The photochemistry of late transition metal systems: Platinum terpyridines and copper phenanthrolines

Joseph Frank Michalec, Purdue University

Abstract

Platinum(II) terpyridine and copper(I) phenanthroline complexes are currently of great interest for their ability to be probes of local environment and to act as potential photosensitizers. These two families of complexes have electronic excited states that are a result of metal-to-ligand charge transfer where an electron is excited from the metal to the ligand. Due to the presence of open coordination sites exciplex (excited state complex) formation is an important deactivation process; therefore, changes in the local environment can be reflected in the spectral characteristics of the complexes. However, both parent complexes show no emission in solution, and therefore are not good candidates as spectroscopic probes. Platinum(II) terpyridine complexes are of great interest due to their ability to interact with DNA. In this study, systematic substitution at the 4′ position of the trpy ligand afforded complexes that possess not only long lived excited states, but also provide unique insights into the role excited state mixing can play in this system. Excited state mixing between metal and ligand centered states is the driving force for the unique properties exhibited by these complexes. Some of the derivatives show promise as DNA probes due their solubility and emissive properties in an aqueous environment. While, upon substitution at the 4′-position of terpyridine with pyrene, a complex that shows totally new and unexpected excited state properties, including the ability to be an oxygen sensor, has been developed. For the copper(I) phenanthrolines the problem plaguing the excited state is mainly a structured one. In the excited state the complex undergoes a flattening distortion which leads to non-radiative decay. Furthermore, due to the flattening distortion, the complex is very susceptible to solvent induced quenching. Therefore, in this study the phenanthroline ligands were substituted at the 2,3,8 and 9 positions to increase their steric bulk. This increased steric bulk has led to complexes that show the longest lived lifetimes yet reported for a copper phenanthroline (up to 920 ns); as well as, resistance to solvent induced quenching.

Degree

Ph.D.

Advisors

McMillin, Purdue University.

Subject Area

Chemistry

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