Copolyfluorenes Slightly Doped with Chromophores: Synthesis, Optoelectronic Properties and Applications in White-Light-Emitting Diodes

• Main Authors: Bar-Yuan Hsieh, 謝栢源
• Other Authors: Yun Chen
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/75514892640280465313

博士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === White organic light-emitting diodes (WOLEDs) have received considerable attention due to their potential application in solid-state lighting and in backlight for liquid crystal displays. Among these devices, white-light OLEDs based on semiconducting polymers (PLEDs) are of particular interest for their facile solution processability that allows spin-coating and printing methods to be utilized for the fabrication of large-area-display devices. Through color mixing method, white-light-emitting devices could be readily obtained. In this dissertation, we devoted to design and prepare new copolyfluorenes to be applied in white-light-emitting devices. The copolyfluorenes were chemically doped (0.0025~50 mol%) with chromophores that emitted green or reddish orange light. The dominant parts of the copolyfluorenes were fluorene segments which acted as blue-emitting host. The guests (chromophores) were derived from seven new dibromo monomers, respectively, which are based on DCM, distyrylbenzene, phenothiazine, thiophene, and triphenylamine moieties. These monomers were incorporated into polyfluorene backbone through the palladium-catalyzed Suzuki coupling reaction. All new synthesized monomers and polymers were identified by 1H NMR, FT-IR, and elemental analysis (EA). Thermal properties of the polymers were determined using TGA and DSC. The optical (UV and PL), electrochemical (CV), and electroluminescent properties of these polymers were investigated in detail. In chapter 4, 5 and 7, four chromophores (DCM, R, PhT and ThT) were designed and their corresponding dibromo monomer synthesized. Their PL emissions located at 522~586 nm region. They were incorporated into polyfluorene to prepare copolyfluorenes with various contents of chromophores. The PLED devices exhibiting dichromatic white-light- emission were realized by using the copolyfluorenes as emitting layer. The EL devices of blends from PF and PFD0.5 (w/w = 4/1 or 9/1) exhibited near white light emission with the CIE coordinates being (0.33, 0.35) and (0.32, 0.34). The PFR devices showed a broad emission band, covering the entire visible region, with chromaticity coordinates being (0.36, 0.35) and (0.32, 0.30) for PFR1 and PFR2 devices, respectively. The maximum brightness and current efficiency of the PFR2 device were 3011 cd/m2 and 1.98 cd/A, respectively. Blending PFPhT2 with PF (w/w = 10/1), the dichromatic white-light emission was realized with the maximum brightness, maximum current efficiency, and CIE coordinates being 10600 cd/m2, 1.85 cd/A, and (0.31, 0.33), respectively. In chapter 6 and 8, three chromophores (MG, TP and TT) were designed and their corresponding dibromo monomers synthesized. Their PL emissions located at 492~536 nm. Copolyfluorenes with varied chromophore contents were prepared from the dibromo monomers. The PLED devices using the copolyfluorenes as emitting layer displayed both blue and green colors. When doping with red-emitting iridium complex, Ir(piq)2(acac), the trichromatic white-light emission was obtained. The trichromatic white EL device was fabricated by using the PFG2 as the host to blend with the iridium complex; the maximum brightness and CIE coordinate was 4120 cd/m2 and (0.31, 0.28), respectively. The other trichromatic white-light emission was realized through blending PFTT1 with polyfluorene and a red-emitting iridium complex, in which the maximum brightness and CIE coordinates were 6880 cd/m2 and (0.31, 0.33), respectively.