Within the large class of cooordination nanoparticles, particularly interesting for the development of molecular based bi-stable compounds, the prussian blue analogs (PBA) are gathering an important interest for their tunable magnetic properties.We are currently working on CoFe-based PBA nanoparticles. This compound is showing a charge-transfer spin transition between a low spin diamagnetic state and a high-spin paramagnetic state under temperature change or light irradiation.In this experiment, we aim at using inelastic neutron scattering on IN6 to investigate the ground and excited states of CoFe-based PBA nanoparticles in both their LS and HS states. Measurements will be performed at different temperatures in between 2K and 300K and before and after in situ light irradiation.