The fatigue performance of a range of donor-acceptor-Stenhouse-adducts (DASAs) has been investigated to identify degradation mechanisms. The dyes were found to fatigue with and without exposure to light in both solution and in films.Excluding light below about 430 nm resulted in almost complete thermal recovery after exposure, however, a range of common film additives including hindered amine light stabilizers (HALS) and other additives (especially bases) were shown to react with the DASAs resulting in irreversible fatigue. The rate of fatigue was also found to increase with the relative strength of the donor and acceptor moieties in the molecule.

Donor‐acceptor Stenhouse adducts (DASAs) are an exciting new class of negative photochromic compounds, offering high colouration and rapid photo‐switching speeds, however the relationship between binder properties and photo‐switching behaviour of DASAs in films is poorly understood. The determination and analysis of rate constants of seven DASAs in five polymer binders showed a complex relationship between the glass transition temperature (Tg) of the binder, the solubility parameters of the matrix and the push‐pull nature of the donor and acceptor moieties. The rate constants of photo‐switching steps that require large degrees of molecular motion such as the actinic and thermal carbon‐carbon double bond rotations (kbleach and k−1) were found to be highly dependent on the Tg of the polymer binder, with higher Tg binders restricting these processes, resulting in slower switching rates and impacting changes in colour intensity. Correlation of rate constants with the Hansen solubility parameter for solvents and binders revealed strong relationships between the sum of the polarity and hydrogen bonding parameters (δP+δH) and the actinic and thermal carbon‐carbon double bond rotations (kbleach and k−1). This is attributed to changes in the zwitterionic resonance contributions of the triene with increases in these two solubility parameters.