Multi scale chiral response in switchable local moment molecules.  

We report on multi scale chiral response in [Fe(NH₂trz)​​L-CSA₃](L-CSA)_{​​​​​​2}(NH₂trz = 4-amino-1,2,4-triazole, L-CSA = L-camphorsulfonate), which is an Fe(II) spin crossover molecular complex. We report circular dichroism in the visible range which switches as a function of the spin state, confirming previously reported results. Significant differences in the chiral response between the L and D chiral isomer are observed.

Using X-ray absorption spectroscopy, we further reveal a chiral response also exists at the X-ray wavelength, specifically at the Fe L3 resonance edge. This chiral response is nearly identical in both isomers. However, like the circular dichroism at the visible range, this also switches as a function of the spin state. We attribute this chiral response to the distorted octahedral coordination of the ligand with the metal center. The switching of the chiral behavior is attributed to change in dipole moment across the spin state transition. This is revealed by temperature dependent X-ray photoemission spectroscopy at N 1s core level and capacitance measurements.