Synthesis, photoluminescent behaviors, and theoretical studies of three novel ketocoumarin derivatives containing an azo moiety

Three new coumarin derivatives, namely, 6-phenylazo-3-[3-(4-formylphenyl)prop-2-enoyl]-coumarin (2a), 6-phenylazo-8-methoxy-3-[3-(4-formylphenyl)prop-2-enoyl]-coumarin (2b), and 6-(4-methoxyphenyl)azo-3-[3-(4-formylphenyl)prop-2-enoyl]-coumarin (2c), were synthesized and characterized. The three compounds exhibited high fluorescence quantum yields, strong blue emissions under UV light excitation, and high thermal stabilities, as determined by thermogravimetric (TG) analysis. The excited-state geometry was optimized at the CIS level of theory, whereas the B3LYP level of theory was applied for the ground state. The absorption and emission spectra were calculated using the time-dependent density functional theory (TD-DFT) in combination with the polarized continuum model (PCM). Resonance frequency calculations were undertaken to study the infrared spectra of the three compounds. The calculated results are in very good agreement with the experimental data.