Chiral multiple-resonance thermally activated delayed fluorescence materials based on chiral spiro-axis skeleton for efficient circularly polarized electroluminescence

Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)characteristics.However,the further development of circularly polarized organic light-emitting diodes(CP-OLEDs)needs to meet the requirements of high efficiency,high color purity,low cost,and high dissymmetry factor(gPLor gEL),chiral multiple resonance thermally activated delayed fluorescence(MR-TADF)materials are considered as candidates in these aspects.Herein,based on a pair of chiral spirofluorene precursors,two pairs of high-performance chiral MR-TADF emitters((R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB)are developed,which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm,respectively.In addition,small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0%and 96.7%are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules,respectively.OLEDs based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6%and 33.8%,respectively.Most importantly,CP-OLEDs present symmetric circularly polarized electroluminescence spectra with|gEL|factors of 3.36×10^(-4)and 7.66×10^(-4)for devices based on(R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB enantiomers,respectively.

Color-tunable circularly polarized electroluminescence from a helical chiral multiple resonance emitter with B–N bonds

Chiral B,N-doped polycyclic aromatic hydrocarbons with circularly polarized luminescence(CPL) and small full-width at halfmaxima(FWHM) are promising multiple resonance(MR) emitters for CP organic light-emitting diodes(CP-OLEDs).This work presents a pair of chiral MR enantiomers,P/M-o[B-N]_(2)N_(2),featuring B–N bonds incorporated within a[7]-helicene skeleton.These enantiomers exhibit narrow 0-0 and 0-1 electronic transition bands,whose relative intensity can be fine-tuned by increasing doping concentrations,resulting in redshifts of the emission peak from 542 to 592 nm.The enantiomers show mirrorsymmetric CPL spectra with an asymmetry factor(|g_(PL)|) of 1.0×10^(-3).The hyperfluorescent CP-OLEDs with double-sensitized emitting layers display a FWHM of 33 nm,an external quantum efficiency of 25.1%,and a|g_(EL)|factor of 7.7×10^(-4).Notably,the CP-OLEDs realize color-tunable CP electroluminescence peak from 553 to 613 nm by regulating the vibrational coupling.This work provides a novel concept for the design of helical CP-MR materials and CP-OLEDs,highlighting their potential for future applications in advanced optoelectronic devices.

Research Advances in Helicene Structure-Based Chiral Luminescent Materials and Their Circularly Polarized Electroluminescence

Benefited from direct generation of circularly polarized(CP) emission with tunable colors, high efficiencies and facile device architectures, CP organic light-emitting diodes(CP-OLEDs) have attracted great attention and are expected to meet industrial applications. Particularly, CP electroluminescence(CPEL) originated from CP-OLEDs has wide potential applications in 3D displays, optical information storage, quantum communication, and biological sensors. The diverse design strategies of chiral luminescent materials for CP-OLEDs, including small organic emitters, lanthanide and transition-metal complexes and conjugated polymers, have been extensively explored. Helicene with twisted extended π-conjugated molecular structure could exhibit special helical chirality and excellent circularly polarized luminescence properties, which has been employed as the ingenious chirality core for constructing efficient chiral luminescent materials. In addition, significant improvements have been made in terms of CP photoluminescence research, however, the development of CPEL with more application prospects in optoelectronic technology still lags behind. In this review, we systematically summarize the recent advances in chiral luminescent materials based on helicene structure and their CPEL properties, including helicene-based chiral fluorescence molecules, transition metal complexes and thermally activated delayed fluorescence molecules, and discuss current challenges and future perspectives for this hot research field. We believe this progress report will provide a promising perspective of OLEDs based on helicene emitters with CPEL properties for extensive researchers, including chemical, physical and material scientists in different disciplinary fields and attract them to this rapidly developing field.

