Fig. 3: Schematic representation of the potential energy curves and phonon modes.

a Charge density maps of the highest occupied crystalline orbital (HOCO, left) and lowest unoccupied crystalline orbital (LUCO, right) in the low-temperature (LT) state, reproduced from ref. ³⁸ with permission from RSC. The calculated HOCO and LUCO filled the charge density on W and Co orbitals, respectively, indicating that the photoexcitation (hν) of the ground LT Co^III_LS-W^IV state leads to the photoexcited (PE) Co^II_LS-W^V state by promoting one electron transfer from W to Co orbitals. b The PE state decays within 130 fs towards the photoinduced (PI) Co^II_HS-W^V state through the spin transition with the activation of the CoN₆ breathing mode. c Schematic representation of the phonon modes. The breathing mode (left) involves Co–N bond elongation (red arrows), while the torsion modes (right) represent distortions of Co–NC–W bridges (black arrows). During structural relaxation, Co–N bonds of the excited Co^II_HS site elongate (approximately 130 cm⁻¹ phonon mode), causing lattice distortions and activation of the lattice torsion mode (approximately 58 cm⁻¹). The modes are shown in Supplementary Movie 1.