Theoretical Study on the Effect of Cyano- and Dimethylamine-Group on ESIPT Behavior and Luminescent Properties of Novel Flavone-Based Fluorophore.

Recently, a new fluorescent senor based on 3-hydroxy-2-(naphthalen-2-yl)-4 H-chromen-4-one (HFN) for selective detection of H₂S_n was obtained in the experiment (Spectrochim. Acta Part A 271(2022)120962). Based on HFN, three new compounds (HFN1, HFN2 and HFN3) are designed to explore the influences of dimethylamine (-N(CH₃)₂) and cyano (-CN) groups on the excited-state intramolecular proton transfer (ESIPT) process and luminescent features of HFN. After analyzing the mainly geometrical parameters, electron densities and infrared spectra, we discovered that the intramolecular hydrogen bonds (IHBs) in the target molecules become stronger upon photo-excitation. Introducing -CN or/and -N(CH₃)₂ groups into HFN indeed influences its ESIPT behavior and luminescent properties. The -N(CH₃)₂ group enhances IHB, reduces ESIPT barrier and caused absorption/ fluorescence (at T form) peak blue-shift, while the -CN group shows a counterproductive effect. The coincidence of -N(CH₃)₂ and -CN made the absorption/fluorescent wavelength of HFN red-shift more than single -N(CH₃)₂ or -CN group does.