Novel β-ketoenamines versus azomethines for organic electronics: characterization of optical and electrochemical properties supported by theoretical studies

A simple and rapid synthesis of six new, stable beta-ketoenamines by coupling 3-amino-1,8-naphthalimide derivatives with 2-(4-pyrimidinyl)-malondialde-hyde in the presence of trifluoroacetic acid was developed. Two of the synthesized 3-amino-1,8-naphthalimide derivatives were condensed with 9H-fluorene-2-carboxaldehyde, resulting in azomethine products. The structure of obtained compounds was confirmed by H-1 and C-13 NMR, COSY, HMQC, FTIR spectroscopy and elemental analysis. The photophysical, electrochemical and thermal properties of the compounds were investigated. Additionally, calculations using density functional theory were performed to obtain the optimized ground-state geometry and distribution of the HOMO and LUMO levels as well as UV-Vis and photoluminescence spectra of the synthesized compounds. DSC measurements revealed that the compounds form amorphous material with glass transition temperature in the range of 41-146 degrees C and are thermally stable up to 300 degrees C. beta-Ketoenamines have higher glass transition temperature, smaller energy gap (2.11-2.47 eV), higher PL quantum efficiency in solution (5.25-12.97%) and ability to aggregation-induced emission than the azomethines.