  We study with exact diagonalization the zero temperature properties of the
quarter-filled extended Hubbard model on a square lattice. We find that
increasing the ratio of the intersite Coulomb repulsion, $V$, to the band width
drives the system from a metal to a charge ordered insulator. The evolution of
the optical conductivity spectrum with increasing $V$ is compared to the
observed optical conductivity of several layered molecular crystals with the
theta and beta'' crystal structures.
