New hydrazide-hydrazone derivatives containing coumarin and indole moiety: Synthesis, spectroscopic characterization and DFT studies

Two new compounds (3 and 4), coumarin indole derivatives with a hydrazide-hydrazone skeleton, were synthesized, and their spesctroscopic properties, including UV-vis, FTIR, and 1H-13C NMR were investigated experimentally and theoretically. The experimental data and DFT (density functional theory) results of the compounds matched well and showed good agreement. Moreover, the DFT/B3LYP/6-311G++(2d,p) calculations were utilized to perform HOMO and LUMO energy, net atomic charges, MEP surface, and NBO analysis for the optimized geometries of 3 and 4. NBO analysis revealed that the synthesized compounds exhibit high molecular stability because of significant hyperconjugative interactions. The experimental and theoretical band gaps (Delta Eg) investigated in some organic solvents with different polarities were determined to be in the range of 2.682.75 eV and 3.22-3.25 eV for compound 3, and 2.69-2.77 eV and 3.41-3.47 eV for compound 4, respectively. The compounds demonstrated thermal stabilities with a Td value higher than 300 degrees C.