Classic Fluorophores With a Horizontal Alignment for Enhancing Light Outcoupling Efficiency (≈30%) and External Quantum Efficiency (≈7%) of Near Ultraviolet (λmax < 400 nm) Organic Light-Emitting Diodes

Based on the classic 1,1 ':4 ',1 ''-terphenyl fluorophore, a novel near-ultraviolet (NUV) fluorescent BB4Ph (4,4 '''-bis(2,3,4,5-tetraphenylphen-1-yl)(1,1 ':4 ',1 ''-terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a lambda(max) of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide-angle X-ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter (S-GIWAXS) of 0.59 for a molecular layer array normal to the substrate; the angle-dependent photoluminescence (ADPL) measurement shows Theta (horizontal-dipole ratios) as high as 95% with the neat film. The non-doped BB4Ph organic light-emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l' Eclairage coordinates (CIEx,y) of (0.16, 0.04), a NUV electroluminescence. With 4P-Cz (9,9 '-(1,1 ':4 ',1 '':4 '',1 '''-quaterphenyl-4,4 '''-diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIEx,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P-Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (eta(out)) of the two individual OLEDs are estimated as 31% and 29%, respectively.

Automated summary

A novel near-ultraviolet (NUV) fluorescent BB4Ph based on the classic 1,1':4',1''-terphenyl fluorophore is designed, synthesized, and characterized. BB4Ph exhibits NUV fluorescence with a lambda(max) of 373 and 380 nm in solution and as a thin film, respectively. The non-doped BB4Ph organic light-emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with a NUV electroluminescence, while doped BB4Ph OLEDs with 4P-Cz as a dopant emitter exhibit the highest EQE of 6.99%.