Amorphous molecular materials have constituted a new class of functional organic materials for use as an emitting layer in organic light-emitting diode (OLEDs). This research is aimed to explore light-emitting materials that realize both high efficiency and low cost without using rare metals. Several emissive cores such as binaphthalene, pyrene, anthracene, benzothiadiazole and naphthathiadiazole have been prepared and the structure-property-performance relationships were investigated.
Two isomeric blue-emitting compounds consisting of arylamine and benzimidazole with a binaphthalene bridge have been developed and used for OLEDs. They exhibit bipolar transporting characteristics and can be used for efficient blue-emitting OLEDs. The difference in the linking modes of the benzimidazole entity to the bridge, i.e., C-linkage (BINAPC) or N-linkage (BINAPN), leads to different photophysical and carrier-transport properties between the two isomers. The N-linkage isomer has more balanced carrier mobilities, leading to higher device efficiency.
Highly thermally stable star-shaped molecules based on tetra-substituted pyrene possessing high glass transition temperature have been synthesized. The compounds containing peripheral arylamines (P1−P4) can be used as hole-transporting and green-emitting materials for electroluminescent devices. The compounds with peripheral fluorenes (P5 and P6) are blue-emitting and exhibit bipolar carrier transport characteristics. Both electron and hole mobilities measured by TOF method surpass 10-3 cm2/Vs. Two-layered devices using these novel materials as the hole-transporting and the emitting layer or as the electron-transporting and the emitting layer exhibited good performance.
The site isolation effect can be achieved for planar emissive cores via encapsulation with oligophenylene dendrons containing peripheral carbazole. As a result, the compounds exhibit excellent fluorescent quantum yield in solution and solid state. In addition, the dendritic structures enable these molecules to be solution processable. The OLEDs fabricated by spin coating of the newly developed materials as guests in four different hosts were studied. Efficient red-, green-, blue-emission were observed with N,N′-dicarbazolyl-4,4′-biphenyl (CBP) as a host materials.

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