Manipulating the Electronic Excited State Energies of Pyrimidine-Based Thermally Activated Delayed Fluorescence Emitters To Realize Efficient Deep-Blue Emission

Ryutaro Komatsu; Tatsuya Ohsawa; Hisahiro Sasabe; Kohei Nakao; Yuya Hayasaka; Junji Kido

doi:10.1021/acsami.6b13482

Manipulating the Electronic Excited State Energies of Pyrimidine-Based Thermally Activated Delayed Fluorescence Emitters To Realize Efficient Deep-Blue Emission

ACS Appl Mater Interfaces. 2017 Feb 8;9(5):4742-4749. doi: 10.1021/acsami.6b13482. Epub 2017 Jan 25.

Authors

Ryutaro Komatsu¹, Tatsuya Ohsawa¹, Hisahiro Sasabe¹, Kohei Nakao¹, Yuya Hayasaka¹, Junji Kido¹

Affiliation

¹ 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.

PMID: 28121118
DOI: 10.1021/acsami.6b13482

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 (τ_d). To overcome this problem, we molecularly manipulated the electronic excited state energies of pyrimidine-based TADF emitters to realize deep-blue emission and reduced τ_d. 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 (E_S) and triplet state (E_T) energies. Among them, Ac-3MHPM, with a high E_T of 2.95 eV, exhibited a high external quantum efficiency (η_ext,max) of 18% and an η_ext of 10% at 100 cd m^-2 with 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.

Keywords: donor−acceptor system; organic light-emitting device; photochemistry; pyrimidine; solid-state emission; thermally activated delayed fluorescence (TADF).