Kazunori Togashi

Low driving voltage characteristics of triphenylene derivatives as electron transport materials in organic light-emitting diodes

Triphenylene-based electron transport materials (ETMs), designated Bpy-TP1-4, with a coplanar molecular structure and a large electron affinity were designed and synthesized for use in organic light-emitting diodes (OLEDs). Spectroscopic ellipsometry measurements clarified that the deposited thin films of these ETMs have optical anisotropy, indicating that the molecules in the deposited thin films tend to be mostly oriented parallel to the substrate. Green OLEDs containing these ETMs allowed a lower driving voltage than that for OLEDs containing tris(8-hydroxyquinolinato)aluminum (Alq3) with a random orientation. In particular, the OLED containing Bpy-TP2 showed a significantly lower driving voltage, achieving lower power consumption when compared with conventional ETMs such as Alq3 and 1,3,5-tris(2-phenyl-1H-benzo[d]imidazol-1-yl)benzene (TPBi). Also, the operational lifetime of a blue OLED containing Bpy-TP2 is equivalent to that of an OLED with TPBi. The increased driving voltage of the device containing Bpy-TP2 is significantly suppressed compared to that of the OLED containing TPBi.

Donor–acceptor-structured 1,4-diazatriphenylene derivatives exhibiting thermally activated delayed fluorescence: design and synthesis, photophysical properties and OLED characteristics

Abstract A new series of luminescent 1,4-diazatriphenylene (ATP) derivatives with various peripheral donor units, including phenoxazine, 9,9-dimethylacridane and 3-(diphenylamino)carbazole, is synthesized and characterized as thermally activated delayed fluorescence (TADF) emitters. The influence of the donor substituents on the electronic and photophysical properties of the materials is investigated by theoretical calculations and experimental spectroscopic measurements. These ATP-based molecules with donor–acceptor–donor (D–A–D) structures can reduce the singlet–triplet energy gap (0.04–0.26 eV) upon chemical modification of the ATP core, and thus exhibit obvious TADF characteristics in solution and doped thin films. As a demonstration of the potential of these materials, organic light-emitting diodes containing the D–A–D-structured ATP derivatives as emitters are fabricated and tested. External electroluminescence quantum efficiencies above 12% and 8% for green- and sky-blue-emitting devices, respectively, are achieved.