On The Nature Of Excited States In Ruthenium Complexes: Towards Renewable Energy

ON THE NATURE OF EXCITED STATES IN RUTHENIUM COMPLEXES:TOWARDS RENEWABLE ENERGYbyRYAN ANTONIO THOMASAugust 2015 Advisors: Prof. John F. Endicott and Prof. Cláudio N. Verani Major: Chemistry (Analytical) Degree: Doctor of Philosophy The 77 K radiative properties (spectra, quantum yields and lifetimes) of ruthenium-polypyridyl complexes are investigated to better understand the effects of electronic mixing onmetal-to-ligand-charge-transfer (MLCT) excited state properties and how metal-centered (MC)excited states affect the properties of potential ruthenium photosensitizers.The radiative rate ofrelaxation (kRAD) determines the maximum possible excited state lifetime when all otherrelaxation pathways are blocked (kn = 0 for all n ≠ RAD). Thus, the excited state will relax onlyby means of an emission characteristic of the polypyridyl chromophore. kRAD is expected toincrease as the excited state energy increases while the value of the non-radiative decay (kNRD)should decrease. Given this relationship in the decay kinetics, the radiative rate constant can bean important factor in determining the lifetimes of high energy photosensitizers. Additionally,the formalisms used in discussions are based on Einsteinian rate constants for atomicfluorescence spectra and not that of phosphorescent donor-acceptor complexes. Other factorsshould be considered such as difference in spin multiplicity and molecular distortions in