Unusual Temperature-Dependent Photophysics of Oligofluorene-Substituted   Tris-Cyclometalated Iridium Complexes

doi:10.1021/ma2024123

CORC > 北京大学 > 化学与分子工程学院

	Unusual Temperature-Dependent Photophysics of Oligofluorene-Substituted Tris-Cyclometalated Iridium Complexes
	Yan, Qifan ; Fan, Yuanpeng ; Zhao, Dahui
刊名	macromolecules
	2012
关键词	METAL POLYPYRIDINE COMPLEXES LIGHT-EMITTING-DIODES IR-III COMPLEXES CONJUGATED POLYMERS HIGH-EFFICIENCY ELECTROPHOSPHORESCENT DEVICES IR(III) COMPLEXES STATE PROPERTIES SOLAR-CELLS PHOSPHORESCENCE
DOI	10.1021/ma2024123
英文摘要	The photophysical properties of a series of tris-cyclometalated h(Ill) complexes bearing oligofluorene-substituted 2-phenylpyridine (ppy) and/ or 1-phenylisoquinoline (piq) ligands were studied at both room temperature and 77 K, for delineating the oligomer-substitution effects on the photophysics in such metal-complex-containing conjugated oligomers/polymers. Unique temperature dependence was observed with the triplet excited-state lifetime of the studied oligomers. Molecules having one of the three ppy ligands substituted with an oligofluorenyl group at varied positions exhibited two distinct types of phosphorescing behaviors. When the oligoflurene group was coupled to ppy in a conjugative fashion (i.e., at 5- or 4'- position), the complexes appeared to emit from a (3)MLCT-dominated state perturbed by LC transition, as evidenced by the relatively short lifetimes of phosphorescence as well as hypsochromic shift upon lowering the temperature. Surprisingly, even shorter triplet lifetimes were detected at 77 K for such oligomers. When the oligofluorenyl was tethered to the phenyl ring of ppy meta to pyridine, emission properties were consistent with a (3)LC-dominated state, mixed with a certain MLCT component. Uniquely, for these oligomers an evident bathochromic shift of emission with a significantly retarded radiative decay rate was observed at 77 K. Furthermore, when a piq ligand was incorporated, red phosphorescence characteristic of Ir-piq-based (3)MLCT transition emerged, disregarding the substation position of the oligofluorene. All these different photophysical behaviors, particularly their unique temperature dependence, were explained by considering an energy transfer process between different triplet states, with dominant MLCT and LC characteristics. In complexes having all ppy-derived ligands, these two states were of similar but different energy. While one played a more important role than the other, both were contributing to the phosphorescence emission. The temperature dependence of the photophysics reflected the equilibrium shifting process. When the (3)MLCT-dominated state was lower in energy, faster radiative decay and shorter lifetimes were manifested upon lowering the temperature, as a result of more favored (3)MLCT-dominated state. Whereas if the (3)LC-dominated state was more stable, slower radiative decay emerged at decreased temperature due to further a reduced MLCT contribution. The bathochromic shift was also a result of equilibrium shifting to the state of lower energy. When the piq ligand was engaged, the emission was governed by the (3)MLCT state of the Ir-piq moiety, which had much lower energy compared to the triplet states localized in oligofluorenyl ppy. DFT calculations substantiated the above hypothesis by identifying separate molecular orbitals possessing mixed but imbalanced MLCT and LC components.; Polymer Science; SCI(E); EI; 11; ARTICLE; 1; 133-141; 45
语种	英语
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/393782]
专题	化学与分子工程学院
推荐引用方式 GB/T 7714	Yan, Qifan,Fan, Yuanpeng,Zhao, Dahui. Unusual Temperature-Dependent Photophysics of Oligofluorene-Substituted Tris-Cyclometalated Iridium Complexes[J]. macromolecules,2012.
APA	Yan, Qifan,Fan, Yuanpeng,&Zhao, Dahui.(2012).Unusual Temperature-Dependent Photophysics of Oligofluorene-Substituted Tris-Cyclometalated Iridium Complexes.macromolecules.
MLA	Yan, Qifan,et al."Unusual Temperature-Dependent Photophysics of Oligofluorene-Substituted Tris-Cyclometalated Iridium Complexes".macromolecules (2012).