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.