Searching for Spin Crossover in Fe(bpy)3(PF6)2 using Femtosecond Electron Diffraction and Ultrafast Transient Absorption

Femtosecond electron diffraction experiments were performed on solid state iron(II) tris(2,2'-bipyridine) bis(hexafluorophosphate). The cation is known to undergo a spin crossover process when solvated in water and irradiated with 400 nm coherent light which results in a transition from a low spin to high spin state within a picosecond which is accompanied by a uniform 0.2 Å Fe-N bond elongation. A femtosecond diffraction experiment was performed on the solid sample and was unable to find evidence of a fast spin crossover transition. Suspecting this may be due to limitations of the apparatus, an ultrafast transient absorption experiment was performed. Emulating the liquid study by Gawelda et al, the pump probe experiment found evidence of spin crossover in the solid state sample. This result awaits verification by an improved transient absorption apparatus and has inspired efforts to perform an improved femtosecond electron diffraction experiment.MAS