Ab initio study of nonlinear optical properties of aromatic fused rings

The nonlinear optical properties of benzene, naphthalene, anthracene, and pyrene are investigated. Static and dynamic polarizability, α(−ω; ω), and second hyperpolarizability, corresponding to dc electric-field-induced Kerr effect (DCKE), intensity dependent refractive index (IDRI), dc electric field-induced second harmonic generation (EFISHG), and third harmonic generation (THG) have been calculated. The calculated α and γ show good agreement with the available theoretical and gas-phase experimental data. The second hyperpolarizabilities exhibit the following trend: γ(THG) > γ(EFISHG) > γ(IDRI) ∼ γ(DCKE) > γ(static). We find that the second hyperpolarizabilities increase as the number of rings in the system increases in either dimension, but the magnitude of increase is more pronounced along the molecular chain axis.