The occurrence of through-bond orbital interactions in an α,ω donor-acceptor substituted bi(cyclohexylidene) and bi(cyclohexyl).: X-Ray diffraction, UV-Vis absorption and photoelectron spectroscopy, ab initio SCF-MO and natural bond orbital analyses

The ground state sigma-pi and pi-pi* interactions in 2-[4-(1-phenylpiperidin-4-ylidene)cyclohexylidene]malononitrile (1) and 2-[4-(1-phenylpiperidin-4-yl)cyclohexylidene]malononitrile (2) have been studied. Both the ionization potentials of 1 and 2, and ab initio RHF/6-31G calculations in combination with a natural bond orbital analysis show that the ground state through-bond interaction (TBI) between the 1-phenylpiperidine electron donor and the dicyanoethylene electron acceptor in 1 and 2 is distinct but small. The olefinic bond in 1 enhances the interaction between the 1-phenylpiperidine electron donor and the dicyanoethylene electron acceptor as compared to 2. The TBI between the N,N-dialkylanilino donor and the olefinic bond in 1 can be modulated by rotation of the phenyl group around the C-N bond. The solid state structures of 1 and 2 have been determined by single crystal X-ray diffraction. In the crystal intermolecular electron-donor-acceptor complexes are formed, which give rise to an intermolecular charge transfer absorption in the solid state.