Second harmonic generation from trinitro-substituted subphthalocyanines films: Evidence of noncentrosymmetric molecular organization

Second-harmonic generation from λ=1.06 μm fundamental light has been measured in both evaporated and spin-coated films of trinitro-substituted subphthalocyanines. Ordering of these noncentrosymmetric molecules with the dipole moment perpendicular to the film face has been achieved either by the deposition process (evaporated samples) or by corona poling (spin-coated samples). The second-order susceptibilities ${\chi }_{31}^{\text{(2)}}{\text{=2.36×10}}^{\text{−9}}$ esu (for vacuum evaporated samples) and ${\chi }_{31}^{\text{(2)}}{\text{=9.62×10}}^{\text{−10}}{\text{–1.14×10}}^{\text{−9}}$ esu (for poled spin-coated samples) have been determined by comparison with an $X$ -cut ${\mathrm{LiNbO}}_3$ crystal used as reference.