Synthesis, electrochemical, photophysical, and electroluminescent properties of organic dyes containing pyrazolo[3, 4-b]quinoline chromophore

• Trifluoromethyl-pyrazolo[3, 4-b]quinolines (PQs) were synthesized and characterized.
• DFT calculation, electrochemical, and photophysical properties were discussed.
• A linear relationship of dipole moments versus Stokes shifts was demonstrated.
• These PQs showed potential applications in organic light-emitting diodes (OLED).

Organic dyes containing trifluoromethylated-pyrazolo[3, 4-b]quinoline were synthesized by using condensation reaction between substituted pyrazolo-4-formaldehyde and aryl amines in moderate yields. Quantum calculation, electrochemical, photophysical, and electroluminescent properties were discussed in detail. Electron-withdrawing groups at 6-position of dyes stabilized the LUMO energy levels significantly resulting in red-shifted absorption/emission spectra. Addition of electron-donating group destabilized the HOMO strongly and the LUMO energy levels slightly resulting in red-shifted absorption maxima, but in blue-shifted emission maxima. Experimental and quantum calculation results are presented here to explain this unusual phenomenon. A linear relationship of dipole moments versus Stokes shifts is obtained for these fluorophores, where the increase of dipole moment is accompanied by a decrease in Stokes shift. Organic light-emitting diodes based on selected dyes showed emission at 456 nm, maximum external quantum efficiency at 1.43%, and current efficiency at 1.95 cd/A.

A linear relationship of dipole moments versus Stokes shifts is obtained for Pyrazolo[3, 4-b]Quinoline derivatives, where the increase of dipole moment is accompanied by a decrease in Stokes shift.Figure optionsDownload as PowerPoint slide