Study of Dipole Moment and Electronic Transitions of Some Oxazolone Derivatives Using Fluorescence and Ultraviolet Spectra

The compounds 4-benzyldine-2-phenyl-5(4H)-oxazolone and (4-methoxy)-4-benzyldine-2-phenyl-5(4H)-oxazolone were prepared. Infrared spectroscopy and mass spectra were used to confirm the structures of the two compounds. The dipole moment values of the ground electronic states were experimentally studied in benzene solution, where the results indicated that the methoxy-substituted compound reduced dielectric values, meaning it aided in forming double layers compared to the unsubstituted compound. However, at the same time, it had no clear effect on the results of the permanent dipole moment values, indicating that the electron-donating methoxy group did not noticeably affect the electronic and geometric structures of the compounds because its molar mass is much smaller than the molar mass of the entire compound. The fluorescence spectra of the two prepared compounds were measured in the wavelength range (200–900) nm in solvents of different polarities (acetonitrile, acetic acid, and ethyl acetate). The measured spectra indicated red-shifts in fluorescence emission peaks, any toward longer wavelengths as solvent polarity increased. The study showed that the dipole moment values of the excited state did not exhibit significant differences between the two compounds. The results of Stokes shift less than 100 nm indicated that the geometric shape of the compounds did not change, meaning that the presence of the electron-donating group in the compound, despite differences in its electrical properties, did not cause any disturbances in the compound’s energy levels overall. The electronic absorption spectra were measured in hexane and methanol, where no clear spectral shifts were observed when transitioning from a polar to a nonpolar solvent. The experimentally measured spectra in hexane were analyzed into ten linearly overlapping spectral bands using Gaussian fitting. To determine the nature of the electronic transitions, molecular orbital calculations were performed using the PM3 wavefunction, which was considered the best mathematical function for determining the geometric shape corresponding to the lowest energy.