Circularly Polarized Luminescence Research Articles

Dynamic Near-Infrared Circularly Polarized Luminescence Encoded by Transient Supramolecular Chiral Assemblies.

Circularly polarized luminescence (CPL) is promising for applications in many fields. However, most systems involving CPL are within the visible range; near‒infrared (NIR) CPL‒active materials, especially those that exhibit high glum values and can be controlled spatially and temporally, are rare. Herein, dynamic NIR‒CPL with a glum value of 2.5[[EQUATION]]10‒2 was achieved through supramolecular coassembly and energy transfer strategies. The chiral assemblies formed by the coassembly between adenosine triphosphate (ATP) and a pyrene derivative exhibit a red CPL signal (glum of 10‒3). The further introduction of sulfo‒cyanine5 resulted in a cooperative energy transfer process, which not only aroused the NIR CPL but also increased the glum value to 10‒2. Temporal control of these chiral assemblies was realized by introducing alkaline phosphatase to fabricate a biomimetic enzyme‒catalyzed network, allowing the dynamic NIR CPL signal to be turned on. Based on these enzyme-regulated temporally controllable dynamic CPL-active chiral assemblies, a multilevel information encryption system was further developed. Our work provides a pioneering example for constructing dynamic NIR CPL materials holding the ability to perform temporal control via the supramolecular assembly strategy, which is expected to aid in the design of supramolecular complex systems that more closely resemble natural biological systems.

Achiral Solvent Inversed Helical Pathway and Cosolvent Controlled Excited-State "Majority Rule" in Enantiomeric Dansulfonamide Assemblies.

Achiral solvents are commonly utilized to induce the self-assembly of chiral molecules. This study demonstrates that achiral solvents can trigger helicity inversion in the assemblies of dansyl amphiphiles and control the excited-state "majority rule" in assemblies composed of pure enantiomers, through variation of the cosolvent ratio. Specifically, enantiomers of dansyl amphiphiles self-assemble into helical structures with opposite handedness in methanol (MeOH) and acetonitrile (MeCN), together with inversed circular dichroism and circularly polarized luminescence (CPL) signals. When a mixture of MeOH and MeCN is employed, the achiral cosolvents collectively affect the CPL of the assemblies in a way similar to that of "mixed enantiomers". The dominant cosolvent governs the CPL signal. As the cosolvent composition shifts from pure MeCN to MeOH, the CPL signals undergo a significant inversion and amplification, with two maxima observed at ≈20% MeOH and 20% MeCN. This study deepens the comprehension of how achiral solvents modulate helical nanostructures and their excited-state chiroptical properties.

Magnetic Assembly of Magnetite/Perovskite Hybrid Nanorods for Circularly Polarized Luminescence

AbstractMagnetic fields are uniquely valuable for creating colloidal nanostructured materials, not only providing a means for controlled synthesis but also guiding their self‐assembly into distinct superstructures. In this study, a magnetothermal process for synthesizing hybrid nanostructures comprising ferrimagnetic magnetite nanorods coated with fluorescent perovskite nanocrystals is reported and their magnetic assembly into superstructures capable of emitting linear and circularly polarized light are demonstrated. Under UV excitation, the superstructures assembled in a liner magnetic field produce linear polarized luminescence, and those assembled in a chiral magnetic field exhibit strong circularly polarized luminescence (CPL) with a glum value up to 0.44 (±0.004). The CPL is believed to originate from the dipolar interaction between neighboring perovskite nanocrystals attached to the chiral assemblies and the chiral‐selective absorption of the perovskite emission by the magnetite phase. The magnetic synthesis and assembly approaches and the resulting distinctive chiral superstructures are anticipated to open up new avenues for designing diverse functional chiroptical devices.

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

Amplified Circularly Polarized Luminescence Behavior in Chiral Co-assembled Liquid Crystal Polymer Films via the Strategic Manipulation of Chiral Inducers.

