Mono- and sub-monolayer films of a high T1/2 spin-crossover molecule on HOPG

We investigated the properties of the spin-crossover complex deposited on highly oriented pyrolytic graphite (HOPG) by x-ray absorption spectroscopy in the temperature range from 10 to 350 for sample thicknesses from 0.9(1) to 1.3(2) ML. The highest temperature at which light can excite the system to a long-lived metastable high-spin (HS) state (TLIESST) and the temperature at which a thermal spin transition occurs (T1/2) for the thin film samples are found as about 45 and 325 , respectively, in agreement with the bulk values. The bulk phase has previously been studied by magnetic susceptibility measurements where it was found that two different polymorphic modifications exist. These findings suggest a potential correlation between TLIESST and the high T1/2 from the different film thicknesses of the tridentate spin-crossover molecule, with thinner samples exhibiting lower T1/2 values. Finally, the highest HS fraction achieved for is 0.77 for samples of 0.9(1) and 1.1(1) ML on HOPG at 10 and constant light irradiation.