Optical and electrochemical properties of novel thermally stable Schiff bases bearing naphthalene unit

• Novel thermally stable Schiff bases with naphthalene unit were investigated.
• They exhibited low electrochemically estimated energy gap about 1.6 eV.
• They emitted blue light as blend with PMMA with quantum yield efficiency in the range of 1.98–9.69%.
• The photovoltaic properties of selected imine as active layer in organic solar cells were tested.
• The highest conversion efficiency was 0.32%, which confirmed its electron acceptor character.

A series of novel Schiff bases via condensation reaction of 2-naphtylamine with benzaldehyde, terephthalaldehyde, 9-anthracenecarboxaldehyde, 9-phenantrenecarboxaldehyde, 2-naphthaldehyde and biphenyl-4-carboxaldehyde was synthesized and examined. In the most cases the prepared compounds exhibited the temperature of 5% weight loss about 270 °C. Resulting imines exhibited similar photoluminescence properties and emitted blue light in its blends with PMMA with quantum yield efficiency in the range of 1.98–9.69%.The highest luminescence intensity exhibited Schiff bases consisting of two naphthalene units. Electrochemical measurements (CV and DPC) revealed, in the most cases, two reversible reduction and irreversible oxidation processes. They showed a low value of electrochemically calculated energy gap (Eg) about 1.6 eV. Additionally, the electronic properties, that is, orbital energies and resulting energy gap were calculated theoretically by density functional theory (DFT). Considering the obtained results it seems that the prepared imines can be interesting for optoelectronic applications. The reversible reduction and low Eg suggest that they can be treated as acceptors. Thus, the activity of selected compound was tested in photovoltaic solar cell with the following architecture ITO/PEDOT:PSS/P3HT or P3OT:imine/Al under illumination 1.3 mW/cm2. The highest conversion efficiency was 0.32%, which confirmed its electron acceptor character.