Asymmetric aggregation-induced emission materials with double stable configurations toward promoted performance in non-doped organic light-emitting diodes
Three novel aggregation induced emission (AIE) active molecules TriPE-PA, TriPE-α-NA and TriPE-β-NA were designed and successfully synthesized through a simple synthetic route. The position 9 of chromophore anthracene was introduced with phenyl, 1-naphthyl and 2-naphthyl group, respectively, and afterwards the triphenylethylene was embedded as AIE active group at the position 10, thus generating two kinds of stable asymmetric configurations in the latter two compounds. These materials display sky-blue emission and typical AIE characteristics, among which TriPE-PA present the best AIE phenomenon with an αAIE value (ΦF(Film)/ΦF(THF)) of 63. Subsequent study shows that they exhibit very similar photophysical and electrochemical properties. However, an observation was captured that TriPE-α-NA and TriPE-β-NA performed much superior than TriPE-PA when they all functioned as the non-doped emitting layers in OLED, among which TriPE-β-NA presented an over six times higher EQE value in comparison with TriPE-PA. This is probably resulted from the support of double stable asymmetric configurations in TriPE-α-NA and TriPE-β-NA, which gives them a better membrane morphology and thermodynamic stability. The theories of energy traps at grain boundaries were employed to explain such causal relationship. Such results reemphasize a neglected strategy which may be helpful for the design of new AIE materials with high stability of efficiency.