@article{oai:oist.repo.nii.ac.jp:00001858,
 author = {Hou, Ian Cheng‐Yi and Berger, Fabian and Narita, Akimitsu and Müllen, Klaus and Hecht, Stefan},
 issue = {42},
 journal = {Angewandte Chemie International Edition},
 month = {Aug},
 note = {Proton-responsive photochromic molecules are attractive for their ability to react on non-invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero-atoms, which are orthogonal to the photo-active pi-center. Here, we incorporate azulene, an acid-sensitive pure hydrocarbon, into the skeleton of a diarylethene-type photoswitch. The latter exhibits a novel proton-gated negative photochromic ring-closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero-atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its pi-system, supported by(1)H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non-alternant hydrocarbons into photochromic systems for the development of multi-responsive molecular switches.},
 pages = {18532--18536},
 title = {Proton‐Gated Ring‐Closure of a Negative Photochromic Azulene‐Based Diarylethene},
 volume = {59},
 year = {2020}
}