Ruthenium phthalocyanine complexes : synethsis, properties and applications
- Publication Type:
- Thesis
- Issue Date:
- 2008
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Ruthenium phthalocyanine and naphthalocyanine complexes are an extremely useful and adaptable class of inorganic complex that have been the focus of a large body of research. They are very stable and may be readily synthesised by a variety of routes. They are able to coordinate a large variety of functionalised ligands, and possess tuneable UV-vis absorbance and electrochemical processes, all of which makes them suitable for a wide variety of applications. Polypyridyl complexes of ruthenium, considered in the latter part of this thesis, also exhibit useful electronic and electrochemical properties that make them appropriate for many applications, particularly in the area of photovoltaic devices. In this thesis the syntheses of thirty new ruthenium phthalocyanine, ruthenium naphthalocyanine and ruthenium polypyridyl complexes are presented, and the properties and applications of these complexes are explored.
Chapter 1 of this thesis reviews the synthesis, properties, and applications of previously reported ruthenium phthalocyanine and naphthalocyanine complexes. The synthesis section examines ring forming syntheses, incorporation of ruthenium into the phthalocyanine macrocycle, and axial ligand exchange reactions. The spectral properties (¹H NMR, UV-vis and infra-red) of ruthenium phthalocyanines are examined, as well as redox and conductivity properties. The application of ruthenium phthalocyanine complexes as thin films and catalysts is explored, together with their use as sensitising dyes in photodynamic therapy and photovoltaic devices.
In Chapter 2 the optical and electrochemical properties of ruthenium phthalocyanine complexes bearing substituted pyridine axial ligands with varying electron withdrawing and donating abilities are discussed. The electron density at the phthalocyanine macrocycle may be adjusted using the axial ligands. Electrochemical data show that the axial pyridine ligands exert significant influence over the phthalocyanine ring-based redox processes. The axial ligands also influence the electronic absorption properties of the complexes with the influence also observed in the electrogenerated oxidised and reduced species.
Chapter 3 explores the synthesis, electrochemistry and spectroscopic properties of the first examples of metal phthalocyanine and naphthalocyanine complexes with axially-coordinated arsine ligands. The AsPh₃ ligands readily dissociate in non-coordinating solvents with the
naphthalocyanine showing more rapid dissociation than the phthalocyanine analog. In cyclic voltammetry experiments, the phthalocyanine analog displayed three macrocycle-centred redox processes; one reduction and two oxidation processes. One reduction and three oxidation processes were observed for naphthalocyanine analog. The reduction and first oxidation are assigned to macrocycle-centred processes. The UV-vis spectra of both complexes recorded over time showed macrocycle-centred oxidation. The rate of oxidation was slowed by removing dioxygen from the solvent or adding excess AsPh₃.
In Chapter 4 the application of ruthenium phthalocyanine complexes as sensitising dyes in Dye-sensitised Solar Cells (DSCs) is explored. Solar energy conversion is emerging as an important area of research and DSCs offer a promising low cost alternative to conventional silicon-based solar cells. In addition to low cost, these cells may be flexible and semitransparent and therefore incorporated into building materials and other devices. A major hurdle to widespread use of DSCs is efficiency, with the best DSCs operating at approximately half the efficiency of silicon-based solar cells. Four monomeric ruthenium phthalocyanine complexes are reported that vary in peripheral substitution and axial ligand anchoring groups. Sensitising dyes that contain two ruthenium centres are also presented. These dyads, which contain phthalocyanine and bipyridyl chromophores, were prepared using a protection/deprotection strategy that allows for convenient purification. DSCs fabricated using the phthalocyanine complexes and dyads were less efficient than those incorporating a standard DSC dye. However, based on the number of molecules bound to the Ti0₂ electrode surfaces, several of the new complexes were more efficient at photocurrent generation. The results highlight the importance of molecular size, and thus the dye coverage of the electrode surface in the design of new sensitising dyes
Literature procedures that describe syntheses of the landmark DSC dye [Bu₄N]₂[Ru(4-carboxy- 4-carboxylate-2,2'-bipyridine)₂(NCS)₂] (N719) either yield an impure product or are highly time consuming. In Chapter 5 a convenient synthesis of N719 is presented. Key to this synthetic procedure is the protection of the carboxyl functionalities with iso-butyl ester groups. This strategy allows the use of silica chromatography to remove the less efficient S- bound isomers and significantly reduces the time and difficulty of the synthesis.
Chapter 6 investigates the absorption of ruthenium phthalocyanine complexes bearing functionalised axial ligands on gold surfaces. The surface chemistry of ruthenium phthalocyanines is fundamental to several topics explored in this thesis, and gold provides a
smooth surface on which to conduct experiments. The chapter also introduces the novel application of Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA ICP-MS) to the analysis of metal containing thin films. It was found that the peripheral substituents on the phthalocyanine ring affect the surface density of thin films. It was also discovered that thin films reach a maximum density after only one minute of immersion of the gold substrate in a solution of the complex.
The final chapter of this thesis, Chapter 7, summarises the work presented in this thesis and highlights the key findings. It also outlines some directions for further possible research continuing from the work presented.
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