Development and characterization of amino donor-acceptor Stenhouse adducts

Donor-acceptor Stenhouse adducts (DASAs) are molecular photoswitches that have spurred a decade of interest because of their dynamic photophysical properties, complex photoswitching mechanism, and diverse applications. Despite breakthroughs in modularity for the donor, acceptor, and triene compartments, the backbone heteroatom has remained static due to synthetic challenges. We provide a predictive tool and sought-after strategy to vary the heteroatom, develop a new subclass of DASA photoswitches, and analyze backbone heteroatom effects on photophysical properties. Amino DASA synthesis is enabled by the first aza-Piancatelli rearrangements on pyrrole substrates, imparting an aromaticity-breaking rearrangement that capitalizes on nitrogen’s additional bonding orbital and the inductive properties of sulfonyl groups. Amino DASA structure was confirmed by single crystal X-ray diffraction, the photochromic properties were characterized, and the photoswitch isomerization was investigated. Complimentary to other DASA compartments, this study furthers our insight into the structure-property relationship of this complex photoswitch and brings DASAs closer to application-specific design.