Publication details

Conjugated Aromatic systems in Synthesis and their Properties



Year of publication 2017
Type Article in Proceedings
Conference 50th Heyrovsky Discussions
MU Faculty or unit

Faculty of Science

Field Physical chemistry and theoretical chemistry
Keywords aromatic system; push-pull mechanism; HOMO; LUMO; cyclic voltammetry; quantum chemistry calculations
Description The work deals with the synthesis, electrochemical and spectral experiments of conjugated systems consisting form three phenyl or thiophene units and their mix. They are substituted with an electron donor (dimethyl amino group) at the one end and with an electron acceptor (formyl, dicyano vinyl and cyclic nitrone) at the other end, resulting in push-pull delocalized pí-electronic system having outstanding optical and electronic properties. Their properties were investigated and their energy gaps were compared. Thus, we synthesized three types of oligomers with pí-electronic bridge using the Suzuki-Miyaura cross-coupling reaction (aromatic boronic acids react with halogen containing aromatic skeleton in the presence of homogenous palladium catalyst and a base. With regard to the possible application of these push-pull systems in nonlinear optics, the enrgy gaps between HOMO and LUMO orbitals were experimentally evaluated by cyclic voltammetry and UV-VIS spectra. The energy gaps were calculated by DFT method. Redox signals of all compounds (1 mM) on a platinum electrode were measured in dichloromethane (DCM) with 0.1 M TBAPF6 as the supporting electrolyte. Two platinum electrodes were used as the working and counter electrodes with the Ag/AgCl/3M KCl as the reference electrode separated by a fritted junction with the same supporting electrolyte (0.1 M TBAPF6 in DCM). The potential was measured vs. ferrocene (0.1 mM) in the same medium. Besides that, absorption, emission and exciattion spectra were measured. The calculation of the nergy gap started with the optimization of molecular geometries at the B3LYP/6-31G* level and the Mullikan charges have been calculated for these optimized geometries. Orbital energies have been determined from an additional B3LYP calculation employing the 6-31G* basis set. All calculations have been performed on isolated molecules in the gas phase. To compare Egap values the lowest energy difference was found in the case of dikyanvinyl group. more detailed studies would be needed for further conclusions. the importance of this research can be summarized into some aspects. The push-pull type of organic molecules consisting of various conjugated systems has found its application as light-emitting, light absorbing and semiconducting materials. Because systems with push-pull substitution strongly affect the levels of the frontier orbitals, they are known to exhibit narrowed energy gaps and strong dipoles due to intramolecular charge transfer. Such materilas have been of interest as long-wavelength absorbing dyes and in nonlinear optics.

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