Excited state electronic structure of polypyridyl complexes of rhenium, ruthenium and osmium

D6 transition metal polypyridyl complexes of Ru(II), Os(II), and Re(I) have been studied extensively for application as photosynthetic reaction center models in solar energy conversion. More recently, these complexes have proven their value as fluorescent tags, light-emitting diodes and biosensors. In order to develop new applications for these robust and photophysically tunable molecules, a systematic and comprehensive understanding of their photophysical and photochemical properties must be undertaken.; Time-resolved infrared spectroscopy (TRIR), used in collaboration with other transient photophysical measurements, is a significant tool for mapping excited state electronic structure in these molecules. In the past, TRIR was commonly applied in the mid-infrared region to decipher correlations between shifting vibrational band energies and electronic changes in the excited state. This dissertation details the tremendous utility of step-scan TRIR.; In Chapter 3, TRIR is applied to reveal excited state electronic properties in several complicated molecular systems based on Re(I) polypyridyl chromophores. In one system, fac-[ReI(dppz)(CO)₃(py-PTZ)] +, two competing excited states are temporally resolved by the time-dependent vibrational band energies of ν(CO). A mapping of ground-to-excited state shifts in ν(CO) is also described for excited states of Re tricarbonyl complexes.; Chapter 4 builds on the knowledge of characteristic ground-to-excited state shifts in ν(CO) by unraveling the major influences on the magnitude of the shifts. These efforts aid in further quantifying correlations between ground-to-excited state shifts and excited state electronic structure. The first measurement of TRIR spectra in polymeric thin films is also described in Chapter 4. In order to successfully use these materials in device applications, incorporation into solid media is essential. TRIR gave valuable insight into the changing electronic structure of excited state species in rigid media.; Another possible application of photo-active complexes is as photochromic materials. One complex with potential in photochromic devices is fac-[Re(phen)(CO)₃(trans-1l,2-(bis-4-pyridyl)ethylene)] +. TRIR was used to follow the photoisomerization of trans -1,2-(bis-4-pyridyl)ethylene on the molecular level while complementary emission measurements followed the photochromic behavior, described in Chapter 5. The first spectroscopic evidence of the photochemical transient involved in the photoisomerization was revealed.; Thus far, time-resolved infrared spectroscopy has been used to map excited state changes at the molecular level, looking at changes in specific vibrational modes. Chapters 6 and 7 describe the first application of step-scan FT-IR to monitor low-energy electronic transitions in the near-infrared region. Intervalence and ligand-to-ligand charge transfer transitions in excited state d6 transition metal polypyridyl complexes give rise to low-energy absorption features. These absorption bands can be analyzed using band shape equations to give detailed insight into the electronic structure of the excited state. From treatment of band shapes for intervalence and ligand-to-ligand charge transfer bands, quantitative descriptions of electronic coupling, electron transfer barriers and rate constants were determined.