2,2-Dicyanovinyl derivatives – Thermal, photophysical, electrochemical and electroluminescence investigations

Abstract

Solid-state emissive organic materials are perspective for applications in organic electronics. Here, the 2,2-dicyanovinyl derivatives bearing thiophene, furan, phenyl, N-methylpyrrole, naphthalene, benzothiophene and benzofuran structures were successfully prepared by the Knoevenagel condensation of propane-1,3-dinitrile with various ketones. The synthesized compounds were crystalline solid with melting temperature between 87 and 161 °C and temperature of 5% weight loss in the range of 140–190 °C based on differential scanning calorimetry and thermogravimetric measurements, respectively. The density functional theory showed that LUMO orbitals are localized more at 2,2-dicyanovinyl moiety whereas in the case of HOMOs slightly higher contribution from the aromatic parts can be observed. The results of cyclic voltammetry showed that both reduction and oxidation process values differ greatly depending on donor properties. Calculated the ionization potentials and electron affinities were in the range of −5.52 – −6.48 eV and −3.3 − −3.64 eV, respectively, which results in energy band gap mainly below 3.0 eV. The 2,2-dicyanovinyl derivatives were emissive both in solution and in the solid, in which higher quantum photoluminescence yield was detected. When 2,2-dicyanovinyl derivatives molecularly dispersed in a solid matrix poly(9-vinylcarbazole) (PVK) and a binary matrix consisting of PVK (60 wt. %) and 2- text-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) (40 wt. %) (guest-host configuration), they show green or yellow or red electroluminescence.