A macroscopic approach to the light-induced instability of cooperative photo-switchable systems

Under permanent irradiation cooperative photo-switchable systems may underg o a light-induced instability of the steady state leading to thermal and op tical hystereses report on a non-linear macroscopic master equation which a ccounts for the competition between a constant photo-excitation and a self- accelerated thermal relaxation process. The equilibrium phase diagram is dr awn and the instability is discussed in terms of spinodes and demixtion. Da ta are from the spin-crossover series [FexCo1-x(btr)(2)(NCS)(2)].H2O (noted [x= ]).