One of the most important factors for the future application of circularly polarized luminescence (CPL) materials is their high dissymmetry factors (gem), and more and more studies are working tirelessly to focus on increasing the gem value. Herein, we chose an achiral liquid crystal polymer (LC-P) and two chiral binaphthyl-based inducers (R/S-3 and R/S-6) with different substitution positions (3,3' positions for R/S-3 and 6,6' positions for R/S-6) to construct chiral co-assemblies and explored their induced amplification CPL behaviors. Interestingly, after the thermal annealing treatment, this kind of chiral co-assembly (R/S-3)0.05-(LC-P)0.95 can emit a superior CPL signal (|gem| = 0.31 and λem = 424 nm), which achieves about 13-fold signal amplification in the spin-coated film, compared to (R/S-6)0.1-(LC-P)0.9 (|gem| = 0.023 and λem = 424 nm). This is because (R/S-3)0.05-(LC-P)0.95 could further co-assemble to form a more ordered arrangement LC state and generate regular helix nanofibers than that of (R/S-6)0.1-(LC-P)0.9. This work provides an efficient method for synthesizing high-quality CPL-active materials through the strategic manipulation of the structure of chiral binaphthyl-based inducers in chiral co-assembled LCP systems.

Cyclic Azahelicene Dimers ShowingBright Circularly Polarized Luminescence and Selective Fluoride Recognition.

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with(1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigidp-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPLin the visible region,and thehighCPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Cyclic Azahelicene Dimers Showing Bright Circularly Polarized Luminescence and Selective Fluoride Recognition

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed‐aza[7]helicenes with (1R)‐menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid p‐frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (BCPL) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region.

Helically Chiral π-Expanded Azocines Through Regioselective Beckmann Rearrangement and Their Charged States.

We report a synthetic approach to p-expanded [6]helicenes incorporating tropone and azocine units in combination with a 5-membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8-membered lactam, azocine, and amine units. As shown by X-ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high-performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near-infrared (NIR) absorption bands extending beyond 3000nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry.

Helically Chiral π‐Expanded Azocines Through Regioselective Beckmann Rearrangement and Their Charged States

We report a synthetic approach to p‐expanded [6]helicenes incorporating tropone and azocine units in combination with a 5‐membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8‐membered lactam, azocine, and amine units. As shown by X‐ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high‐performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near‐infrared (NIR) absorption bands extending beyond 3000 nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry.

Tunable circularly polarized luminescence behaviors caused by the structural symmetry of achiral pyrene-based emitters in chiral co-assembled systems

The regulation of circularly polarized luminescence (CPL) behavior is of great significance for practical applications. Herein, we deliberately designed three achiral pyrene derivatives (Py-1, Py-2, and Py-3) with different butoxy-phenyl substituents and the chiral binaphthyl-based inducer (R/S-B) with anchored dihedral angle to construct chiral co-assemblies, and explored their induced CPL behaviors. Interestingly, the resulting co-assemblies demonstrate tunable CPL emission behaviors caused by the structural symmetry effect of achiral pyrene-based emitters during the chiral co-assembly process. And in spin-coated films, the dissymmetry factor (gem) values were 9.1 × 10-3 for (R/S-B)1-(Py-1)10, 5.6 × 10-2 for (R/S-B)1-(Py-2)7, and 8.6 × 10-4 for (R/S-B)1-(Py-3)1, respectively. The strongest CPL emission (|gem| = 5.6 × 10-2, λem = 423 nm, QY = 34.8 %) was detected on (R/S-B)1-(Py-2)7 due to the formation of regular and ordered helical nanofibers through the strong π-π stacking interaction between the R/S-B and the achiral Py-2 emitter. The strategy presented here provides a creative approach for progressively regulating CPL emission behaviors in the chiral co-assembly process.

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence

Circularly polarized luminescence (CPL)‐active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high‐energy (HE) photons for excitation to emit low‐energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion‐downshifting‐synergistic systems offers avenues for dual‐excitation or dual‐emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their senergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence.

Circularly polarized luminescence (CPL)-active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high-energy (HE) photons for excitation to emit low-energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion-downshifting-synergistic systems offers avenues for dual-excitation or dual-emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their senergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Switchable Dual Circularly Polarized Luminescence in Through-Space Conjugated Chiral Foldamers.

