title: Manipulating the Electronic Excited State Energies of Pyrimidine-Based Thermally Activated Delayed Fluorescence Emitters To Realize Efficient Deep-Blue Emission.
abstract: The development of efficient and robust deep-blue emitters is one of the key issues in organic light-emitting devices (OLEDs) for environmentally friendly, large-area displays or general lighting. As a promising technology that realizes 100% conversion from electrons to photons, thermally activated delayed fluorescence (TADF) emitters have attracted considerable attention. However, only a handful of examples of deep-blue TADF emitters have been reported to date, and the emitters generally show large efficiency roll-off at practical luminance over several hundreds to thousands of cd m-2, most likely because of the long delayed fluorescent lifetime (τd). To overcome this problem, we molecularly manipulated the electronic excited state energies of pyrimidine-based TADF emitters to realize deep-blue emission and reduced τd. We then systematically investigated the relationships among the chemical structure, properties, and device performances. The resultant novel pyrimidine emitters, called Ac-XMHPMs (X = 1, 2, and 3), contain different numbers of bulky methyl substituents at acceptor moieties, increasing the excited singlet (ES) and triplet state (ET) energies. Among them, Ac-3MHPM, with a high ETof 2.95 eV, exhibited a high external quantum efficiency (ηext,max) of 18% and an ηextof 10% at 100 cd m-2with Commission Internationale de l'Eclairage chromaticity coordinates of (0.16, 0.15). These efficiencies are among the highest values to date for deep-blue TADF OLEDs. Our molecular design strategy provides fundamental guidance to design novel deep-blue TADF emitters.
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Komatsu
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ohsawa
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Hisahiro
authors.identifier: http://orcid.org/0000-0002-1312-0111
authors.initials: H
authors.lastname: Sasabe
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Nakao
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Yuya
authors.initials: Y
authors.lastname: Hayasaka
authors.affiliation: Department of Organic Materials Science, Graduate School of Organic Materials Science, Research Center for Organic Electronics (ROEL), and Frontier Center for Organic Materials (FROM), Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
authors.forename: Junji
authors.initials: J
authors.lastname: Kido
keywords: donor−acceptor system; organic light-emitting device; photochemistry; pyrimidine; solid-state emission; thermally activated delayed fluorescence (TADF)