The Synthesis and Optoelectronic Properties of Electroluminescent Polymers Containing Coumarin Side Chains

• Main Authors: Cheng-Jang Tsai, 蔡成章
• Other Authors: Yun Chen
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/27112888737013570938

博士 === 國立成功大學 === 化學工程學系碩博士班 === 95 === In this investigation, we synthesized new polymeric electroluminescent (EL) materials, which can be divided into three parts: (1) poly(p-phenyleneviny1ene) (PPV) derivatives P1 and P2, containing hexyloxy side groups and 7-oxy-4-methylcoumarin (OMC) groups via hexyloxy spacer, respectively; (2) four copolyethers (P3-P6) consisting of two isolated emitting chromophores [2,5-dihexyloxy-1,4-distyrylbenzene (HODSB) and 2,5-dihexyloxy-1,4- di(4-methylenestyryl)benzene (HOMDSB) for P3 and P4, 2,5-dihexyl-1,4-distyrylbenzene (HDSB) and HOMDSB for P5 and P6 in the backbone, in which P4 and P6 further contain electron-transporting chromophores (OMC) in the side chain; (3) poly[2,5-dialkoxy-p-phenyleneethynylene-2,7-(9,9-dihexylfluorene ethynylene)]s (PPEF) consisting of conjugated emitting chromophores of the backbone and pendant hexyloxy groups (P7) or pendant OMC chromophores via flexible spacer (P8). The emissions of polymers (P2, P4, P6, and P8) and corresponding model polymers (P1, P3, P5, and P7) films are similar which is attributed to polymer backbone, respectively. Accordingly, efficient energy transfer from the OMC chromophores to polymer backbone occurred readily in P2, P4, P6, and P8. Double-layer EL devices revealed blue (P5 and P6), green (P1, P2, P3 and P4) and yellow (P7 and P8) electroluminescence, respectively. The electron affinity of P2, P4, P6, and P8 were enhanced by introducing electron-transporting OMC chromophores. Moreover, incorporation of OMC side groups effectively reduced turn-on electric field and enhanced luminance maxima of the EL devices due to increased electron affinity. However, P2 exhibited higher photo-crosslinking rated due to pendant 4-methylcoumarin chromophores. Patterned emission from PLED utilizing this effect was also demonstrated. Furthermore, seven polyoxadiazoles (PO5-PO10 and PO12) have been also synthesized. Corresponding model compounds (MO5-MO10 and MO12), consisting of two terminal mesogenic 2,5-bisphenyl-1,3,4-oxadiazole units and central polymethylene spacers, were also prepared for comparison. Both polymers and model compounds exhibit extraordinary odd-even effect, i.e. odd ones show higher transition emperatures (Tm, Ti). Moreover, oxadiazol groups effectively reduced turn-on electric field and enhanced luminance maxima of the EL devices (ITO/PEDOT/P7+PO7/Ca:Al) dued to increase electron affinity.