Circularly Polarized Luminescence Signals Research Articles

Stimulating and harnessing circularly polarized luminescence of helically assembled carbonized polymer dots via interfacial dynamics

AbstractStimulating and harnessing circularly polarized luminescence (CPL) is not only a sine qua non for fundamentally unveiling chirogenesis in physical chemistry, but also a pivotal prerequisite for implementation of such phenomenon in research fields including chiral optoelectronics and theranostics. Herein, red‐emissive carbonized polymer dots (CPDs)‐based helical structures were synthesized in this work via biomolecule‐tailored organic–inorganic co‐assembly strategy. The surface states‐related chirality exhibits enhanced circular dichroism (CD) and CPL activities with anisotropic factors as high as gCD,max = 5.4 × 10−3 and glum,max = 1.5 × 10−2, respectively. The obtained CPL signals can be further manipulated in an excitation‐dependent manner, indicating that a synergistic‐competition phenomenon exists between configurational chirality and intermolecular energy‐transfer dynamics, which is further supported by simulations based on density function theory (DFT). Such tunable CPL behavior triggers revolutionary designs and applications of these chiral CPDs into the realm of chirality‐related biological issues and next‐generation chiral optoelectronics.

A supramolecular assembly-based strategy towards the generation and amplification of photon up-conversion and circularly polarized luminescence.

For the molecular properties in which energy transfer/migration is determinantal, such as triplet-triplet annihilation-based photon up-conversion (TTAUC), the overall performance is largely affected by the intermolecular distance and relative molecular orientations. In such scenarios, tools that may steer the intermolecular interactions and provide control over molecular organisation in the bulk, become most valuable. Often these non-covalent interactions, found predominantly in supramolecular assemblies, enable pre-programming of the molecular network in the assembled structures. In other words, by employing supramolecular chemistry principles, an arrangement where molecular units are arranged in a desired fashion, very much like a Lego toy, could be achieved. This leads to enhanced energy transfer from one molecule to other. In recent past, chiral luminescent systems have attracted huge attention for producing circularly polarized luminescence (CPL). In such systems, chirality is a necessary requirement. Chirality induction/transfer through supramolecular interactions has been known for a long time. It was realized recently that it may help in the generation and amplification of CPL signals as well. In this review article we have discussed the applicability of self-/co-assembly processes for achieving maximum TTA-UC and CPL in various molecular systems.

Plasmon-coupled circularly polarized luminescence: generation and enhancement

Two efficient methods to modulate circularly polarized luminescence (CPL) signals by plasmonic metal nanoparticles: amplified and induced CPL signals.

The Role of Surface Groups in Dictating the Chiral-Solvent-Induced Assembly of Carbon Dots into Structures Exhibiting Circularly Polarized Luminescence.

Here, the use of achiral nanoparticles and solvent-induced chirality transfer is combined for the making of large structures exhibiting chiroptical properties in the form of circularly polarized luminescence (CPL). The nanoparticles that the authors use are carbon dots (C-Dots) that are known for their bright luminescence and the ability to tune their surface moieties by using different precursors in their synthesis. Here, the result of adding the chiral solvent limonene into an aqueous solution of various C-Dots is explored, differentiated by their surface group. It is shown that only nitrogen-containing C-Dots with amine functional groups see the emergence of a CPL signal and the formation of a large fibrillar assembled structure. The various forces happening in the interface between the C-Dots and the limonene phase and the role of the amine groups in both the chirality transfer interactions and the interactions between C-Dots in the assembly process are discussed, whereas these two processes intertwine with each other. The ability to form fluorescent chiral structures exhibiting CPL from achiral nanoparticles and the understanding of the various interactions in this process are both important to the rationale design of any supramolecular chiral assemblies.

Reversible Chiral Optical Switching Based on Co-Assembled Spiropyran Gels.

