Date of Award

12-31-2014

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Jonathan Rochford

Second Advisor

Michelle Foster

Third Advisor

Wei Zhang

Abstract

Transition metal complexes are of interest for a variety of applications making the ability to tune their electrochemical and photophysical properties highly desirable. Ruthenium(II) polypyridyl complexes have attracted much attention due to their unique properties including strong absorption in the visible spectrum, reversible redox behavior, and long lived excited states which appropriately position them for applications such as solar-to-electric energy conversion. Manipulation of traditionally metal based energetics in ruthenium(II) polypyridyl complexes has been realized by incorporating ligands with appropriate bonding capabilities and electronic properties to create non-innocent boding interaction between ligand and metal. The work of Van Koten, Graetzel and Burlinguette which explores metal-ligand interactions in cyclometalated ruthenium(II) polypyridyl complexes is covered in Chapter 1. This thesis aims to contribute to the existing literature exploring ruthenium(II) polypyridyl complexes through a study of heteroleptic complexes analogous to the protoypical ruthenium(II) trisbipyridine ([Ru(bpy)3]+) and isoelectronic to the cyclometalated systems in Chapter 1. The anionic [8-oxyquinolate]- (OQN-) ligand, well studied in its own right for its electron conduction properties, and its π-extended analogs have been introduced at the ruthenium center resulting in a series of compounds [Ru(bpy)2R-OQN]+ complexes where bpy= 2,2'-bipyridine and R = 5,7-Me2; 5-phenyl; 5,7-diphenyl; 2,4-diphenyl; 5,7-bis(4-methoxyphenyl); 5,7-bis(4-(diphenylamino)phenyl. The extent of mixing in the Ru(dπ)-OQN(π) complexes and the effect of increasing the π-network at the OQN- ligand on the electrochemical and photophysical properties relative to [Ru(bpy)3]+ is discussed in Chapter 2. UV/vis and electrochemical experimental results show a trend of red-shifted absorptions and negatively shifted oxidation potentials with the increase of the π-network consistent with the increased donating capacity of the ligands. Experimental results are in agreement with TD-DFT results that predict a metal-ligand based HOMO and increased orbital delocalization away from the metal throughout the series. Additionally, electron paramagnetic resonance (EPR) spectroscopy has been utilized to gain insight into the nature of the one electron oxidized species which shows an increase in hole delocalization away from the metal center with increase in the electron donating nature of the ligand.

Comments

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