Efficient green electroluminescence from 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxaline dyes in dye-doped polymer based electroluminescent devices

We demonstrate several polymer based electroluminescent devices with active poly(N-vinylcarbazole) (PVK) layer doped with diphenylpyrazoloquinoxaline (PQX) dyes, RPQX, with lateral substituent R = Me, MeO, F or Cl. The electronic properties of these fluorescence emitters and relevant electroluminescence devices are characterized by optical spectroscopy techniques. The first absorption bands of the RPQX dyes considerably overlap with the fluorescence emission band of the host PVK matrix resulting in efficient radiative energy transfer between them. Using the measured electroluminescent spectra the emission color is characterized in CIE 1931 XYZ color space. The electroluminescence devices with a dye-doped active layer PVK:RPQX (R = Me, MeO, F or Cl) emit light with different shades of green color. The electroluminescent performance is characterized in terms of current efficiency determined from the luminance-current-voltage measurements. Depending on the fluorescent dopant it ranges from about 0.5 to above 2.2 cd/A. Such efficiency has been achieved on a simple dye-doped device configuration without significant optimization. Accordingly, RPQX dyes may be considered as prospective fluorescence emitters for electroluminescent applications. The measured spectral characteristics of RPQX fluorescent emitters and relevant electroluminescent devices are compared with quantum-chemical DFT/TDDFT calculations based on re-parameterized long-range corrected functional and corrected linear response solvation. Relevant analysis, due to its good performance and predicability, appears to be helpful not only for understanding of the origin of electronic transitions, but may serve as useful tool for chemical engineering dealing with design and synthesis of novel organic dyes for optoelectronic applications.