Photodissociation of Cr(CO)$_4$bpy: A non-adiabatic dynamics investigation

TL;DR

This study uses non-adiabatic dynamic simulations to investigate the ultrafast photodissociation mechanism of Cr(CO)$_4$bpy, revealing a ballistic dissociation process and explaining ligand selectivity.

Contribution

It provides the first non-adiabatic dynamic simulation analysis of Cr(CO)$_4$bpy photodissociation, challenging previous mechanistic assumptions.

Findings

86 fs lifetime of the $S_3$ state matches experimental data

13% quantum yield observed in simulations

Photodissociation occurs via a ballistic mechanism, independent of electronic state

Abstract

Carbonyl complexes of $d^6$ metals with an alpha-diimine ligand exhibit both emission and ligand-selective photodissociation from MLCT states. Studying this photodissociative mechanism is challenging for experimental approaches due to an ultrafast femtosecond timescale and spectral overlap of multiple photoproducts. The photochemistry of a prototypical system Cr(CO)$_4$bpy is investigated with non-adiabatic dynamic simulations. Obtained 86 fs lifetime of the bright $S_3$ state and 13% quantum yield are in good agreement with experimental data. The present simulations suggest a ballistic mechanism of photodissociation, which is irrespective of the occupied electronic state. This is in contrast to the previously established mechanism of competitive intersystem crossing and dissociation. Selectivity of axial photodissociation is shown to be caused by the absence of an avoided crossing in the equatorial direction.