George B. Shaw

The influence of bridging ligand electronic structure on the photophysical properties of noble metal diimine and triimine light harvesting systems.

This manuscript discusses the photophysical behavior of transition metal complexes of Ru(II) and Os(II) employed in development of light harvesting arrays of chromophores. Particular emphasis is placed on the relationship between the photophysical behavior of complexes having metal-to-ligand charge transfer (MLCT) excited states and the electronic characteristics of bridging ligands used in preparing oligometallic complexes. Examples are presented that discuss intramolecular energy migration in complexes having two distinct MLCT chromophores with bridging ligands that only very weakly couple the two chromophores. In addition, systems having bridging ligands with localized triplet excited states lower in energy than the MLCT state of the metal center to which they are attached are discussed. These systems very often have excited states localized on the bridging ligand with excited state lifetimes on the order of tens of microseconds. Finally, systems having Fe(II) metal centers, with very low energy MLCT states, are discussed. In complexes also containing bridging ligands with low energy triplet states, energy partitioning between the Fe center MLCT state (or Fe localized ligand field states) and the ligand triplet state is observed; the two states relax to the ground state via parallel pathways, but the Fe(II) center does not serve as an absolute excitation energy sink.

Molecular structural dynamics of photoactive transition metal complexes in solar energy conversion studied by ultrafast optical spectroscopy and LITR-XAS

Transition metal complexes play important roles in solar energy conversion due to their intense absorption within the solar spectrum, their capability of transferring electron and energy through the metal to ligand charge transfer (MLCT) or ligand to metal charge transfer (LMCT) excited state, and their capability of binding substrates through coordination geometry changes. Hence, structural dynamics of these complexes in their excited states need to be understood in order to gain knowledge of controlling solar energy conversion processes. We will present our recent studies on structural dynamics of two metal complexes using both ultrafast optical Spectroscopy and laser initiated time‐resolved x‐ray absorption Spectroscopy (LITR‐XAS). In order to fully understand the roles of transition metal complexes in solar energy conversion, structural dynamics of these molecules in their excited states on ultrafast time scales are needed. We will discuss mainly two different transition metal complex systems, 1) ultr...