title: Convergent modulation of singlet and triplet excited states of phosphine-oxide hosts through the management of molecular structure and functional-group linkages for low-voltage-driven electrophosphorescence.
abstract: The controllable tuning of the excited states in a series of phosphine-oxide hosts (DPExPOCzn) was realized through introducing carbazolyl and diphenylphosphine-oxide (DPPO) moieties to adjust the frontier molecular orbitals, molecular rigidity, and the location of the triplet excited states by suppressing the intramolecular interplay of the combined multi-insulating and meso linkage. On increasing the number of substituents, simultaneous lowering of the first singlet energy levels (S(1)) and raising of the first triplet energy levels (T(1), about 3.0 eV) were achieved. The former change was mainly due to the contribution of the carbazolyl group to the HOMOs and the extended conjugation. The latter change was due to an enhanced molecular rigidity and the shift of the T(1) states from the diphenylether group to the carbazolyl moieties. This kind of convergent modulation of excited states not only facilitates the exothermic energy transfer to the dopants in phosphorescent organic light-emitting diodes (PHOLEDs), but also realizes the fine-tuning of electrical properties to achieve the balanced carrier injection and transportation in the emitting layers. As the result, the favorable performance of blue-light-emitting PHOLEDs was demonstrated, including much-lower driving voltages of 2.6 V for onset and 3.0 V at 100 cd m(-2), as well as a remarkably improved E.Q.E. of 12.6%.
authors.affiliation: Key Laboratory of Functional Inorganic Material, Chemistry, Ministry of Education, Heilongjiang University, 74 Xuefu Road, Harbin 150080, PR China.
authors.forename: Chunmiao
authors.initials: C
authors.lastname: Han
authors.forename: Zhensong
authors.initials: Z
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Xu
authors.forename: Guohua
authors.initials: G
authors.lastname: Xie
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhao
authors.forename: Zhaopeng
authors.initials: Z
authors.lastname: Deng
authors.forename: Shiyong
authors.initials: S
authors.lastname: Liu
authors.forename: Pengfei
authors.initials: P
authors.lastname: Yan