Organic materials with switchable dual circularly polarized luminescence (CPL) are highly desired because they can not only directly radiate tunable circularly polarized light themselves but also induce CPL for guests by providing chiral environment in self-assembled structures or serving as the hosts for energy transfer systems. However, most organic molecules only exhibit single CPL and it remains challenging to develop organic molecules with dual CPL. Herein, novel through-space conjugated chiral foldamers are constructed by attaching two biphenyl arms to the 9,10-positions of phenanthrene, and switchable dual CPL with opposite signs at different emission wavelengths are successfully realized in the foldamers containing high-polarizability substitutes (cyano, methylthio and methylsulfonyl). The combined experimental and computational results demonstrate that the intramolecular through-space conjugation has significant contributions to stabilizing the folded conformations. Upon photoexcitation in high-polar solvents, strong interactions between the biphenyl arms substituted with cyano, methylthio or methylsulfonyl and the polar environment induce conformation transformation for the foldamers, resulting in two transformable secondary structures of opposite chirality, accounting for the dual CPL with opposite signs. These findings highlight the important influence of the secondary structures on chiroptical property of the foldamers and pave a new avenue towards efficient and tunable dual CPL materials.

Switchable Dual Circularly Polarized Luminescence in Through‐Space Conjugated Chiral Foldamers

Organic materials with switchable dual circularly polarized luminescence (CPL) are highly desired because they can not only directly radiate tunable circularly polarized light themselves but also induce CPL for guests by providing chiral environment in self‐assembled structures or serving as the hosts for energy transfer systems. However, most organic molecules only exhibit single CPL and it remains challenging to develop organic molecules with dual CPL. Herein, novel through‐space conjugated chiral foldamers are constructed by attaching two biphenyl arms to the 9,10‐positions of phenanthrene, and switchable dual CPL with opposite signs at different emission wavelengths are successfully realized in the foldamers containing high‐polarizability substitutes (cyano, methylthio and methylsulfonyl). The combined experimental and computational results demonstrate that the intramolecular through‐space conjugation has significant contributions to stabilizing the folded conformations. Upon photoexcitation in high‐polar solvents, strong interactions between the biphenyl arms substituted with cyano, methylthio or methylsulfonyl and the polar environment induce conformation transformation for the foldamers, resulting in two transformable secondary structures of opposite chirality, accounting for the dual CPL with opposite signs. These findings highlight the important influence of the secondary structures on chiroptical property of the foldamers and pave a new avenue towards efficient and tunable dual CPL materials.

Longitudinal Extension of Double π-Helix Enables Near-Infrared Amplified Dissymmetry and Chiroptical Response.

Near-infrared (NIR) circularly polarized light absorbing or emitting holds great promise for highly sensitive and precise bioimaging, biosensing, and photodetectors. Aiming at designing NIR chiral molecular systems with amplified dissymmetry and robust chiroptical response, herein, we present a series of double π-helical dimers with longitudinally extended π-entwined substructures via Ullmann or Yamamoto homocoupling reactions. Circular dichroism (CD) spectra revealed an approximate linear bathochromic shift with the rising number of naphthalene subunits, indicating a red to NIR chiroptical response. Particularly, the terrylene diimide-entwined dimers exhibited the strongest CD intensities, with the maximal |Δε| reaching up to 393 M-1 cm-1 at 666 nm for th-TDI[2]; and a record-high chiroptical response (|ΔΔε|) between the neutral and dianionic species of 520 M-1 cm-1 at 833 nm for th-TDI[2]Cl was achieved upon further reduction to its dianionic state. Time-dependent density functional theory (TDDFT) calculations suggested that the pronounced intensification of the CD spectra originated from a simultaneous enhancement of both electric (μ) and magnetic (m) transition dipole moments, ultimately leading to an overall increase in the rotatory strength (R). Notably, the circularly polarized luminescence (CPL) brightness (BCPL) reached 77 M-1 cm-1 for th-TDI[2]Cl, among the highest values reported for NIR-CPL emitters. Furthermore, all chiral dianions exhibited excellent air stability under ambient conditions with half-life times of up to 10 days in N-methylpyrrolidone (NMP), which is significant for future biological applications and chiroptic switches.

