Bidirectional photo-switching of the spin state of iron(II) ions in a triazol based spin crossover complex within the thermal hysteresis loop

We have investigated the effect of short laser pulses (532 nm, 4 ns, <30 mJ cm−2) on the spin state of iron(II) ions in the spin crossover compound {[FeII(Htrz)2(trz)](BF4)} within the hysteresis region of the high-spin (HS) to low-spin (LS) first-order thermal phase transition. Using Raman spectroscopy we have evidenced quasi-complete HS → LS as well as LS → HS photo-conversions, which can be induced by a single laser shot in the descending (351 K) and ascending (378 K) branches of the hysteresis loop, respectively. No effect has been observed, however, close to the center of the hysteresis loop even for repeated exposures.