Spectral-Luminescent Properties of Some Benzaldehyde Derivatives

Substituted benzaldehydes, which are widespread in nature, exhibit antibacterial, anti-inflammatory, antiviral, and anticarcinogenic activity with low toxicity, which makes them promising in medicine. The results of an experimental and theoretical study of the spectral-luminescent properties of four neutral forms of hydroxy- and methoxy-substituted benzaldehydes are presented. The absorption spectra of the studied compounds in hexane and ethanol were obtained. The spectra of fluorescence and fluorescence excitation of the substances in ethanol solutions were measured. Based on quantum chemical calculations, the orbital nature of electronic transitions, the features of the electron density distribution upon excitation, and changes in the structure of the compound are determined and the rate constants of photophysical processes are estimated. According to calculations, in all the compounds studied, the S1 state is formed by the nπ* transition and the intensity of the long-wavelength bands in these compounds is formed by one or two ππ* transitions. The fluorescence quantum yield is estimated from experimental and theoretical data. The results of analysis and comparison of experimental data with the results of quantum chemical calculations allow a conclusion that the neutral forms of the studied substituted benzaldehydes are not responsible for the fluorescence observed in experiments with ethanol solutions.