Since the first attempt that was made to obtain direct circularly polarized (CP) light from OLEDs by Meijer
et al.
in 1997, considerable efforts have been devoted to the development of circularly ...polarized organic light-emitting diodes (CP-OLEDs), particularly in the recent years. Circularly polarized electroluminescence (CPEL) based on OLEDs has attracted increasing interest for its efficient ability to generate CP light directly and wide potential applications in 3D displays, optical data storage, and optical spintronics. In this review, we systematically summarize the recent progress in chiral emitter based OLEDs with CPEL properties including CPEL based on chiral conjugated polymers, CPEL based on chiral metal complexes, and CPEL based on chiral simple organic molecules, especially chiral thermally activated delayed fluorescence (TADF) molecules. We believe that this review will provide a promising perspective of chiral emitter based OLEDs with CPEL properties for a broad range of scientists in different disciplinary areas and attract a growing number of researchers to this fast-growing research field.
This review summarizes the recent advances in CP-OLEDs based on chiral conjugated polymers, chiral metal complexes, and chiral simple organic molecules.
The use of a chiral, emitting skeleton for axially chiral enantiomers showing activity in thermally activated delayed fluorescence (TADF) with circularly polarized electroluminescence (CPEL) is ...proposed. A pair of chiral stable enantiomers, (−)‐(S)‐Cz‐Ax‐CN and (+)‐(R)‐Cz‐Ax‐CN, was designed and synthesized. The enantiomers, both exhibiting intramolecular π‐conjugated charge transfer (CT) and spatial CT, show TADF activities with a small singlet–triplet energy difference (ΔEST) of 0.029 eV and mirror‐image circularly polarized luminescence (CPL) activities with large glum values. Notably, CP‐OLEDs based on the enantiomers feature blue electroluminescence centered at 468 nm with external quantum efficiencies (EQEs) of 12.5 and 12.7 %, and also show intense CPEL with gEL values of −1.2×10−2 and +1.4×10−2, respectively. These are the first CP‐OLEDs based on TADF‐active enantiomers with efficient blue CPEL.
Let's twist again: Axially chiral molecules with thermally activated delayed fluorescence and circularly polarized electroluminescence (CPEL) are presented. CP‐OLEDs based on these molecules display high efficiencies and blue CPEL with large gEL values.
Aromatic‐imide‐based thermally activated delayed fluorescent (TADF) enantiomers, (+)‐(S,S)‐CAI‐Cz and (−)‐(R,R)‐CAI‐Cz, were efficiently synthesized by introducing a chiral 1,2‐diaminocyclohexane to ...the achiral TADF unit. The TADF enantiomers exhibited high PLQYs of up to 98 %, small ΔEST values of 0.06 eV, as well as obvious temperature‐dependent transient PL spectra, thus demonstrating their excellent TADF properties. Moreover, the TADF enantiomers showed mirror‐image CD and CPL activities. Notably, the CP‐OLEDs with CPEL properties based on the TADF enantiomers not only achieved high EQE values of up to 19.7 and 19.8 %, but also displayed opposite CPEL signals with gEL values of −1.7×10−3 and 2.3×10−3, which represents the first CP‐OLEDs, based on the enantiomerically pure TADF materials, having both high efficiencies and intense CPEL.
It's intense: Thermally activated delayed fluorescenct (TADF) enantiomers were developed by introducing a chiral 1,2‐diaminocyclohexane to the achiral TADF unit. They exhibited high PLQYs (98 %), small ΔEST values (0.06 eV), and mirror‐image CD and CPL spectra. Moreover, they represent the first example of CP‐OLEDs, based on the enantiomerically pure TADF materials, having both high efficiencies (EQE: 19.8 %) and intense CPEL.
