title: High-Performance Blue OLEDs Based on Phenanthroimidazole Emitters via Substitutions at the C6- and C9-Positions for Improving Exciton Utilization.
abstract: Donor-acceptor (D-A) molecular architecture has been shown to be an effective strategy for obtaining high-performance electroluminescent materials. In this work, two D-A molecules, Ph-BPA-BPI and Py-BPA-BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6- and C9-positions of a locally excited-state emitting phenylamine-phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge-transfer properties, both molecules show high performances as blue emitters in nondoped organic light-emitting devices (OLEDs). An OLED using Ph-BPA-BPI as the emitting layer exhibits deep-blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A(-1) , and 3.66 lm W(-1) , respectively. On the other hand, a Py-BPA-BPI-based, sky-blue OLED delivers the best results among nondoped OLEDs with CIEy values of < 0.3 reported so far, for which a very low turn-on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A(-1) , 10.5 lm W(-1) , and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll-off and high singlet exciton-utilizing efficiencies of 36.2 % for Ph-BPA-BPI and 39.2 % for Py-BPA-BPI.
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.|Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, P. R. China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.
authors.forename: Dan
authors.initials: D
authors.lastname: He
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.
authors.forename: De-Yue
authors.initials: DY
authors.lastname: Huang
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.
authors.forename: Cheng-Yuan
authors.initials: CY
authors.lastname: Luo
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.|Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, P. R. China.
authors.forename: Ze-Lin
authors.initials: ZL
authors.lastname: Zhu
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China.
authors.forename: Feng
authors.initials: F
authors.lastname: Lu
authors.affiliation: Department of Chemistry and Key laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong, 515063, P. R. China. qxtong@stu.edu.cn.
authors.forename: Qing-Xiao
authors.initials: QX
authors.lastname: Tong
authors.affiliation: Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong SAR, P. R. China. apcslee@cityu.edu.hk.
authors.forename: Chun-Sing
authors.identifier: http://orcid.org/0000-0002-3486-5665
authors.initials: CS
authors.lastname: Lee
keywords: chromophores; donor-acceptor systems; exciton-utilizing efficiency; organic light-emitting devices; phenanthroimidazole