Control of sulfur-containing hydrogen bonding interaction and novel thiol-type ESIPT behavior by different functional groups: A TD-DFT study

There have been more and more studies on the excited-state intramolecular proton transfer (ESIPT) reaction involving sulfur atom in recent years. Based on 3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (TFN1), its four derivatives, 6-amino-3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (ATFN1), 6-dimethylamine-3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (DTFN1), 6-trifluoromethyl-3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (FTFN1) and 6-cyano-3-mercapto-2-(naphthalen-2-yl)-4H-chromen-4-one (CTFN1) were designed. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the ESIPT processes and photophysical properties of TFN1 derivatives were explored, and the substituent effects on the ESIPT behavior and spectral properties of TFN1 were investigated in detail. The introduction of electron-donating groups (–NH2, –N(CH3)2) can strengthen the intramolecular hydrogen bond (IHB), decrease the ESIPT barrier and blue-shift the absorption and fluorescence wavelengths, while the role of electron-withdrawing groups (–CF3, –CN) is completely opposite to that of electron-donating groups.