Inclusion of pyrene in the pores of a 3D iron(ii) spin-crossover Hofmann-type material allows thermal and light-induced ON–OFF switching of the resulting exciplex luminescence and provides an analytical tool to control the spin-state of the iron(ii) nodes.

Two series of coordination polymers have been synthesized to exhibit extrinsic or intrinsic luminescence modulated by spin crossover behavior. This study provides further insight into the features governing the synergy between both properties.

Integration of the ON-OFF cooperative spin crossover (SCO) properties of Fe II coordination polymers as components of electronic and/or spintronic devices is currently an area of great interest for potential applications. This requires the selection and growth of thin films of the appropriate material onto selected substrates. In this context, two new series of cooperative SCO two-dimensional Fe II coordination polymers of the Hofmann-type formulated {Fe II (Pym)2[M II (CN)4]•xH2O}n and {Fe II (Isoq)2[M II (CN)4]}n (Pym = pyrimidine, Isoq = isoquinoline; M II = Ni, Pd, Pt) have been synthesized, characterized and the corresponding Pt derivatives selected for fabrication of thin films by liquid-phase epitaxy (LPE). At ambient pressure, variable-temperature single-crystal, magnetic and calorimetric studies of the Pt and Pd microcrystalline materials of both series display strong cooperative thermal induced SCO properties. In contrast, this property is only observed for higher pressures in the Ni derivatives. The SCO behavior of the {Fe II (L)2[Pt II (CN)4]}n thin films (L = Pym, Isoq) were monitored by magnetization measurements in a SQUID magnetometer and compared with the homologous samples of the previously reported isostructural {Fe II (Py)2[Pt II (CN)4]}n (Py = pyridine). Application of the theory of regular solutions to the SCO of the three derivatives allowed us to evaluate the effect on the characteristic SCO temperatures and the hysteresis, as well as the associated thermodynamic parameters when moving from microcrystalline bulk solids to nanometric thin films.

The mutual influence between spin crossover and phase transitions in a doubly bistable molecular material enables effective discrimination between two thermal memory channels through isomorphous molecular alloying.