Interaction between a pyridyl and a naphthyl/pyrenyl moiety in covalently linked systems

Photophysical properties of two bichromophoric systems comprising a pyridyl moiety and a naphthyl/pyrenyl moiety covalently linked through a dimethylene bridge have been investigated. The spectral behavior of the systems suggests the formation of an intramolecular complex between the two terminal moieties of the molecules in the ground state. Interestingly, no intermolecular complexation could be observed with a 1:1 mixture of the constituting components. This contrasting behavior has been interpreted taking into consideration the difference in the entropy change associated with the complexation process. Based on the effect of solvent polarity on the absorption and emission behavior of the complex and taking into consideration the molecular geometry, it is concluded that the interaction between the aromatic hydrocarbon and pyridyl moieties is primarily driven through an overlap of the π-clouds.