Luminescent Platinum(ii), Palladium(ii) and Gold(iii) Complexes Containing Isocyanide, Alkynyl and N-Heterocyclic Carbene Ligands

Download or read book Luminescent Platinum(ii), Palladium(ii) and Gold(iii) Complexes Containing Isocyanide, Alkynyl and N-Heterocyclic Carbene Ligands written by Faan-Fung Hung and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Luminescent Platinum(II), Palladium(II) and Gold(III) Complexes Containing Isocyanide, Alkynyl and N-heterocyclic Carbene Ligands: Synthesis, Photophysical Properties and Material Applications" by Faan-fung, Hung, 孔繁峰, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Several cyclometalated Pt(II) isocyanide complexes containing C-deprotonated C DEGREESN DEGREESC ligands (C DEGREESN DEGREESC = 2,6-diphenylpyridine derivatives) were synthesized. These complexes display orange-red emissions with max at 582-619 nm and quantum yields of up to 26% in CH2Cl2 at room temperature. The incorporation of carbazole/fluorene/thiophene unit(s) to C DEGREESN DEGREESC ligands leads to minimized structural distortion of complexes in their excited states and thereby suppresses non-radiative decay pathways. The high thermal stability (Td >300 C) renders these complexes good candidates as phosphorescent dopants in organic light-emitting diodes (OLEDs). Red-emitting OLEDs with CIE coordinates of (0.650.01, 0.350.01) were fabricated by vacuum deposition, showing a maximum external efficiency of 12%. In addition, well-defined nano/microstructures were obtained from self-assembly of these complexes driven by π∙∙∙π, C-H∙∙∙π and C-H∙∙∙H-C interactions as observed in the crystal structures. Two series of organopalladium(II) alkynyl complexes containing a terpy (terpy = 2,2':6',2''-terpyridine) or C DEGREESN DEGREESC pincer carbene ligand (C DEGREESN DEGREESC = 2,6-bis(1-butylimidazol-2-ylidenyl)pyridine) were prepared. These complexes are non-emissive in solution at room temperature except that the one containing both C DEGREESN DEGREESC and pyrenylacetylide ligands shows phosphorescence (Φ = 0.3%) originating from intraligand state of the acetylide ligand. This could be attributed to the strong -donating N-heterocyclic carbene (NHC) in the pincer ligand that strongly destabilizes d-d state, the population of which provides an efficient non-radiative decay channel. To make comparison between Pd(II) and Pt(II) complexes with the two ligand systems, Pt(II) C DEGREESN DEGREESC alkynyl complexes were also prepared. They are emissive in solution and some display excimer emissions at high concentration (〖10〗 DEGREES(-4)-〖10〗 DEGREES(-3) mol 〖10dm〗 DEGREES(-3)). The X-ray crystal structures of [Pd(L)(CCPh)](〖PF〗_6) (L = terpy and C DEGREESN DEGREESC) revealed one-dimensional chain stacking of complex cations with alternating Pd(II)∙∙∙Pd(II) contacts of about 3.29-3.35 A and π-π interactions of about 3.4 A . Well-defined submicron/nanostructures were obtained from self-assembly of Pd(II) and Pt(II) alkynyl complexes driven by π-π interactions between aromatic moieties and/or metal∙∙∙metal interactions. DFT calculations on the optimized structures of [M(L)(CCPh)]+ (M = Pd(II) and Pt(II)) revealed the existence of metal∙∙∙metal closed-shell interactions. In addition, the complex containing the C DEGREESN DEGREESC ligand exhibits slightly enhanced metal∙∙∙metal interactions and larger "bonding" energy upon dimerization. Furthermore, spin-orbit coupling between singlet and triplet excited states is more effective which promotes rapid intersystem crossing. A new class of cyclometalated Au(III) complexes containing C-deprotonated C DEGREESN ligands (C DEGREESN = 2-phenylpyridine and its derivatives) and cis-chelating bis-NHC ligands was synthesized. These are the first examples of Au(III) complexes supported by cis-chelating bis-NHC ligands. They display emissions in solution under degassed condition at room temperature with &