Dimeric phenanthroimidazole for blue electroluminescent materials: the effect of substituted position attached to biphenyl center

Two isomers of 4,4'-bis(1-phenyl-phenanthro[9,10-d]-imidazol-2-yl)biphenyl (BPPI), L-BPPI and Z-BPPI were prepared by tuning the substituted position on the biphenyl from para-to meta-coupling. Because of the conjugated degree change at the C2-position in the phenanthroimidazole block, the fluorescent color of L-BPPI (433 nm) and Z-BPPI (402 nm) showed an obvious blue-shift compared with that of BPPI (468 nm) in the films. Meanwhile, their non-doped devices exhibited more valuable and stable deep-blue emissions with a CIE coordinate of (0.16, 0.10) and (0.16, 0.11), respectively. Furthermore, some valuable information on structure-properties was obtained by density functional theory calculations, and photophysical and electrochemical characterization.