Fine Tuning the Energetics of 2-(2′-Hydroxyphenyl)oxazoles to Obtain Highly Efficient Organic White-Light-Emitting Devices

By using the strategy of fine-tuning the energetics to explore single-molecule white materials with reversible excited-state intramolecular proton transfer (ESIPT), compound 4′-(di-p-tolylamino)-3-(5-(4′-(diphenylamino)-[1,1′-biphenyl]-4-yl)oxazol-2-yl)-5-methyl-[1,1′-biphenyl]-4-ol (2a) has been synthesized and then fabricated as organic white-light-emitting devices. The rhodium-catalyzed C–H activation reaction offers an effective method to construct the white-emitting molecules. The 2a-based devices display white electroluminescence with white region CIE coordinates, which is the first reported organic white-light-emitting device (WOLED) based on the single-molecule 2-(2′-hydroxyphenyl)oxazoles with a reversible ESIPT equilibrium. The external quantum efficiency (EQE) of the white-light device reached 6.3%, achieving the highest EQE in the single-molecular cold WOLEDs using an ESIPT material as the emitter. Furthermore, the hybridized local charge transfer (HLCT)-state feature of 2a has been confirmed by a fluorescence test and density functional theory (DFT) calculations. The result shows the first example of single-molecule cold WOLEDs with HLCT material.