Synthesis of Fluorene-Thiophene Copolymers Containing Polycyclic Aromatic Imidazolyl Substituents and Their Applications in Organic White Light-Emitting Devices
|摘要:||本研究之目的在於合成含多環咪唑側團基之芴–噻吩共聚物，並探討其在熱性質、光學及電化學性質之影響，亦作為發光層材料以製備高分子發光元件。本研究同時合成聚(9,9’-二辛基芴) (PFO)作為對照。含剛硬咪唑側團基之聚芴衍生物分子量較PFO小。其熱裂解溫度與PFO相差無幾，且於高溫有更多的殘留重量，證明引入咪唑側團基可提高材料熱穩定性。其玻璃轉換溫度遠高於PFO，有利於PLED元件操作之耐久性。引入咪唑側團基之聚芴衍生物吸收光譜與PFO相似，顯示咪唑側團基並不影響主鏈之吸收；放射光譜較PFO紅移，其中P1最大吸收峰更大幅紅移至510 nm。電化學分析顯示咪唑團基的引入導致材料LUMO下降，HOMO亦隨之降低，P1具有比PFO更好的電子電洞注入能力，而P2–P4卻因HOMO過低導致巨大的電洞注入能障。本研究製備ITO/PEDOT/polymer/P1-BF4/Al之高分子發光元件，其中P1-BF4為電子傳輸材料。材料色光分別為P2–P4的藍綠光及P1的綠光，顯示引入咪唑側團基確實可改變材料之發光波段。本研究最後將PFO:P1:MEH-PPV以300:100:1重量比混合以製備出白光元件，其亮度與效率分別為509 cd/m2及0.20 cd/A，其CIE’1931座標為(0.32, 0.37)。以上結果顯示其具有固態照明之應用潛力。|
The goal of this research is to synthesize fluorene-thiophene copolymers containing polycyclic aromatic imidazolyl substituents, and to study the influence of those substituents on thermal, optical, and electrochemical properties of polymers. Those polymers are used as emitting layer for fabrication of polymer light-emitting devices. Poly(9,9’-dioctylfluorene) (PFO) are also synthesized for comparison in this research. The molecular weights of polyfluorene derivatives containing rigid imidazolyl substitutes are lower than that of PFO. The decomposition temperatures of all polymers are almost the same; meanwhile, those derivatives possess more weight residues than PFO after heating, indicative of enhanced thermal stabilities of materials by the introduction of imidazolyl substitutes into polymer main chains. The glass transition temperatures of those derivatives are much higher than that of PFO, showing benefit on operation stability of PLED. The absorption spectra of those polyfluorene derivatives containing imidazolyl substitutes are similar to that of PFO, referring that those substitutes have no influence on the absorption of polymer main chains. The emission spectra of those derivatives show red-shifts compared with PFO; among them P1 generates a heavily red-shifted emission maximum to 510 nm. Electrochemical analysis shows that introducing imidazolyl groups into polymer main chains results in decreasing LUMO levels of derivatives compared with PFO, and their HOMO levels are decreased as well. P1 behaves better hole and electron injection abilities than those of PFO, while P2, P3, and P4 possess huge hole injection barrier owing to low-lying HOMO levels. Polymer light-emitting devices with configuration of ITO/PEDOT/polymer/P1-BF4/Al were fabricated in this research, using P1-BF4 as electron transport material. The emissive light of those materials are bluish-green for P2, P3, and P4, and green for P1, proving that the introduction of imidazolyl substitutes into polymer main chains indeed brings change on the emission bands of materials. Finally, a polymer blend was prepared by using PFO:P1:MEH-PPV = 300:100:1 in weight ratio for fabrication of white-light-emitting devices. The brightness and current efficiency of the device achieved 509 cd/m2 and 0.20 cd/A, respectively, with CIE’1931 coordinating at (0.32, 0.37). The above results reveal its potential use in solid-state lighting.