Charge‐Transfer Exciton Manipulation Based on Hydrogen Bond for Efficient White Thermally Activated Delayed Fluorescence

Abstract

Despite the success of thermally activated delayed fluorescence (TADF) emitters in monochromatic organic light‐emitting diodes (OLED), only few efficient full‐TADF white OLEDs (WOLED) are reported because of the challenge in rational exciton allocation between blue and other color emitters. Herein, it is demonstrated that the appropriate exciton delocalization in blue TADF matrixes can simultaneously support the sufficient blue emission and the energy loss–free charge and exciton transfer to yellow TADF emitters. Through introducing steric hindrance–modulated intermolecular hydrogen bond networks, a fluorinated carbazole‐phosphine oxide hybrid realizes the balance of exciton localization and delocalization, giving rise to state‐of‐the‐art external quantum efficiency beyond 20% from its simple trilayer full‐TADF WOLEDs, accompanied by excellent spectral stability. The correlation between the efficiencies of the blue TADF matrixes and their intermolecular interactions reveals that the exciton delocalization is crucial for the exciton allocation optimization in multicomponent emission systems.

Design of highly efficient deep-blue organic afterglow through guest sensitization and matrices rigidification

“…Therefore, an excellent H-bonding network is formed after the introduction the third component of water, resulting in significantly rigidified matrices of the composites with much suppressed non-radiative decays and reduced penetration of oxygen and its quenching effects for greatly improved OURTP performance. Furthermore, H-bonds is beneficial to enhance ISC and Dexter energy transfer 34,35 , contributing further to the increased phosphorescence intensity and PhQY after water implement. It should be noted that when other solvents were added to the CT5-0 powder, the phosphorescence intensity and lifetime were generally reduced, confirming that only water can play this bridging role here in forming H-bonds for the matrices rigidification ( Supplementary Fig.…”

Pure-organic phosphine oxide luminescent materials

“…Although the universal PO host SFXSPO was used to realize the double-EML-based full-TADF WOLED, how to realize the high-performance single-EML full-TADF WOLED is still a real challenge due to the difficulties in suppressing the intermolecular-interaction-induced quenching between different TADF emitters and regulating the blue-to-yellow ET for both white emission and high efficiency. To address this challenge, two blue TADF molecules named 'TArDFTPPO' (Ar = Cz and tBCz) were developed, with Ar as the donor and difluorinated triphenylphosphine oxide (DFTPPO) as the acceptor [45]. Fluorine atoms in opposite directions and the outward P = O formed the continuous intermolecular hydrogen bond networks to enhance the intermolecular CT interactions and exciton delocalization, which were delicately regulated with the steric hindrance of tert-butyl in TtBCzDFTPPO for the balance of CT exciton localization and delocalization.…”

Suppressing dimer formation by increasing conformational freedom in multi-carbazole thermally activated delayed fluorescence emitters

“…1), are prone to dimerization, which may also be responsible for their mechanochromism [24][25][26][27][28] and thermochromism. 23 The investigation by Etherington et al has been followed by further detailed investigation into the stimuliresponsive behaviour of TADF emitters 13,[29][30][31][32][33][34] and a recent minireview. 35 This previous work established that dimerization causes significant shifts in the photoluminescence and electroluminescence colour ( 1 CT emission energy) of the TADF materials, beyond that expected by packing and polarizability effects alone.…”