Utilization of newly configured carbazole-cyanopyridone structural hybrids towards achieving high-performance cyan fluorescent organic light-emitting diodes

Abstract

Herein, we report the synthesis, characterization, and device fabrication of novel D–A–D (donor–acceptor–donor) type cyanopyridone-based cyan light-emitting organic materials. These small molecules feature a strong electron-donating N-alkylated carbazole unit affixed to a powerful electron-withdrawing cyanopyridone core that is appended with varying secondary donor groups, producing bipolarity in their structures. All the synthesized molecules were well characterized by employing FT-IR, ¹H NMR, and ¹³C NMR spectroscopy, followed by in-depth photophysical, thermal, electrochemical, and electroluminescent studies. Furthermore, we used the density functional theory (DFT) computational approach in the theoretical investigations to gain deeper insights into their electron cloud distributions and structural features. These fluorophores exhibit emission in the 489–510 nm range accompanied by high Stokes shift values, and their TGA data validate the excellent thermal stability (384 °C). As estimated by cyclic voltammetry, the HOMO and LUMO energy levels were found to be 5.35–5.69 eV and 2.92–3.02 eV, respectively, with band gaps of 2.36–2.74 eV. The optical and electrochemical properties of the luminogens have been successfully fine-tuned by varying the auxiliary donors at the carbazole-cyanopyridine hybrids. Electroluminescent studies proved the compatibility of the novel compounds to be an efficient cyan emissive layer with good performance characteristics. Interestingly, amongst the luminophores, Cz-CyP₅ bearing a 4-hydroxyphenyl moiety exhibited a maximum current efficiency of 13.16 cd A⁻¹, high power efficiency of 9.85 lm W⁻¹, and good external quantum efficiency of 5.41%.