title: Phosphorescent cyclometalated complexes for efficient blue organic light-emitting diodes.
abstract: Phosphorescent emitters are extremely important for efficient organic light-emitting diodes (OLEDs), which attract significant attention. Phosphorescent emitters, which have a high phosphorescence quantum yield at room temperature, typically contain a heavy metal such as iridium and have been reported to emit blue, green and red light. In particular, the blue cyclometalated complexes with high efficiency and high stability are being developed. In this review, we focus on blue cyclometalated complexes. Recent progress of computational analysis necessary to design a cyclometalated complex is introduced. The prediction of the radiative transition is indispensable to get an emissive cyclometalated complex. We summarize four methods to control phosphorescence peak of the cyclometalated complex: (i) substituent effect on ligands, (ii) effects of ancillary ligands on heteroleptic complexes, (iii) design of the ligand skeleton, and (iv) selection of the central metal. It is considered that novel ligand skeletons would be important to achieve both a high efficiency and long lifetime in the blue OLEDs. Moreover, the combination of an emitter and a host is important as well as the emitter itself. According to the dependences on the combination of an emitter and a host, the control of exciton density of the triplet is necessary to achieve both a high efficiency and a long lifetime, because the annihilations of the triplet state cause exciton quenching and material deterioration.
authors.affiliation: Innovation Center for Organic Electronics, Yamagata University, 1-808-48, Arcadia, Yonezawa, Yamagata, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Suzuri
authors.affiliation: KONICA MINOLTA, Inc., 2970 Ishikawa-machi, Hachioji-shi, Tokyo, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Oshiyama
authors.affiliation: KONICA MINOLTA, Inc., 2970 Ishikawa-machi, Hachioji-shi, Tokyo, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Ito
authors.affiliation: KONICA MINOLTA, Inc., 2970 Ishikawa-machi, Hachioji-shi, Tokyo, Japan.
authors.forename: Kunihisa
authors.initials: K
authors.lastname: Hiyama
authors.affiliation: KONICA MINOLTA, Inc., 2970 Ishikawa-machi, Hachioji-shi, Tokyo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kita
keywords: OLED; cyclometalated complex; iridium complex; phosphorescent emitter