Near UV/Deep-Blue Phenanthroimidazole-Based Luminophores for Organic Light-Emitting Diodes: Experimental and Theoretical Investigation

Two new deep blue phenanthroimidazole base luminophores 2-(4-(4-(4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenoxy)butoxy)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imid -azole (DPIPOBn) and 2-(4-(4-(4-(1-(4-tert-butylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl) phenoxy)butoxy)phenyl)-1-(4-tert-butylphenyl)-1H-phenanthro[9,10-d]imidazole (DPITBOBn) were designed and synthesized by linkage two phenanthroimidazole functional units via the highly flexible alkyl (butane) spacer with different N1 functional groups (benzene and tert-butylbenzene). The synthesized luminophores were structurally characterized by spectroscopic method (H-1, C-13, and mass). The photophysical, electrochemical and electroluminescence properties of the luminophores were systematically studied. These luminophores emit intense blue PL emission in both solution and solid phase. The HOMO-LUMO energy level of the luminophores was calculated from Cyclic Voltammetry (CV) analysis and which agreed with the results from the density-functional-theory (DFT) calculation. The time-dependent DFT (TD-DFT) calculation was performed to know the excited states (singlet and triplet) of the luminophores. The solution-processed OLED was fabricated to test these materials as emissive materials and as emitters. All the doped devices exhibited near-UV emission with EL peaks centered around 380-395 nm with Commission International deL'Eclairage (CIE) coordinate of (0.16, 0.09 or 0.10). Among all the doped devices, DPITBOBn (3 wt%) based device displayed a power efficiency (PE) of 0.5 lm/W, a current efficiency (CE) of 1.2 cd/A and external quantum efficiency (EQE) of 1.9% at the brightness 100 cd/m(2).