Increased Excited State Metallicity in Neutral Cr2On Clusters (n < 5) upon Sequential Oxidation

Excited state lifetimes of neutral Cr2On (n < 5) clusters were measured using femtosecond pump-probe spectroscopy. Density functional theory calculations reveal that the excited state dynamics are correlated with changes in the cluster's electronic structure with increasing oxidation. Upon absorption of a UV (400 nm) photon, the clusters exhibit features attributed to three separate relaxation processes. All clusters exhibit similar subpicosecond lifetimes, attributed to vibrational relaxation. However, the similar to 30 fs transient signal fraction grows linearly with oxidation, matching the amount of O to Cr charge transfer character of the photoexcitation and highlighting a gradual transition between semiconducting and metallic behavior at the molecular level. A longlived (>2.5 ps) response is recorded only in clusters with significant d-electron character, suggesting that adiabatic relaxation back to the ground state is efficient in heavily oxidized clusters, due to the presence of terminal O atoms. The simple picture of sequential oxidation of Cr2On reveals a linear variation in the contributions of each relaxation component to the total transient signals, therefore opening possibilities for the design of new molecular spintronic materials.