THE SYNTHESIS AND STUDY OF 4-AZA-ACRIDINE TYPE LIGANDS AND THEIR RU(II) COMPLEXES
With increasing human population and energy consumption, it is obvious that we need to find alternative sources of energy. Of all renewable energy sources, solar power is one of the most easily exploitable. It is abundant and adaptable to a wide variety of applications that produce energy. To be able to use the sun as an energy source, an effective photosensitizer will play a critical role. We find that polypyridine complexes of Ru(II) show excited state characteristics that are favorable for certain photoredox behavior. In this dissertation we will consider two applications of this property:
- Use of Ru(II) polypyridine complexes as sensitizers for dye sensitized solar cells (DSSCs). The photoexcited complex can inject an electron into the conduction band of a semi-conductor as the critical step in a possible solar cell.
- The use of the excited state properties Ru(II) polypyridine complexes to facilitate the bond breaking and bond making steps in the decomposition of water into its elements, thus accomplishing artificial photosynthesis. The incorporation of an additional non-coordinating nitrogen into the 4-position of 2,2'-bipyridine is anticipated to lower the π* level of the ligand, causing a red-shift of the MLCT band which might increase the light-harvesting efficiency. To this purpose, a series of alkyl substituted 4-(pyrid-2'-yl)-pyrimidines and 2-(pyrid-2'-yl)-quinoxalines and their ruthenium polypyridyl complexes were synthesized. To extend the absorption spectrum further into the IR region [Ru(48)(NCS)3] was synthesized as an analog to the "black dye". The operating principles of the DSSC, design, synthesis, characterization, and photophysical properties of the studied dyes are discussed in Chapter 3. The 2,2'-polymethylene-3,3'-bi-4-azaacridines 76a-d and [Ru(76a-d)(tpy)(H2O)]2+ and [Ru(76a-d)(bpy)2]2+ complexes were synthesized to study possible excited-state proton coupled electron transfer (PCET) reactions. An additional benzo ring fused to the 6,7-position of the 1,8-naphthyridine unit extends the π-conjugation and is expected to help stabilize an intermediate radical anion that might be formed in the excited state. The synthesis, characterization and properties of these complexes are discussed in Chapter 4. The ruthenium complexes of [Ru(84-85,102)(4-pic)2(H2O)]2+ have been studied for water oxidation. The synthesis, characterization, properties, and catalytic activity of these complexes are discussed in Chapter 5.