Efficient non-doped blue emitting devices based on bis(phenanthrimidazolyl)biphenyl derivatives

Abstract

Efficient blue-emitting isomers of bis(phenanthrimidazolyl)biphenyl derivatives, 4,4′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (4,4′-BNPIB), 3,4′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]imidazole-2-yl)biphenyl (3,4′-BNPIB) and 3,3′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]-imidazol-2-yl)-biphenyl (3,3′-BNPIB) have been synthesised by tuning the coupling position on the biphenyl from the para- to meta-position. These compounds exhibit excellent thermal properties with a high glass-transition temperature of 152–198 °C and emit intense blue light in solution at ca. 396 nm. Because of changes in the degree of conjugation at the C-2 position in the phenanthrimidazole unit, the emission of 3,4′-BNPIB (413/430 nm) and 3,3′-BNPIB (396/426 nm) is blue-shifted when compared with that of 4,4′-BNPIB (422/450 nm) in both solution and film. The fabricated non-doped devices based on these materials exhibit blue emission at 431 nm (4,4′-BNPIB), 412 nm (3,4′-BNPIB) and 400 nm (3,3′-BNPIB), and 3,4′-BNPIB exhibits efficient performance with a maximum luminance of 39 823 cd m⁻², a current efficiency of 8.01 cd A⁻¹, a quantum efficiency of 4.85% and a power efficiency of 7.02 lm W⁻¹.