A new Tröger's base containing fluorenone organic polymer (TB-FL-COP) was synthesized and used as a fluorescence sensor for discriminative sensing of antibiotics in water. TB-FL-COP showed the highest fluorescence quenching, reversible sensing responses, and excellent sensitivity of 56 ppb level for sulfamethazine antibiotics. The Stern-Volmer quenching constant (KSV) was calculated to be 1.2 × 106 M−1. The fluorescence sensing ability was also reflected by sharp visual color changes and further demonstrated in real water samples. © 2023 The Royal Society of Chemistry