Ultrafast electronic deactivation and vibrational dynamics of photoexcited uranium(IV) porphyrin sandwich complexes

The ground- and excited-state optical spectra of two U^IV bis(porphyrin) sandwich complexes reveal features characteristic of porphyrins held within van der Waals contact. The photoexcited complexes exhibit ultrafast (∼1 ps) deactivation to the ground electronic state in a multistep process involving intersystem crossing into the triplet manifold and subsequent relaxation via ligand-field (f,f) excited state(s). This ultrafast and highly energetic electronic deactivation is followed by complex time-dependent spectral changes on the picosecond time scale that are ascribed to vibrational relaxation in the ground electronic state.