Single laser pulse induces spin state transition within the hysteresis loop of an Iron compound

Within the thermal hysteresis loop of the [Fe(PM-BiA)2(NCS)2] compound, a single laser pulse of 14 mJ cm−2 induces a photo-conversion from the low spin (LS, S = 0) to the high spin (HS, S = 2) state of the Fe2+ metallic center. The temporal dynamic of this phenomena indicates that the system is firstly photo-excited into the HS state and then slowly relaxes to a mixture of HS/LS state. Subsequent laser pulses do not affect the HS/LS ratio. The system can be brought back to its initial LS state by adjusting the temperature of the compound. A simple model accounts qualitatively for the observed phenomenon.