UGT1A1-IN-1 (compound 2) is a non-competitive inhibitor of UGT1A1 , which can inhibit the 1-O-glucuronidation process mediated by UGT1A1 with a K i value of 5.02 μM. UGT1A1-IN-1 (compound 2) can bind on UGT1A1 at the same ligand-binding site as bilirubin. UGT1A1-IN-1 can serve as a ‘turn-on’ fluorescent probe substrate for UGT1A1.