Homoconjugation vs. Exciton Coupling in Chiral α, β-Unsaturated Bicyclo[3.3.1]nonane Dinitrile and Carboxylic Acids

The chiroptical properties of enantiomerically pure bicyclo[3.3.1] nona-2,6diene-2,6-dicarbonitrile and related acids were studied by circular dichroism spectroscopy and theoretical computations. A consideration of the molecular structure of the synthesized difunctional compounds revealed that chromophores are predisposed to transannular through-space interaction due to a favourable conformation of the bicyclic skeleton and a rather small interchromophoric distance. Evidence for non-exciton-type coupling between the two acrylonitrile and acrylate moieties in 3 and 4, respectively, was obtained by chiroptical spectroscopy and DFT calculations.