Second harmonic generation and electro-optical Pockels effect of 1- and 3-nitro-6-azabenzo[a]pyrene N-oxide isomers: A Hartree–Fock and Coulomb-attenuating density functional theory investigation

Abstract

Structural, energetic, spectroscopic, linear and nonlinear optical (NLO) properties of the environmental mutagens 1- and 3-nitro-6-azabenzo[a]pyrene N-oxides were characterized by means of Hartree–Fock as well as B3LYP and CAM-B3LYP density functional theory computations. The NLO investigations were performed for the second harmonic generation (SHG) and electro-optical Pockels effect (EOPE) at the incident wavelength of 1064 nm. The results show that, the predicted structures, vibrational spectra, nucleus independent chemical shifts, ionization energy, electron affinity as well as electronic polarizabilities are little influenced by the position of the nitro substituent. Differently, the dipole moment (μ) and the first-order hyperpolarizabilities (β μ ) are significantly dependent on the isomerization. The rather different mutagenic activity of the investigated isomers could be related to their diverse polarity. At the CAM-B3LYP level, when passing from the 1- to the 3-nitro-6-azabenzo[a]pyrene N-oxide isomer, the μ datum increases by about 5 D (a factor of three), whereas the static and dynamic β μ values decrease by ca. 50%. Dipole moment measurement and SHG and EOPE NLO techniques are potentially useful to distinguish these important environmental mutagens. Dipole moment (μ) and first-order hyperpolarizability (βvec) vectors of 1- and 3-nitro-6-azabenzo[a]pyrene N-oxide isomers were investigated.