Unraveling the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in aqueous host-guest complexation

In biological systems, nucleosides play crucial roles in various physiological processes. In this study, we designed and synthesized four achiral anthracene-based tetracationic nanotubes (1–4) as artificial hosts and chiroptical sensors for nucleosides in aqueous media. Notably, different nanotubes exhibit varied chirality sensing on circular dichroism (CD)/circularly polarized luminescence (CPL) spectra through the host-guest complexation, which prompted us to explore the factors influencing their chiroptical responses. Through systematic host-guest experiments, the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in the host-guest complexation was unraveled. Firstly, the CD response originates from the anthracene rings situated at the side-wall position, resulting from the right-handed (P)- or left-handed (M)-twisted conformation of the macrocyclic structure. Secondly, the CPL signal is influenced by the presence of anthracene rings at the linking-wall position, which results from intermolecular chiral twisted stacking between these anthracene rings. Therefore, these nanotubes can serve as chiroptical sensor arrays to enhance the accuracy of nucleotide recognition through principal component analysis (PCA) analysis based on the diversified CD spectra. This study provides insights for the construction of adaptive chirality from achiral nanotubes with dynamic conformational nature and might facilitate further design of chiral functional materials for several applications.

A Multiple Circularly Polarized Luminescence Regulation Platform Driven by Acid, Base, and Primary Amines

AbstractFunctional materials that exhibit circularly polarized luminescence (CPL) have shown immense potential in applications such as 3D optical displays and advanced information encryption. However, facile and efficient regulation of the multiple emission properties in chiral systems has remained a challenge due to the scarcity of suitable materials and the complexity of the systems. Herein, a multiple CPL regulation platform is fabricated by the helical co‐assembly of an aldehyde‐functionalized fluorane dye (Rhodol‐CHO, 6′‐(diethylamino)‐3′‐hydroxy‐3‐oxo‐3H‐spiro[isobenzofuran‐1,9′‐xanthene]‐4′‐carbaldehyde) and chiral liquid crystals, which can efficiently combine multiple stimuli‐responsive characteristics and high optical activity. By introducing acid, base, and compounds containing primary amino (─NH2) groups, the CPL property of the system can be easily modified. The obtained CPL systems exhibit apparent asymmetry, with glum values reaching 0.54–0.75). Further, these CPL modules are successfully applied in multi‐mode information encryption, highlighting their practical utility. Therefore, this study presents a novel strategy for developing materials with diverse CPL behaviors based on a simple‐designed platform, advancing further applications of CPL materials.

Temperature-Induced Sign Inversion of Circularly Polarized Luminescence of Binaphthyl-Bridged Tetrathiapyrenophanes.

D2-symmetric (R)-binaphthyl-bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature-induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left-handed twist excimer at low temperatures, while they form a thermodynamically favored right-handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers.

Synthesis and Characterization of a Cyclic Trimer of a Chiral Spirosilabifluorene.

A chiral shape-persistent macrocyclic compound (Si-[3]), designed by the C/Si substitution in the spiro-atom of spirobifluorene in the cyclic trimer (C-[3]), has been successfully synthesized in this study. The C/Si substitution made the spiro-conjugation and energy levels of HOMO and LUMO decrease. Due to the silicon substitution, the macrocyclic compound Si-[3] was able to be degraded by fluoride ions, but its reaction rate was slower than that of the unsubstituted spirosilabifluorene, showing the chemical stability of Si-[3]. Furthermore, the chiroptical properties of Si-[3] with D3-symmetric macrocyclic structure were investigated, and (M,M,M)-Si-[3] showed high emission quantum yield (Φf = 80%) and moderate dissymmetry factor of circularly polarized luminescence (CPL) (glum,exp = -1.2 × 10-3). According to the the time-dependent density-functional theory (TD-DFT)calculations using polarizable continuum model (PCM), the bright CPL from Si-[3] was explained by a planarization of one bisilafluorenyl moiety at the excited state, which is responsible for the almost fully-allowed radiative transition with a short emission lifetime of tf = 1.89 ns.

Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism.

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.