Electronic Structure of a Spin Crossover Molecular Adsorbate

We have investigated the occupied and unoccupied electronic structure of ultrahigh vacuum (UHV) evaporated molecular thin films of the spin crossover [Fe(H 2 B(pz) 2 ) 2 (bipy)] complex (with H 2 B(pz) 2 = bis(hydrido)bis(1 H -pyrazol-1-yl)borate and bipy = 2,2′-bipyridine) by ultraviolet photoelectron spectroscopy (UPS), inverse photoemission (IPES), and X-ray absorption spectroscopy (XAS). A bandgap of 2–3 eV is deduced from combined UPS and IPES measurements of the molecular films on Au substrates. The matching Fe XAS and IPES spectra indicate that the electronic unoccupied states have a significant Fe weight. The shift of the unoccupied density of states seen in inverse photoemission is consistent with the thermally induced spin crossover transition for [Fe(H 2 B(pz) 2 ) 2 (bipy)] deposited on the organic ferroelectric copolymer poly(vinylidene fluoride) with trifluoroethylene (PVDF–TrFE).