Light-induced thermal hysteresis and intensity thresholds in molecular switcheable solids, by mean-field macroscopic master equation approach: Discussion of the experimental data obtained for Co-Fe Prussian Blue Analogues

The mean-field macroscopic master equation (MFMME) provides a convenient first approach to the static and dynamic properties of photo-switcheable molecular solids under irradiation. The MFMME static approach is formally equivalent to those of the Ising-like or regular solution models in mean-field (or Bragg) approximation. In addition to the previously described light-induced instability of the low-temperature photo-stationary states [A. Desaix, O. Roubeau, J. Jeftic, J.G. Haasnoot, K. Boukheddaden, E. Codjovi, J. Linares, M. Nogues, F. Varret, Eur. Phys. J. B6 (1998) 183], the MFMME approach also provides all easy access to the intensity threshold values involved in photo-switching experiments performed in the thermal hysteresis loop [N. Shimamoto, S. Ohkoshi, O. Sato, K. Hashimoto, Chem. Lett. 4 (2002) 486-487; H.W. Liu, K. Matsuda, Z.Z. Gu, K. Takahashi, A.L. Cui, R. Nakajima, A. Fujishima, O. Sato, Phys. Rev. Lett. 90 (2203) 167403; E. Freysz, S. Montant, S. Letard, and JF Letard, Chem. Phys. Lett. 394 (2004) 318] and to the reversible mechanism suggested in [H.W. Liu, K. Matsuda, Z.Z. Gu, K. Takahashi, A.L. Cui, R. Nakajima, A. Fujishima, 0. Sato, Phys. Rev. Lett. 90 (2203) 167403]. The kinetic aspects of photo-switching are also accounted for. The light-induced thermal hysteresis loop of a photomagnetic Prussian Blue Analogue is reported for the first time, and the resulting value for the threshold intensity is discussed. (c) 2005 Elsevier Ltd. All rights reserved.