A Macroscopic Approach to the Light-Induced Instability of Cooperative Photo-Switchable Systems

Abstract
Under permanent irradiation cooperative photo-switchable systems may undergo a light-induced instability of the steady state leading to thermal and optical hystereses[1,2]. We report on a non-linear macroscopic master equation which accounts for the competition between a constant photo-excitation and a self-accelerated thermal relaxation process. The equilibrium phase diagram is drawn and the instability is discussed in terms of spinodes and demixtion. Data are from the spin-crossover series [FexCo1−x(btr)2(NCS)2].H2O (noted [x=]).