A chiral spirofluorene-embedded multiple-resonance thermally activated delayed fluorescence emitter for efficient pure-green circularly polarized electroluminescence

The simultaneous achievement of chiral multiple-resonance thermally activated delayed fluorescence(MR-TADF)emitters with narrowband and circularly polarized electroluminescence(CPEL)poses a challenge.Herein,a MR-TADF emitter,Spiro-BNCz,embedding spirofluorene structure was developed and chiral separated,whose emission peaks at 528 nm in toluene with Commission Internationale de L’Eclairage coordinates of(0.26,0.69).The conjugation extension caused by embedding sulfur substituted spirofluorene on B/N framework shortens the singlettriplet energy gap and increases spin-orbital coupling matrix element.Therefore,a fast reverse intersystem crossing rate constant of 2.8×10^(6)s^(−1)and a high photoluminescence efficiency of 92%in film were achieved.The organic light-emitting diode(OLED)exhibits a maximum external quantum efficiency of 32.3%.Particularly,the circularly polarized OLEDs based on Spiro-BNCz enantiomers show symmetric CPEL with dissymmetry factors(|gEL|)≈10^(−3).

Chiral electron transporting material for circularly polarized organic light-emitting diode

Circularly polarized organic light-emitting diode(CP-OLED) has attracted increasing interest for its efficient ability to generate circularly polarized light directly. So far, many CP-OLEDs were successfully fabricated with chiral emitters or chiral hosts. In this study, a new strategy based on chiral electron transporting layer is proposed to construct CP-OLEDs. A pair of chiral electron transporting materials, 1,3,5-tris((R/S)-4-isopropyl-4,5-dihydrooxazol-2-yl)benzene((R/S)-TOx^(i)Pr), are firstly designed and synthesized. The crystalline films of(R/S)-TOx^(i)Pr show circularly polarized photoluminescence with photoluminescence dissymmetry factors of-0.067 and +0.041, respectively. The CP-OLEDs based on(R/S)-TOx^(i)Pr and three types of achiral emitters all exhibit circularly polarized electroluminescence, showing feasibility and strong versatility of this new strategy. The mechanism is attributed to in-situ electrical excitation instead of simply light filtering of non-circularly polarized light. This work demonstrates a new approach for realizing circularly polarized electroluminescence which may provide a valuable strategy to develop CP-OLEDs.

Efficient circularly polarized photoluminescence and electroluminescence of chiral spiro-skeleton-based thermally activated delayed fluorescence molecules

Chiral thermally activated delayed fluorescence(TADF) molecules showing circularly polarized luminescence(CPL) have great potential in 3D displays. However, the relationships among CPL property, device performance and molecule structure are still not clear. In this article, we develop a strategy to promote dissymmetry factors without sacrifice in device performance and study the impact of molecule structures towards CPL property. Three novel TADF enantiomers are synthesized and studied.(R/S)-SCN with diminutive cyano group as an acceptor shows dissymmetry factor |gPL| ≈ 1.4×10^(-3) and noticeable organic light-emitting diode(OLED) performances with a maximum external quantum efficiency(EQEmax) of 23.0%. For(R/S)-SPHCN, the prolonged electron withdrawing group benzonitrile enhances |gPL| up to 3.6×10^(-3) with decreased device EQEmaxof 15.4%. By further replacing benzonitrile with(trifluoromethyl)pyridine, the enantiomers of(R/S)-SCFPY show similar |gPL| factors of 3.5×10^(-3) and device EQE_(max)up to 23.3%, which represents the highest efficiency among sprio-type TADF materials based OLEDs. Furthermore, the OLEDs also show obvious circularly polarized electroluminescence with gELfactors of-1.4/1.8×10^(-3),-3.6/3.6×10^(-3) and-3.7/3.6×10^(-3), respectively. These results indecate by delicate functional group engineering, high g factor can be achieved while maintaining decent device performances. Besides,(R/S)-SCFPY represents an impressive TADF emitter, which shows promoted g factor and recorded high device EQE_(max)among similar molecules.

Recent Progress of Circularly Polarized Luminescence Materials from Chinese Perspectives

The research on circularly polarized luminescence(CPL)has garnered significant attention in recent years due to its many potential applications.One aspect of this research involves the pursuit of chiral materials that posess both high luminescence efficiency and dissymmetry factors.The investigation of CPL behavior is of paramount importance because the structural information of chiral luminescent systems in the excited state can be uncovered.The objective of this review is to offer a comprehensive overview of the latest advancements in the CPL research field,with a particular focus on the development of chiral emissive materials,including organic,inorganic,and hybrid substances.Furthermore,this review outlines the recent applications of these materials in areas such as displays,photoelectric devices,anticounterfeiting measures,and sensors.Finally,we highlight the primary challenges and potential prospects of CPL materials.Our aspiration is that this endeavor will contribute new perspectives and insights that further advancements in related research fields.