In recent years, it has been very interesting to dynamically adjust the emission of circularly polarized luminescence (CPL) materials through external stimulation due to their applications and the fundamental interest in them. In this work, luminescence-tunable and light-responsive supramolecular co-assembly CPL-active materials are fabricated by mixing an achiral functional spiropyran (SP-COOH) molecule with a chiral gelator. The spiropyran achieves a reversible change between a white closed ring state spiropyran and a purple zwitterionic merocyanine state in supramolecular co-assembly gels under alternate visible (vis) and ultraviolet (UV) light irradiation. The gel shows strong CPL signals due to the chirality transfer in co-assembly systems. These signals could change reversibly under alternate exposure to UV and vis light. Therefore, utilizing the multistimulus-responsive CPL signals in different states, a CPL switch of the supramolecular system signal according to the combinatorial control of UV-vis light irradiation is constructed.

Circularly polarized luminescence of pinene-modified tetradentate platinum(II) enantiomers containing fused 5/6/6 metallocycles

In this study, a couple of tetradentate Pt(II) enantiomers ((−)-1 and (+)-1) and a couple of tetradentate Pt(IV) enantiomers ((−)-2 and (+)-2) containing fused 5/6/6 metallocycles have been synthesized by controlling reaction conditions. Two valence forms could transform into each other through mild chemical oxidants and reductants. Single-crystal X-ray diffraction confirms the structures of (−)-1 and (−)-2. The coordination sphere of the Pt(II) cation in (−)-1 displays a distorted square-planar geometry and a platinum centroid helix chirality. In contrast, the structure of (−)-2 reveals a distorted octahedral geometry. The solution and the solid of (−)-1 are highly luminescent. Complex (−)-1 shows a prominent aggregation-induced emission enhancement (AIEE) behavior in DMSO/water solution with emission quantum yield (Φem) up to 73.2%. Furthermore, highly phosphorescent Pt(II) enantiomers exhibit significant circularly polarized luminescence (CPL) with a dissymmetry factor (glum) of order 10−3 in CH2Cl2 solutions at room temperature. Symmetrically appreciable CPL signals are observed for the enantiomers (−)-1 and (+)-1.

In Situ Regulation of Microphase Separation-Recognized Circularly Polarized Luminescence via Photoexcitation-Induced Molecular Aggregation.

Circularly polarized luminescence (CPL) has attracted great interest owing to its extensive optical information and chiral structural dependence. However, rationally regulating solid-phase CPL signals remains difficult because of the close packing of molecules in solid-state materials and the lack of structural visualization. In this work, we proposed a microphase-separation-recognized CPL regulation strategy via coassembly of a hexathiobenzene-based luminophore and chiral block copolymer (cBCP) with in situ photocontrollability. As a consequence to the continuous increase in the luminophore-to-cBCP ratio, the CPL signal of the supramolecular system exhibited an increasing trend until a critical point. Then, further increasing the ratio stretched the helical pitch of cBCP, which led to CPL reduction. With the photoexcitation-induced molecular aggregation of the luminophore, which was implemented using in situ photoirradiation, the helical pitch was retracted along with the restoration of the CPL signal. These processes were fully recognized and monitored by the microphase-separated nanomorphological change of the coassembled system, which indicated that such a structural contrast could be an effective method for rationally regulating the supramolecular chiropticity of solid-state materials.

Anion-Driven Circularly Polarized Luminescence Inversion of Unsymmetrical Europium(III) Complexes for Target Identifiable Sensing.

Anion-responsive sign inversion of circularly polarized luminescence (CPL) was successfully achieved by N3O6-type nona-coordinated europium(III) (Eu3+) complexes [(R)-1 and (S)-1] composed of a less-hindered unsymmetrical N3-tridentate ligand (a chiral bis(oxazoline) ligand) and three O2-chelating (β-diketonate) ligands. Here, (R)-1 exhibited a positive CPL signal (IL – IR > 0) at the 5D0 → 7F1 transition of Eu3+, which can be changed to a negative sign (i.e., IL – IR > 0 → IL – IR < 0) by the coordination of trifluoroacetic anions (CF3COO–) to the Eu3+ center. However, (R)-1 preserved the original positive CPL signal (i.e., IL – IR > 0 → IL – IR > 0) in the presence of a wide range of competing anions (Cl–, Br–, I–, BF4–, ClO4–, ReO4–, PF6–, OTf–, and SbF6–). Thus, (R)-1 acts as a smart target identifiable probe, where the CPL measurement (IL – IR) can distinguish the signals from the competing anions (i.e., IL – IR < 0 vs IL – IR > 0) and eliminate the background emission (i.e., IL – IR = 0) from the background emitter (achiral luminescent compounds). The presented approach is also promising in terms of bio-inspired optical methodology because it enables nature’s developed chiral sensitivity to use circularly polarized light for object identification (i.e., IL – IR = 0 vs | IL – IR | > 0).

