2,5-Di(aryleneethynyl)pyrazine derivatives: synthesis, structural and optoelectronic properties, and light-emitting device
作者:Liang Zhao、Igor F. Perepichka、Figen Türksoy、Andrei S. Batsanov、Andrew Beeby、Karen S. Findlay、Martin R. Bryce
DOI:10.1039/b401867m
日期:——
A series of 2,5-di(aryleneethynyl)pyrazine derivatives has been synthesised in 23–41% yields by two-fold reaction of 2,5-dibromo-3,6-dimethylpyrazine 3 with ethynylarenes (arene = phenyl, 2-pyridyl, 4-ethylphenyl, 4-chlorophenyl, 4-biphenyl) under standard Sonogashira conditions [CuI, Pd(PPh3)2Cl2, NEt3, THF]. Compound 3 has been converted into 2,5-diethynyl-3,6-dimethylpyrazine, which reacts with 2-iodothiophene to yield 2,5-bis(thien-2-ylethynyl)-3,6-dimethylpyrazine. In the X-ray crystal structure of 2,5-di(phenylethynyl)-3,6-dimethylpyrazine 4 the two phenyl rings are parallel and the pyrazine ring is inclined to their planes by 14.2°. Quantum chemical calculations establish that the HOMO–LUMO gap for 4
(3.56 eV) is lower than that of di(phenylethynyl)benzene 12
(3.72 eV). The nitrogen atoms of 4 serve to localise the HOMO on the central ring’s carbon atoms, resulting in a quinoidal-type population, in contrast to 12. Cyclic voltammetric studies establish that 4 undergoes a reduction to the radical anion at ca.
−1.9 V (vs. Ag/Ag+ in MeCN), which is almost reversible at high scan rates (500 mV s−1). The UV-vis absorption and photoluminescence profiles of 4 in cyclohexane are similar to those of 12; the emission for 4
(λmax 379 and 395 nm) is red-shifted compared to 12. Single-layer OLEDs using MEH-PPV as the emissive polymer show significantly enhanced external quantum efficiencies (up to 0.07%) when 20% by weight of 2,5-di(biphenyl-4-ethynyl)-3,6-dimethylpyrazine 8 is added as a dopant: this is ascribed to the enhanced electron-transporting properties of the pyrazine system.
通过2,5-二溴-3,6-二甲基吡嗪3与乙炔基芳烃(芳烃=苯基、2-吡啶基、4-乙基苯基、4-氯苯基、4-联苯基)在标准Sonogashira条件下[CuI, Pd(PPh3)2Cl2, NEt3, THF]进行二重反应,合成了一系列2,5-二(芳撑乙炔基)吡嗪衍生物,产率为23%-41%。化合物3已转化为2,5-二乙炔基-3,6-二甲基吡嗪,它与2-碘噻吩反应生成2,5-二(苯并噻吩-2-乙炔基)-3,6-二甲基吡嗪。在2,5-二(苯乙炔基)-3,6-二甲基吡嗪4的X射线晶体结构中,两个苯基环平行,吡嗪环与它们的平面倾斜14.2°。量子化学计算表明,4的最高占据分子轨道-最低未占分子轨道能隙(3.56 eV)低于二(苯乙炔基)苯12的(3.72 eV)。与12相反,4的氮原子使最高占据分子轨道局域在中心环的碳原子上,导致类醌型分布。循环伏安研究表明,4在大约-1.9 V(相对于MeCN中的Ag/Ag+)处被还原为自由基阴离子,在高扫描速率(500 mV s-1)下几乎可逆。4在环己烷中的紫外-可见吸收和光致发光光谱与12相似;4的发射峰(λmax 379和395 nm)比12的红移。使用MEH-PPV作为发光聚合物时,当2,5-二(联苯-4-乙炔基)-3,6-二甲基吡嗪8以20%的重量作为掺杂剂添加时,单层有机发光二极管的外部量子效率显著提高(高达0.07%):这归因于吡嗪系统的增强电子传输特性。