Synthesis And Property Of Blue Light-Emitting Materials With D-π-A Structure

Organic optoelectronic materials play an important role in organic light-emitting diodes(OLED). The luminescence property and lifetime of OLED devices are determined by the structures and characteristics of organic optoelectronic materials. Thus, design and synthesis of novel organic optoelectronic materials with excellent properties is important to obtain high performance OLED devices. In the field of full-color displays and solid-state lighting of OLEDs, especially white OLED, it is made up of three basic color including red, green, blue or blue, orange. However, compared with red and green light-emitting materials, blue light-emitting materials need much higher excitation energy, inducing the energy transfer and insufficient chromaticity. So highly efficient and stable blue light-emitting materials are the bottleneck of full-color OLED. It requires some strategies and thoughts to design and synthesize blue light-emitting materials. Fluorene derivatives and anthracene derivatives with specific steric configurations have been attracting much attention as an organic functional material with specific physical properties. This thesis focuses on the design, synthesis of novel fluorene derivatives and anthracene derivatives and their applications in OLED. The main results in this thesis are as follows:Firstly, fluorene derivatives FI with acetylene moieties was successfully designed and synthesized for blue emitters in non-doped OLEDs. The optical properties of FI were characterized by UV-vis absorption, photoluminescence(PL) and electroluminescence(EL)spectra. The thermal properties was determined by DSC and TGA, their HOMO、LUMO energy were calculated by cyclic voltammetry(CV). The organic light-emitting diodes were fabricated with the structure of ITO/PEDOT: PSS(30 nm)/FI(20 nm)/TPBi(40 nm)/Li F(1nm)/Al(100 nm), which exhibited a maximum current efficiency of 1.52 cd·A-1, the power efficiency was 0.63 lm·W-1 as well as a blue emission with CIE coordinates of(0.25, 0.17).Our results provide a way to design and synthesize blue emitter based on fluorene derivatives for solution-processed OLEDs.Secondly, anthracene derivatives DTPAAN and DTPABAN with triphenylamine moieties were successfully designed and synthesized. The optical properties of DTPAAN and DTPABAN were characterized by UV-vis absorption, PL and EL spectra. The thermal properties were determined by differential scanning calorimetry(DSC) and thermogravimetry analysis(TGA). The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) energy were calculated by CV. The results show that they have good thermal stability with decomposition temperature of 378 ℃ and390 ℃, respectively. The energy band gaps of the DTPAAN and DTPABAN were estimated by the UV-vis spectrum with more than 3.0 e V, indicating they meet the requirements of blue-emitting materials. No obvious changes were observed in the emission peak in the film state for the substitution of a anthracene for a bianthracene. This phenomenon should beattributed to the twisted equilibrium conformation of the twisted internal charge transfer(TICT) state results in low fluorescence transition moments, because the TICT-state always adjusts the dihedral angle between the two anthracene planes by the torsional relaxation to accommodate with the change of the surrounding medium polarity. The twisted geometry of DTPABAN could efficiently prevent recrystallization in the film due to the large torsional stresses, which can induce the formation of either an exciplex or excimer. Thus, these materials were good candidate for fluorescence blue-emitting materials.Thirdly, spirobifluorenes derivatives DTPAAN-SF with symmetrical triphenylamine moieties and anthracene moiety was successfully designed and synthesized. Triphenylamine moieties were linked by anthracene moiety at C-2, C-7 of spirobifluorenes, which improved the speed of the hole transporting. The optical properties of DTPAANSF were characterized by UV-vis absorption, PL and EL spectra. The thermal properties were determined by DSC and TGA, their HOMO, LUMO energy were calculated by CV. The results show that it shows a good thermal stability with decomposition temperature of 505 ℃.The energy band gap of DTPAAN and DTPABAN were more than 3.0 e V, indicating they meet the requirements of blue-emitting materials.