Microwave accelerated synthesis and evaluation of conjugated oligomers based on 2,5-di-thiophene-[1,3,4]thiadiazole
作者:Mark C. McCairn、Theo Kreouzis、Michael L. Turner
DOI:10.1039/b922714h
日期:——
A series of π-conjugated 2,5-di-thiophene-[1,3,4]thiadiazole based pentamers have been synthesised by microwave promoted palladium catalysed cross-coupling reactions. The aromatic groups that terminate each pentamer have a profound effect on the observed optical, electrochemical and liquid crystalline properties. Substitution of progressively less electron rich aromatic groups at the periphery of the pentamers decreased the energy gap between the ground state and the first excited state and also lowered the energy of the frontier orbitals sufficiently to impede oxidation and facilitate reduction. The thermotropic calamitic mesogen, 2,5-bis-[5-(4-hexyl-phenyl)-thiophen-2-yl]-[1,3,4]thiadiazole, 7 showed non-dispersive ambipolar charge transport in the nematic, smectic and crystalline phases. The charge mobility increased concomitantly with increasing molecular order of the mesophase to a maximum in the highest ordered smectic phase (µhole ≈ 4 × 10−3 cm2 V−1 s−1, µelectron ≈ 8 × 10−3 cm2 V−1 s−1).
一系列基于π共轭的2,5-二噻吩-[1,3,4]噻二唑的五聚体通过微波促进的钯催化交叉偶联反应合成而成。终止每个五聚体的芳香基团对观察到的光学、电化学和液晶特性具有深远的影响。在五聚体外围逐渐替换为电子富集程度较低的芳香基团,减小了基态与第一激发态之间的能量间隔,同时也降低了边际轨道的能量,足以阻碍氧化并促进还原。热致液晶梅索材料2,5-双-[5-(4-己基-苯基)-噻吩-2-基]-[1,3,4]噻二唑7在向列相、层状相和结晶相中表现出无分散的双极电荷输运。随着介相分子有序性的增加,电荷迁移率也相应提高,在最高有序的层状相中达到最大值(µhole ≈ 4 × 10−3 cm2 V−1 s−1,µelectron ≈ 8 × 10−3 cm2 V−1 s−1)。