Hyper-Rayleigh scattering in solution is used for the determination of the hyperpolarizability of nonlinear optical molecules. Obtaining the first hyperpolarizability β without having to independently determine the dipole moment μ and the second hyperpolarizability γ is an advantage over the electric-field-induced second-harmonic generation technique. Values of the first hyperpolarizability β of 23×${10}^{\mathrm{-}30}$ esu for para-nitroaniline, 105×${10}^{\mathrm{-}30}$ esu for 4-methoxy-4’-nitrostilbene, and 95×${10}^{\mathrm{-}30}$ esu for 4-hydroxy-4’-nitrostilbene dissolved in chloroform have been obtained. The equivalent-internal-field model is shown to hold for small saturated molecules.

This paper deals with recent and important developments in the field of organic materials for second-order nonlinear optics. Attention is drawn to current trends in chromophore design with a discussion of current progress and problems in this field. A number of important classes of chromophores, such as one-dimensional charge-transfer molecules, octopolar compounds, ionic materials, multichromophore systems and organometallics, are discussed.

The experimental setup for the implementation of a new technique to determine the hyperpolarizability of nonlinear optical molecules in solution is presented. The new technique, hyper‐Rayleigh scattering in solution [K. Clays and A. Persoons, Phys. Rev. Lett. 66, 2980 (1991)], has the advantage over the electric‐field‐induced second‐harmonic generation technique that the dipole moment μ and the second hyperpolarizability γ do not have to be independently determined to obtain the first hyperpolarizability β. No electric field is needed to lower the intrinsic symmetry of the isotropic solution, leading to a simpler cell design and a simpler local field factor. The internal reference method, when applicable, completely eliminates the local field factor. With the technique presented, values of the first hyperpolarizability β of 23×10⁻³⁰ esu for para‐nitroaniline (PNA), 105×10⁻³⁰ esu for 4‐methoxy‐4’‐nitrostilbene (MONS), and 95×10⁻³⁰ esu for 4‐hydroxy‐4’‐nitrostilbene (HONS) dissolved in chloroform have been obtained.