  We study the existence of solution for the following class of nonlocal
problem, $$ -\Delta u +V(x)u =\Big( I_\mu\ast F(x,u)\Big)f(x,u) \quad \mbox{in}
\quad \mathbb{R}^2, $$ where $V$ is a positive periodic potential,
$I_\mu=\frac{1}{|x|^\mu}$, $0<\mu<2$ and $F(x,s)$ is the primitive function of
$f(x,s)$ in the variable $s$. In this paper, by assuming that the nonlinearity
$f(x,s)$ has an exponential critical growth at infinity, we prove the existence
of solutions by using variational methods.
