad application prospects in the field oforganic electroluminescent devices. However, polyfluorene and its derivatives has arigid planar biphenyl unit, poor solubility, which largely limits the application of thefluorene. Since1997, researchers at home and abroad, conduct a lot of work to try toimprove the physical properties of the molecular structure by modifying the main andside chains.By now, the polyfluorene material is mainly concentrated in the structuralmodification on C (9). By introducing aromatic ring, aliphatic chain or other groupsas side chains, the viscosity and the solubility of polyfluorene in an organic solventcan be effectively improved, and the film forming properties of the materialprocessing are improved; Further more, in a certain temperature range to maintain themicrostructure of the polyfluorene stable, increase the steric hindrance of the sidechain to adjust the aggregation state of the material structure, prevent excitonquenching in the main chain of polymer passed, can improve the luminous efficiencyof the material; In addition, introducing the electron-rich or electron deficient group,can adjust the electrical properties of the material.The hydroxyl group is a water-soluble group, it can improve the solubility of thepolymer, increase the density of the electron cloud in the polymer main chain,enhance fluorescence quantum yield of the polymer, reduce band gap and oxidationpotential of the polymer, and adjust the properties of the polymer. In this study, a simple, economic and security of route was explored to synthesis （9,9-bis(hydroxyethyl)-2,7-dibromo-fluorene）, then through Suziki coupling reaction themonomer is reacted with other monomers such as fluorenyl borate andbenzothiadiazole obtaining the five conjugated polymer containing hydroxyl alkylchain. At last, a series of photoelectric properties of these five polycondensate arecarried out. The main work includes the following aspects:1．Fluorenyl is brominated to get2,7-dibromo-fluorene，and then introducedlong-chain alkyl functional group in the C（9）position. during the experiment,alkylated fluorene monomer, fluorenyl boric acid ester monomer, and9,9-bis(hydroxyethyl)-2,7-dibromo-fluorene are mainly prepared, then productstructure is characterized, and then the monomer purity is effective purificated.2．Five different mix of copolymers are synthesized through Suziki couplingreaction, the structure and molecular weight of the copolymers are characterized byNMR and gel chromatography. The obtained polymers are determined by nuclearmagnetic resonance to make sure the structure is consisted with designed structure,and the molecular weight and the molecular weight dispersion index of the polymersare calculated through datas from the gel chromatography. Molecular weightdistribution of the five kinds of polymers is moderate, ranging between1.4-3.2, whichis consistent with the traditional molecular weight of polymers synthesized throughSuzuki coupling reaction, having excellent mechanical properties and processability.Seen from thermal gravimetric analysis performed on the five polymers, the thermaldecomposition temperature is high, showing that the thermal stability of the polymeris preferred. The introduction of hydroxyl groups can also improve the solubility ofthe polymers in polar solvents, The polymer is soluble in common solvents, such astetrahydrofuran (THF), chloroform and toluene. PFOH has a good solubility indimethylsulfoxide (DMSO),which can achieve2mg/ml.This shows that theintroduction of hydroxyl groups improve the solubility of the polymers in polarsolvents.3．The test characterization of fluorescence spectroscopy, UV-visible absorptionspectroscopy and electrochemical cyclic voltammetry performed on the five polymers show that, peak intensity fluorescence spectra of the polymers is in THF solutionconcentration of0.02mg/ml. For emission peak of BT and DTBT units, theperformance of the fluorescence spectra of the thin-film state and solution state arealmost identical. A little inconsistency occurred in THF solution. This inconsistencysuggests that the increasing of molar ratio (monomer DTBT) enhances the conjugatedegrees of the polymer, and thus result in redshift of emission wavelength.From theabsorption and fluorescence spectra characterization of BT and DTBT unit incopolymer, BT and DTBT unit were successful introduced in the main chain ofpolymer, the content of the BT and DTBT unit significantly affect the UV-visibleabsorption and fluorescence spectra of polymer. There are two absorption peaks onUV-visible-absorption-spectrum of the polymer PFBTOH-1, PFBTOH-2,PFDTBTOH-1, PFDTBTOH-2,438nm and526nm absorption peak corresponding tothe absorption of BT and DTBT monomer, the narrow absorption peak intensityproportional gap between the proportion of the monomer, we have successfullyproved once again different ratios of monomer were introduced into the main chain ofthe polymer.