Microenvironments, Binding Interactions, and Photophysics of Polyelectrolyte-Bound Tris-(2,2'-Bipyridine)ruthenium(ii)
Bartolo, Robert Gregory
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https://hdl.handle.net/2142/70418
Description
Title
Microenvironments, Binding Interactions, and Photophysics of Polyelectrolyte-Bound Tris-(2,2'-Bipyridine)ruthenium(ii)
Author(s)
Bartolo, Robert Gregory
Issue Date
1988
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Chemistry, Polymer
Abstract
This research concerns the understanding of the underlying factors and mechanisms which give rise to the altered photophysical behavior and nonexponential decay kinetics of tris-(2,2$\sp\prime$-bipyridine)ruthenium(II) (Ru(bpy)$\sb3\sp{2+}$) upon immobilization in "organized" or inhomogeneous media. To gain a fundamental understanding of these factors and mechanisms it was necessary to characterize the interactions between the complex and the medium of interest, which in this study was poly(styrenesulfonate) (PSS). This thesis addressed three basic questions: (1) How does the complex interact with the polyelectrolyte? (2) How do these interactions affect the photophysics of the complex? (3) How can the decay kinetics be described in chemical terms?
A variety of time-resolved and steady-state luminescence experiments were utilized to characterize the microenvironments and binding interactions between Ru(bpy)$\sb3\sp{2+}$ and PSS. Through the use of inert salts, it was found that the thermodynamic driving force for binding, which is relatively large, included both electrostatic and nonionic contributions. Quenching experiments demonstrated that the complex resides totally within the potential field of the polyelectrolyte, but in binding sites which are rather accessible to hydrophobic species. The deuterium isotope effect was used to show that the binding microenvironment is somewhat shielded from water and spectral characteristics of the complex indicated a hydrophobic binding microenvironment. The results also indicated the presence of inhomogeneous binding.
A large number of varied experiments were performed to rule out various possible causes for the observed nonexponential decays (e.g. inhomogeneous quenching, triplet-triplet annihilation, or self-quenching). Two techniques were developed to test various models, which were used to show that the double exponential rate law was an inadequate description for the system. Evidence was presented which indicates that the nonexponential behavior arises from a distribution of binding sites within the PSS, producing populations of excited states having lifetimes which are dependent on their relative solvent accessibility. The results from these studies were used to formulate two models, lifetime distributions (fixed shape, cumulants, and exponential sampling) and bipolar. Both approaches were able to describe the data well and produced results which were easy to interpret.
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