Structures and calculated NLO properties of (acenaphthylene)- and (acenaphthene)Cr(CO)3

To be useful in elucidating structure-property relationships for the planar fused ring bearing metal π-complexation, the structures of (acenaphthylene)Cr(CO)3 (3) and (acenaphthene)Cr(CO)3 (4) were determined by X-ray crystal analyses, and their nonlinear optical activities investigated by using density functional theory calculations. The title molecules exhibit the intense electronic absorptions characteristic of charge-transfer capability and moreover, the observed negative solvochromicity in the low-energy transition is proposed to be associated with the organometallic modification of the electronic structure. These results are compared with the behavior of the corresponding free ligands, indicating that chromium tricarbonyl complexation can be used to create an unique non-centrosymmetric metal-organic architecture with the more extensive π-delocalization and, therefore, improve the nonlinear optical response.