From Color to Control: The Emerging Power of Stenhouse Photoadducts in Adaptive Molecular Systems.

Donor-acceptor Stenhouse adducts (DASAs) and related Stenhouse salts (SSs) represent a distinctive class of visible-light-responsive molecular photoswitches that transduce optical stimuli into pronounced structural and physicochemical transformations. In contrast to classical photoswitches that require ultraviolet excitation, these systems function predominantly under visible light and exhibit complex switching mechanisms involving photoinduced isomerization followed by thermal electrocyclization. Over the past decade, progress in molecular design, mechanistic elucidation, and materials integration has significantly broadened the functional landscape of Stenhouse photoswitches. This Perspective reviews the evolution of Stenhouse photoadducts from their initial discovery to their integration in contemporary adaptive molecular systems, with a focus on structure-property relationships, design methodologies, and incorporation into responsive materials. Key limitations impeding broader application, such as solvent sensitivity, switching fatigue, and restricted aqueous compatibility, are critically assessed. The complementary relationship between DASAs and their structural analogues, SSs, is also examined, particularly regarding their potential advantages in aqueous and polymeric environments. Finally, emerging strategies, including supramolecular confinement, hybrid material platforms, and computationally guided molecular design, are evaluated as promising avenues for addressing current challenges and facilitating future developments in adaptive materials and light-controlled technologies.