Effect of intermolecular hydrogen bonds on the proton transfer and fluorescence characteristics of 1′-hydroxy-2′-acetonaphthone

Abstract

1′-hydroxy-2′-acetonaphthone (HAN) is a useful fluorescence probe based on excited state intramolecular proton transfer (ESIPT). A number of experiments had explored the fluorescence properties of HAN in different microenvironments and applied HAN to bioimaging. However, the mechanism of fluorescence properties of HAN in different microenvironments was not been fully reported. Thus, our research aims to investigate the proton transfer (PT) and fluorescence characteristics of HAN in different microenvironments, focusing on revealing the hydrogen bond dynamics in high-polar aqueous solution (HAN-H2O) and low-polar hydrophobic pocket of bovine serum albumin by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Explicit water molecules were placed around HAN to simulate the hydrogen bond interactions between HAN and the water molecules in an aqueous solution. The intermolecular hydrogen bonds slightly affect the geometric structures of HAN, but would inhibit the ESIPT process while increasing the charge transfer distance, leading to red shift of fluorescence. Upon photoexcitation, the intramolecular hydrogen bond had been strengthened, providing the driving force of PT, which resulted in HAN and HAN-H2O undergoing ultrafast ESIPT process. Meanwhile, after photoexcitation, the intermolecular hydrogen bonds were significantly enhanced, decreasing the energy of HAN-H2O in the excited state and promoted the radiationless deactivation of HAN-H2O. Therefore, HAN has weak fluorescence in the aqueous solution.