  The solution to the long standing problem of the cohesion of organic chain
compounds is proposed. We consider the tight-binding dielectric matrix with two
electronic bands per chain, determine the corresponding hybridized collective
modes, and show that three among them are considerably softened due to strong
dipole-dipole and monopole-dipole interactions. By this we explain the unusual
low frequency optical activity of TTF-TCNQ, including the observed 10meV
anomaly. The softening of the modes also explains the cohesion of the
mixed-stack lattice, the fractional charge transfer almost independent of the
material, and the formation of the charged sheets in some compounds.