Photon loss in optical fibers prevents long-distance distribution of quantum information on the ground. Quantum repeater is proposed to overcome this problem, but the communication distance is still ...limited so far because of the system complexity of the quantum repeater scheme. Alternative solutions include transportable quantum memory and quantum-memory-equipped satellites, where long-lived optical quantum memories are the key components to realize global quantum communication. However, the longest storage time of the optical memories demonstrated so far is approximately 1 minute. Here, by employing a zero-first-order-Zeeman magnetic field and dynamical decoupling to protect the spin coherence in a solid, we demonstrate coherent storage of light in an atomic frequency comb memory over 1 hour, leading to a promising future for large-scale quantum communication based on long-lived solid-state quantum memories.
The faithful storage and coherent manipulation of quantum states with matter-systems would enable the realization of large-scale quantum networks based on quantum repeaters. To achieve useful ...communication rates, highly multimode quantum memories are required to construct a multiplexed quantum repeater. Here, we present a demonstration of on-demand storage of orbital-angular-momentum states with weak coherent pulses at the single-photon-level in a rare-earth-ion-doped crystal. Through the combination of this spatial degree-of-freedom (DOF) with temporal and spectral degrees of freedom, we create a multiple-DOF memory with high multimode capacity. This device can serve as a quantum mode converter with high fidelity, which is a fundamental requirement for the construction of a multiplexed quantum repeater. This device further enables essentially arbitrary spectral and temporal manipulations of spatial-qutrit-encoded photonic pulses in real time. Therefore, the developed quantum memory can serve as a building block for scalable photonic quantum information processing architectures.
A strategy of chiral donor–acceptor copolymerization is proposed to develop chiral nonconjugated polymers with thermally activated delayed fluorescence (TADF). Based on this strategy, two pairs of ...chiral polymers (R,R)‐/(S,S)‐pTpAcDPS and (R,R)‐/(S,S)‐pTpAcBP were synthesized. The alternating copolymerization of the chiral donors and acceptors could effectively separate the frontier molecular orbitals, which made the polymers show small ΔEST of 0.01–0.03 eV and efficient TADF properties. Moreover, the polymers also showed the quantum yield of up to 92 % and the circularly polarized luminescence. The solution‐processed circularly polarized organic light‐emitting diodes showed circularly polarized electroluminescence signals with high external quantum efficiencies of up to 22.1 % and maximum luminance of up to 34350 cd m−2. This is the first report of CP‐OLEDs based on chiral TADF polymer, which provides a useful and valuable guidance for the development of high‐efficiency CPEL polymers.
Based on a chiral donor–acceptor copolymerization strategy, two pairs of chiral nonconjugated TADF polymers with low ΔEST values and high PLQYs were constructed. The corresponding solution‐processed CP‐OLEDs exhibited intense CPEL signals and high device efficiencies with an EQEmax of up to 22.1 %.
Macrocycles denoted as saucernarenes (n=4,5) were easily synthesized by the one‐pot condensation of 2,7‐dimethoxynaphthalene (2,7‐DMN) and paraformaldehyde in the presence of TFA or catalytic ...BF3⋅OEt2. With 1,1‐dimethylpiperidin‐1‐ium as the template, saucer4arene was selectively obtained. Crystal structures show that saucernarenes are all composed of 2,7‐DMN moiety bridged by the methylene groups at 1,6‐positions: all of the 7‐methoxy groups lie on one face, and all of the 2‐methoxy groups lie on the other. Saucernarenes exhibit strong fluorescence properties with the quantum yields of 19.6 % and 23.4 %. They form 1:1 complexes with ammonium salts in both solution and solid state (association constant up to 105 M−1 in CDCl3). Chiral quaternary ammonium salts can induce the chirality of the dynamically racemic inherently chiral saucernarenes in solution, and thus show mirror‐imaged circular dichroism signals and circularly polarized luminescence (CPL) properties.
Starting from 2,7‐dimethoxynaphthalene, a new kind of macrocyclic arenes named saucernarenes (n=4,5) are synthesized by one‐pot and templated methods. Saucernarenes show strong fluorescence properties and form 1:1 complexes with various ammonium salts. Moreover, the chiral guests can induce the chirality of dynamically racemic saucernarenes in the host–guest systems, which provides a new way to construct CPL organic materials.
