Anisotropic dissociation and spectral response of 1-Bromo-4-chlorobenzene under static directional electric fields

Abstract Halogenated aromatic hydrocarbons, owing to the stable structure imparted by their halogen substituents and benzene ring, are among the Persistent Organic Pollutants (POPs) with relatively high toxicity and are notoriously resistant to degradation. In this work, the density functional method with the B3LYP/6-311G(d,p) level set was employed to investigate the effects of external electric fields on the total energy, LUMO(lowest unoccupied molecular orbital), HOMO, (highest occupied molecular orbital), E G (energy gap) and dissociation characteristics of 1-Bromo-4-chlorobenzene molecule. The results show that the electric field along the X axis changes from −0.025 a.u. to 0.025 a.u. During the process, the C–Br bond length of 1-Bromo-4-chlorobenzene molecule increases gradually, while the C–Cl bond length changes inversely. The dipole moment initially decreases and then increases, while the total energy of the molecular system shows a trend of first increasing and then decreasing. The E G first increases and then decreases with the strengthening with the external electric field. The positive external electric field causes the C–Br bond vibration peak to redshift, and the C–Cl bond vibration peak to blue shift. Simultaneously, the first 9 excited states undergo a red shift in wavelength, resulting in a decrease in excitation energy. In addition, C–Br and C–Cl are found to break in sequence by scanning in the external electric field, which provides a theoretical basis for the dissociation of 1-Bromo-4-chlorobenzene molecule.