【作者】 刘香兰；

【导师】 徐法强；

【作者基本信息】 中国科学技术大学 ， 核技术及应用， 2008， 博士

【摘要】 近几年来,由于聚噻吩衍生物在发光器件、光伏电池及场效应管等方面的潜在应用而备受关注。要使这类新型的光电聚合物材料走向实用化,还需要进一步的改善和提高它们的光电特性和效率。这些性能除了与材料本身的化学结构有关外,还与聚合物的物理形貌及分子形态有着密切的关系。目前聚合物物理形貌对光电特性的影响研究主要集中在导电性能方面,而对光学方面的研究较少。本论文分别用氧化聚合法和电化学聚合法合成和制备了聚[3-（2-甲氧基苯）噻吩]薄膜和纳米线阵列,详细分析了它们的发光特性和机理。利用同步辐射X射线近边吸收技术（NEXAFS）,分析了不同电负性的取代基对聚噻吩电子结构和分子取向的影响。取得的结果包括以下几个方面:（1）通过格氏反应合成了3-（2-甲氧基苯）噻吩,再用FeCl₃作催化剂氧化合成了聚[3-（2-甲氧基苯）噻吩]（PMP-Th）。热重分析表明聚合物在400℃才出现失重现象,具有较高热稳定性。聚合物的最大发光波长为687nm,谱带较窄,是较好的近红外发光材料。X射线衍射技术证明聚合物内有微晶区,这可能是由分子的局域有序排列造成的。（2）以高纯铝为原料,分别在草酸溶液和硫酸溶液中,采用二次阳极氧化法制备了孔洞高度有序的阳极氧化铝（AAO）模板。通过改变制备条件,获得了孔径在30 nm-80 nm,孔密度为～10¹⁰孔/cm²的一系列氧化铝模板。用以上自制的不同孔径的多孔氧化铝为模板,采用循环伏安法,制备了PMP-Th的纳米线阵列,纳米线的直径与模板的孔径大小相当,纳米线的长度可通过控制电量来调控。结果证明循环伏安法电化学技术与模板法相结合是制备一维聚合物纳米阵列的有效方法,易于调控纳米线的长度和维度。（3）分析研究了各种直径的PMP-Th纳米线阵列在由草酸溶液中制得的AAO模板中的发光特性,与PMP-Th薄膜的发光光谱相比,纳米线阵列的发光波长都有较大蓝移,强度显著增强。纳米线阵列的发光显示显著的尺寸依赖性,随着AAO孔径由80nm减小到60nm,发光波长逐渐从580nm蓝移至560nm,当孔径从60nm减至40nm时,发光峰从560nm红移至580nm。经过红外光谱分析和对分子环境的比较探讨发现发光谱的蓝移是由模板的孔洞限制效应引起的,小孔径中发光的红移是聚合物分子有序取向使有效共轭程度增加带隙能降低导致的。结合聚合物薄膜和AAO的吸收光谱和光致发光激发谱,对光强增强的机理进行了探讨,认为光强增强是由AAO与聚合物分子间的能量转移造成的,光强随孔径减小而降低是给体的发光谱与受体的吸收谱覆盖度降低以及分子有序堆积使荧光效率降低的结果。（4）分别比较了PMP-Th纳米线阵列和聚（3-溴代噻吩）（PBr-Th）纳米线阵列在硫酸溶液中制得的AAO（S-AAO）和草酸溶液中制得的AAO（C-AAO）中的发光特性,发现PMP-Th纳米线阵列在S-AAO中的发光峰位和强度的尺寸依赖性与C-AAO一致,说明PMP-Th线阵列在AAO的发光特性与AAO孔壁的化学环境无关,也进一步说明了PMP-Th纳米与AAO之间没有化学反应。与PMP-Th在C-AAO和S-AAO中的发光特性显著不同的是,PBr-Th纳米线在C-AAO和S-AAO中的发光强度相比于薄膜PBr-Th的光强大大降低,这可能是PBr-Th分子在模板中的取向度较高或者是PBr-Th与AAO有较复杂的相互作用造成的。与PMP-Th纳米线相同的是PBr-Th在两种模板里的发光波长的尺寸依赖性是一致的。因此对这一体系的研究还需要进一步的深入和扩展。（5）利用同步辐射NEXAFS技术,分析了PMP-Th和PBr-Th的电子结构,通过分析角分辨NEXAFS谱,确定了PMP-Th分子和PBr-Th分子在Pt片电极上的分子取向:PBr-Th分子链“倾斜”于金属表面,而PMP-Th由于甲氧基苯的位阻和电子效应的双重影响表现为无序。更多还原

