Imidazole-Pyrene Hybrid Luminescent Materials for Organic Light-Emitting Diodes: Synthesis, Characterization & Electroluminescent Properties

Abstract A series of multichromophoric, pyrene-imidazole-phenyl based hybrid luminescent small molecules (PA, PI, PnB, PtB, PoM and PnDM) with different donating groups at the para position of the phenyl attached to N1 position of imidazole moiety were designed, synthesized, and characterized, for use in blue organic light-emitting diodes (OLEDs). The photophysical, thermal and electrochemical properties of the molecules were systematically investigated. All the molecules displayed delayed fluorescence at room temperature with a lifetime ranging from 7.1 to 8.5 µs. The synthesized fragment molecules (tetraphenyl-imidazoles: IA, IoM and InDM) revealed high triplet energies of ∼ 2.90eV. Glass transition temperatures determined to range from 77°C to 123°C and decomposition temperatures are found to be above 280°C. The molecules possess appropriate HOMO and LUMO energy levels for effective charge injection. The crystal structure for PI is reported. OLED devices were fabricated based on the pyrene-imidazole-phenyl hybrids as emitters and as dopants with CBP as host. OLED devices with PI doped (5% wt.) with CBP exhibits excellent device performance with a current efficiency of 9.82 cd/A, the power efficiency of 8.32 lm/W and external quantum efficiency of 4.64%.