Ultrafast Dynamics of Zinc Tetraphenylporphyrin and [FeII(bpy)3](PF6)2

In this work, femtosecond transient absorption (TA) spectroscopy is applied for the first time to solid state, single-crystal ZnTPP. Absence of the solvent environment leads to a monoexponential decay of the S2 excited state, as opposed to the biexponential decay in the solution state. The results provide insight for the first time into the structural dynamics of this molecule on the femtosecond and picosecond timescale. Ultrafast electron diffraction (UED) does not reveal a significant structural change for ZnTPP, as is expected for a full d-shell metalloporphyrin. A decrease in Bragg peak intensity is noted on a timescale of tens of picoseconds; this is explained by the Debye-Waller effect. UED was also used to probe the SCO dynamics of [FeII(bpy)3](PF6)2 (BPY), a prototypical SCO compound. Results from these experiments revealed ultrafast structural dynamics consisting of four key modes: Fe-N bond elongation, Fe-ligand motion, Fe-N rotation, and Fe-ligand rotation.M.Sc