Effects of amino- and dimethylamine-groups on the fluorescent properties of novel flavone-based derivatives with ESIPT behavior: A TD-DFT study

In this work, the effects of different functional groups on the excited-state intramolecular proton transfer behavior and fluorescent features of 3-hydroxy-2-(naphthalen-2-yl)-4H-chromen-4-one (HFN) are explored in detail. Three new compounds (HFN-1, HFN-2, and HFN-3) are designed based on the HFN by introducing the electron-donating groups (–NH₂, –N(CH₃)₂). The mainly geometrical parameters of optimized configuration showed that the intramolecular hydrogen bonds of the studied compounds are enhanced in the excited (S₁) state, confirming by the ground (S₀) and excited states infrared spectra, electron densities and reduced density gradient isosurfaces. The S₀ → S₁ transitions of HFN derivatives are dominated by ππ* charge transfer transition. The introduction of electron-donating group (–NH₂, –N(CH₃)₂) weakens the intramolecular hydrogen bond, increases the excited-state intramolecular proton transfer barrier and red-shifts the absorption/fluorescence peak. The coexistence of –NH₂ and –N(CH₃)₂ make the absorption and fluorescence wavelengths of HFN-1/HFN-2 red-shift/blue-shift.