Synthesis And Properties Of Organic Photoelectric Materials Based On Carbazole-Substituted Fluorene Derivatives

As key materials of organic light-emitting diodes (OLEDs), organic electroluminescentmaterials have attracted much attention in today’s society. To get blue light-emittingmaterials with outstanding performance,13fluorene derivatives were designed,synthesized and characterized by1H NMR,13C NMR and elemental analysis, and theiroptical, electrochemical and thermal properties were studied.(1)6fluorene derivatives end-capped by carbazole were synthesized through Ullmanncoupling and Suzuki coupling reactions, which were2,7-bis{4-(carbazol-9-yl)phenyl}-9,9-dibutylfluorene (CPhF-a),2,7-bis{4-(carbazol-9-yl)phenyl}-9,9-dihexylfluorene (CPhF-b),2,7-bis{4-(carbazol-9-yl)phenyl}-9,9-dioctylfluorene (CPhF-c),2,7-bis{4-(carbazol-9-yl)-4-biphenyl-4-yl}-9,9-dibutylfluorene (CPh2F-a),2,7-bis{4-(carbazol-9-yl)-4-biphenyl-4-yl}-9,9-dihexylfluorene (CPh2F-b) and2,7-bis{4-(carbazol-9-yl)-4-biphenyl-4-yl}-9,9-dioctylfluorene (CPh2F-c). Their emission peak wavelengths are between393and411nmin dilute CH2Cl2, so they all emit blue-violet fluorescence. Their HOMO energy levels arebetween-5.50eV and-5.57eV, and they all possess hole-injection and transmissioncharacteristics. They have good thermal stability for their decomposition temperatures (Td)are all above365°C. The glass transition temperatures (Tg) of CPhF-a, CPh2F-a andCPh2F-b are130,161and111°C, respectively. The high Tgis conducive to the stabilityand working life of devices.(2) Three triphenylamine-disubstituted fluorene derivatives were synthesized throughSuzuki coupling reaction, which were2,7-bis(4-diphenylaminophenyl)-9,9-dibutylfluorene(DAF-a),2,7-bis(4-diphenylaminophenyl)-9,9-dihexylfluorene (DAF-b) and2,7-bis(4-diphenylaminophenyl)-9,9-dioctylfluorene (DAF-c). Their emission peak wavelengths indilute CH2Cl2are about428nm, so they emit blue fluorescence. Their HOMO energylevels are between-5.42eV and-5.47eV, so they possess better hole-injectioncharacteristics than CPhF(a-c). Their decomposition temperatures are354,413and375°C,respectively. The glass transition temperatures of DAF-a and DAF-b are97and66°C, andthat of DAF-c is below50°C.(3) Two dendritic small molecules2-(N,N-bis-4-bromophenyl4-aminophenyl)-7-{N-4-bromophenyl-N-4-(carbazol-9-yl)phenyl4-aminophenyl}-9,9-dihexylfluorene (CAF) and2,7-bis(N,N-bis-4-diphenylaminophenyl4-aminophenyl)-9,9-dihexylfluorene (AAF) weresynthesized based on compound DAF-b. The emission peak wavelengths of CAF and AAF in dilute CH2Cl2are436and530nm, so they emit blue and green fluorescences,respectively. Their HOMO energy levels are-5.51eV and-5.22eV, and the latter is closeto the work function of positive electrode (ITO), so it possesses excellent hole-injectionability. The decomposition temperatures of CAF and AAF are377and397°C, and the Tgof them are268and114°C, so the former is conducive to the stability and working life ofdevices better.(4) Two novel dicarbazolyl triphenylethylene-substituted fluorene derivatives DctF andDct2F were synthesized by Wittig-Honor and Suzuki coupling reactions. The emissionpeak wavelengths of their films are467nm and469nm, respectively. They both emit bluefluorescence, and have AIEE property. They possess good hole transmission characteristics,for their HOMO energy levels are-6.08eV and-5.87eV, respectively. They have highdecomposition temperatures (Td=409,418°C) and melting temperatures were notobserved, only DctF has glass transition temperature (Tg=105°C).The compounds synthesized in this paper have good solubility in common organicsolvent, so they can be deposited to forming films via a cheap solution process. Among thecompounds, CPhF-a, CPh2F-a, CPh2F-b, CAF, DctF and Dct2F are blue-light emittingmaterials with good thermal stability. Specially, DctF and Dct2F have AIEE property, andtheir films emit high fluorescence. Therefore, the six electroluminescent materials arehopeful to be used as hole-transporting and blue light-emitting materials in OLEDs.