published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

New classes of luminescent transition metal complexes, including the systems of rhenium(I) tricarbonyl diimine, cyclometalated iridium(III) diimine, cyclometalated rhodium(III) diimine, ruthenium(II) diimine and ruthenium(II) terpyridine complexes tethered with rhodamine moieties, have been synthesized. The X-ray crystal structure of one of the cyclometalated rhodium(III) diimine complexes with rhodamine pendants, [Rh(SPLC2N2)(ppy)2](PF6) has been determined. The molecular structure of [Rh(SPLC2N2)(ppy)2](PF6) showed a distorted octahedral geometry and the rhodamine moiety was found in a spirolactam closed-ring form. All of them were found to exhibit emission in fluid solution. The emissions of rhenium(I) tricarbonyl diimine and ruthenium(II) polypyridyl complexes are derived from the triplet metal-to-ligand charge transfer (3MLCT) excited state, i.e. from dπ orbital of the rhenium(I) or ruthenium(II) metal center to the π* orbital of the diimine ligand; while that of cyclometalated iridium(III) diimine complexes is (3MLCT) [dπ(Ir) → π*(N^N)] and that of cyclometalated rhodium(III) diimine complexes involves the (3IL) [π → π*(N^C)] excited state, probably mixed with (3MLCT) [dπ(Rh) → π*(N^C)] character. The cation-binding properties of these complexes toward alkali, alkaline-earth and transition-metal cations were investigated by electronic absorption and emission spectrophotometries. Some of them were found to exhibit new low-energy absorption and emission bands, characteristic of the rhodamine absorption and emission, with high selectivity and sensitivity for certain transition metal cations. A series of rhodamine-appended Schiff base organic compounds has also been synthesized in order to explore their capability as luminescent lanthanide ion sensors. The lanthanide ion binding properties of one of the compounds in acetonitrile were examined. Upon addition of lanthanide ions, new intense low-energy electronic absorption and emission bands were also observed, characteristic of the rhodamine absorption and emission, demonstrating its lanthanide ion sensing behaviour. / published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

Chapter One serves as an introduction to the photophysical properties of square-planar 2,2':6',2/1-terpyridyl and 6-phenyl-2,2'-bipyridylligand complexes of platinum(II). A brief description is provided of the absorption and emission spectra of each complex, the latter generally both in solution and the solid state. The assignments made to the absorption and emission bands are reported, together with the lifetimes ofthe emitting states where these have been measured. The relationship between the molecular and/or crystal structure of the complex and its photophysical properties is discussed. Given this background, the overall aims of the work in this dissertation are presented. In Chapter Two the synthesis and characterisation of nine novelligands are described. These are 4'-(O-naphthyl)-2,2':6',2/1-terpyridine (4'-fJNp-terpy), 4'-(meta-biphenyl)-2,2':6',2/1-terpyridine (4'-mBiph-terpy), 4'-(para-biphenyl)-2,2':6',2"-terpyridine (4'-pBiph-terpy), 4-(fJnaphthyl)- 6-pheny1-2,2'-bipyridine (H4-fJNp-phbipy), 4-(para-biphenyl)-6-pheny1-2,2'bipyridine (H4-pBiph-phbipy), 4-phenyl-6-(2'-pyrazinyl)-2,2'-bipyridine (4-Ph-pzbipy), 4(ortho-CH3-phenyl)-6-(2'-pyrazinyl)-2,2'-bipyridine (4-oMePh-pzbipy), 4-(ortho-CF3-phenyl)6-pyrazinyl-2,2'-bipyridine (4-oCF3Ph-pzbipy) and 4-phenyl-2,6-bis(2'-pyrazinyl)-pyridine (4-Ph-pybipz). In Chapter Three the synthesis, characterisation and photophysical properties of platinum(II) complexes ofthe ligands 4'-jlNp-terpy, 4'-mBiph-terpy and 4'-pBiph-terpy are described. The complexes are salts prepared of the following composition: [Pt(4'-jlNp-terpy)CI]SbF6 (1), [Pt(4'-jlNp-terpy)Cl]BF4 (~), [Pt(4'-jlNp-terpy)Cl]CF3S03 (J), [Pt(4'-mBiph-terpy)Cl]SbF6 (1), [Pt(4'-mBiph-terpy)Cl]BF4 (~), [Pt(4'-mBiph-terpy)Cl]CF3S03(~), [Pt(4'-pBiph-terpy)CI]SbF6 (1), [Pt(4'-pBiph-terpy)Cl]BF4 (~) and [Pt(4'-pBiph-terpy)Cl]CF3S03 (2). Each ligand is characterised by a substituent in the 4'-position that has been designed to permit free rotation of that substituent about the interannular bond to the terpyridyl fragment. The rotational freedom allows the 4'-substituent to adopt an orientation nearly coplanar with