The excited-state intramolecular proton transfer of 2-(2-aminophenyl)benzothiazole (APBT) in different environments was detected by steady-state and transient fluorescence spectral measurements and quantum chemical calculations. The results showed that the polarity and protonation of the solution strongly affect the proton transfer of APBT. When APBT and cucurbit [7]uril (CB[7]) were mixed with each other, we found that the proton transfer process of APBT was restrained by the formation of a complex with a stoichiometric ratio of 1 : 1. The association constant and thermodynamic parameters of this complex were calculated. 1 H NMR spectroscopy and quantum chemical calculation data indicated that a 1 : 1 APBT@CB[7] complex of the amine or imine tautomer of APBT formed.