At 150 K, we have recorded the evolution of the energy threshold versus the wavelength and the kinetic of formation and relaxation of the spin state phase transition induced by a single laser pulse in the [Fe(PM-BiA)(2)(NCS)(2)] compound. We demonstrate that different absorption bands of the complexes can drive the phase transition. The saturation-energy and the threshold-energy of the laser pulses are not directly related to the absorption cross-section of the sample. Both the switching and the relaxation kinetics are well fitted using two different time-constants. The switching lasts about 50 mu s. The relaxation time-constants are independent of the used excitation-wavelength. (C) 2009 Elsevier B. V. All rights reserved.