a b s t r a c t Cup-shaped calix[4]arenes bearing one or two ketocyanine fluorophore fragments at the wide rim of the macrocycle are synthesized by condensation of formyl calix[4]arenes with arylmethylene(hetarylmeth-ylene)cyclopentanones in the presence of the ionic liquid, dimethylammonium dimethylcarbamate (DIMCARB) and characterized using UV–vis and fluorescence spectroscopy. Strong positive solvatofluoro-chromism for the calixarene ketocyanines is observed. Molecular sensing is a rapidly developing field in science and technology. 1 The key task in construction of efficient chemosensors is the design of sensor systems capable of producing a high-ampli-tude physical signal upon selective molecular recognition. Among a variety of chemosensory devices, fluorescence systems are com-monly considered superior due to their simple construction and extremely high sensitivity. 2 On the other hand, calixarenes are phenol-derived macrocycles that possess a unique cup-shaped molecular cavity and are able to demonstrate high selectivity in the formation of supramolecular host–guest complexes with metal cations, anions, and organic and biomolecules. 3 This ability makes calixarenes an attractive framework for construction of optical sensing systems. A chromo(fluoro)phore electronic system can be