A supramolecular strategy to construct thermally activated delayed fluorescence (TADF) materials through host–guest charge transfer interactions was proposed. Consequently, a new class of macrocycle ...namely calix3acridan was conveniently synthesized in 90 % yield. The host–guest cocrystal formed by calix3acridan and 1,2‐dicyanobenzene exhibited efficient TADF properties due to intense intermolecular charge transfer interactions. Moreover, the spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital resulted in a very small singlet–triplet energy gap of 0.014 eV and hence guaranteed an efficient reverse intersystem crossing for TADF. Especially, a high photoluminescence quantum yield of 70 % was achieved, and it represents the highest value among the reported intermolecular donor–acceptor TADF materials.
A novel supramolecular strategy to construct thermally activated delayed fluorescence (TADF) materials has been developed, which has led to the convenient synthesis of a new kind of macrocycle, namely calix3acridan. The host–guest cocrystal formed from calix3acridan and 1,2‐dicyanobenzene exhibited efficient TADF with a high photoluminescence quantum yield of 70 % as a result of intense intermolecular charge transfer (ICT).
A couple of fluorescent enantiomers, which are suitable for the emitters of high‐efficiency TADF‐sensitized CP‐OLEDs, have been developed. The enantiomers show configurational stability, high PLQY of ...98 %, large kr of 7.8×107 s−1, and intense CPL activities with |glum| values of about 2.5×10−3. Notably, by using matchable TADF sensitizer, the enantiomers were then exploited as emitter to fabricate CP‐OLEDs. The TADF‐sensitized CP‐OLEDs not only show mirror‐image CPEL activities with gEL values of +1.8×10−3 and −1.4×10−3, but also display fast start‐up featuring with low VT of 3.0 V as well as driving voltage of 4.8 V at 10 000 cd m−2. Meaningfully, the TADF‐sensitized fluorescent devices show high EQEmax of 21.5 % and extremely low efficiency roll‐off, whose EQEs are 21.2 % and 15.3 % at 1000 and 10 000 cd m−2, respectively. The obtained EQEs are comparable to those of CP‐TADF emitters, which provides a promising perspective to break through the EL efficiency limit of CP‐FL emitters.
A couple of fluorescent enantiomers with high PLQY of 98 % and mirror‐imaged CPL activities have been developed to fabricate TADF‐sensitized CP‐OLEDs. The resulting devices not only display intense CPEL with |gEL| of about 1.8×10−3, but also show high EQEmax of 21.5 % with remarkably low efficiency roll‐off, whose EQE is 15.3 % even at 10 000 cd m−2.
A promising strategy of thermally activated delayed fluorescence (TADF) sensitized circularly polarized luminescence (CPL) has been proposed for improving the electroluminescence efficiencies of ...circularly polarized fluorescent emitters. Compared with chiral TADF emitters which suffer from the dilemma of small ΔEST accompanied by small kr, the TADF‐sensitized CPL (TSCP) strategy using TADF molecules as sensitizers and CP‐FL molecules as emitters might be the most promising method to construct high‐performance circularly polarized organic light‐emitting diodes (CP‐OLEDs). Consequently, by taking advantage of the theoretically 100 % exciton utilization of TADF sensitizers, especially, by designing CP‐FL emitters with high PLQY, narrow FWHM and large glum values, TSCP‐type CP‐OLEDs with excellent overall performances can be realized.
A new strategy of thermally activated delayed fluorescence (TADF)‐sensitized CPL (TSCP) is proposed to realize efficient circularly polarized electroluminescence (CPEL) by taking TADF molecule as sensitizer to improve exciton utilization and CP‐FL molecule as emitter to realize CPEL. In this article, we highlight the research status of CPEL and CP‐TADF, mainly focus on the concept of TSCP and its applications in CP‐OLEDs, and finally give the prospects of TSCP in CPEL research area.
PDF
