RESUMEN
A group of new mononuclear boron chelate compounds [BPh2{κ2N,N'-5-R-NC4H2-2-C(H)[double bond, length as m-dash]N-Ar}] (R = Ar = C6H57; R = C6H5, Ar = 2,6-iPr2C6H38; R = Anthracen-9-yl (Anthr), Ar = C6H59; R = Anthr, Ar = 2,6-iPr2C6H310) were synthesized via the reaction of B(C6H5)3 with the corresponding 5-substituted 2-(N-arylformimino)pyrrole ligand precursors 3-6. These complexes were prepared in order to evaluate the luminescence potential derived from the substitution of the position 5 of the pyrrolyl ring with an aromatic group. Compounds 7-10 were photophysically characterized in solution and in the solid state. The 5-phenyl-2-iminopyrrolyl-BPh2 complexes 7 and 8 are blue emitters and have enhanced photoluminescence quantum yields in the solid state (ΦPL) up to 0.95, whereas the 5-anthracenyl derivatives 9 and 10 have green-bluish fluorescence and a ΦPL of 0.49 and 0.24, respectively. DFT and TDDFT studies were performed, considering the effect of solvent and dispersion, in order to show how the geometries of compounds 7-10 changed from the ground to the excited state, to assign electronic transitions, and to rationalize the observed luminescence. These materials were applied in organic light-emitting diodes (OLEDs), with various device structures, the best showing an external quantum efficiency of 2.75% together with a high luminance of 23 530 cd m-2.
RESUMEN
In this work, we employ a thermally activated delayed fluorescence (TADF) exciplex formed between the emissive layer (EML) host, 26DCzPPy, and the electron transport layer (ETL) 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine at the interface between the EML and the ETL to improve the stability and efficiency of a phosphorescence organic light-emitting diode based on Ir(dmpq)2acac. We show that the presence of the TADF exciplex at the EML-ETL interface induces an efficient localization of the recombination zone, which is confined within the 5 nm thick EML. Furthermore, the TADF exciplex allows harvesting of the holes and electrons that piled up at the EML-ETL interface and transfers the resultant excited state energy to the phosphorescent emitter through Förster and/or Dexter energy transfer. This approach effectively improves the LT90 of devices from <1 min to 6 h by limiting recombination processes outside of the 5 nm EML.
RESUMEN
This study shows a molecular design strategy for controlling the dihedral angle of two carbazole donors linked to a 2,4-diphenyl-1,3,5-triazine acceptor by a phenyl unit. Using this approach, six thermally activated delayed fluorescence emitters were synthesized with donors placed in various positions around a central phenyl core, and the photophysical relationship between the donor position and its dihedral angle was investigated. We demonstrate that this angle can affect both the strength of the charge transfer state and the conjugation across the entire molecule, effectively changing the singlet-triplet energy gap of the system. We conclude that materials containing two substituted -ortho donors or one -ortho and an adjacent -meta have the smallest energy gaps and the shortest delayed fluorescence lifetimes. On the other hand, emitters with no -ortho substituted donors have larger energy gaps and slow-to-negligible delayed fluorescence. When applying these materials to organic light-emitting diodes, these blue-emitting devices have a range of electrical properties, the best producing efficiencies as high as 21.8% together with high resistance to roll-off that correlate with the reverse intersystem crossing rates obtained.
RESUMEN
We report on the engineering of full thermally activated delayed fluorescence - based white organic light emitting diodes (W-OLEDs) composed of three emitters (2,7-bis(9,9-dimethyl-acridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), 2,7-bis(phenoxazin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DPO-TXO2) and 3,11-di(10H-phenoxazin-10-yl)dibenzo[a,j]phenazine (POZ-DBPHZ) in two different hosts. By controlling the device design through the study of the emission of DDMA-TXO2 and DPO-TXO2, the behaviour of POZ-DBPHZ in a device with more than one emitter, and the combination of the three materials, respectively, we show that external quantum efficiencies as high as 16% can be obtained for a structure with a correlated colour temperature close to warm white, together with colour rendering index close to 80. However it is in their performance stability that provides the true breakthrough: at 1000 cd/m2 the efficiencies were still above 10%, which is one of the best for this type of devices.
