An analytical model for the nonlinear behavior of the electro-optic (EO) coefficient in chromophore-polymeric materials is developed. The sharp decline of the EO coefficient above a threshold chromophore concentration is attributed to a second order phase transition transforming the chromophore dipolar system into an antiferroelectric state. The rise of antiferroelectric correlations between chromophore dipoles deteriorates the efficiency of the poling process aimed at achieving a noncentrosymmetric chromophore ordering by application of an electric field. The location of the phase transition and the magnitude of the EO coefficient are investigated as functions of molecular and thermodynamic parameters. Particularly remarkable observations are made regarding the dependence of the EO coefficient on the macroscopic shape of samples used for poling. Slab shaped samples that are common in practice are least efficient for the poling process. Any degree of sample elongation in the direction of the poling field shifts the antiferroelectric phase transition towards higher chromophore concentrations and radically increases the maximum value of the EO coefficient. The theory is applied to two chromophore systems that are typical of materials used in EO devices. Fine agreement with the experimental data is achieved with little adjustment.