Rong-Huei Yi

Nature, Published online: 12 May 2022; doi:10.1038/d41586-022-01320-y

Publication date: August 2022

Source: Dyes and Pigments, Volume 204

Author(s): Xiangming Wang, Mengjiao Dong, Zijuan Li, Zepeng Wang, Fu-Shun Liang

Publication date: July 2022

Source: Dyes and Pigments, Volume 203

Author(s): Yuting He, Deyun Zhou, Cheng Zhang, Hao Yan, Yongshuai Chai

Two donor–acceptor (D–A) achiral dichroic dyes, P1 and N1, are designed as anisotropic chromophores in the long and short molecular axes with chiral 1,1′-binaphthyl derivatives in SLC1717 medium. Dynamic circularly polarized luminescence (CPL) handedness and intensity are achieved by changing the N1:P1 mass ratio, and the luminescence dissymmetry factor (g _em) value reaches |0.71|.

Abstract

Cholesteric liquid crystals (CLCs) are chiral supramolecular systems that self-assemble into a highly regular helical arrangement in a liquid crystal (LC) medium. Such an arrangement is highly beneficial for the chiral enlargement effect on circularly polarized luminescence (CPL) signals. Dichroic dyes with rod-like molecular structures can exhibit fluorescence anisotropy along both the long and short molecular axes owing to their transition dipole moment (TDM) vectors. In this work, a pair of donor–accepter (D–A) achiral dichroic dyes is prepared, namely, 3,4-ethylenedioxythiophene derivative (P1, whose TDM vector is parallel to the long axis of the molecule, i.e., F _|| > F _⊥) and anthraquinone derivative (N1, whose TDM vector is perpendicular to the long axis of the molecule, i.e., F _|| < F _⊥). CLCs can be fabricated by doping P1 or N1 together with chiral 1,1′-binaphthyl-derived inducers into SLC1717 medium. Dynamic CPL with tunable handedness and intensity is achieved by changing the N1:P1 mass ratio, and the luminescence dissymmetry factor (g _em) value reaches |0.71|. This work describes the first observation of dynamic CPL with tunable handedness and intensity enabled by TDM regulation of achiral dichroic dyes in a CLC medium.

A rational molecular design of thermally activated delayed fluorescence (TADF) emitters for enabling ultrashort exciton lifetimes (<1 µs) is presented. The effective utilization of quadrupolar π-systems, which can induce degenerate charge-transfer excited states contributing to the spin-flip acceleration, endows the emitters with a high luminescence efficiency and short emission lifetime concurrently.

Abstract

Exciton lifetime is a critical factor in determining the performance of optoelectronic functional systems and devices. Thermally activated delayed fluorescence (TADF) emitters that can concurrently achieve a high fluorescence quantum yield and short exciton lifetime are desirable for application in organic light-emitting diodes (OLEDs) with suppressed efficiency roll-off. Herein, phenoxaborin and xanthone-cored TADF emitters with quadrupolar electronic structures are reported to exhibit sub-microsecond TADF lifetimes as short as 650 and 970 ns, respectively, while preserving high fluorescence quantum yields. By extending the El-Sayed rule to the quadrupolar π-systems, the contribution of doubly degenerate charge-transfer excited states induced by dual donor units can enhance the spin–orbit coupling between them, leading to a spin-flip acceleration between the excited triplet and singlet states. This electronic feature is advantageous for mitigating exciton annihilation processes in the emission layer, thereby reducing the efficiency roll-offs in OLEDs. Consequently, a high external electroluminescence quantum efficiency over 20% can be retained, even under operating the device at a high luminance of 1000 cd m⁻².

A simple design tactic for narrowband blue emitter is demonstrated by incorporating sulfone unit into the boron/nitrogen (B/N) embedded polycyclic skeleton. The resulting blue organic light-emitting diodes achieve a high external quantum efficiency of 32.0% and low efficiency roll-off.

Abstract

The blue multi-resonance thermally activated delayed fluorescence materials, simultaneously realizing narrow full-width at half-maximum, high external quantum efficiency (EQE), and low efficiency roll-off, remains a formidable challenge. Herein, three novel emitters, namely PTZBN1, PTZBN2, and PTZBN3, are designed by gradual peripheral modification in boron/nitrogen (B/N) embedded polycyclic skeleton, which exhibit progressively hypsochromic-shifted emission from 490 nm (PTZBN1) to 468 nm (PTZBN3) with photoluminescence quantum yields up to 98%. In particular, the incorporation of sulfone unit in the boron/nitrogen (B/N) embedded polycyclic skeleton provides a simple but effective tactic for narrowband blue emission. The organic light-emitting diodes based on PTZBN2 achieve one of the-state-of-the-art EQEs of 34.8% with electroluminescence (EL) peak at 478 nm. Impressively, PTZBN3-based device exhibits not only a high maximum EQE of 32.0% with EL peak at 468 nm, but also low efficiency roll-off.

