Tactfully regulating the ESIPT mechanism of novel benzazolyl-4-quinolones fluorophore by atomic electronegativity

The effects of atomic electronegativity (O, S and Se) on the excited state intramolecular proton transfer (ESIPT) behavior of fluorescent benzazolyl-4-quinolones derivatives have been investigated theoretically. Analysis of structure parameters and infrared vibrational spectra indicate that the intramolecular hydrogen bonds (O₁H₁⋯N₁) are gradually strengthened in the first (S₁) excited state as the atomic electronegativity diminishes (O → S → Se). The topological parameters, reduced density gradient (RDG) scatter plots and interaction region indicator (IRI) isosurface further confirm our results. The energy gap of molecular orbitals reflect that the less atomic electronegativity prompt greater excited state reactivity. In addition, the constructed potential energy curves (PECs) reveal that Se substituent has lower potential barrier (0.42 kcal/mol), which is more likely to accelerate the occurrence of ESIPT process. These results show that the atomic electronegativity helps to regulate the ESIPT process, which will pave the way for the design and synthesis of ESIPT-based fluorophores in future.