title: Delayed fluorescence in a solution-processable pure red molecular organic emitter based on dithienylbenzothiadiazole: a joint optical, electroluminescence, and magnetoelectroluminescence study.
abstract: The discovery of triplet excitons participating in the photoluminescent processes in a growing number of pure organic emitters represents an exciting impetus for a diversity of promising opto, bio, and optoelectronic applications. In this contribution, we have studied a small-molecule dithienylbenzothiadiazole-based red-emitting dye red-1b, which shows clearly delayed fluorescence under optical and electrical excitation. The OLED device that contained red-1b as a nondoped solution-processable emitter exhibited a moderately high utilization of exciton amounting to ≈31% and slow efficiency roll-off. Magnetoelectroluminescence measurements revealed the coexistence of reverse intersystem crossing from the lowest triplet state to singlet state (RISC, E-type triplet to singlet up-conversion) and triplet-triplet annihilation (TTA, P-type triplet to singlet up-conversion). Specifically, in low current-density regime, the moderately high exciton utilization is attributed to RISC (i.e., thermally activated delayed fluorescence, TADF), whereas in high current-density regime, TTA may contribute to suppressing efficiency roll-off. Furthermore, the results showed that red-1b may represent a new kind of organic red emitters that display delayed fluorescence in a way differing from the few red emitters investigated so far.
authors.affiliation: State Key Laboratory of Supramolecular Structure and Materials, Jilin University , Changchun, 130012, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: Wang
authors.forename: Wan-Yi
authors.initials: WY
authors.lastname: Tan
authors.forename: Qi-Ming
authors.initials: QM
authors.lastname: Peng
authors.forename: Shi-Tong
authors.initials: ST
authors.lastname: Zhang
authors.forename: Xu-Hui
authors.initials: XH
authors.lastname: Zhu
authors.forename: Feng
authors.initials: F
authors.lastname: Li
keywords: electroluminescence; exciton utilization; magnetoelectroluminescence; reverse intersystem crossing; triplet−triplet annihilation