Anisotropic second-order nonlinearities of organic monolayers

Monolayers prepared from hemicyanine chromophores of high second-order nonlinearity (β=1.3×${10}^{\mathrm{-}26}$ esu at resonance) have been used to study anisotropies of the concomitant ${\mathrm{\chi }}^{\mathrm{}\left(2\right)\mathrm{}}$-susceptibility tensor. All components of this third-rank tensor have been determined by Fourier analysis of the anisotropic coverage density ${\mathit{N}}_{\mathit{s}}$(φ) with respect to the angle of rotation about surface normal. Depending on the preparation both ${\mathit{C}}_{\mathit{s}}$ and ${\mathit{C}}_{2\mathit{v}}$ symmetry could be identified.