Branched azomethines based on tris(2-aminoethyl)amine: Impact of imine core functionalization on thermal, electrochemical and luminescence properties

Abstract

A series of imines based on tris(2-aminoethyl)amine was designed and synthesized to evaluate the effect of core functionalization with biphenyl, pyrene, anthracene, triphenylamine and phenanthrene units on selected properties. Their chemical structure was thoroughly characterized by NMR and FTIR spectroscopy and elemental analysis. All compounds were crystalline (except for imine with triphenylamine units) and melted in the wide temperature range of 99–187 °C, according to the structure of the substituent. DSC measurements revealed that the studied compounds can be converted into amorphous material with glass transition occurring for temperatures between 16 and 55 °C. The imines were electrochemically active and underwent oxidation and reduction processes as found using CV and DPV methods. Density functional theory was employed for optimizing the imines geometry, as well as for calculating HOMO and LUMO orbital energies together with ionization potentials and electron affinities. The absorption and photoluminescence in the UV–Vis spectral range, both in solution and in the solid state as films on glass substrates were studied. When dissolved in chloroform, they emitted light with quantum yields ranging from 0.54 to 22%. In the solid state they exhibited emission in the range of 380–515 nm. The selected compounds were preliminarily tested as components in light emitting diodes. The ability neat azomethines for electroluminescence in diode ITO/PEDOT:PSS/imine/Al was demonstrated.