Molecular Design and Synthesis of New Cyanopyridone-Based Small Molecules for Oled Applications

Abstract

In recent years, due to their widespread use in electronic devices like organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic light emitting transistors (OLETs), organic solid-state lasers, organic solar cells (OSCs) and biomedical devices, the development of efficient organic π-conjugated small molecules has been a vital part in the field of electronics. Essentially, these materials mainly stand out because of their well-organized molecular structures, simple synthetic methods, straightforward purification procedures, amenability to solution and vacuum deposition processing while fabrication, and the ability to fine-tune functional properties through relatively straightforward structural engineering. Over the past decade, due to their potential applications in the next-generation solid-state lighting sources and flat panel displays, OLEDs have garnered a lot of attention. Several efforts have been devoted to the development of new emissive materials to satisfy market requirements such as high luminescence quantum yield in the solid state, good amorphous film-forming properties, high thermal stability, and color purity.Based on the detailed literature survey, forty-two new conjugated small molecules, viz. C1-42 (Series 1-7) were designed as potential emitters for OLED applications. All of them were successfully synthesized and well characterized. Further, they were subjected to in-depth optical, electrochemical, thermal, theoretical, and electroluminescence studies. The solvatochromic study clearly indicated the nonpolar nature of the ground state and the presence of ICT behavior in the molecules. New OLEDs were fabricated employing selected twenty-eight newly synthesized compounds (Series 1-4) as emitters. From these studies, it is clear that the synthesized molecules possess all the prerequisites to act as an emissive layer in an OLED device. DFT calculations revealed their FMO, HOMO-LUMO energy levels, and spatial charge distribution in the molecules. Interestingly, fabricated devices containing C3, C11, C19 and C26 showed an EQE of 5.32, 5.91, 4.18 and 4.18 %, respectively. In the OLED devices, C3 gives yellow emission, C11 shows green light emission C19 exhibits cyan light and C26 shows bluish-green light.