<p>Some molecular complexes exhibiting bistability between two different spin states have been subject to vast investigations. Spin crossover and valence tautomerism interconversion molecular compounds are such examples showing this dynamic switching behavior and are a route toward designing molecular devices with a facile readout due to the change in the spin state that accompanies the change in conductance. Due to their extensive potential applications in industry and research, they are among the most interesting topics in spintronics. Spin state switching processes provide the foundation for applications in molecule-based devices. The main goal is to study the parameters that affect the intramolecular electron transfer between different spin states in spin crossover molecular thin films and the electron transfer between the metal center and redox-active ligands in valence tautomer thin films. </p> <p>Because substrate effects are important for any molecular-based device, there are increasing efforts to study the influence of the substrate on spin state transition. While some non-metallic substrates like graphite seem to be promising from experimental measurements, theoretical and experimental studies indicate that 2D semiconductor surfaces will have minimum interaction with spin crossover molecules.</p> <p>In this work, the functionality of two different spin crossover molecules sublimated on the ferroelectric Polyvinylidene Fluoride Hexafluoropropylene (PVDF-HFP) layer and 2D Ti3C2 MXene thin film is studied. We report the temperature-dependent spin state transition of spin crossover molecules, [Fe{H2B(pz)2}2 (bipy)], thin films, and valance tautomer [Co(sq)(cat)(3-tpp)2] thin films. Using a UV-Vis spectrometer and a specific lab-built sample holder we were able to perform the measurement at temperatures as low as 90 K and as high as 440 K. Temperature-dependent UV-Vis data show that the transition temperature from the high spin state to the low spin state and vice versa is well below the room temperature. However, for isothermal switching purposes, we designed and fabricated a bilayer device with PVDF-HFP thin films as the substrate to facilitate isothermal switching close to room temperature. The retention of voltage-controlled nonvolatile changes to the electronic structure in bilayers of PVDF-HFP/[Fe{H2B(pz)2}2(bipy)] and PVDF-HFP/[Co(sq)(cat)(3-tpp)2] strongly depends on the thickness of the PVDF-HFP layer. </p> <p>While the electric transport measurement revealed that doping the SCO layer with Ti3C2 MXene flakes can significantly improve the conductivity of the spin crossover molecular thin films, the temperature-dependent UV-Vis measurements represent that the adjacent MXene layer can cause a lock in the given spin state or a change in the transition temperature dramatically.</p> <p><br></p>