Photoinduced Ligand Exchange and Photoluminescence Dynamics in Tungsten Carbonyl Complexes

Photoinduced ligand exchange in transition-metal carbonyl complexes couples bond dissociation, coordination rearrangement, and excited-state relaxation, yet the relationship among these processes and the resulting optical response remains incompletely understood. Here, tungsten carbonyl–bipyridine complexes are investigated using density functional theory, time-dependent excited-state molecular dynamics (TDESMD), and nonadiabatic density-matrix calculations. Laser-driven TDESMD trajectories show CO dissociation together with changes in W–N coordination, including sequential formation of two W–N bonds in the bpy-coordinated complex. Fragment analysis further identifies carbonyl-loss products consistent with the evolution from to . Across representative structures containing zero, one, and two W–N bonds, the calculated final transition energies decrease, indicating substantial reorganization of the low-energy electronic states as the coordination changes. The structure, which contains two W–N bonds, additionally exhibits a low-energy absorption feature at approximately 800–850 nm in the near-infrared region (NIR). Selected molecular-orbital isosurfaces reveal substantial metal–ligand mixing, with several occupied-to-unoccupied state pairs displaying spatial distributions consistent with metal-to-ligand charge-transfer (MLCT) character. Nonadiabatic density-matrix calculations show that electron and hole relaxation rates depend on the coordination environment and produce distinct population-weighted emission profiles for the three representative complexes. Despite access to lower-energy optical transitions, the calculated photoluminescence quantum yields of the bpy-coordinated complexes remain below that of the reference. These results connect photoinduced changes in carbonyl content and W–N coordination with electronic-state reorganization, nonadiabatic relaxation, and optical response, while showing that spectral shifts toward lower energies do not necessarily lead to enhanced photoluminescence efficiency.