Structure-Property Relationships of Dibenzylidenecyclohexanones

A series of symmetrical dibenzylidene derivatives of cyclohexanone were synthesized with the goal of studying the physicochemical properties of cross-conjugated dienones (ketocyanine dyes). The structures of the products were established and studied by X-ray diffraction, NMR spectroscopy, and electronic spectroscopy. All products had the E,E-geometry. The oxidation and reduction potentials of the dienones were determined by cyclic voltammetry. The potentials were shown to depend on the nature, position, and number of substituents in the benzene rings. A linear correlation was found between the difference of the electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum. This correlation can be employed to analyze the properties of other compounds of this type. The frontier orbital energies and the vertical absorption and emission transitions were calculated using quantum chemistry. The results are in good agreement with experimental redox potentials and spectroscopic data.

Light-Induced Direct Arylation in the Solid Crystalline State as a Strategy Towards π-Expanded Imidazoles

π-Expanded imidazoles bearing the 2-iodophenyl substituent at position 2 undergo direct photoinduced intramolecular arylation in the solid, crystalline state leading to large non-planar heterocycles. An analogous reaction employing 2-bromophenyl and 2-chlorophenyl substituents is considerably slower. Such processes have never before been demonstrated to occur in crystals and have allowed the efficient synthesizes of structurally unique compounds containing either the phenanthro[9',10':4,5]imidazo[1,2-f]phenanthridine moiety or structurally related skeletons. The reaction occurs in the thin crystalline layers irradiated with UV photons in an almost quantitative manner over 48-72 h. Several previously unknown architectures have been prepared using this methodology. Furthermore, the optical properties of these π-expanded imidazoles can be altered with the addition of heteroatoms and/or electron-donating groups.