Electric field poling of acceptor–donor molecules

The Maier–Saupe theory for liquid crystals is extended to describe poling by an electric field of side-chain polymers with π-conjugated acceptor–donor molecules as pendant groups. Applications of the theory are in the field of nonlinear-optical materials. By using a quasi-one-dimensional description of the acceptor–donor molecules, our model is capable of going beyond the linear approximation and is intended for the strong-field regime. The theory takes both the dipole moment and the anisotropic polarizability of the side chains into account. A field-induced phase transition to the nematic phase is predicted for isotropic materials. This leads to enhanced polar order and thus to a larger nonlinear susceptibility than is predicted by the simpler isotropic model. The difference between initially liquid-crystalline and initially isotropic materials becomes smaller if the field-induced axial order is taken into account.