that of the terpyridyl fragment. As a result ofthe extensive n-conjugation, there is a strong ligand-centred influence in their excited state emission spectra. Evidence is also presented for 3MLCT (metal 111 to ligand charge transfer) character in the emitting state, in particular that the emission is quenched in coordinating solvents. In addition, an 3ILCT (intraligand charge transfer) contribution has been proposed to account for the exceptionally long lifetimes measured in fluid solution for [Pt(4'-j3Np-terpy)C!t (12 jJs), [Pt(4'-pBiph-terpy)Cq+ (4 jJs) and [Pt(4'-aNpterpy) C!t (17 jJs). We conclude that large easily ionisable substituents in the 4'-position of the terpyridyl moiety ensure long lifetimes in fluid solution for platinum(II) complexes of these ligands. The same assignments apply to the solid state spectra of the yellow or pale orange salts that exhibit monomeric emission in the solid state, these being: [Pt(4'-j3Np-terpy)CI]SbFu (l), [Pt(4'-j3Np-terpy)CI]BF4 (I), [Pt(4'-j3Np-terpy)CI]CF3S03(J.), [Pt(4'-pBiph-terpy)CI]SbFu (1) and [Pt(4'-pBiph-terpy)CI]BF4 (~). In the solid state two additional types of solid state emission have been identified in cases where intermolecular interactions are present. The first type is typical of red or dark orange salts viz., [Pt(4'-mBiph-terpy)Cl]SbFu(1), [Pt(4'-pBiphterpy) Cl]BF4 (red form) (~) and [Pt(4'-pBiph-terpy)Cl]CF3S03 (.2). All three salts exhibit MMLCT (metal-metal to ligand charge transfer) emission brought about by close intermolecular Pt···Pt interactions in the solid. Finally, the three orange compounds [Pt(4'mBiph-terpy)Cl]SbFu.CH3CN (4a), [Pt(4'-mBiph-terpy)Cl]BF4 (~) and [Pt(4'-pBiphterpy) Cl]CF3S03(.2) exhibit simultaneous emission from IL (intraligand) and MMLCT states that are similar in energy. In the case of [Pt(4'-mBiph-terpy)Cl]SbF6.CH3CN (4a) the assigmnent ofMMLCT emission is supported by a X-ray crystal structure determination that shows the cations interacting in dimeric pairs which have a platinum-platinum separation of 3.356(2) A. In Chapter Four the synthesis, characterisation and photophysical properties of the neutral complexes [Pt(4-j3Np-phbipy)Cl] (10) and [Pt(4-pBiph-phbipy)Cl] (11) are described. The ligands, 4-j3Np-phbipy and 4-pBiph-phbipy are closely related to 4'-j3Np-terpy and 4'-pBiphterpy, the only difference being that the terpyridyl fragment is replaced by a phenyl-bipyridyl moiety that binds to the platinum via a deprotonated carbon atom in the ortho-position of the phenyl ring. The stronger a-donor strength of the anionic carbon atom is shown to result in: (i) a marked shift to the red in the MLCT absorption bands for the two complexes and (ii) a significant lowering of the energy ofthe emitting state, as compared to that observed for the cationic terpyridylligand derivatives. The assignment of the emission as 3ILPMLCTin origin remains the same, however, both in solution and in the solid state. In Chapter Five we report the synthesis, characterisation and photophysical properties of a series of platinum(II) complexes of the ligands 4-Ph-pzbipy, 4-oMePh-pzbipy, 4-oCFJPhpzbipy and 4-Ph-pybipz viz., [Pt(4-Ph-pzbipy)CI]BF4 (12), [Pt(4-oMePh-pzbipy)CI]SbF6 (14), [Pt(4-oMePh-pzbipy)CI]BF4 (15), [Pt(4-oMePh-pzbipy)CI]CFJSOJ (16), [Pt(4-oCFJPhpzbipy) CI]SbF6 (17), [Pt(4-oCFJPh-pzbipy)CI]BF4 (18) and [Pt(4-oCFJPh-pzbipy)CI]CFJSOJ (19). These ligands coordinate to platinum via a binding domain analogous to the terpyridyl fragment except that one (or both in the case of 4-Ph-pybipz) of the outer pyridine rings is replaced with a pyrazine ring. The ligands 4-oMePh-pzbipy and 4-oCFJPh-pzbipy are distinguished from 4-Ph-pzbipy by the presence of bulky methyl and trifluoromethyl substituents, respectively, in the ortho position of the peripheral phenyl ring. Monomer emission measured in room temperature fluid solution in a 77 K rigid glass for the three luminophores viz. [Pt(4-Ph-pzbipy)CIt, [Pt(4-oMePh-pzbipy)CIt and [Pt(4-oCFJPhpzbipy) Clr derives from an excited state of JILPMLCT mixed orbital parentage. Their emission energies are stabilised compared to their terpyridyl analogues but emission lifetimes are essentially the same. Solid state emission spectra have been recorded for salts ofthe [Pt(4oMePh- pzbipy)CW and [Pt(4-oCFJPh-pzbipy)CW cations. In every case emission is derived from an excited state brought about by