This review presents various synthetic approaches to 3,4-ethylenedioxythiophene (EDOT) and its derivatives. EDOT-based polymer (PEDOT) is one of the most widely used electroconducting high molecular weight heterocyclic compounds and it is often referred as the gold standard of electroconducting p-conjugated polymers. It is well known that embedding of substituents of different nature into the structure of any organic compound affects its properties. Thereby it is of undoubted interest to search new synthetic approaches with an aim to obtain EDOT-based monomers for the further preparation of conducting oligomers, polymers, and copolymers as potential materials for creating organic electronic devices.
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 π-conjugation chain elongation results in the red shift of the UV absorption and fluorescence maxima (λmax). The absorption red edge values (λonset) 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 (Egopt) calculated on the basis of the λonset 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 (Eoxonset) were determined and used for calculation of such important characteristics of molecules as the frontier orbital energies (EHOMO и ELUMO). The structures of the synthesized compounds were confirmed by elemental analysis and by IR and 1H NMR spectral data.
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