Excited State Study of Metal Complex Chromophores with Photogenerated Donor-Acceptor Biradical Ligands

The work within this document describes the synthesis, characterization and excited state study of three rationally-designed series of metal complex chromophores bearing nitronylnitroxide (NN) radicals. The goal of this work is to investigate how pendent spin and subsequent excited state exchange coupling(s) fundamentally affect the excited state properties and lifetimes. The first series which included Fe(III)(Catechol-NN), was investigated through variable temperature spectroscopies, magnetometry and ultrafast transient absorption spectroscopy. The collective results for this series demonstrated that photophysical differences due to radical substitution were unobservable due to dominate metal-based processes. The second series, which included NN-substituted (diimine)Pt(catecholates), was studied through various spectroscopies including resonance Raman and ultrafast transient absorption to show that the radical substituents decreased excited state lifetimes. Additionally, variable temperature magnetooptical spectroscopic studies of this series demonstrated a new method to visualize excited state structure and excited state mixing. The results of these studies were indicative of enhanced triplet-chromophore character mixing into the singlet-chromophore core of the radical appended complexes. The third system, which featured NN-substituted (diimine)Pt(dithiolbenzenes), was studied through variable temperature and time resolved emission spectroscopies to show that radical substitution resulted in faster excited state lifetimes but the emissive properties of the molecules were not lost.