Polyphenylnaphthalene as a Novel Building Block for High-Performance Deep-Blue Organic Light-Emitting Devices

A new member of polycyclic aromatic hydrocarbons named 1,2,3,4-tetraphenylnaphthalene (TNa) is exploited and used as a potential building block in deep-blue organic light-emitting devices (OLEDs) for the first time. By incorporating TNa with phenanthroimidazole, three blue emitters named TNa-PI, TNa-BPI, and TNa-DPI featuring different length of phenyl linkers are designed and synthesized via a facile approach, and systematically characterized with thermal, morphological, theoretical, photophysical, electrical, and electroluminescent (EL) studies. The new fluorophores show intramolecular charge transfer properties in excited state evidenced by positive solvatochromic effect in emission. Theoretical calculation suggests that TNa serves as an electron acceptor in the new molecules. All the new materials can emit intense deep-blue fluorescence in thin film and show bipolar carrier transport properties, with electron conductivity much better than that of hole. Nondoped OLEDs based on TNa-DPI exhibit excellent EL performance with a maximum external quantum efficiency (EQE) of 5.78% and deep-blue emission with color purity of (0.152, 0.085). Furthermore, in the 30 wt.% doped device, TNa-PI emits efficient violet-blue EL with Commission Internationale de l'Èclarage coordinates of (0.156, 0.043) and shows a decent EQE of 2.52% at a practical brightness of 1000 cd m⁻².