  We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.
