MOLECULAR SIMULATION OF THE COMPLEXATION EFFECTS ON CONFORMATIONS AND ELECTRONIC ABSORPTION-SPECTRA OF CROWN-ETHER STYRYL DYES

The structure and spectra of new styryl dyes containing a crown ether moiety and a sulfoalkyl group along with their complexes with metal cations are investigated using spectroscopic methods and computer simulation. Large differences between the absorption spectra of the cis form and its complexes with alkaline earth metals are found. The absorption maximum of the high intensity longwave band is at 429 nm for the cis form and at 321-328 nm for the complexes. We show that this difference results from a large distortion of the chromophore geometry, which arises from the formation of an intramolecular coordination bond between the sulfo group and the metal cation captured in the crown cavity. For the distorted geometry, the first electronic transition is symmetry forbidden. The disappearance of the longwave band results in a large hypsochromic shift, observed experimentally.