Ogranic Electroluminescent Materials Based On Triphenylamine-substituted Fluorene:Synthesis And Properties

Fluorene derivatives have emerged as very promising materials for blue emission due to their highly thermal stability,and high photoluminescence quantum yields in solution and in solid state.However,an obvious deficiency of fluorene derivatives concerns their tendency to form long-wavelength aggregates/excimers or keto defects in the solid state upon thermal annealing or device operation.Another intractable issue is the low highest occupied molecular orbital(HOMO)energy level,which leads to inefficient hole injection/transporting.Generally,the above-mentioned two aspects are major challenges in the development of fluorene materials.A series of fluorescent conjugated oligomers containing fluorene-triphenylamine structure was designed and synthesized.Their optical properties were investigated by UV-Vis spectroscopy and fluorescence spectrum,and no unwanted long wavelength emission was observed.The emission wavelength can be tuned by changing the electronegativity of the substituent group of triphenylamine derivatives.Cyclic voltammetry showed that the HOMOs of compounds were located between-5.05 to-5.52 eV.All these compounds had good electrochemical stability and hole transporting ability.Simultaneously,the spiro-skeleton molecules possessed high glass transition temperature(Tg ? 178 ?)and retained good morphological stability.The thermogravimetric curves of the compounds showed a thermal-decomposition temperature higher than 390?.A list of fluorene-triphenylamine derivatives containing an electron donor-acceptor(D-A)structure based on 9,9-diarylfluorene was designed and synthesized.Their optical properties were investigated by UV-Vis spectroscopy and photoluminescence(PL)techniques in solution as well as in the solid state.The maximum PL emission wavelengths of the compounds ranged from 430 nm to 530 nm and the relationship between emission properties and molecular structures was studied.The results revealed the existence of a charge transfer excited state in the molecules.Moreover,the PL properties of these compounds depended on the structure of the compound and also on the polarity of solvent.The molecular constitution of the compounds improved the hole-injection issue for fluorene-based materials because of the introduction of a triphenylamine group.Cyclic voltammetry showed that the HOMO energy level of the compounds was located between-5.24 to-5.50 eV and it can be tailored by changing the electronegativity of the substituent group.Moreover,the spiro-skeleton molecular structure lead to excellent thermal stability(Td?400?;Tg?192 ?).A general method for the synthesis of 9,9-diarylfluorene in which the 2,2',7,7'-position were asymmetrically or symmetrically substituted under mild reaction conditions was developed.Raw materials are commercial supported.Additionally,the yield was high by the method.All the compounds synthesized were investigated by UV-Vis absorption and fluorescence spectrum.The results showed all the products were high blue fluorescent.