The fluorescent photoinduced electron-transfer (PET) chemosensor 1, which can function as "off-on" fluorescence switch for dicarboxylic acids has been designed and synthesized for the first time. The carboxylic acid binding takes place through charge neutral pyridine amine receptor sites and the sensor is found to be selective for glutaric acid. The binding has been examined by fluorescence, UV-vis, and NMR spectroscopic methods.