Bifunctional Molecular Switches in Fused Diarylethene–Rhodamine Systems

A synthetic route for a novel rhodamine‐based diarylethene (DAE) systems 1 and 2 is reported. The key synthetic steps involve the preparation of 6′‐ and 7′‐bromo rhodamine precursors, their conversion into azide derivatives, and subsequent Huisgen 1,3‐dipolar cycloaddition with a perfluorocyclopentene acetylene unit. The target compounds, 1 and 2 , isolated in their “closed” rhodamine and “open” DAE forms, are characterized through nuclear magnetic resonance (NMR), infrared, and UV–vis absorption spectroscopies, revealing distinct electronic environments for the triazole moiety in both derivatives. Spectroscopic studies highlight their intense UV–vis absorption with minimal visible‐light absorption, supported by theoretical time‐dependent density‐functional theory (TD‐DFT) calculations. Investigation of chemo‐switching behavior with trifluoroacetic acid and metal ions in dichloromethane reveals a two‐step protonation process involving the triazole and rhodamine moieties, confirmed by UV–vis absorption and NMR spectroscopies. Such a process is reversible upon triethylamine addition. Selectivity tests show strong responses toward Hg 2+ and Zn 2+ , for compound 1 displaying an additional response with Fe 3+ . Photoswitching experiments and TD‐DFT calculations reveal distinct behaviors for compounds 1 and 2 . UV irradiation of 1 results in the formation of an unexpected open‐spiro rhodamine species, potentially due to photoinduced acid production. In contrast, 2 undergoes a different spectral feature arising from a degraded product with lower‐lying transitions.