<p>In this study, a new fluorescent sensor was occurred from pyrene-substituted calix[4]arene derivatives and its usability in the detection of Cu²⁺ ions and triazole-based pesticides was investigated. Calix[4]arene derivatives formed complexes that exhibited an "on–off-on" fluorescence response by interacting with pesticides containing triazole groups and showed significant changes in their optical properties. This innovative sensor plays an effective binding role especially for Cu²⁺ ions and the change in the fluorescence properties of the complexes formed with these ions can be used for the detection of pesticides. In the study, "turn-on–off-on" fluorescence responses were observed as a result of the interaction of calix[4]arene-pyrene complex with triazole-based pesticides (tebuconazole, tetraconazole, penconazole and difenoconazole). In addition, it is emphasized that the sensor is a potential tool for the rapid and sensitive detection of pesticides, which are important in terms of environmental pollution and food safety. The results obtained show that calix[4]arene derivatives have great potential in the detection of environmental pollutants and in the development of optical sensors sensitive to these pollutants.</p> Graphical Abstract <p></p>