【作者】 王宝玲；

【导师】 马於光； Ullrich Scherf；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 梯形聚苯(LPPP)及其衍生物具有结构明确的刚性全共轭主链结构及一系列独特的光、电、热等方面性质,近年来这类材料在化学及物理相关领域都引起了广泛关注。LPPP被应用于光电领域的各类器件中,如电致发光器件、场效应晶体管、薄膜激光及光伏器件等。本论文以功能为导向设计并合成了几种具有新型结构的梯形聚苯,并对其光电性质进行了研究。工作主要包括以下几个方面:(1)将咔唑基团引入主链骨架结构中,提高了LPPP的空穴注入能力。由于全苯撑结构LPPP具有较低的HOMO能级,在电致发光过程中空穴的注入较难。我们将空穴注入与迁移能力较强的咔唑基团嵌入到LPPP的主链骨架结构中,成功制备了具有明确结构、高分子量、良好溶解性的含咔唑LPPP。电化学的分析表明含咔唑LPPP的HOMO能级相对于全苯撑结构的LPPP明显提高,空穴注入能力得到明显提升。(2)合成了具有热稳定性的螺芴-LPPP。由于梯形聚苯是一种主链由桥键连接的聚合物,桥键处易于发生氧化形成酮式缺陷,引起发光过程中的低能量发射。我们将具有高光/热稳定性的螺芴基元引入LPPP骨架结构中,合成了具有良好溶解性、主链由螺芴构筑的LPPP。该聚合物薄膜在空气条件下热处理结果表明120℃热退火24小时后,发射光谱依然稳定,聚合物材料表现出优异的热稳定性。(3)将环戊二噻吩(CPDT)引入LPPP主链骨架中,实现光谱的红移并研究其在光伏器件中的初步应用。梯形聚苯具有非常高的载流子迁移能力,由于材料的吸收光谱处于较高能量的吸收范围,与太阳光谱重叠较小,导致材料在光伏器件领域的应用受到限制。将CPDT基元引入到聚合物主链中,成功制备了一种具有良好溶解性,主链含有CPDT的梯形聚苯(LPPT)。LPPT的吸收光谱相对于经典的梯形聚苯明显红移,与受体材料PCBM进行1:1掺杂的光伏器件结果显示材料具有光伏器件中的潜在应用的价值。更多还原

【Abstract】 Since the first synthesis of ladder-type poly (p-phenylene) (LPPP) by Scherf and Müllen in 1991, LPPP and its derivatives have received a great deal of attention as blue light emitting materials. LPPPs possess a rigid and fully conjugated backbone, exhibiting nice blue emission with high luminescence quantum yield. LPPP with its the two-dimensional ladder-type framework does not show any steric inhibition ofπ-electron delocalization due to the drastically reduced conformational freedom of the conjugated, ladder-type backbone. LPPP found various applications in fields such as polymer light-emitting diodes, field-effect transistors, plastic lasers and photovoltaic devices etc.Main problems in the applications of LPPP are the poor charge injection properties and the occurrence of an additional low energy emission component during the operation of organic light emitting diodes (OLEDs) or after heat treatment. This thesis containing three parts; the first two parts are focused on design and synthesis of two novel LPPPs which contribute in solving the problem of charge injection and unwanted low energy emissions. In the last part, we describe the generation of a new ladder-type polyarylene containing cyclopentadithiophene moieties which shows a red-shift of absorption/emission and may be used as donor component of organic photovoltaic device. (1) One effective route to overcome the poor charge injection in conjugated ladder polymers of the LPPP-type is the incorporation of carbazole units into the polymer backbone, due to the electron-donating capabilities associated to the nitrogen of the carbazole units. In the first part of the thesis, we describe a soluble ladder-type conjugated polymer (LPFC) with N-alkyl-2,7-carbazole units in the polymer backbone. The N-alkyl-2,7-carbazole monomers are prepared by nitration of dibromobiphenyl followed by a ring closure reaction to carbazole. The ladder polymer LPFC is prepared in a reaction sequence involving a Suzuki-type cross coupling reaction, a carbonyl reduction and subsequent ring closing to form the final ladder-type polymers. The structural characterization of LPFC and its optical and electroluminescence properties are presented. LPFC shows high molecular weight, excellent thermal stability, and good solubility in common organic solvents. It presents a blue photoluminescence (PL,λmax=465 nm) with high PL efficiency (70%). Electrochemical analysis for LPFC gave an increased HOMO level of -5.29 eV if compared to the reference LPPP (-5.5 eV) thus indicating an improved charge injection ability from ITO or PEDOT anodes. A single layer light-emitting device using LPFC as the active layer showed blue light emission (λmax=470 nm) (CIE coordinates: 0.18, 0.34) with high maximum luminescence of ~ 2000 cd/m2 and maximum luminance efficiency of 0.43 cd/A, The blue light emission is obtained with a low turn-on voltage of 4 V. These attractive properties characterize LPFC as promising material for polymer-based optical and electrooptical devices.(2) One very effective attempt to inhibit the unwanted low-energy emission component of LPPP-type polymers is the generation of a ladder backbone composed of spirobifluorene units. Spirobifluorene contains two biphenylene units connected via a tetrahedrally carbon. In this chapter we report a simple way to synthesize spiro-LPPP that is thoroughly composed of spirobifluorene building blocks. The route involves only two steps: a single-stranded precursor polymer containing bis(biphenyl-2-oyl)benzene building blocks is made in a Suzuki-type coupling reaction, followed by a subsequent two-fold cyclization cascade using methanesulfonic acid to form the target spiro-LPPP. The PL spectra of the spiro-LPPP in THF solution and thin film, respectively, indicate spiro-LPPP as a promising blue light emitting material with the main emission band peak at 455 and 456 nm, respectively. Spiro-LPPP shows a high PL quantum yield of 94% in THF solution. Annealing a thin film of spiro-LPPP to 120 oC in air for 3 to 24 hours its emission spectra keep unchanged thus reflecting an excellent thermooxidative stability of spiro-LPPP. Spiro-LPPP is a good candidate for realization of a stable blue light emitting in OLEDs and polymer lasers.(3) LPPP with rigid and fully planar conjugated backbone shows a relatively high charge carrier (especially hole) mobility of up to 2×10-3 cm2V-1s-1 in the bulk and up to 600 cm2 V-1s-1 for single polymer chains. However, the use as active material in organic solar cells is hindered by the large mismatch with the solar spectrum. To improve the absorption properties of LPPP-type ladder polymers, we have introduced bridged bithiophene building block (cyclopentadithiophene, CPDT) into the ladder-type polymer backbone. The new CPDT-based ladder polymers are generated in a sequence involving a Still-type cross coupling reaction, carbonyl reduction and subsequent ring closure to form the ladder-type framework. The new LPPP containing CPDT units (LPPT) displays a distinct red-shift the UV-Vis absorption (λmax= 525 nm) and PL (red emission,λmax= 582 nm) as well as a lower band-gap energy of 2.03 eV when compared with the corresponding all-phenylene ladder polymer LPPP (-5.5 eV). First bulk heterojuction-type photovoltaic devices with the LPPT/PCBM couple (1:1) as active blend showed a power conversion efficiency under white light illumination of 0.15% without optimization of blend composition and morphology. The promising properties of LPPT qualify it as a potential candidate for application as donor polymer in bulk heterojunction-type organic photovoltaic devices.更多还原