Publication date: 15 October 2022

Source: Chemical Engineering Journal, Volume 446, Part 1

Author(s): Chengjun Wu, Jingsheng Miao, Lian Wang, Youming Zhang, Kai Li, Weiguo Zhu, Chuluo Yang

Publication date: July 2022

Source: Dyes and Pigments, Volume 203

Author(s): Daiyu Ma, Guimin Zhao, Haowen Chen, Renyin Zhou, Guanghao Zhang, Wenwen Tian, Wei Jiang, Yueming Sun

A highly efficient anthracene-based 5-(4-(10-phenylanthracen-9-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (ATDBF) with nearly 100% exciton utilization efficiency is developed for highly efficient nondoped blue organic light-emitting diodes through inter- and intramolecular triplet exciton up-converting mechanisms. The ATDBF emitter opens hybridized hot excitons, triplet–triplet fusion (TTF), and mixed TTF/hot exciton channels for triplet exciton to singlet exciton conversion.

Abstract

A highly efficient anthracene-based 5-(4-(10-phenylanthracen-9-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (ATDBF) with nearly 100% exciton utilization efficiency is developed for highly efficient nondoped blue organic light-emitting diodes (OLEDs) through inter- and intramolecular triplet exciton up-converting mechanisms. The ATDBF emitter opens hybridized hot excitons, triplet–triplet fusion (TTF), and mixed TTF/hot exciton channels for triplet exciton to singlet exciton conversion. The molecular design adopting a benzofuro[3,2-c]carbazole (BFCz) donor manages the singlet and triplet excited states for hybridized triplet exciton up-conversion mechanisms, which enable a high external quantum efficiency (EQE) of 7.93% in the ATDBF blue device with color coordinates of (0.15, 0.06). This is one of the best efficiencies of the nondoped blue OLEDs with a y color coordinate below 0.06.

Publication date: July 2022

Source: Dyes and Pigments, Volume 203

Author(s): Jie Li, Zhi Li, Hui Liu, Heqi Gong, Jincheng Zhang, Xiaoyu Li, Yanqing Wang, Qiang Guo

Sky-blue organic light-emitting diodes based on newly designed pyridine-containing [3+2+1] iridium (III) dopants have exhibited maximum external quantum efficiencies (EQE_max) and current efficiency (CE) of 17.3% and 42.3 cd A^-1, respectively. To note, a very small efficiency roll-off value of 4.3% at 1000 cd m^-2 has been reached.

Abstract

A new series of blue phosphorescent cyclometalated [3+2+1] coordinated iridium (III) complexes containing 2-(2′,4′-difluoropyridyl) pyridine derivatives have been designed and synthesized to investigate their structure–property relationship on the nature of excited states and tune their emission wavelengths from saturated-blue to sky-blue region at 437−489 nm. These complexes exhibit high photoluminescent quantum yields (PLQYs) of up to 90% and short excited state lifetime in the range of 2−5 µs in polymethylmethacrylate (PMMA) thin films. Sky-blue organic light-emitting diodes (OLEDs) based on such pyridine-containing [3+2+1] iridium (III) dopants have exhibited maximum external quantum efficiencies (EQE_max) and current efficiency (CE) of 17.3% and 42.3 cd A^–1, respectively. To note, very small efficiency roll-off value from 4.3% to 19.7% is achieved at the luminance level of 1000 cd m^–2. The well-balanced electron and hole injection currents, the short lifetime of excited excitons, and wide recombination zone by leveraging the obtained iridium (III) dopants and exciplex co-host have greatly decreased the accumulation of triplet excitons at the high luminescence level, leading to dramatically reduced efficiency roll-off. It is anticipated that this work provides new insights into the design of saturated-blue-emitting iridium (III) complexes with reduced efficiency roll-off in their fabricated OLEDs.

Publication date: July 2022

Source: Dyes and Pigments, Volume 203

Author(s): Bowen Li, Zhiyi Li, Xiangan Song, Fengyun Guo, Ying Wang, Shiyong Gao, Yong Zhang

Owing to the synergetic horizontal dipole orientation induction on the transition dipole moment of orange-red emitter and carrier recombination modulation in the binary thermally activated delayed fluorescence (TADF) host–guest system (DspiroS-TRZ and TPA-AQ), an external quantum efficiency of 31.2% and stable electroluminescence spectra are achieved for all-TADF white organic light-emitting diodes.

Abstract

Radiative exciton generation and light out-coupling are two crucial factors for highly efficient organic light-emitting diodes (OLEDs). Herein, a thermally activated delayed fluorescence (TADF) material DspiroS-TRZ with high horizontal dipole ratio (HDR, Θ_// = 82%) is utilized as the blue emitter as well as the host for an orange-red TADF emitter TPA-AQ to fabricate white OLEDs. A synergetic horizontal dipole orientation induction on the transition dipole moment of TPA-AQ is achieved by the highly orientated DspiroS-TRZ, resulting in high HDR (Θ_// = 96%) of the orange-red emitter. Owing to the simultaneous efficient triplet exciton utilization and highly orientated binary system, a maximum external quantum efficiency (EQE_max) of 29.3% is achieved for single emission layer (EML) white OLED, with an excellent white light out-coupling efficiency of 34%. In addition, the carrier recombination in the EML is further regulated by inserting an exciton regulation emission layer, which can relieve the trapping effect of the orange-red emitter and guarantee stable Langevin recombination and energy transfer processes for improved electroluminescence spectral stability. An EQE_max of 31.2% is ultimately achieved for the double-EML white OLED, highlighting the key role of horizontal dipole orientation induction and carrier recombination modulation for highly efficient and spectral stable white OLEDs.