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 (–NH 2 , –N(CH 3 ) 2 ). The mainly geometrical parameters of optimized configuration showed that the intramolecular hydrogen bonds of the studied compounds are enhanced in the excited (S 1 ) state, confirming by the ground (S 0 ) and excited states infrared spectra, electron densities and reduced density gradient isosurfaces. The S 0 → S 1 transitions of HFN derivatives are dominated by ππ* charge transfer transition. The introduction of electron‐donating group (–NH 2 , –N(CH 3 ) 2 ) weakens the intramolecular hydrogen bond, increases the excited‐state intramolecular proton transfer barrier and red‐shifts the absorption/fluorescence peak. The coexistence of –NH 2 and –N(CH 3 ) 2 make the absorption and fluorescence wavelengths of HFN‐1/HFN‐2 red‐shift/blue‐shift.