6533b861fe1ef96bd12c4d3c

RESEARCH PRODUCT

Deviations from Kleinman symmetry of the second-order polarizability tensor in molecules with low-lying perpendicular electronic bands

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Abstract 4-Nitroaniline (pNA) and 3,5-dinitro-aniline (3,5-DNA) were studied by electric field induced second harmonic generation (EFISH) and electrooptical absorption measurements (EOAM) in dioxane solution at T = 298 K. The measurements were carried out for two polarization conditions, the electric field vector of the linearly polarized incident light being parallel or perpendicular to the static electric field. The second-order polarizability tensor of pNA is confirmed to be Kleinman symmetric, while a strong deviation from index permutation symmetry is observed for 3,5-DNA. The latter is quantitatively interpreted by contributions of a low-lying electronic band with transition dipole perpendicular to the symmetry axis. New design possibilities for second-order nonlinear optical materials are pointed out.