Robust Red‐Absorbing Donor‐Acceptor Stenhouse Adduct Photoswitches

Abstract

AbstractDonor‐Acceptor Stenhouse Adduct (DASA), a class of push‐pull negative photochrome, has received large interest lately owing to its versatile synthesis, modularity and excellent photoswitching in solutions. From a technological perspective, it is imperative for this class of photoswitches to work robustly in solid state, e. g. thin films. We feature a molecular framework for the optimized design of DASAs by introducing a new thioindoline donor (D3) and assessing its performance against known 2nd generation indoline‐based donors. The systematic structure‐function investigations suggest that to achieve robust reversible photoswitching, a ground state with low charge separation is desired. DASAs with stronger electron donors and a larger charge separation in the ground state result in a low population of the photothermalstationary state (PTSS) and reduced photostability. The DASA with thioindoline donor (D3A3) seems to be a special case among the donor series as it causes a red shift (ca. 15 nm), however with less polarization of the ground state and marginally better photostability as compared to the unsubstituted 2‐methyl indoline (D1A3). We also emphasize the consideration of the key additional factors that can modulate the red‐light photoswitching properties of DASA chromophores in polymer thin films, which might not be dominant in homogenous solution state.