Pulsed-laser switching in the bistability domain of a cooperative spin crossover compound: a critical study through calorimetry

The photoswitching from the low spin (LS) to high spin (HS) state and the reverse process in the bistability domain of spin crossover (SCO) compounds is a promising function to be used in molecular electronic devices, and evidenced mainly through spectroscopy. The phenomenon, and in particular its mechanism, is however still under debate since some controversial experimental results have been reported. Here we present a calorimetric experimental study of the photoswitching of the [Fe(pyrazine)Pt(CN)4] SCO material by a nanosecond-pulsed green laser. Our results confirm that the single laser pulse of varying energies results in significant LS to HS transformations and show that calorimetry provides an accurate quantification of the overall conversion. Successive pulses allow increasing the conversion, achieving a maximum of 60% under our experimental conditions. The HS to LS transformation is on the other hand not induced at any laser fluences contrary to previous reports. The results are compared with those reported with Raman spectroscopy and critically discussed in terms of efficiency of the transformation and potential thermal effects.
This work has been supported by the Spanish MINECO and European Commission FEDER under projects MAT2011-24284, MAT2011-27233-C02-02, CTQ2011-23862-C02-01, CSD2007-00010, and CTQ2013-46275-P, by the Gobierno de Aragón through grants E98-“MOLCHIP” and E100-“Propiedades Termicas de Materiales”, and by the Generalitat Valenciana through PROMETEO/2012/049. L.P.L. thanks the Generalitat Valenciana for a predoctoral fellowship in the frame of the project PROMETEO/2012/049. JARV acknowledges CSIC for a JAE-doc contract.