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The interaction of 2-(3-acetamido-2-pyridyl)-benzimidazole (2-3Am2PyBI) with cucurbit[7]uril (CB7) macrocycle and the effect of inclusion on the proton transfer of 2-3Am2PyBI were studied by using emission fluorescence, 1 H NMR spectra and quantum chemical calculation. By the way, the proton transfer of the dye with and without acetyl (2-3A2PyBI) was also studied. The results indicate that the acetyl promoted the process of proton transfer of the benzimidazole and the cationic form binds with CB7 easier than the other forms of the dye. The fluorescence studying at selected pHs suggest that the proton transfer process of the dye was retarded by interacting with CB7 nanocavity and the molar rate is host∶guest＝1∶1 analyzed by the Benesi-Hildebrand method. The dye entered into the CB7 cavity with its benzene ring was proved by the 1 H NMR titration experiment and the protonated forms were verified by the quantum calculation with fluorescence spectra.

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.