【作者】 刘太宏；

【导师】 房喻；

【作者基本信息】 陕西师范大学 ， 材料学， 2012， 博士

【摘要】 寡聚噻吩及其衍生物是一类具有优异光电性能的π电子系共轭化合物,具有易纯化、结构和分子量明确、聚合度和衍生结构易控制、荧光量子产率高和Stokes位移大等特点。作为聚噻吩的模型化合物,近年来寡聚噻吩在有机功能材料和荧光化学传感器等方面获得了大量应用。研究发现,由于寡聚噻吩含有活性S杂原子,较低的最高已占轨道(HOMO)能量和较宽的能隙,在紫外光或可见光照射下易与空气中的氧气和水发生作用,影响以其为基础所制备器件或传感器的使用稳定性,限制了这类材料的实际应用。文献调研表明,提高寡聚噻吩及其衍生物热化学和光化学稳定性的有效途径之一就是以苯、萘、芴和芘等稠环化合物对寡聚噻吩进行末端修饰,这种结构改造有助于调节寡聚噻吩及其衍生物的能级结构和电子云密度分布,从而改善其光电性能和化学稳定性。利用被分析物与某种荧光分子或材料之间特定的相互作用引发荧光强度的增加或降低,荧光发射波长的移动、荧光发射光谱形状的改变等实现对分析物的检测或检测信号的传递是荧光化学传感器实现传感功能的主要方式。一般来讲,荧光化学传感器主要由三部分组成：荧光报告基团,识别基团以及二者之间的连接臂。其中,识别基团可以选择性地识别底物,而荧光报告基团则察觉并传导识别基团引起的化学信号变化。在荧光化学传感器的研究中,荧光报告基团即荧光传感元素的选择对传感器的识别能力和传感灵敏度起着至关重要的作用。荧光化学传感器主要分为两类,即在溶液中使用的均相荧光传感器和易于重复使用且能进行气相检测的薄膜荧光化学传感器。相比于均相荧光传感器,经由自组装单层膜(Self-assembled Monolayers, SAMs)技术制备的薄膜荧光化学传感器具有不污染待测体系,可以重复使用等优点。此类薄膜荧光化学传感器可以解决,至少是部分解决以物理方法所制备的薄膜荧光化学传感器在使用中存在的荧光分子泄漏和分析物膜内扩散困难等问题,从而可以大幅度提高薄膜荧光化学传感器的综合性能。基于上述考虑,本论文在对化学组装荧光薄膜材料和寡聚噻吩光物理研究概况综述的基础上,立足本实验室已有的工作基础,选用寡聚噻吩及其衍生物作为传感元素,将其经由柔性连接臂化学单层组装于玻璃基片表面,制备得到了可用于气相甲醛、气相和液相含硝基类爆炸物检测的荧光传感薄膜材料。所制备的SAMs膜材料具有选择性高、稳定性好、响应可逆、使用寿命长等优点,为后续器件化奠定了良好基础。同时也利用寡聚噻吩及其衍生物溶液中优异的荧光性能,实现了均相溶液中含硝基类爆炸物和金属离子的灵敏传感,并研究了其可能的传感机理。具体来讲,本论文共有四大部分,第一部分为研究背景,包含第一章和第二章,分别对化学组装荧光薄膜材料的研究现状和应用,以及寡聚噻吩光物理研究概况进行了比较全面的阐述。其余三部分主要是围绕寡聚噻吩衍生物的光物理性质和传感应用这一主题,开展实验研究,相关工作主要包括：1)甲醛气体传感薄膜研究。以寡聚噻吩为传感元素,将其经由γ一氨丙基三甲氧基硅烷化学键合到玻璃基质表面,得到了一种对甲醛气体特异响应的"turn-on"型荧光薄膜传感材料。寡聚噻吩的成功键合得到接触角、XPS、静态荧光测定等实验结果的证实。实验发现,在光照下固定化寡聚噻吩易被空气氧化,薄膜的荧光强度也随光照时间的延长而减弱。紫外光照约1h后薄膜荧光不再发生变化。光照处理后的薄膜在气相甲醛中产生新的荧光发射,该荧光发射强度随甲醛浓度增大而增强,30min后增大至原来的18.6倍,且伴随甲醛的消除,该荧光发射也随之消失,具有很好的回复性。常见物质氯化氢、氨、醋酸、苯、甲苯、乙醇等气氛的存在基本不干扰薄膜对甲醛的传感。在大量对照试验和空白试验的基础上,提出了寡聚噻吩光化学生成物和甲醛之间可能的作用机理。2)含硝基类爆炸物荧光材料研究。基于Grignard偶联反应,采用芳香基团萘和芘对α-三聚噻吩(3T)进行封端修饰,改善了寡聚噻吩衍生物的HOMO能级和能隙。在保留其优异荧光性质的同时大大提高了其功能化SAMs膜的光化学稳定性,得到了一类新型荧光传感薄膜材料。结合共轭寡聚物SAMs膜特性和电子授受机理,实现了对气相以及液相微痕量含硝基类爆炸物,尤其是苦味酸(PA),的高选择性、高灵敏度检测,且此检测不受常规干扰物的影响。所发展的PA传感薄膜具有响应速度快,响应可逆等特点。机理研究发现,荧光猝灭过程主要是得益于质子转移所产生的PA阴离子与柔性连接臂中的质子化亚氨阳离了之间的静电吸引。盐效应和pH效应研究结果佐证了这种缔合作用的存在。此外,我们还设计合成了稠环双端修饰寡聚噻吩衍生物并研究了其在均相溶液中对含硝基类爆炸物的传感性能。结果表明,此类化合物对含硝基类爆炸物PA和2,6-双(2′,4′,6′-三硝基苯胺基)-3,5-二硝基吡啶(PYX)的存在非常敏感,同时具有非常好的选择性,大大拓宽了寡聚噻吩及其衍生物荧光传感材料的设计思路及应用范围。紫外灯下,化合物5,5"-二(1-芘)-2,2′：5′,2″-三聚噻吩(Py-3T-Py)对PA和PYX的检测过程产生从黄绿色到无色的颜色变化,可直接与其他含硝基类爆炸物通过裸眼分辨。传感机理表明,含硝基类化合物的拉电子能力及与荧光物质的结合能力决定着对荧光物质的猝灭程度。这类共轭寡聚物有望发展成一类对含硝基类爆炸物高灵敏度、高选择性的新型荧光传感材料。3)金属离子荧光传感材料研究。以三联吡啶为识别基团,寡聚噻吩为荧光报告基团,基于三联吡啶与金属离子之间的螯合作用,实现了对金属离子的灵敏定量检测以及配体5-(2,2′：6′,2″-三联吡啶)-2,2′：5′,2″-三聚噻吩(3T-Terpy)的光物理性质调控,并研究了其猝灭和色变的作用本质。配体3T-Terpy具有易溶于有机溶剂、量子产率高、Stokes位移大等特点。荧光测定表明甲醇中配体3T-Terpy的最大荧光发射波长在505nm处,对不同金属离子表现出丰富的传感行为。甲醇中Cd2+的加入使得3T-Terpy与之形成结合比为2：1螯合物,荧光发射红移至572nm,同时荧光强度增大,光学能隙减小,摩尔吸光系数增大。紫外灯下,溶液颜色由蓝绿色荧光变成亮黄色荧光。CU2+,Co2+及Ni2+等离子的加入能完全猝灭配体3T-Terpy的荧光,猝灭程度与金属离子浓度有关,Ksv值分别为2.33×107M-1,2.74×106M-1和6.73×105M-1,明显大于其他金属离子,其中对Cu2+传感现象最灵敏,检出限为2.91×10-mol/L；而Zn2+的加入也使得配体3T-Terpy的荧光发射红移,但荧光强度降低；Hg2+, Pb2+和Pd2+离子部分猝灭配体3T-Terpy的荧光,而Na+、K+、NH4+、Fe3+、Mg2+和Ba2+等离子及H+OH-和水对荧光发射光谱改变很小,基于此现象可以实现溶液中金属离子的灵敏检测和可视化检测。本论文的创新点在于：(1)发展了一系列以寡聚噻吩为核心结构的新型高化学稳定性荧光分子,拓展了荧光传感元素种类,深化了对决定寡聚噻吩类共轭寡聚物光电性能结构本源的认识,为构建新的高效荧光传感平台奠定了基础。(2)发现紫外光照单分子层组装寡聚噻吩荧光薄膜是获得高性能“turn-on "型气相甲醛检测荧光薄膜的有效途径,突破了甲醛气体的传统检测模式,为发展高选择性气相甲醛传感器打下了坚实的基础。(3)设计、制备了多种稠环封端寡聚噻吩衍生物,提高了其光化学稳定性,得到了综合性能优异、对气相及液相微痕量含硝基类爆炸物敏感的传感材料。(4)设计制备了以三联吡啶为识别基团的寡聚噻吩衍生物,实现了对部分金属离子的灵敏可视化检测,侧重研究了Cd2+与配体分子之间的作用本质,实现了对配体光物理性质的有效调控。更多还原