intermolecular interactions, either in the form of excimeric or of MMLCT emission. In general orange compounds ([Pt(4-oCFJPhpzbipy) CI]SbF6 (orangeform ) (17) and [Pt(4-oCFJPh-pzbipy)CI]BF4 (18)} displayexcimeric emission and dark red compounds {[Pt(4-oMePh-pzbipy)CI]SbF6 (14), [Pt(4-oMePhpzbipy) CI]BF4 (15), [Pt(4-oMePh-pzbipy)CI]CFJSOJ(16), [Pt(4-oCFJPh-pzbipy)CI]SbF6 (red form) (17) and [Pt(4-oCFJPh-pzbipy)CI]CFJSOJ (19)} display emission from a MMLCT excited state. The [Pt(4-oCFJPh-pzbipy)CI]SbF6 (17) salt displays polymorphism, existing in two formS, one red and the other orange. In all cases the lower energy of the n-acceptor orbitals of the pyrazinyl-bipyridyl moiety causes emission to be at lower energies compared to that recorded for closely related terpyridyl analogues. Finally, attempts to coordinate the bis-pyrazinylligand, 4-Ph-pybipz, to platinum to form [Pt(4-Ph-pybipz)CI]SbF6 (13) were unsuccessful. / Thesis (PhD.)-University of Natal, Pietermaritzburg, 2002. / National Research Foundation. De Beers Industrial Diamond Division.

This thesis documents the successful syntheses of six novel 2,2':6',2"-terpyridine-amine based polydentate ligands and a range of mono-, di-, and polynuclear complexes derived from them. The ability of some dinuclear complexes to affect the rate of hydrolysis of the phosphate diester group in the DNA model compound, bis-p-nitrophenyl phosphate (BNPP) has also been explored. Owing to the presence of two potential ligating groups in each polydentate ligand, a number of dinuclear, tetranuclear and serendipitous supramolecular architectures have been produced and characterised during this research. The polydentate ligands were synthesised by stepwise functionalisation of the progenitor ligand, 4'-(2"'-toluyl)-2,2':6',2"-terpyridine (L2.1), at its ortho methyl position via free radical bromination, and where various amine groups were appended by nucleophilic substitution reactions. The detailed ligand syntheses, and characterisation are discussed in Chapter 2, along with the crystal structures of some ligands. Chapter 3 describes coordination chemistry of 4'-(2"'-toluyl)-2,2':6',2"-terpyridine with transition metal ions. Thirteen new complexes of Ni(II), Cu(II), Zn(II) and Ag(I) are reported, where Ag(I) produced a striking spiral shaped polymer with L2.1 having unusual „hyperdentate‟ nitrogen atoms. Two polydentate ligands, 4'-[2"'-{(2-pyridylmethyl)aminomethyl}phenyl]-2,2':6',2"-terpyridine, L2.3, and 4'-[2"'-{bis(2-pyridylmethyl)aminomethyl}phenyl]-2,2':6',2"-terpyridine, L2.4, produced six different dinuclear and tetranuclear metal complexes (Chapter 4). The Zn(II) dinuclear complexes were used to study kinetics of hydrolysis of BNPP, and the enhanced rates were reported compared to the analogous mononuclear complexes. The detailed experimental methodology and results are discussed in Chapter 5. The most interesting outcome of this research was formation of the box and wheel shaped complexes, where the ligand L2.3 binds with different metal ions via different coordination modes. The box shaped tetranuclear complexes were synthesised deliberately via structural control over the coordination chemistry of terpyridine-type site of L2.3, where the coordination flexibility of the pendent picolylamine-type site of the ligand was used to bind with other metal ions. The tetranuclear [M¹₂M²₂(L2.3)₄X₂]⁶⁺ box shaped complexes were formed when two divalent M¹ ions bridge between the ligands to produce octahedral bis-terpyridine type complex M¹(L2.3)₂, and then two divalent M² ions link two M¹(L2.3)₂ units together through picolylamine binding sites, where X = Cl⁻, Br⁻, CH₃COO⁻; M¹ = Fe(II), Zn(II), Ni(II); M² = Zn(II), Cu(II). The bis-bidentate bridging ligand terephthalate was also deliberately encapsulated in the middle of Fe₂Zn₂L2.3 box to produce the complex where X₂ = terephthalate. These structures invite speculation that it may be possible to bind and react molecules within these boxes. In a more fortuitous outcome, Ni(II) ions were found to bind to both sites of L2.3 to give, exclusively, an unprecedented decanuclear wheel-shaped structure. A halide ion occupies the central position in the wheel, with Br⁻ being preferred over Cl⁻. The detailed crystal structures, and properties of the wheels shaped Ni₁₀(L2.3)₁₀ complexes are discussed in Chapter 6.

No description available.