The electronic structure and optical properties of carbazole-based conjugated oligomers and polymers: A theoretical investigation
The electronic structure and optical properties of carbazole-based conjugated oligomers and polymers: A theoretical investigation
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DOI：
10.1016/j.polymer.2005.12.065
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发表时间：
2006-02
期刊：
影响因子：
4.6
通讯作者：
Li Yang;Ji-Kang Feng;Aimin Ren;Jia-Zhong Sun
中科院分区：
文献类型：
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作者：
Li Yang;Ji-Kang Feng;Aimin Ren;Jia-Zhong Sun
聚荧烯(PFS)在聚合物发光二极管(PLED)中的应用一直受到限制，因为在器件制造和运行过程中，由于电荷注入困难和在长波长(>；500 nm)形成拖尾发射带的麻烦，导致颜色不稳定和效率降低。聚咔唑已被证明能有效地抑制酮缺陷的发射。在这一贡献中，我们应用量子化学技术研究了聚(N-甲基-2，7-咔唑二基)(PCZ)及其共聚物poly(N-methyl-2，7-carbazolediyl-alt-2，5-thiophene)(PCZT)和聚(N-甲基-2，7-咔唑乙炔)(PCZE)，并详细了解了咔唑单元和不同载流子的引入对电子和光学性质的影响。用B3LYP泛函方法研究了中性分子HOMO-LUMO能隙(ΔH-LUMO)以及IPs和EAs的电子性质。用含时密度泛函理论研究了它们的最低激发能和最大吸收波长λ。计算结果表明，咔唑类聚合物的HOMO能级提高了约0.3 eV，介电常数降低了约0.3 eV，空穴接收和传输能力显著提高。更重要的是，通过引入载流子噻吩环和乙炔，PCZT和PCZE中的LUMO能量分别降低了约0.4 eV和0.6 eV，这有助于EAs的降低，从而改善了电子的接受和传输性能。此外，随着共聚物链平面度的增加，能隙变窄，吸收峰和发射峰逐渐红移到较长的波长。
The application of polyfluorenes (PFs) in polymeric light-emitting diodes (PLEDs) has been hampered because of the charge injection difficulties and the troublesome formation of a tailed emission band at long wavelengths (>500nm) during device fabrication and operation, leading to both a color instability and reduced efficiency. The polycarbazoles have been proved to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate poly(N-methyl-2,7-carbazolediyl) (PCz), and its copolymers poly(N-methyl-2,7-carbazolediyl-alt-2,5-thiophene) (PCzT) and poly(N-methyl-2,7-carbazoleethynylene) (PCzE), and gain a detailed understanding of the influence of carbazole units and the introduction of different charge carriers on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO–LUMO gaps (ΔH–L), in addition to IPs and EAs, are studied using B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength λabsare studied employing the time dependent density functional theory (TDDFT). The calculated results show that the HOMO energies lift about 0.3eV and thus the IPs decrease about 0.3eV in all the carbazole-based polymers, suggesting the significant improved hole-accepting and transporting abilities. More important, by introducing the charge carriers thiophene ring and ethynylene, the LUMO energies in PCzT and PCzE decrease around 0.4 and 0.6eV, respectively, which contributes to the decreasing EAs and the consequent improved electron-accepting and transporting properties. In addition, the energy gap tends to narrow and the absorption and emission peaks are gradually red-shifted to longer wavelengths with an increase in chain planarity in the copolymers.