Oxford University Press (OUP) Acta Medica Okayama 0366-7022 54 5 2025 Highly emissive and robust diarylethene fluorophore incorporating imide-fused phenanthryl moieties upaf091 EN Keito Nose Department of Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Minoru Yamaji Program of Applied Chemistry, Cluster of Materials and Environment, Gunma University Tadashi Mori Research Center for Environmental Preservation and Graduate School of Engineering, The University of Osaka Fumito Tani Institute for Materials Chemistry and Engineering, Kyushu University Kenta Goto Institute for Materials Chemistry and Engineering, Kyushu University Hideki Okamoto Department of Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University The fluorescence properties and photostabilities of (E)-diarylethenes (DPEs), featuring two 3-phenanthryl moieties, were investigated. Pristine (E)-di-1,2-(3-phenanthryl)ethene and its ester derivative, respectively referred to as DPE-H and DPE-E, exhibited blue fluorescence. However, they underwent a two-step photoreaction sequence that yielded [7]helicenes, resulting in a gradual reduction of the fluorescence intensity. In contrast, the imide-fused derivative DPE-I displayed intense green fluorescence and it was unexpectedly photostable in solution, maintaining its highly efficient fluorescent nature even after prolonged light exposure. DPE-I, thus, provides a new type of highly efficient and robust diarylethene fluorophore. No potential conflict of interest relevant to this article was reported.