【Abstract】 a-Oligothiophene and its derivatives have attracted much attention in the field of organic functional material and material science because of their well-defined, easily adjustable and controllable molecular structures, and remarkable electronic properties. Additionally, it also has advantages as strong absorption, high quantum yield and large Stokes’shift characterized by a good sensing fluorophore. Extensive studies found that this kind of fluorophores is photochemically unstable in sensing, particularly when they are immobilized onto substrate surfaces, which greatly limited its applications. Obviously, the first challenge we encountered in the work is to improve the photochemical stability of the oligothiophenes. The functionalization in its α-or β-position with a variety of aromatic moieties have been reported to adjust the energy gap of the compounds and increase their photochemical stabilities. This method has been widely applied in fabricating oligothiophene functionalized devices in the area of organic light-emitting diodes (OLEDs) and field-effect transistors (FETs).The development of fluorescent chemsensors has been an active research topic for many research fields. A fluorescent chemsensor realizes the sensing functions based on the change of sensor-relative fluorescence intensity and emission wavelength of them as signals. A typical fluorescent chemsensor includes three building units, namely, a receptor responsible for the molecular recognition of the analyte, a fluorophore responsible of signaling the recognition event and a linker between them. Compared with physical method, the self-assembled monolayers functionalized fluorescent film sensor, where the sensing element is immobilized on substrate surface via chemical bonds, can avoid the leaking of the chemicals and the contamination to the analytical system. In addition, the films prepared by chemical ways have shown several advantages of highly stable, re-useable, non-consumptive, and easy to be made into devices, etc. Design, synthesis and development of novel fluorophores for sensor construction are especially important to the sensitivity and selectivity of the fluorescent film sensors. On the basis of the considerations mentioned above, combining the reviews on chemically modified self-assembled fluorescent films and the current status of oligothiophenes, several film sensors were designed and prepared by immobilizing a-oligothiophene and its derivatives on glass slide surfaces via different flexible spacers. The obtained sensing films show high sensitivity and selectivity to formaldehyde vapor, nitro-containing explosives in the vapor phase and aqueous phase. Furthermore, their remarkable sensing ability, high sensitivity, ideal reversibility and long lifetime make them worthwhile to be exploited further. We also designed and synthesized several symmetrical aromatic end-capped oligothiophene derivatives and2,2’:6’,2"-terpyridine functionalized oligothiophene, which can be used to detect nitro-containing explosives and metal ions in aqueous solution, respectively.There are four parts in this thesis. The first part is about the reviews on chemically modified self-assembled fluorescent films and photophysical properties of oligothiophenes. The other three parts are about the experimental researches based on oligothiophene and its derivatives. More concretely, we get the following main results.In the second part of this thesis, novel fluorescent sensing films were fabricated by monomolecular layer assembly of oligothiophene onto an amine-terminated