Synthesis and Properties of Organic Lambda (Λ) Shape Molecules as Quadratic Nonlinear Optical Materials

Abstract

For the efficient second-order optical nonlinearity, the organic molecules must possess a large second-order hyperpolarizability β and also must crystallize into the lack of inversion center. We investigated a new molecular concept for noncentrosymmetric crystal structure. MO calculation by MOPAC AM 1 method demonstrated that the conformations of the methanediamine derivatives became lambda (Λ) -shape. The Λ-shape molecules formed easily noncentrosymmetric crystals because they could easily stack along one direction and thus exhibited Second-Harmonic Generation. The crystal structure analyses demonstrate that the Λ-shape molecules stack along one direction parallel to the crystal axis. This orientation is close to an optimum condition for maximizing crystal phase-matched nonlinearity. We demonstrate that methanediamine derivatives forming Λ-shape conformation are promising as efficient χ ⁽²⁾ materials.