A doubly-interlocked [2]catenane – or Solomon link – undergoes a complex conformational change upon addition of sulfate in methanol.

The metal ion and anion recognition abilities of the newly synthesized acridone derivative having amide and ester groups were studied by UV–vis and fluorescence spectroscopies. The sensor molecule revealed selective recognition toward Ca(II), Hg(II), and fluoride in acetonitrile. Based on X‐ray crystallographic and ¹ H NMR analyses, intramolecular bifurcated H‐bond is formed between the acridone NH and the amide oxygens in the free receptor. Addition of Ca(II) and Hg(II) induced large fluorescence enhancements and changes in the ¹ H NMR shifts due to complexation, while fluoride deprotonated the sensor molecule giving rise to a new emission band. Selective sensing of Hg(II) based on absorption changes was also observed, presumably due to the tautomerization of the acridone unit upon complexation. The optical spectroscopic behavior in the presence or absence of Ca(II) and fluoride as chemical inputs provided an opportunity to construct IMP, INH, XOR, and XNOR molecular logic gates as well as a complementary IMP/INH circuit, and integrated logic functions such as a half‐subtractor (XOR/INH combination) and a magnitude comparator (XNOR/INH combination).