Synthesis and Photoluminescence of Copper(I) Triazole Complexes and Copper(I)/Gold(I) Clusters

Luminescent copper(I) complexes are well known for their efficient, long-lived photoluminescence. These complexes show potential for use in electroluminescent devices as dopant emitters; however, many classes of Cu(I) emitters exhibit undesirable properties such as air sensitivity, irreversible electrochemical processes, and thermal instability. This thesis explores the design, synthesis, and photophysical studies of new emissive copper(I) complexes with the goal of discovering molecules with desirable properties for use in electroluminescent devices. Research toward this goal has also led to the discovery of mixed-metal gold(I) copper(I) clusters and a new type of tetradentate terpyridyl-quinoline ligand which coordinates readily to Ir(III).;Chapter 2 describes a series of of tetranuclear Cu4I 4(Ln)2 clusters containing chelating 4,4'-(4,5-di X-1,2-phenylene)bis(1-benzyl-1H-1,2,3-triazole) ligands (X = H, CH3, F). Crystal structure determinations have shown that the clusters adopt a distorted step-type geometry in which the triazole ligands exhibit both chelating and bridging coordination modes to Cu(I) ions. In addition, a cocrystallization of a tetranuclear and dinuclear cluster was obtained under specific reaction conditions. X-ray structures of show the presence of close Cu…Cu contacts in the tetranuclear and dinuclear forms. 1H NMR experiments indicate that rapid exchange occurs in these systems. All clusters are brightly luminescent in the solid state at 77 K and at room temperature with λmax = 495-524 nm. Emission intensity decays fit a single exponential function with lifetimes on the order of 10 to 35 microseconds at room temperature and 90 to 140 microseconds at 77 K. The origin of emission is assigned as a metal-to-ligand phenylene π* charge transfer.;In Chapter 3, the preparation and properties of heteroleptic copper(I) complexes incorporating amido-triazole and diphosphine ligands are discussed. The complexes adopt a distorted tetrahedral geometry in the solid state with the amido-triazole ligand forming a six-member ring with the Cu(I) ion. The complexes exhibit long-lived photoluminescence with colors ranging from yellow to red-orange in the solid state, in frozen glass at 77 K, and in fluid solution with modest quantum yields of up to 0.022. Electrochemically, complexes show irreversible or quasi-reversible oxidations as determined by cyclic voltammetry. For congeners differing by a single substituent in the para position of the amido ligand, the emission energy and oxidation potential are found to vary linearly with the Hammett parameter σp of that substituent. For complexes differing by N3 substitution in the triazole, large differences in spectroscopic properties are observed. Density functional theory calculations have been performed on the singlet ground states (So) of all complexes at the BP86/6-31G(d) level to assist in assignment of the excited states. Based on both experimental and computational results, the excited states have been assigned as intraligand + metal-to-ligand charge transfer 3(ILCT+MLCT) or ligand-to-ligand charge transfer mixed with MLCT 3(MLCT +LLCT) in these complexes.;In Chapter 4, a new class of dimeric copper(I) complexes is discussed. Two Cu(I) ions are bridged by anionic N,N-ligands of pyrazole or benzotriazole ligands to form six-membered Cu2N4cores. The coordination of Cu is completed by the diphosphine ligands 1,2-bis(diphenylphosphino)benzene (dppb) and oxydi-2,1-(phenylene)bis(diphenylphosphine) (DPEPHOS). For complexes with the dppb, the energy of the metal-to-ligand + ligand-to-ligand charge transfer (MLCT + LLCT) emission depends on the nature of the bridging ligand and its influence on the highest occupied molecular orbital energy. Conversely, the DPEPHOS complex emission is more appropriately assigned as arising from as metal-to-ligand charge transfer + intraligand excited state.;Chapter 5 explores gold(I) bis-acetylides complexes of the type [PPN][AuR 2] where PPN = bis(triphenylphoshpine)iminium) and R = ethisterone, 1-ethynylcyclopentanol, or 1-ethynylcyclohexanol and their reaction with copper(I) ions to form mixed-metal clusters. The reaction of the [Au(ethisterone) 2][PPN] with [Cu(MeCN)4][PF6] in a 1:1 or 3:2 ratio provides the octanuclear complex [Au4Cu4(ethisterone) 8] or the pentanuclear complex [PPN][Au3Cu2(ethisterone) 6]. Gold bis-acetylides with 1-ethynylcyclopentanol, or 1-ethynylcyclohexanol react with [Cu(MeCN)4][PF6] to form only pentanuclear mixed metal Au(I)/Cu(I) complexes [PPN][Au3Cu2(1-ethynylcyclopentanol) 6] and [PPN][Au3Cu2(1-ethynylcyclohexanol) 6]. These two pentanuclear clusters form polymorphs in which the structures differ by Au···Au, Au···Cu, and Cu-C distances. The polymorphs exhibit different emission energies with colors ranging from blue to yellow in the solid state. In solution, the pentanuclear clusters emit with λmax = 570-580 nm and Ф = 0.05-0.19. The octanuclear complex [Au4Cu4(ethisterone)8] emits at 496 nm in CH2Cl2 with a quantum yield of 0.65 and exists in equilibrium with the gold(I) precursor and the related pentanuclear cluster in the presence of methanol, ethanol, ethyl acetate, or water. This equilibrium has been probed by X-ray crystallography, NMR spectroscopy, and luminescence experiments. DFT calculations have been performed to analyze the orbitals involved in the electronic transitions of the pentanuclear and octanuclear complexes.;In Chapter 6, a method for the rapid preparation of tetradentate terpyridyl-quinoline (tpy-Q) ligands via Suzuki coupling of easily-accessed intermediates is discussed. The geometry of the ligand is appropriate for octahedral or square planar metal centers and its coordination to Ir(III) and Ru(II) ions has been explored. The reaction of tpy-Q with RuCl3 resulted in a mixture of products by NMR spectroscopy. The X-ray structure of one product was determined as [Ru(tpy-Q)2][SbF6]2 with terpyridyl coordination to the metal ion and dangling quinoline groups. The reaction of tpy-Q with IrCl3 provided [Ir(tpy-Q)Cl2][Cl] as indicated by NMR spectrometry and mass spectroscopy. This complex is intensely luminescent with λmax = 557 nm, and &PHgr; = 0.31. Replacement of a terminal pyridine ring with a phenyl ring and reaction with IrCl3 provides a neutral, cyclometalated complex with λmax = 655 nm, and &PHgr; = 0.0050. The difference spectroscopic properties between the two complexes is explained by the comparative amount of MLCT or LC contributions to the emissive state.