Structure–Property Relationships of Dibenzylidenecyclohexanones

Abstract

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.

Synthesis, Structure and Photochemistry of Dibenzylidenecyclobutanones

“…The calculation confirms the conclusion about the effect of the electron-donating properties of the substituents on the shifts of the cathodic and anodic peaks and the band gap ΔE. The ionization mechanism is similar to that found for dienones based on cyclopentanone and cyclohexanone [ 34 , 35 ]. An electron is removed from the HOMO-1 quasi-degenerate with HOMO and is accepted by the LUMO.…”

“…The NOESY spectrum of dienone 2 also exhibits intense intramolecular cross-peaks, indicating the coupling of the H(2′) and H(6′) protons of the benzene ring and the H(3) methylene protons of the cyclopentanone moiety. Apart from the indicated cross-peaks, the H(6′) aromatic protons of dienone 2 give a small NOESY cross-peak with the H(α) ethylene protons [ 35 ].…”

“…A cyclic voltammetry (CV) study of compounds 1a – d , f was carried out on a cleaned surface of a glassy carbon (GC) electrode in MeCN in order to reveal the effect of substituents in the aromatic rings of cross-conjugated dibenzylidene cyclobutanones on the frontier orbital energies in comparison with the same characteristics of the cyclopentanone- and cyclohexanone-based dienones studied previously [ 34 , 35 ]. The CV curves were recorded starting from 0 V and moving towards the cathodic and anodic potentials.…”

“…The cathodic peak potentials of dibenzylidene cyclobutanones shift to the anodic region relative to the potentials of similar cyclopentanone derivatives and, to a larger extent, relative to cyclohexanone derivatives ( Table 3 [ 34 , 35 ]). This may be due to the more planar molecular geometry of the dibenzylidene cyclobutanone derivatives, resulting in a higher degree of conjugation in comparison with similar cyclopentanone and cyclohexanone derivatives.…”

“…The structures in question are chromophore models of crown ethers and aza/thia-crown ethers. Cyclobutanone was chosen as the central moiety as an analog of cyclopentanone derivatives, such as 2, and cyclohexanone derivatives, addressed in our previous studies [ 34 , 35 ].…”