Effects of dipole orientations on nonlinear optical properties of oxo-bridged dinitroaniline systems

We have considered several oxo-bridged dinitroaniline compounds in various dipole configurations. An extensive semiempirical calculations based on singles configuration interactions (CIS) was performed to calculate their nonlinear optical properties. While keeping one of the nitroaniline dipole moieties fixed, we rotate the other nitroaniline molecule along the oxygen-carbon bond to generate a number of dipole orientations. We also change the position of the donor-acceptor functionalities from ortho and meta to para and study the variation in the nonlinear optical properties with the twist angle. We find that the best conformation is where the nitroaniline dipoles are arranged parallel to each other in the same plane. In real systems steric interaction between the two aromatic rings would force the double molecule to be nonplanar. We suggest molecular systems where the moieties can be made parallel, thereby exhibiting very high hyperpolarizabilities. We interpret these results on the basis of dipole-dipole interactions and the ground-state properties