Multicolor Circularly Polarized Photoluminescence and Electroluminescence with 1,2-Diaminecyclohexane Enantiomers

Fluorescent octahydrophenazines as novel inhibitors against herpes simplex viruses

A new series of racemic fluorescent octahydrophenazines (rac-PZ1-11) have been designed and synthesized via the efficient nucleophilic aromatic substitution (SNAr) of tetrafluorobenzenedinitriles (1a-c) and racemic cyclohexane-1,2-diamines (rac-2a and b). The bioactivities of these racemic rac-PZs (20 μM) against herpes simplex virus type-1 (HSV-1) were evaluated by the relative cell viability of Vero cells infected with HSV-1. It was found that rac-PZ3 shows much higher anti-HSV-1 activity than others, with EC50 = 9.2 ± 1.4 μM. Further investigation into the anti-HSV activities of rac-PZ3 and its enantiomers RR- and SS-PZ3 indicates that rac-PZ3 can also efficiently inhibit HSV-2 and even ACV-resistant HSV-2 (EC50 = 11.0 ± 2.3 and 14.9 ± 2.8 μM, respectively), SS-PZ3 has better activities against HSV-1, HSV-2 and ACV-resistant HSV-2 (EC50 = 4.1 ± 1.1, 5.8 ± 1.0 and 7.9 ± 1.2 μM, respectively), but RR-PZ3 has almost no antiviral activities. The primary mechanism study indicates that rac-PZ3 efficiently reverses the HSV-1/2-induced cytopathic effect and suppresses the expression of viral mRNA and proteins. In addition, rac-, RR- and SS-PZ3 possess excellent fluorescence properties with almost the same emission wavelength and high fluorescence quantum yields (ΦF = 90.3-92.3 % in cyclohexane solutions and 54.4-57.3 % in solids) and can target endoplasmic reticulum and cell membrane. The efficient anti-HSV bioactivities and excellent fluorescence of PZ3 prove its potential applications in antiviral therapy and biological imaging.

Tetraborated Intrinsically Axial Chiral Multi-resonance Thermally Activated Delayed Fluorescence Materials

Chiral multi-resonance thermally activated delayed fluorescence (CP-MR-TADF) materials hold promise for circularly polarized organic light-emitting diodes (CP-OLEDs) and 3D displays. Herein, we present two pairs of tetraborated intrinsically axial CP-MR-TADF materials, R/S-BDBF-BOH and R/S-BDBT-BOH, with conjugation-extended bidibenzo[b,d]furan and bidibenzo[b,d]thiophene as chiral sources, which effectively participate in the distribution of the frontier molecular orbitals. Due to the heavy-atom effect, sulfur atoms are introduced to accelerate the reverse intersystem crossing process and increase the efficiency of molecules. R/S-BDBF-BOH and R/S-BDBT-BOH manifest ultra-pure blue emission with a maximum at 458/459 nm with a full width at half maximum of 27 nm, photoluminescence quantum yields of 90 %/91 %, and dissymmetry factors (|gPL|) of 6.8×10-4/8.5×10-4, respectively. Correspondingly, the CP-OLEDs exhibit good performances with an external quantum efficiency of 30.1 % and |gEL| factors of 1.2×10-3.

Hybridization of short-range and long-range charge transfer boosts room-temperature phosphorescence performance

At present, mainstream room-temperature phosphorescence (RTP) emission relies on organic materials with long-range charge-transfer effects; therefore, exploring new forms of charge transfer to generate RTP is worth studying. In this work, indole-carbazole was used as the core to ensure the narrowband fluorescence emission of the material based on its characteristic short-range charge-transfer effect. In addition, halogenated carbazoles were introduced into the periphery to construct long-range charge transfer, resulting in VTCzNL-Cl and VTCzNL-Br. By encapsulating these phosphors into a robust host (TPP), two host-guest crystalline systems were further developed, achieving efficient RTP performance with phosphorescence quantum yields of 26% and phosphorescence lifetimes of 3.2 and 39.2 ms, respectively.

