Assistant acceptor induced hybrid local and charge transfer blue-emissive electro-fluorescent materials based on locally excited triphenylamine-phenanthroimidazole backbone

Abstract

Introducing charge-transfer (CT) excited state components is an important method to enhancing the electro-exciton utilization (ηs) to break the 25% spin-statistic limit. Herein, based on two locally-excited (LE) backbone materials that are of limited ηs, we reported two materials with the introduction of "assistant acceptor" cyanophenyl ring to induce larger charge-separation on the backbone materials and construct proper hybrid local and charge-transfer (HLCT) excited state. Theoretical and experimental characterizations are carried out to explore the excited state and photophysical properties of the two materials. The ηs of the non-doped OLED of the two materials both exceed the 25% spin-statistic limit, in which the CT dominated material TPM2CN demonstrates a large ηs of 72%, showing great potential for the next-generation blue-emissive material. This work gives a good example for the construction of HLCT blue-emissive materials by discussing and summarizing the details of molecular design method of “assistant acceptor”.