Second order nonlinear optical properties of organic molecules.

Second-order nonlinear optical susceptibilities (beta) of a series of organic conjugated pi-electron molecules were measured using electric field induced second harmonic generation. This study was directed at revealing structure- property relationships that affect beta, which include the electronic properties of substituents, the length and type of pi-electron system, molecular configuration, and dispersion. A new class of compounds was found which posses the largest values of beta reported to date. Results of semi-empirical quantum, mechanical calculation of beta indicate that, in these molecules, the origin of these exceptional susceptibilities resides in properties of the lowest- lying electronic excited state. Details of the material synthesis and experimental configuration are presented. Prospects for use of these molecules in poled polymer films are also discussed.