Investigation of the spin crossover behaviour of a sublimable Fe(II)-qsal complex: from the bulk to a submonolayer on graphene/SiO 2 .

We synthesized a sublimable molecular spin crossover Fe(II) complex based on the Schiff base tridentate ligand qsal-NEt ₂ (5-diethylamino-2-((quinolin-8-ylimino)methyl)phenol). The compound undergoes a transition in temperature with thermally induced excited spin state-trapping (TIESST) for high-temperature sweep rates, which can be suppressed by reducing the sweep rate. The X-ray absorption spectroscopy (XAS) studies on the microcrystalline powder confirm the TIESST effect. The molecules are deposited under ultra-high vacuum on a graphene/SiO ₂ substrate as a submonolayer. Investigation of the submonolayer by XAS reveals the molecular integrity and shows a spin crossover for the whole temperature range from 350 to 4 K, with residual HS species at low temperature and no TIESST effect. DFT calculations suggest a distribution of energetically similar adsorption configurations on graphene, i.e. , with smooth crossover behaviour and the absence of TIESST, consistent with very weak intermolecular interactions and the absence of large molecular islands within the submonolayer.