Synthesis and Characterization of Luminescent Conjugated Polymers

• Main Authors: Tzi-yi Wu, 吳知易
• Other Authors: Chen, Yun
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/73722668219629983524

博士 === 國立成功大學 === 化學工程學系碩博士班 === 93 === 　The purpose of this study is to synthesize new polymeric electroluminescent (EL) materials and investigate their optical, electrochemical and EL properties. We design EL copolymers containing novel hole transport chromophores (iminodibenzyl and phenothiazine) or electron-affinitive 2,3-divinylquinoxaline, oxadiazole and pyridine units. The final reports are divided into five parts as follows: (1) Luminescent copolymers containing iminodibenzyl and phenothiazine Chromophores. 　Novel copolymers carrying N-hexyl-3,8-iminodibenzyl and N-hexyl-3,7-phenothiazyl chromophores have been synthesized by Wittig-Horner or Knoevenagel reaction. The oxidation potential of model N-hexyliminodibenzyl (1.33 V) is much smaller than that of conventional N-hexylcarbazole (1.73 V), indicating iminodibenzyl is an effective chromophore in raising HOMO level. Photoluminescence measurement reveal that cyano substitution at vinylene moiety brings about significant bathochromic shift and leads to electroluminescence color change from green to orange. Iminodibenzyl chromophore is contrasted with previous polymers using carbazole. I prepared and characterized of one carbazole polymer for reference. From electrochemical study, iminodibenzyl is an effective chromophore in raising HOMO level. New arylenevinylene polymers containing phenothiazine group have been synthesized. Phenothiazine chromophore contains extra electron-donating sulfur in addition to nitrogen. I synthesized and analyzed the effects of phenothiazine moieties on optical, electrochemical and electroluminescent characteristics. Comparing with other hole transport materials containing only nitrogen, such as carbazole, alkyldiphenylamine, triphenylamine, and iminodibenzyl chromophores, copolymers with phenothiazine moieties exhibit the longest PL wavelength and narrowest band gap. (2) Luminescent copolymers containing quinoxaline units. 　In order to enhance charges affinity, electron affinitive 2,3-divinylquinoxaline and a series of hole-transporting chromophores (iminodibenzyl, phenothiazine, dihexyloxybenzene and didodecyloxydistyrylbenzene) were incorporated alternately into polymeric main chain. The resulting copolymers are basically amorphous materials and thermally stable below 300oC. They show significant positive solvatochromism in formic acid. Electrochemical study reveals they exhibit lower band gaps (< 2.3 eV) due to alternating donor and acceptor conjugated units (push-pull structure). (3) Electroluminescent copolymers containing distyrylbenzene and oxadiazole units. 　In order to balance the rates of injection of electrons and holes, and to enhance the charge injecting/transporting ability. A new series of bipolar polymers that possesses both a hole injecting/transporting segment and an electron-affinitive segment (oxadiazole) have been designed and synthesized. Excimer formation in P15~P20 was confirmed by their absorption and PL spectral peak transition in solution at different concentration and in thin films. Unusual absorption and fluorescence were observed in acid media which have been related to photoinduced charge transfer in alternating donor-acceptor architecture. The photoinduced charge transfer led to blueshift in iminodibenzyl-containing copolymers (P12~P14) and redshift in fluorene-containing copolymers (P20), reflecting the fact that iminodibenzyl is a stronger electron-donating unit. The optical band gaps of the dioxadiazole-containing copolymers show great discrepancy with the electrochemical band gap energy due to donor-acceptor feature of the dioxadiazole unit. The brightness and luminance efficiency of ITO/ PEDOT/polymer (distyrylbenzene and dioxadiazole units)/Ca/Al configuration emits bright yellow emission, the maximum brightness and luminance efficiency are 3190 cd/m2 and 0.66 cd/A, respectively. (4) Electroluminescent copolymers containing sterical hindered phenyl substituent at the 2,5-positions of the 1,4-phenylene moiety in the PPV backbone. 　We synthesized and characterized a new soluble PPV derivatives (P21) containing 2,5-diphenyl-1,4-phenylene and 2,5-didodecyloxy-1,4-phenylene moieties. The polymer has good solubility, high thermal stability properties and shows high PL efficiency in thin film state (0.36). From electrochemical study, the HOMO and LUMO levels of P21 are estimated to be -5.16 eV and -2.89 eV, respectively. The threshold voltage and luminance of single layer ITO/P21/Al device are 5 V and 104 cd/m2, respectively. Electroluminescence measurement reveals that P21 emits bright yellow light. The luminance of LED made from P21 is about three times higher than the one made from MEH-PPV, suggesting that P21 could be a potential emitting material when used in PLEDs. (5) Fluorescent sensory characteristics of 2,6-pyridylene chromophore for acid and 3,7-phenothiazylene for oxidation. 　A novel copolymer Poly(N-hexyl-3,7-phenothiazylene-1,2- ethenylene-2,6-pyridylene-1,2-ethenylene) (P24) has been synthesized to investigate the effect of protonation, metal complexation and chemical oxidation on its absorption and photoluminescence (PL). Electrochemical investigations reveal that P24 exhibits lower band gaps (2.34 eV) due to alternating donor and acceptor conjugated units (push-pull structure). The absorption and PL spectral variations of P24 can be easily manipulated by protonation, metal-chelation, or chemical oxidation. Thus P24 displays significant bathochromic shift when protonated with trifluoroacetic acid in chloroform. Complexation of P24 with Fe3+ leads to a significant absorption change and fluorescence quenching, implying the coordination of ferric ion to the 2,6-pyridylene groups in backbone. Moreover, phenothiazylene-containing copolymer shows conspicuous PL quenching with slight redshift when oxidized with NOBF4.