Syntheses, Structures, and Electroluminescence of New Blue/Green Luminescent Chelate Compounds: Zn(2-py-in)2(THF), BPh2(2-py-in), Be(2-py-in)2, and BPh2(2-py-aza) [2-py-in = 2-(2-pyridyl)indole; 2-py-aza = 2-(2-pyridyl)-7-azaindole]

Abstract

Four novel blue/green luminescent compounds, Zn(2-py-in) 2 (THF) ( 1 ), BPh 2 (2-py-in) ( 2 ), Be(2-py-in) 2 ( 3 ), and BPh 2 (2-py-aza) ( 4 ), where 2-py-in = 2-(2-pyridyl)indole and 2-py-aza = 2-(2-pyridyl)-7-azaindole, have been synthesized and fully characterized. The 2-py-in ligand and 2-py-aza ligand in the new compounds are chelated to the central atom. Compounds 2 − 4 are air stable and readily sublimable, with a melting point above 250 °C. In the solid state, compounds 1 − 4 have an emission maximum at λ 488, 516, 490, and 476 nm, respectively. The structures of compounds 2 and 4 are similar. The blue shift of emission energy displayed by compound 4, in comparison to that of 2, is attributed to the presence of an extra nitrogen atom in the 2-py-aza ligand as confirmed by ab initio calculations on compounds 2 and 4 . Electroluminescent devices of compounds 3 and 4 were fabricated by using N,N ‘ -di-1-naphthyl- N,N ‘ -diphenylbenzidine (NPB) as the hole transporting layer, Alq 3 (q = 8-hydroxyquinolato) as the electron transporting layer, and compound 3 or 4 as the light emitting layer. At 20 mA/cm 2 the EL device of 3 has an external efficiency of 1.06 cd/A while the EL device of 4 has an external efficiency of 2.34 cd/A, demonstrating that compounds 3 and 4 are efficient and promising emitters in electroluminescent devices.