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

Double charge transfer processes enable a green multiple resonance-induced thermally activated delayed fluorescence emitter for an efficient narrowband OLED

Benefitting from short-range charge transfer (SR-CT) and through-space charge transfer (TSCT) effects, an efficient green narrowband emitter, BNDCN, was developed. Owing to the synergistic effect of double CT processes, a BNDCN-based organic light-emitting diode showed a high external quantum efficiency of 32.3%.

Boosting quantum yields and circularly polarized luminescence of penta- and hexahelicenes by doping with two BN-groups

The incorporation of boron-nitrogen (BN) units into polycyclic aromatic hydrocarbons (PAHs) as an isoelectronic replacement of two carbon atoms can significantly improve their optical properties, while the geometries are mostly retained. We report the first non-π-extended penta- and hexahelicenes comprising two aromatic 1,2-azaborinine rings. Comparing them with their all-carbon analogs regarding structural, spectral and (chir)optical properties allowed us to quantify the impact of the heteroatoms. In particular, BN-hexahelicene BN[6] exhibited a crystal structure congruent with its analog CC[6], but displayed a fivefold higher fluorescence quantum yield (φfl = 0.17) and an outstanding luminescence dissymmetry factor (|glum| = 1.33 × 10-2). Such an unusual magnification of both properties at the same time makes BN-helicenes suitable candidates as circularly polarized luminescence emitters for applications in materials science.

Conversion of amino-terephthalonitriles to multi-substituted single benzene fluorophores with utility in bioimaging

Substitution of two fluorine atoms of the tetrafluoroterephthalonitrile (TFTN) ring (ortho to each other) by amine nucleophiles through SNAr chemistry is achievable. However, tri- and tetra-substitution towards multi-substituted single benzene fluorophores (SBFs) is harder due to increased electron richness of the TFTN moiety. Tertiary amine donors promote the molecule towards such multi-substitution guided by the steric obstruction to intramolecular charge transfer to the TFTN ring. Contrarily, secondary amine substituents with better lone pair donation to the TFTN ring cannot induce the SNAr pathway and instead promote hydrolysis of the nitrile groups of the TFTN moiety. Theoretical investigations have helped unearth the reasons for this observed difference in chemical reactivities and also explain the differences in the emission spectra. Finally, the success of the synthetic method towards multi-substitution is showcased through creation of a highly lipophilic SBF bearing an octyl unit and demonstrating its utility in in vitro cellular imaging.

Circularly polarized luminescence of natural products lycorine and narciclasine: role of excited-state intramolecular proton-transfer and test of pH sensitivity

Circularly polarized luminescence (CPL) is increasingly gaining interest not only for its applicative potentialities but also for providing an understanding of the excited state properties of chiral molecules. However, applications of CPL are mainly in the field of materials science: special organic molecules and polymers, metal (lanthanide) complexes, and organic dyes are actively and intensely studied. So far natural compounds have not been investigated much. We fill the gap here by measuring circular dichroism (CD) and CPL of lycorine and narciclasine, the most abundant known alkaloid and isocarbostyril from Amaryllidaceae, which exhibit a large spectrum of biological activities and are promising anticancer compounds. Dual fluorescence detection in narciclasine led us to unveil an occurring excited-state intramolecular proton transfer (ESIPT) process, this mechanism well accounts for the Stokes shift and CPL spectra observed in narciclasine. The same molecule is interesting also as a pH chiroptical switch. Both in absorption and emission, lycorine and narciclasine are also studied computationally via density functional theory (DFT) calculations further shedding light on their properties.

Efficient Circularly Polarized Electroluminescence from Achiral Luminescent Materials

Circularly polarized electroluminescence (CP-EL) is generally produced in organic light-emitting diodes (OLEDs) based on special CP luminescent (CPL) materials, while common achiral luminescent materials are rarely considered to be capable of direct producing CP-EL. Herein, near ultraviolet CPL materials with high photoluminescence quantum yields and good CPL dissymmetry factors are developed, which can induce blue to red CPL for various achiral luminescent materials. Strong near ultraviolet CP-EL with the best external quantum efficiencies (η_ext s) of 9.0 % and small efficiency roll-offs are achieved by using them as emitters for CP-OLEDs. By adopting them as hosts or sensitizers, commercially available yellow-orange achiral phosphorescence, thermally activated delayed fluorescence (TADF) and multi-resonance (MR) TADF materials can generate intense CP-EL, with high dissymmetry factors and outstanding η_ext s (30.8 %), demonstrating a simple and universal avenue towards efficient CP-EL.