glass wafer surface. Contact angle, X-ray photoelectron spectroscopy (XPS) and steady-state fluorescence measurements demonstrated that the fluorophore was successfully immobilized on the substrate surface. The fluorescence emission of the film, however, is not stable in air, and it decreased along with increasing scanning number. Continuous irradiation of the film with UV-light decreased, but stabilized the fluorescence emission of the film. Exposure of the specially treated film into formaldehyde (HCHO) vapor generated a new fluorescence emission, which appeared in a shorter wavelength (458nm) in comparison with that of the original one. The intensity of the emission increased along with increasing the exposure time, as an example for2,2’:5’,2"-terthiophene (3T) functionalized sensing film, the intensity can be increased more than18.6times in30min. Furthermore, interference experiments revealed that the sensitization process is selective, and solvents including common acids, bases and alcohols have little effect upon the process. More interestingly, the process is reversible. We also proposed the possible sensing mechanism based on abundant blank tests and control tests. Accordingly, it is believed that the oligothiophene functionalized film should be a strong candidate for developing a novel and sensitive HCHO fluorescent film sensor.In the third part of this thesis, aromatic end-capped oligothiophene derivatives were synthesized and chemically immobilized onto a glass wafer surface via flexible spacers by employing a single-layer chemistry technique. Unlike the film fabricated in the same way but with3T as the fluorophore, the film fabricated in the present study possesses unprecedented photochemical stability at ambient conditions. Fluorescence studies revealed that the emission of the film as fabricated is significantly and selectively quenched by the presence of nitro-containing explosives both in the vapor phase and in aqueous solution. Experimental and theoretical studies demonstrated that the quenching may be a result of electron transfer from the electron-rich aromatic end-capped oligothiophene derivatives to the electron-deficient nitro-containing explosives. It was found that the response time and the quenching efficiency of the systems are dominantly determined by the vapor pressures of the nitro-containing explosives tested for the vapor phase sensing. The sensing performances of the film to nitro-containing explosives in aqueous phase were also investigated. In this case, however, the specific binding of the film to picric acid (PA) makes the compound show a superior quenching efficiency than other nitro-containing explosives. Moreover, the response is fast and reaches equilibrium within90s. Furthermore, acids, bases, apple juice, perfume and some commonly found organic solvents show little effect upon the sensing process. Both the vapor phase sensing and the aqueous solution sensing are reversible. Furthermore, the film is stable for at least6months provided it is properly preserved. The basic contribution of the present work is not only creating a new fluorescent film of superior sensing properties to nitro-containing explosives in the vapor phase, in particular to PA in the aqueous phase, but also providing a series of novel photochemically stable fluorophores, which may combine the advantages of small molecular fluorophores