光掺杂(Photo-Doping) When trans-(CH)x for example, is exposed to radiation of energy greater than its band gap, electrons are promoted across the gap and the polymer undergoes ªphoto-dopingº. Under appropriate experimental conditions, spectroscopic signatures characteristic of, for example, solitons can be observed
• p-Doping can also be accomplished by electrochemical anodic oxidation by immersing a trans-(CH)x film in, for example, a solution of LiClO4 dissolved in propylene carbonate and attaching it to the positive terminal of a DC (direct current) power source, the negative terminal being attached to an electrode also immersed in the solution.
导电高分子 Conducting Polymers
董常明 上海交通大学化学化工学院 高分子科学与工程系419室
Tel: 54748916(O) Email: cmdong@
Nobel Prize in Chemistry 2000 Electrically Conductive Plastic
Comparison of chemical and electrochemical CP polymerization
Synthesis of PA using Ziegler–Natta catalysts
Fig. 15. Polymerization of acetylene at various temperatures using Ziegler–Natta catalysts (trialkylaluminum reagents mixed with titanium alkoxides/ Ti(O-n-C4H9)4/(C2H5)3Al).
Synthetic methods of conducting polymers
• Conducting polymers are categorized as the cationic and anionic salts of highly conjugated polymers. Whereas the cation salts are obtained by chemical oxidation and electrochemical polymerization, it is also possible to produce the anion salts of the highly conjugated polymers using electrochemical reduction or chemical reduction with reagents such as sodium naphthalide. • An oxidized conducting polymer has electrons removed from the backbone, resulting in a cationic radical. On the other hand, a reduced conducting polymer has electrons added to the backbone, resulting in an anionic radical. However, this reduced conducting polymer is much less stable than thecation counterpart. • In general, there are two synthetic methods of conducting polymers: chemical polymerization and electrochemical polymeri 脱掺杂态所对应的颜色变化
导电高分子的导电原理
掺杂(Doping)
• 导电聚合物的共轭链上每单体单元对应的对离子数称为掺杂浓度。对 几种常见的导电聚合物，聚乙炔的掺杂浓度为0.1—0.2，聚吡咯和聚噻 吩为0.25—0.35，聚苯胺为0.4—0.5。
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导电聚合物的掺杂结构涉及对离子的掺杂。但更一般地，只要有电荷 入共轭聚合物主链，都可以称为掺杂(doping)。导电聚合物的掺杂可 过给体或受体的电荷转移、电化学氧化还原、界面电荷注入等手段来 现。 可见-近红外吸收光谱是判断导电聚合物掺杂状态的有效手段，掺杂导 电态在近红外区有较强的吸收，脱掺杂后的本征态则近红外区吸收消 从共轭聚合物中性本征态的紫外-可见吸收光谱可计算其禁带宽度，常 见共轭聚合物本征态的禁带宽度（E）为1.8—3.0 eV。
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图. 聚吡咯的可见-近红外吸收光谱：a. 掺杂态; b. 本征态
化学掺杂：化学掺杂包括p 型掺杂和n 型掺杂两种。 • p 型掺杂
• n 型掺杂
电化学掺杂 • 电化学掺杂是通过电化学反应实现导电聚合物的掺杂。许多共轭聚合 物在高电位区可发生电化学p 型掺杂/脱掺杂(氧化/再还原) 过程，在低 电位区又可发生电化学n 型掺杂/脱掺杂(还原/再氧化) 过程。 • 但有些导电聚合物(如聚吡咯、聚苯胺等) 因其发生n 型掺杂的电位太 低(< - 3.0 V vs. SCE) 而无法观察到n 型掺杂/脱掺杂反应。
典型的导电高分子
导电高分子的性能
• 导电高分子室温电导率可在绝缘体-半导体-金属态范围内(10-9S/cm - 105S/ cm ) 变化。这是迄今为止任何材料无法比拟的。
图
导电高聚物电导率覆盖范围
• 导电高分子在掺杂-脱掺杂的过程中伴随着完全可逆的颜色变化。 • 聚苯胺从- 0. 2 至+ 0. 8V 氧化-还原过程伴随着发生淡黄- 蓝色- 紫色的变
极化子理论
聚苯的极化子和双极化子 （a) 基态A；（b)基态B; (C)极化子；（d）双极化
能带理
电子聚合物能带结构示意图 （a) 孤子能带; (C)极化子能带；（d）双极化子能
Fig. 4. The valence-effective Hamiltonian band structure evolution of PPy (top) and PT (bottom) upon doping. PPy (top): (A) undoped and (B) intermediate doping level. Formation of non-interacting bipolarons at 0.45 eV above the valence band (VB) and 0.9 eV below the conductive band (CB). (C) 33% doping level: Formation of bipolaron bands with width of 0.25 eV. (D) 100% doping level per monomer. Merging of bipolaron bands with VB and CB. Note the decrease in band gap from 4 to 1.4 eV.
酸掺杂
孤子理论(SSH)
W. P. Su, J. R. Sebrieffer, A. J. Heeger, Phys. Rev. Lett. 1979, 42, 1698.
反式聚乙炔孤子结构图
（a) 基态A；（b)基态B; (C)二基态的结合部位；（d）键长逐步过渡； （e）相对于等距离原子核排布的原子核位移服从Tanh函数。
• 导电高分子：由具有共轭π键的高分子，经化学或电化学“掺杂”使其由 绝缘体转变为(半)导体的一类高分子材料。 • 导电高分子的结构特征：由有高分子链结构和与链非键合的一价对阴离 子（p-型掺杂）或对阳离子（n-型掺杂）共同组成。 • 导电高分子不仅具有由于掺杂而带来的金属（高电导率）和半导体(p-和 n-型) 的特性之外，还具有高分子的可分子设计结构多样化，可加工和比 重轻的特点。
Fig. 5. Introduction of polaron and bipolaron lattice deformation upon oxidation (p-type doping) in heterocyclic polymers. X = S, N, or O. A polaron or radical cation is introduced into the conjugated backbone after the loss of an electron. When oxidation of the same segment of the conjugated backbone occurs the unpaired electron of the polaron is lost and a dication (i.e., bipolaron) is formed.
界面电荷注入掺杂 在聚合物半导体器件, 如聚合物发光二极管 (LED) 和聚合物场效应管(FET ) 中，在电场的作用下电荷可以直接从金属电极通过接触界面注入共轭聚合物， 成共轭聚合物的电荷“掺杂”，空穴注入共轭聚合物的价带形成p 型掺杂，电子 入共轭聚合物的导带形成n 型掺杂。这种掺杂与前面提到的化学掺杂和电化学 杂有所不同，这里没有对离子。