UV-VIS spectroscopy study of room temperature spin state switching in a Fe(II) spin crossover molecular thin film

For many spin crossover (SCO) complexes, transition from high spin to low spin occurs at a very low temperature. To implement this molecular system for device applications, it is crucial to tune the transition near room temperature. A ferroelectric layer with the capability of changing the electric polarization direction in the presence of an external electric field facilitates the switching of spin states in SCO molecules at room temperature. For this purpose, a polyvinylidine fluoride-hexafluoropropylene (PVDF-HFP) thin film prepared in the beta phase is crucial. In our study, a series of bilayer samples of [Fe{H₂B(pz)₂}₂(bipy)] (pz = tris(pyrazol-1-1y)-borohydride, bipy = 2,2’-bipyridine) thin films on ferroelectric PVDF-HFP substrates were fabricated. PVDF-HFP thin films annealed at different temperatures were studied using Fourier-transform infrared spectroscopy (FTIR) and bilayer samples with different PVDF-HFP thin film thicknesses were studied by UV-Vis spectroscopy. FTIR data indicates that PVDF-HFP is dominated in the beta phase and UV-Vis spectroscopy reveals that room temperature switching of spin states in those molecules shows a strong dependence on the thickness of the ferroelectric substrate.