The effect of the intramolecular coupling on the spectral properties of an ensemble of two-level systems carrying homogeneously distributed resonance frequencies is studied. Each molecule is described by two coupled harmonic curves of electronic energies with the same force constant and with minima displaced in energy and nuclear coordinate. The coupled states interact with two electromagnetic fields of different frequency and propagation vector, one of which is the pump beam and the other is the probe beam. The generated four-wave mixing signal generated has a frequency ω-3$/ = 2 ω-1$/-ω-2$/ and propagation vector k3≈2k1-k2. The intensity of the generated four-wave mixing signal is proportional to the square of macroscopic nonlinear induced polarization.