109192-11-2Relevant articles and documents
2,5-Di(aryleneethynyl)pyrazine derivatives: Synthesis, structural and optoelectronic properties, and light-emitting device
Zhao, Liang,Perepichka, Igor F.,Tuerksoy, Figen,Batsanov, Andrei S.,Beeby, Andrew,Findlay, Karen S.,Bryce, Martin K.
, p. 912 - 918 (2007/10/03)
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) 2CI2, 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 (λ max 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.