An indolo[3,2,1-jk]carbazole-fused multiple resonance-induced thermally activated delayed fluorescence emitter for an efficient narrowband OLED

By inserting a tricoordinate B atom into an indolo[3,2,1-jk]carbazole precursor, an efficient fused multiple resonance-induced thermally activated delayed fluorescence emitter was prepared, which exhibits a narrowband emission and a considerable reverse intersystem crossing rate. The corresponding organic light-emitting diode displays an external quantum efficiency of 27.2% with a suppressed efficiency roll-off.

Theoretical perspective of relationship between molecular structure and luminescence properties for circularly polarized thermally activated delayed fluorescence

Circularly polarized luminescence (CPL) molecules with thermally activated delayed fluorescence (TADF) features show promising applications in high-efficiency circularly polarized organic light emitting diodes (CP-OLEDs). Herein, a pair of chiral molecules (R)-ImNT and (S)-ImNT are studied, two kinds of conformations are found by molecular dynamic conformation search, namely the quasi-axial and the quasi-equatorial conformations. Moreover, molecule with quasi-axial conformation is conducive to achieve outstanding CPL properties due to the large contributions of chiral groups to natural transition orbitals. While the energy gaps for quasi-equatorial conformations are significantly reduced and spin-orbit coupling effects between them are obviously increased. In addition, the quasi-equatorial configuration can facilitate the reverse intersystem crossing process to achieve remarkable TADF feature. Relationships between molecular geometries and CPL as well as TADF properties are revealed. Our research elucidates the relationship between geometric structure and luminescence mechanism, which could provide valuable insights for the design of efficient CPL-TADF emitters.

Chiral Conjugated Thermally Activated Delayed Fluorescent Polymers for Highly Efficient Circularly Polarized Polymer Light-Emitting Diodes

Two novel chiral conjugated polymers R-P and S-P designed and synthesized from a pair of circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers are presented in this work. The two polymers exhibited excellent TADF properties with small singlet-triplet energy gaps (ΔE_ST) of 0.045 and 0.061 eV and relatively high photoluminescence quantum yields (PLQYs) of 72 and 76%, respectively. Besides, intense mirror-image circularly polarized luminescence signals were detected from R-P and S-P in both solution and film states with dissymmetry factors (|g_lum|) of up to 1.9 × 10^-3. Furthermore, solution-processed circularly polarized polymer light-emitting diodes (CP-PLEDs) fabricated with R-P and S-P achieved high maximum external quantum efficiencies of 14.9 and 15.8% and high maximum brightness (L_max) of 8940 and 12,180 cd/m² with yellowish-green emission peaks at 546 and 544 nm, respectively. Moreover, intense circularly polarized electroluminescence signals with electroluminescence dissymmetry factors (g_EL) of -1.5 × 10^-3 and +1.6 × 10^-3 were detected from the CP-PLED devices fabricated with R-P and S-P, respectively.

D-π*-A type planar chiral TADF materials for efficient circularly polarized electroluminescence

Planar chiral organic fluorescent materials that exhibit high chiral stability, high efficiency and circularly polarized luminescence (CPL) currently remain an unresolved issue despite their promising applications in optical encryption and 3D-display. Herein, a pair of new donor-chiral π-acceptor (D-π*-A) type planar chiral thermally activated delayed fluorescence (TADF) enantiomers, namely R/S-PXZ-PT, are developed. Such a D-π*-A type structure completely suppresses the racemisation of the planar chirality, making it possible to prepare circularly polarized organic light-emitting diodes (CP-OLEDs) by vacuum deposition processing. Moreover, this design perfectly integrates the chiral unit into the luminescent unit to achieve intense CPL activity with luminescence asymmetry factors (g_lum) of ±1.9 × 10^-3. Notably, the enantiomer-based devices exhibit a yellow coloured emission with a maximum external quantum efficiency (EQE) of 20.1%, and mirror-image circularly polarized electroluminescence signals with electroluminescence dissymmetry factors (g_EL) of +1.5 × 10^-3/-1.3 × 10^-3. This work not only enriches the diversity of chiral TADF molecular design, but also provides a new perspective for the development of highly-efficient CP-OLEDs with stable planar chiral TADF materials.

