Pyrenylpyridines: Sky-Blue Emitters for Organic Light-Emitting Diodes

• Published in: ACS omega Vol. 4; no. 16; pp. 16867 - 16877
• Main Authors: De Silva, Thenahandi Prasanthi Deepthika, Youm, Sang Gil, Tamas, George G, Yang, Boqian, Wang, Chun-Han, Fronczek, Frank R, Sahasrabudhe, Girija, Sterling, Sierra, Quarels, Rashanique D, Chhotaray, Pratap K, Nesterov, Evgueni E, Warner, Isiah M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15.10.2019
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.9b01948

A novel sky-blue-emitting tripyrenylpyridine derivative, 2,4,6-tri­(1-pyrenyl)­pyridine (2,4,6-TPP), has been synthesized using a Suzuki coupling reaction and compared with three previously reported isomeric dipyrenylpyridine (DPP) analogues (2,4-di­(1-pyrenyl)­pyridine (2,4-DPP), 2,6-di­(1-pyrenyl)­pyridine (2,6-DPP), and 3,5-di­(1-pyrenyl)­pyridine (3,5-DPP)). As revealed by single-crystal X-ray analysis and computational simulations, all compounds possess highly twisted conformations in the solid state with interpyrene torsional angles of 42.3°–57.2°. These solid-state conformations and packing variations of pyrenylpyridines could be correlated to observed variations in physical characteristics such as photo/thermal stability and spectral properties, but showed only marginal influence on electrochemical properties. The novel derivative, 2,4,6-TPP, exhibited the lowest degree of crystallinity as revealed by powder X-ray diffraction analysis and formed amorphous thin films as verified using grazing-incidence wide-angle X-ray scattering. This compound also showed high thermal/photo stability relative to its disubstituted analogues (DPPs). Thus, a nondoped organic light-emitting diode (OLED) prototype was fabricated using 2,4,6-TPP as the emissive layer, which displayed a sky-blue electroluminescence with Commission Internationale de L’Eclairage (CIE) coordinates of (0.18, 0.34). This OLED prototype achieved a maximum external quantum efficiency of 6.0 ± 1.2% at 5 V. The relatively high efficiency for this simple-architecture device reflects a good balance of electron and hole transporting ability of 2,4,6-TPP along with efficient exciton formation in this material and indicates its promise as an emitting material for design of blue OLED devices.