On the experimental evidence for a departure from first-order photochemical kinetics in bistable photochromic materials

We discuss the apparent discrepancy between experimental results and the mono-exponential decay law (which is characteristic of first-order kinetics) for two-state photochromic materials during activation and bleaching. Although deviations from first-order kinetics could be expected for realistic samples, we show that the experimental data presented are actually compatible with a mono-exponential decay law, and that the apparent discrepancy is attributable to an inappropriate description of the photo-stationary state.