Understanding the interplay between geometry and ultrafast dynamics in ligand field excited states of inorganic chromophores.

摘要

After photoexcitation, the relaxation dynamics between excited states of a molecule are governed by both the energies and displacement of these states. For transition metal complexes in particular, ligand modification (via electron withdrawing substituents, electron donating substituents, aromatic substituents, etc) to alter the energetics of the excited states has been well studied. Recently, interest in the displacement of these surfaces from the ground state and the geometric ramifications of this displacement have spurred many studies in several research groups. Here, ligand modifications are made to modify molecular distortions (i.e. displacement), rather than the energetics.;The research presented in this thesis focuses on intersystem crossing processes in electronically simple chromium(III) compounds. With only a few excited states accessible after visible excitation, interpretation of the excited state dynamics is significantly simplified. Ligand substitution and its effect on the kinetics of the system have been studied using ultrafast transient absorption spectroscopy with ~50 fs pulses. The first study presented in this work focuses on identifying the molecular vibrations occurring immediately after excitation and how those motions facilitate intersystem crossing. The second study presented here focuses on modulating the energetics, not through ligand substitution, but with high (25 T) magnetic fields. Over the course of pursuing these measurements, various instrumental and software advances were necessary to both collect and analyze the data. These advancements, along with the findings from both studies, are the focus of the discussions herein.