title: 2,5-difluorenyl-substituted siloles for the fabrication of high-performance yellow organic light-emitting diodes.
abstract: 2,3,4,5-Tetraarylsiloles are a class of important luminogenic materials with efficient solid-state emission and excellent electron-transport capacity. However, those exhibiting outstanding electroluminescence properties are still rare. In this work, bulky 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and 9,9'-spirobifluorenyl substituents were introduced into the 2,5-positions of silole rings. The resulting 2,5-difluorenyl-substituted siloles are thermally stable and have low-lying LUMO energy levels. Crystallographic analysis revealed that intramolecular π-π interactions are prone to form between 9,9'-spirobifluorene units and phenyl rings at the 3,4-positions of the silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with a certain extension of π conjugation, respectively. With increasing substituent volume, intramolecular rotation is decreased, and thus the emissions of the present siloles gradually improved and they showed higher fluorescence quantum yields (Φ(F) =2.5-5.4%) than 2,3,4,5-tetraphenylsiloles. They are highly emissive in solid films, with dominant green to yellow emissions and good solid-state Φ(F) values (75-88%). Efficient organic light-emitting diodes were fabricated by adopting them as host emitters and gave high luminance, current efficiency, and power efficiency of up to 44,100 cd m(-2), 18.3 cd A(-1), and 15.7 lm W(-1), respectively. Notably, a maximum external quantum efficiency of 5.5% was achieved in an optimized device.
authors.affiliation: College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036 (China).
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.forename: Yibin
authors.initials: Y
authors.lastname: Jiang
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Han
authors.initials: H
authors.lastname: Nie
authors.forename: Bairong
authors.initials: B
authors.lastname: He
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.forename: Herman H Y
authors.initials: HH
authors.lastname: Sung
authors.forename: Ian D
authors.initials: ID
authors.lastname: Williams
authors.forename: Hoi Sing
authors.initials: HS
authors.lastname: Kwok
authors.forename: Anjun
authors.initials: A
authors.lastname: Qin
authors.forename: Zujin
authors.initials: Z
authors.lastname: Zhao
authors.forename: Ben Zhong
authors.initials: BZ
authors.lastname: Tang
mesh_terms: D055615:Electrical Equipment and Supplies; D004563:Electrochemistry; D054879:Halogenation; D008027:Light; D049449:Luminescence; D049408:Luminescent Agents / Q000737:chemistry*; D008958:Models, Molecular; D012821:Silanes / Q000737:chemistry*
chemical_list: D049408:Luminescent Agents; D012821:Silanes; C540376:silole
keywords: aggregation; luminescence; organic light-emitting diodes; siloles; steric hindrance