Red-emitting materials derived from 2,3-dicyanopyrazine for organic light emitting devices

Abstract

Styryl-substituted derivatives of 2,3-dicyanopyrazine were designed and synthesised by the Knoevenagel condensation of 2,3-dicyano-5-methylpyrazines with 4-(diphenylamino)benzaldehyde for use as red-emitting fluorescent dyes in organic light-emitting devices. Structural analysis of the red-emitting styryl fluorescent dyes was carried out using H-1 NMR, FT-IR, and elemental analysis. The electroluminescent performance of multi-layered organic light-emitting devices fabricated with the triphenylamine-substituted dicyanopyrazine compound as the emitting layer achieved a current efficiency of 1.57 cd A(-1) in the green region with CIE coordinates of (0.37, 0.51). However, the green emission (525 nm) observed from the tris-(8-hydroxyquinolinato)aluminum(III) (Alq(3)) electron-transport layer indicated the action of a recombination phenomenon between the emitting layer and the Alq(3) electron-transport layer. The device fabricated with the tert-butylphenyl-substituted compound achieved a current efficiency of 0.238 cd A(-1) in the red region with CIE coordinates of (0.54, 0.42) and showed no recombination phenomenon.