TADF-Sensitized Fluorescent Enantiomers: A New Strategy for High-Efficiency Circularly Polarized Electroluminescence*

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 ΔE_ST accompanied by small k_r , 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 g_lum values, TSCP-type CP-OLEDs with excellent overall performances can be realized.

High-Efficiency Circularly Polarized Electroluminescence from TADF-Sensitized Fluorescent Enantiomers

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 k_r of 7.8×10⁷  s^-1 , and intense CPL activities with |g_lum | 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 g_EL values of +1.8×10^-3 and -1.4×10^-3 , but also display fast start-up featuring with low V_T 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 EQE_max 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.

Chiral polymer hosts for circularly polarized electroluminescence devices

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (g_abs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (g_PL) of the order of 10⁻³ were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of g_abs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (g_EL) of 1.09 × 10⁻⁴ and −1.02 × 10⁻⁴ at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications.

Integrating molecular rigidity and chirality into thermally activated delayed fluorescence emitters for highly efficient sky-blue and orange circularly polarized electroluminescence

By integrating high molecular rigidity and stable chirality, two pairs of D*-A type circularly polarized thermally activated delayed fluorescence (CP-TADF) emitters with an almost absolute quasi-equatorial conformer geometry and excellent photoluminescence quantum efficiencies (PLQYs) are developed, achieving state-of-the-art electroluminescence performance among blue and orange circularly polarized organic light-emitting diodes (CP-OLEDs).

Solution-Processed White Circularly Polarized Organic Light-Emitting Diodes Based on Chiral Binaphthyl Emitters

By combining the blue and orange CPL or functionalized bis-benzoxanethones emitters (S-/R-BN-tCz and S-/R-BN-PXZ), warm white CP-OLEDs were fabricated using solution-processed single emitting layer strategy. The successful realization of white CP-EL benefited from the same stable binaphthyl chirality and similar rigid structure of the two emissive CPL emitters. The devices exhibited the low turn-on voltage of ≈4.3 V, maximum luminance of ≈10200 cd m^-2 and maximum current efficiency of ≈2.0 cd A^-1 . Most significantly, the devices with CIE coordinates of (0.32, 0.45) displayed intense CP-EL signals in the spectral range of 450 to 650 nm, and showed stable g_EL values of ≈10^-3 as the luminance increased from 100 to 6000 cd m^-2 . To the best of our knowledge, this work provides for the first time a simple and feasible strategy to fabricate solution-processed white CP-OLEDs based on the co-doping of the CPL emitters.

Enantiomeric MOF Crystals Using Helical Channels as Palettes with Bright White Circularly Polarized Luminescence

The host-guest chemistry of metal-organic frameworks (MOFs) has enabled the derivation of numerous new functionalities. However, intrinsically chiral MOFs (CMOFs) with helical channels have not been used to realize crystalline circularly polarized luminescence (CPL) materials. Herein, enantiomeric pairs of MOF crystals are reported, where achiral fluorophores adhere to the inner surface of helical channels via biology-like H-bonds and hence inherit the helicity of the host MOFs, eventually amplifying the luminescence dissymmetry factor (g_lum ) of the host l/d-CMOF (±1.50 × 10^-3 ) to a maximum of ±0.0115 for the composite l/d-CMOF⊃fluorophores. l/d-CMOF⊃fluorophores in pairs generate bright color-tunable CPL and almost ideal white CPL (0.33, 0.32) with a record-high photoluminescence quantum yield of ≈30%, which are further assembled into a white circularly polarized light-emitting diode. The present strategy opens a new avenue for propagating the chirality of MOFs to realize universal chiroptical materials.

An axially chiral thermally activated delayed fluorescent emitter with a dual emitting core for a highly efficient organic light-emitting diode

An axially chiral TADF emitter with a dual-emitting-core showed a high PLQY and EQE (20.8%), while its enantiomers also exhibited CPL properties.