Excited-state electronic structure and dynamics of asymmetric ruthenium bipyridyl complexes

The study of the photophysical and electrochemical properties of transition metal complexes is of great interest. Ruthenium tris(2,2′-bipyridine), or [Ru(bpy)3]2+, has particularly intriguing properties, including a relatively long excited-state lifetime, good chemical stability, and ease of synthetic modification. We have studied the relationship between systematic compositional changes in [Ru(bpy)₃] 2+-type complexes and the resulting changes in electronic structure and excited-state dynamics. Structural changes can be made synthetically (as in the substituted-bipyridine series studied herein) or environmentally (e.g. with a change of solvent). The effect of these changes on electronic structure can be understood through a combination of electrochemical and spectroscopic measurements. Toward this end, we have utilized both infrared and electronic spectroscopic and spectroelectrochemical measurements on the static and nanosecond timescales, as well as femtosecond electronic transient-absorption spectroscopy.; In Chapter 1, a brief motivation and historical context for our studies is presented. The synthesis and characterization of a series of four ruthenium complexes containing two substituted bipyridyl ligands, 4,4′ -dimethyl-2,2′-bipyridine (dmb) and 4,4 ′-bis(diethylamino)-2,2′-bipyridine (dea), is described in Chapter 2. Static and nanosecond electronic and infrared spectroscopic data, as well as electrochemical and spectroelectrochemical measurements, of the series in acetonitrile (CH₃CN) allow a complete picture of the energetics to be understood.; Design and data analysis considerations for an in situ attenuated total reflection FTIR spectroelectrochemical device are outlined in Chapter 3, as well as details of the step-scan FTIR spectrometer used for our nanosecond infrared measurements. Analogous measurements to those presented in Chapter 2 were also performed in methanol (CH₃OH) and are presented in Chapter 4. The results are remarkably similar to those obtained in CH ₃CN, and we discuss possible interpretations of these similarities and implications for future femtosecond studies.; Chapter 5 contains femtosecond transient absorption kinetic and full-spectral studies of the series in CH₃CN. These data indicate that regardless of excess excitation energy or initial wavepacket localization, intersystem crossing occurs extremely rapidly (<200 fs) in all complexes in the series, followed by slower attenuation of signal due to vibrational cooling (several ps and longer). (Abstract shortened by UMI.)...