Abstract: In this paper, a comparison has been made of the absorption spectra of nine aromatic monoketones in acetone. It can be seen from our results that the dispersiveness of aromatic monoketones is inhomogeneous in solution. The equilibrium between monomers and dimers shifts to the side of the latter with increasing the concentration of monoketones. A number of factors have been suggested as promotion for the aggregation of aromatic monoketones. This red-shifted absorption was assigned by the method of Davydov-Kasha as the allowed exciton dimer transitin. Furthermore, the geometry of dimer is “face to face”.