Semi-empirical calculations of the nonlinear optical properties of polycyclic aromatic compounds

Abstract A systematic study of factors influencing nonlinear optical properties, in particular the second hyperpolarizability 〈γ〉, is conducted for a series of polycyclic aromatic hydrocarbons (PAHs). The HOMO-LUMO gap, polarizability 〈α〉, first hyperpolarizability 〈β〉, and second hyperpolarizability 〈γ〉 of polycyclic aromatic compounds are computed by using semi-empirical MNDO-FF calculation implemented in the MOPAC package. For linear polyacenes, the linear and nonlinear properties and total resonance energy are found to increase while the HOMO-LUMO gap and resonance energy per electron decrease as the number of six-membered rings increases. For nonlinear PAHs, the chain topology should be taken into account. An empirical formula is given to relate the computed 〈γ〉 and 〈α〉.

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