【Abstract】 In recent years, poly（thiophene）s have attracted considerable attention because of their great potential in light-emitting diodes, photovoltaic cells and field-effect transistors, etc.. In order to realize the practical application, their photoelectric properties still need to be further improved. Besides the chemical structure of materials, photoelectric properties have a close relationship with physical morphology and behavior of the molecular. Up to now, most of the studies about the effects of physical morphology on the photoelectric properties of poly（thiophene）s have been focused on the effect on conductivity and only a few researches were centered on the fluorescence. In this dissertation, poly[3-（2-methoxyphenyl）thiophene]（PMP-Th） power and PMP-Th nanowire arrays were synthesized and fabricated via chemical oxide polymerization and electropolymerization, respectively. Fluorescence properties of the PMP-Th power and nanowire arrays as well as the corresponding mechanism were investigated in detail. Using the near edge X-ray absorption fine structure spectroscopy （NEXAFS） technique based on synchrotron radiation, the effects of different electronic properties of lateral chains on the electron structure and molecular orientation have been studied.The main results of this dissertation are described as follows:1. 3-（2-methoxyphenyl）thiophene was successfully synthesized via Grignard reaction and then polymerized to PMP-Th by means of the catalyst of FeCl₃ TGA analysis demonstrated that PMP-Th has good thermal stability because its critical temperatures of weight loss in air are 330℃. The polymer exhibited red photoluminescence with a main peak at approximately 687 nm and narrow spectral bandwidth. These results demonstrate PMP-Th is a good near-infrared emission material. XRD analysis indicated that there are smaller crystal domains in the sample which would be possibly attributed to the molecule regioregularity.2. Highly ordered porous anodic aluminum oxide （AAO） templates were obtained in oxalic solution and sulfuric solution by a two-step anodization process. respectively using high purity （99.999%） aluminum foils as the starting materials. The pore diameter of the AAO was tuned from 30 nm to 80 nm by changing the condition for the fabrication. The pore density is about 10¹⁰ pore/cm². Using the home-made AAOs with various pore diameters as templates, the PMP-Th nanowire arrays were fabricated by cyclic voltammetry （CV）. The diameters of the nanowires are close to the pore diameters of AAO. The length of the nanowires could be tuned by controlling the total charges consumed. It has been demonstrated that CV method combined with AAO template is a simple and effective rout to fabricate ordered polymer nanostructures, which is easy to tune the nanostructure growth and control the dimention.3. The photoluminescence （PL） properties of PMP-Th nanowires in AAO with different pore diameters fabricated from oxalic solution were studied. Compared to the PL of PMP-Th film, PMP-Th nanowires in AAO exhibit obvious blue-shifts and great intensity enhancement. Interestingly, the PMP-Th nanowires in AAO with various pore diameters showed evident size dependent emissions. The maximum peak position of the emission spectra gradually shifted from 580 nm to 560 nm as the diameter decreased from 80 nm to 60 nm, while when the diameter continued to decrease to 40 nm, the emission peak gradually shifted back to 580 nm. According the results of FT-IR and considering the different behavior of the polymeric molecules in the nanowires and the thin film, it is reasonable to attribute the blue-shift to the nanosize confined effect. The red shift in small pore diameters comes from the alignment of the polymeric chains in AAO which results in the increase of conjugated length and the band gap decreased. The intensity enhancement mechanism was discussed according to the absorption spectra and PL excitation spectra of AAO and PMP-Th film. It was proposed that the efficient Forster energy transfer from AAO to the polymer molecules is responsible for the PL enhancement. The PL enhancement decrease with the decreasing of the pore diameter is caused by the decreasing of the spectral superposition of donor and acceptor together with low PL efficiency which results from the molecule alignment.4. The PL comparison of PMP-Th nanowires in AAO fabricated from oxalic solution （C-AAO） with that from sulfuric solution （S-AAO） showed that the optical properties of these two composites have the same nano-size confinement effect. This demonstrated that the different chemical surroundings of the pores have no effect on the PL properties of the nanowires and further illuminated that there isn’t chemical interaction between the polymer and the AAO. Unlike PMP-Th, the PL intensity of poly（3-Brthiophene） （PBr-Th） nanowires in C-AAO and S-AAO remarkably decrease compared to the PBr-Th film. This may be attributed to the high alignment of PBr-Th chains in AAO and complex interactions between the polymer and AAO. However, PL peak shifts of PBr-Th nanowires in S-AAO and C-AAO have the same nano-size confinement as PMP-Th nanowires. So, systematic studies on this system are needed.5. NEXAFS based on the synchrotron radiation was employed to investigate the electronic structure of PMP-Th and PBr-Th. The angle dependent NEXAFS evidenced the preferential orientation of PMP-Th and PBr-Th molecules on Pt electrode, respectively. PBr-Th chains tilt away from the Pt surface, while the orientation of PMP-Th molecules at the surface is nearly random owing to the double effect of steric hindrance and electronic property of methoxypheny lateral.更多还原