2‐D. charge‐transfer molecules for second order nlo: off‐diagonal orientation

Second order nonlinear optical materials based on two‐dimensional charge‐transfer molecules rather than one‐dimensional molecules offer a number of advantages. For example, the 2‐D CT molecules retain their second order nonlinearity even if they are inclined away from normal to the substrate. This interesting class of new materials is presented and the factors influencing the performances of the materials, such as the incorporation of long π‐conjugated segments into the molecules, are discussed.