In order to utilize earth abundant low-spin iron(II) polypyridyls for photo-induced electron transfer, the nature of their excited-state dynamics must be characterized to inform synthetic design for both energetic and kinetic control. Synthesis of a series of structurally similar iron(II) polypyridyl complexes spanning from low-spin to high-spin with a spin crossover intermediate allowed for the determination of reorganization energy through a combination of variable temperature transient absorption and magnetic susceptibility measurements. In addition to experimentally determining the reorganization energy (6000 cm-1) and electronic coupling constant (2.0 cm-1) associated with conversion from the lowest energy excited state (5T2) back to the ground state (1A1), we have demonstrated based on the convergence of analyses from semi-classical to fully quantum mechanical non-radiative decay theories that the kinetically relevant degree of freedom is not the Fe-N stretching mode. These results thus provide new guidelines for ligand design toward the goal of controlling excited-state dynamics in this class of compounds.

Decoding the nuclear coordinate for ground-state recovery in iron(II) polypyridyls

2019 Spring National Meeting

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