Complete kinetic and photochemical characterization of the multi-step photochromic reaction of donor–acceptor Stenhouse adducts

Donor-acceptor Stenhouse adducts (DASA) are negative photochromic compounds exhibiting a multi-step photoisomerization mechanism. Previous studies have described a first photoactivated step, followed by a thermally controlled one. This study emphasizes the key role of the intermediate species, using high-rate acquisition photokinetic absorption spectroscopy. We have investigated the multi-step processes at different temperatures and irradiation power values. For the first time, we have combined our experimental setup with a three-species photokinetic model to determine the kinetic constants and quantum yields of each step of a DASA compound. Finally, we have identified the key role of the intermediate species, showing that double irradiation experiments allow the tuning of the photochromic reaction.