Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, ...blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin-orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor-acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance.
Near‐IR organic light‐emitting diodes (NIR‐OLEDs) are potential light‐sources for various sensing applications as OLEDs have unique features such as ultra‐flexibility and low‐cost fabrication. ...However, the low external electroluminescence (EL) quantum efficiency (EQE) of NIR‐OLEDs is a critical obstacle for potential applications. Here, we demonstrate a highly efficient NIR emitter with thermally activated delayed fluorescence (TADF) and its application to NIR‐OLEDs. The NIR‐TADF emitter, TPA‐PZTCN, has a high photoluminescence quantum yield of over 40 % with a peak wavelength at 729 nm even in a highly doped co‐deposited film. The EL peak wavelength of the NIR‐OLED is 734 nm with an EQE of 13.4 %, unprecedented among rare‐metal‐free NIR‐OLEDs in this spectral range. TPA‐PZTCN can sensitize a deeper NIR fluorophore to achieve a peak wavelength of approximately 900 nm, resulting in an EQE of over 1 % in a TADF‐sensitized NIR‐OLED with high operational device durability (LT95>600 h.).
A highly efficient NIR‐TADF emitter with high kRISC is developed for NIR‐OLEDs. The NIR‐TADF‐OLED showed a significantly high EQE of 13.4 % with an EL peak at 734 nm. Notably, the NIR‐TADF molecule can sensitize a deeper‐NIR‐fluorophore, resulting in an EQE of 1.1 % at over 900 nm in the TADF‐sensitized NIR‐OLED.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In the traditional molecular design of thermally activated delayed fluorescence (TADF) emitters composed of electron‐donor and electron‐acceptor moieties, achieving a small singlet–triplet energy gap ...(ΔEST) in strongly twisted structures usually translates into a small fluorescence oscillator strength, which can significantly decrease the emission quantum yield and limit efficiency in organic light‐emitting diode devices. Here, based on the results of quantum‐chemical calculations on TADF emitters composed of carbazole donor and 2,4,6‐triphenyl‐1,3,5‐triazine acceptor moieties, a new strategy is proposed for the molecular design of efficient TADF emitters that combine a small ΔEST with a large fluorescence oscillator strength. Since this strategy goes beyond the traditional framework of structurally twisted, charge‐transfer type emitters, importantly, it opens the way for coplanar molecules to be efficient TADF emitters. Here, a new emitter, composed of azatriangulene and diphenyltriazine moieties, is theoretically designed, which is coplanar due to intramolecular H‐bonding interactions. The synthesis of this hexamethylazatriangulene‐triazine (HMAT‐TRZ) emitter and its preliminary photophysical characterizations point to HMAT‐TRZ as a potential efficient TADF emitter.
A new strategy is proposed for the molecular design of efficient thermally activated delayed fluorescence (TADF) emitters that combine small singlet–triplet energy gaps and large fluorescence oscillator strengths. This strategy goes beyond the traditional framework of twisted TADF emitters and opens the way for coplanar molecules to be efficient TADF emitters.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes ...can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor–acceptor–donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, UL, UM, UPUK
Highly efficient blue and green thermally activated delayed fluorescence (TADF) molecules bearing trifluoromethane-modified carbazole groups were developed. The trifluoromethane groups on carbazole ...induced blue-shifted emission and improved the photoluminescence quantum yield. The photostability of the TADF molecules was strongly related to the modification position of trifluoromethane on carbazole.
The carbazolophane (Czp) donor unit (indolo2.2paracyclophane) is introduced to the design pool of donors in thermally activated delayed fluorescence emitters. The increased steric bulk of the ...annelated donor unit forces an increased torsion between the carbazole and the aryl bridge resulting in a decreased Δ
and an enhancement of the thermally activated delayed fluorescence in the triazine-containing emitter
. Further, the closely stacked carbazole and benzene units of the paracyclophane show through-space π-π interactions, effectively increasing the spatial occupation for the HOMO orbital. The chiroptical properties of enantiomers of 2.2paracyclophane reveal mirror image circular dichroism (CD) and circularly polarized luminescence (CPL) with
of 1.3 × 10
.
is a sky-blue emitter with
of 480 nm, a very small Δ
of 0.16 eV and high
of 70% in 10 wt% doped
films. Sky blue-emitting OLEDs were fabricated with this new TADF emitter showing a high maximum EQE of 17% with CIE coordinates of (0.17, 0.25). A moderate EQE roll-off was also observed with an EQE of 12% at a display relevant luminance of 100 cd m
. Our results show that the Czp donor contributes to both a decreased Δ
and an increased photoluminescence quantum yield, both advantageous in the molecular design of TADF emitters.
Full text
Available for:
IJS, KILJ, NUK, UL, UM, UPUK
We report on light-emitting electrochemical cells, comprising a solution-processed single-layer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated ...delayed fluorescence. Our optimized devices delivers a luminance of 120 cd m
at an external quantum efficiency of 7.0%. As such, it outperforms the combined luminance/efficiency state-of-the art for thermally activated delayed fluorescence light-emitting electrochemical cells by one order of magnitude. For this end, we employed a polymeric blend host for balanced electrochemical doping and electronic transport as well as uniform film formation, an optimized concentration (<1 mass%) of guest for complete host-to-guest energy transfer at minimized aggregation and efficient emission, and an appropriate concentration of an electrochemically stabile electrolyte for desired doping effects. The generic nature of our approach is manifested in the attainment of bright and efficient thermally activated delayed fluorescence emission from three different light-emitting electrochemical cells with invariant host:guest:electrolyte number ratio.
The photophysical analysis of thermally activated delayed fluorescence (TADF) materials has become instrumental for providing insights into their stability and performance, which is not only relevant ...for organic light-emitting diodes but also for other applications such as sensing, imaging, and photocatalysis. Thus, a deeper understanding of the photophysics underpinning the TADF mechanism is required to push materials design further. Previously reported analyses in the literature of the kinetics of the various processes occurring in a TADF material rely on several a priori assumptions to estimate the rate constants for forward and reverse intersystem crossing. In this report, we demonstrate a method to determine these rate constants using a three-state model together with a steady-state approximation and, importantly, no additional assumptions. Further, we derive the exact rate equations, greatly facilitating a comparison of the TADF properties of structurally diverse emitters and providing a comprehensive understanding of the photophysics of these systems.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Organic light‐emitting diodes (OLEDs) displaying a wide range of emission colors with emission peaks from 450 to 665 nm using a single emitting material, avobenzone boron difluoride (AVB‐BF2), are ...reported. Color tuning is achieved by controlling the aggregation of AVB‐BF2 and the formation of a “triadic” exciplex of an AVB‐BF2 dimer and a host molecule. Various electroluminescent devices containing AVB‐BF2 cover the whole visible light spectrum and a white‐emitting device with CIE coordinates of (0.35, 0.37) is obtained with a single emitting material in a single emissive layer. Furthermore, an exceptionally high external quantum efficiency of nearly 13% is achieved for a green‐emitting OLED because AVB‐BF2 exhibits thermally activated delayed fluorescence by forming the exciplex.
Full‐color‐tunable OLEDs that can also achieve white emission are demonstrated by using a single emitter and a single emissive layer through a new strategy exploiting both aggregation and exciplex formation. The aggregation formation induces emission color shift from blue to green. Further color shift to red is provided by the aggregation induced exciplex formation through the triadic exciplex formation between aggregated emitter and host molecules.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