and those of conjugated polymers/oligomers, for developing new fluorescent sensing films. At the same time, a series of novel π-electron rich fluorophores which differ by the terminal units of3T have been synthesized and found that all the fluorophores are sensitive to the presence of nitro-containing explosives, in particular, PA and3,5-dinitro-2,6-bispicrylamino pyridine (PYX). On the basis of their structure-property relationships, a mechanism was proposed to explain the possible interactions between the compounds as prepared and the nitro-containing explosives under study. Considering the optical and sensing properties of these novel π-conjugated aromatic end-capped oligothiophenes, it is anticipated that they can be developed into fluorescent sensory materials for real applications.In the fourth part of this thesis, it is reported that design and synthesis of an oligothiophene derivative modified by2,2’:6’,2"-terpyridine unit as the fluorescent binding group. The photochromism of the free ligand and the influence of metal ions on the photochemical properties have been thoroughly characterized by monitoring the changes in their fluorescence emission spectra. Furthermore, the fluorescence results show that this kind of material can be used for selective and sensitive detecting of metal ions. The chemical structure of the product was identified by fluorescence, UV-Vis, FT-IR, MS and NMR. The photochromic properties of the ligand have been found to be strongly influenced by the bridging transition metal ions, the results indicate that Cd2+and Zn2+can interact with the fluorophore, make the fluorescence emission red-shifted and the fluorescence intensity increased for Cd2+and decreased for Zn2+, respectively. Metal ions such as Co2+, Cu2+, Ni2+, Pb2+Pd2+and Hg2+can effectively quench the fluorescence intensity. Whereas, Na+, K+NH4+, H+, Mg2+, Ba2+, Fe3+, OH-and H2O do not produce obvious fluorescence changes of the ligand. It is worth noting that the optical properties of π-conjugated oligomer incorporating2,2’:6’,2"-terpyridine as recognition site can be greatly improved and adjusted by functionalized with terpyridine units and further coordinated with metal ions.The key contributions of this study can be generalized as follows:(1) We employ α-oligothiophenes as the sensing fluorophores, deeply study their fluorescence properties and broaden their applications for the fabraction of fluorescent self-assembled monolayers.(2) We firstly discover the special interactions between UV-light treated fluorescent sensing film based on oligothiophene and formaldehyde vapor, propose the possible sensing mechanism and realize a new sensing way for detecting formaldehyde vapor.(3) In order to enhance the photophysical stability of a-oligothiophenes, we design and synthesis several novel aromatic end-capped oligothiophene derivatives and obtain excellent fluorescent sensing materials for nitro-containing explosives in the aqueous and vapor phase.(4) A new fluorescent chemosensor, using oligothiophene derivative modified by2,2’:6’,2"-terpyridine unit as the binding group is fabricated. The fluorescence results show that this kind of materials can be used for selective and sensitive detecting for metal ions. The optical properties of oligothiophene derivatives can be greatly improved by functionalized by terpyridine unit and further coordinated with metal ions.更多还原