New 3,5-Disubstituted 2,6-Dicyanoanilines Containing 3,4-Ethylenedioxythiophene Fragments: Synthesis And Further Transformation

Some novel 3,5-disubstituted 2,6-dicyanoanilines incorporating 3,4-ethylenedioxythiophene (EDOT) fragment were prepared and investigated. Two different synthetic procedures have been applied for this purpose. One of them consists in the cyclization of chalcones with the malononitrile excess, another one relies on the one-pot three-component strategy. Condensation of thus prepared 3,5-disubstituted 2,6-dicyanoanilines with 3,4-ethylenedioxythiophene-2-carboxaldehyde (EDOT-CHO) has successfully given rise to the corresponding Schiff bases. UV absorption and fluorescence spectra were recorded for the chloroform solutions of the synthesized compounds. The influence of the changes in the compounds' molecular structure on the UV absorption and fluorescence maxima as well as on the absorption edge position has been analyzed. It has been revealed that the pi-conjugation chain elongation results in the red shift of the UV absorption and fluorescence maxima (lambda(max)). The absorption red edge values (lambda(onset)) of the Schiff bases' solutions were found to be crucially shifted to the longwave region if compared with the ones obtained for the solutions of the initial 2,6-dicyanoanilines (142 and 170 nm). The strong bathochromic shifts were also detected for their fluorescence maxima (72 and 114 nm). The optical bandgaps (E-g(opt)) calculated on the basis of the lambda(onset) values were found to be less than 2.5 eV for all prepared compounds. Cyclic voltammetry method was used to study the electrochemical behavior of the Schiff bases, as a result the values of the onset oxidation potentials (E-ox(onset)) were determined and used for calculation of such important characteristics of molecules as the frontier orbital energies (E-HOMO u E-LUMO). The structures of the synthesized compounds were confirmed by elemental analysis and by IR and H-1 NMR spectral data.