A library of luminescent cyclometalated gold(III) complexes containing
various bis-cyclometalating R-C^N^C ligands derived from 2,6-diphenylpyridine
and ancillary alkynyl ligands, [Au(R-C^N^C)(C≡CR’)], has been synthesized.
Some of the complexes have been structurally determined by X-ray
crystallography. These complexes were found to exhibit intense emission in
dichloromethane solution at 298 K, originating from metal-perturbed triplet
intraligand (IL) excited states of the R-C^N^C ligand, with substantial charge
transfer character from the aryl moiety to the pyridyl ring. In the presence of
electron-rich alkynyl ligands, the emission origin could be switched to an
alkynyl-to-cyclometalating ligand ligand-to-ligand charge transfer (LLCT) excited
state. This class of complexes was also demonstrated to show rich
electroluminescence properties as emitters in organic light-emitting devices. In
addition, the supramolecular assembly of this class of complexes has also been
revealed in gelation studies.
N-Heterocyclic carbenes have been incorporated into the gold(III) metal
center to prepare a series of luminescent mononuclear and dinuclear gold(III)
complexes, [{Au(C^N^C)}n(NHC)](PF6)n and [{Au(tBuC^N^CtBu)}n(NHC)]-
(PF6)n
(n = 1, 2). The X-ray crystal structures of most of the complexes have been
determined. The emissions of these complexes were assigned to originate from the
metal-perturbed intraligand excited state of the bis-cyclometalating ligand. One of
the C2-bridged dinuclear complexes was found to exhibit two distinct reduction
couples, tentatively correlated to the presence of significant intramolecular π-π
interaction in the complex.
Two novel series of luminescent mononuclear alkynylgold(III) complexes,
[Au(C^N)(C≡CR)2] (HC^N = 2-phenylpyridine (Hppy) and derivatives) and
[Au(C^N^N)(C≡CR)]PF6 (HC^N^N = 6-phenyl-2,2’-bipyridine and derivatives),
have been synthesized. Some of the X-ray crystal structures have been determined.
The former class of complexes with bidentate C^N ligands has been observed to
show tunable emission spanning across the visible spectrum from 462 to 697 nm.
With the exception of [Au(ppy)(C≡C-C6H4-NH2-p)2] which showed a low-energy
band originated from a 3LLCT [π(C≡C-C6H4-NH2)→π*(C^N)] excited state, all
complexes exhibited vibronic-structured emission bands originated from the
intraligand transition of the cyclometalating C^N ligand in dichloromethane
solution at 298 K. On the other hand, most of the complexes with the tridentate
C^N^N-type ligand have been observed to exhibit vibronic-structured emission
bands attributed to the intraligand transition of the C^N^N ligand in
low-temperature butyronitrile glass. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/207995 |
| Date | January 2012 |
| Creators | Au, Ka-man, 區嘉雯 |
| Contributors | Yam, VWW |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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