Synthesis Of Blue And White Light Electroluminescent Copolymers And Study On Luminescence Properties

As a novel kind of functional polymer, polymeric electroluminescent materials have attracted much attention due to the low turn-on voltage, ease to realize full color display, wide viewing angles, light weight, and simple manufacture process of the PLEDs. So far, among the conjugated polymers that emit three basic colors, red and green light emitting materials have fulfilled the requirement for EL devices. However, blue light emitting materials have become the choke point due to their wide energy region, relatively low color purity and electroluminescence efficiency.White polymeric light-emitting diodes (WPLEDs) have received great attention due to their potential applications in full-color displays with color filters, as backlights for liquidcrystal displays, and even in lighting applications. Compared with other display and lighting technologies, WPLEDs have the great advantage of ease of fabrication and low-cost solution processing for large displays when the recombination white-emitting and color fiters have been employed. Full-color displays are realized by several strategies from WPLEDs with color filters, but the most of the approach is that a polymer can demonstrate containing red-, green-, and blue-light-emitting or blue- and yellow-emitting, and emission spectra can cover all of visible spectrum (400-700nm). It is extremely difficult that white-emitting was abtained from a single polymer with containing red-, green-, and blue-light-emitting. At present, the two general approaches which gained white-emitting from a single polymer are to blend polymers with polymers or polymers with small molecules. But they have unconquerable disadvantages, namely, phase separation and dependent voltage.In this thesis, two kinds of blue and a white light emitting copolymers have been designed and synthesized, the blue light emission copolymers can get by polymerized fluorene and p-phenylenevinylene; the main chain of white light emission copolymer contains blue-, green- and yellow emission units, three colors conbine and emit pure white light. Photoluminescence properties, electrochemical properties, and the electroluminescence properties of their single-layered PLEDs are studied.1. Two fluorene-co-p-phenylenevinylene conjugated copolymers containing saturated aliphatic segments in the main chain have been synthesized through Wittig polycondesation reaction. Introduction of soft segments might reduce the tendency of chain aggregation in the solid state. The weight loss temperatures of the four amorphous copolymers are higher than 365℃, and the glass transition temperatures are in the range of 97-115℃. The single-layered PLEDs based on the copolymers with the configuration of ITO/PEDOT/copolymer/Ca/Al all emit pure blue light under low driving voltage. Especially, the PLED based on P1 shows good performance. The maximum brightness is reached to 3936 cd/m~2 with a current-luminescence efficiency of 0.70 cd/A.2. The copolymers consisting blue- and green-yellow light emission have been designed and synthesized. We try to obtain white light-emission by combining the two equalized light-emission and adjust emission colors by changing the content of green-yellow light emission unit. Electrochemical properties, photoluminescence and electroluminescence properties of a series of copolymer with different content are studied detailedly. The results indicated there is strong energy transfer between blue- and green-yellow light emission units, so only single blue- or green-yellow emission peak appears in the PL and EL spectra and white light-emission cannot get.3. A white light emitting copolymers including blue-, green- and yellows-light emitting units have been designed and synthesized. Both contents of green and yellows emitting unit are 0.8%. Introduction of triphenylamine moiety in the main chain of green-light-emitting might increase the ability of hole-transporting. Photoluminescence properties and electrochemical properties of the polymers are studied. The single-layered PLED based on the copolymer with the configuration of ITO/PEDOT/copolymer/Ca/Al emits pure white light, The Commission Internationate de I, Enclairage coordinates (CIE) of the WPLED is (0.36, 0.33) that is close to the ideal CIE chromaticity coordinates for pure white light (0.33, 0.33).