Two Cholesterol-Containing Pyrene Derivatives: Subtle Spacer Difference, Diverse Stimuli-Responsive Luminescence, Chirality, and Self-Assembly Behaviors.

Two chiral molecules 1 and 2 were designed and synthesized with a pyrene moiety directly linked to a chiral cholesterol moiety and connected through a methylene spacer, respectively. Influence of the spacer on their stimuli-responsive luminescence, chirality, and self-assembly behaviors was systematically investigated. Molecules 1 and 2 had similar aggregation-induced emission enhancement (AIEE) in solution, because of carrying the same fluorescence moiety. Both molecules displayed mechanochromism (MC) property but with different color contrast, whereas only 2 showed mechanoluminescence (ML) activity. When doping in liquid crystal molecule 5CB, both molecules induced the formation of chiral nematic liquid crystals (N*-LCs) with strong circularly polarized luminescence (CPL). Molecule 2 induced single handedness signal, irrespective of doping ratios, while 1-doped N*-LCs showed an inversion of CPL signal from negative to positive upon the increase of doping ratios. Molecules 1 and 2 also self-assembled into different coassemblies with 5CB. Their distinct behaviors were attributed to the influence of the methylene spacer, which caused different molecular conformation and steric bulkiness; accordingly, it changed intermolecular interactions and molecular packing of the two molecules and led to diverse chirality and luminescence. This work provided important model molecules to better understand the molecular structure-property relationship and guide the design of novel functional molecules.

Tuning the Circularly Polarized Luminescence of Supramolecules via Self-Assembly Morphology Control.

Tuning the circularly polarized luminescence (CPL) is a paramount yet challenging issue in the research field of chiral materials. Here, the chiral supramolecules were constructed with a chiral inducer LL-diphenylalanine (LPFF) and a triphenyl-1,3,5-triazine-derived achiral molecule (DMAC-TRZ) to generate differentiated aggregates, giving rise to tunable responses of CPL. Specifically, the well-defined supercrystallines had an exceptional superior CPL emission located at 485 nm with a large luminescence dissymmetry factor (glum) value as high as +0.16, whereas the formed organic gel possessed a relatively strong CPL emission peaked at 495 nm with a glum value of -0.04 in respect to the water fraction about 50%. The distinguished glum value was assigned to the choice of spatial arrangement of the π-chromophores of DMAC-TRZ responding to the volume water fraction in the H2O/DMSO system, resulting in a tunable glum value. This strategy provides an efficient way to regulate CPL signals by modulating the π-stacking way of organic materials responding to external stimuli.

Discriminating Chiral Supramolecular Motions by Circularly Polarized Luminescence.

Molecular motions are closely associated with the behaviors and properties of organic materials. However, monitoring molecular motions is challenging. Herein, a chiral supramolecular system consisting of L-/D-phenylalanine (LPF/DPF) as a chiral inducer and an achiral tetraphenylethene derivative (TPEF) as a molecular rotor has been proposed and explored for real-time discriminating the supramolecular motions by the visualization of circularly polarized luminescence (CPL) signal variations. Derived from the ordered molecular motions of TPEF induced by LPF/DPF, highly organized aggregates have been progressively assembled in a controlled manner with differentiated morphologies, including spherical particles, one-dimensional fibers, and floor-shaped supercrystals. Notably, increasing level of ordered aggregates, in turn, led to quenching emissions, while the CPL signals have been dramatically amplified accompanying by a sharp enhancement of luminescence dissymmetry factors (glum ) from nearly 0 to -0.1. The significant amplification of CPL is attributed to the ordered aggregates of supramolecules, leading to the decrease of electric transition dipole moments in supramolecular system. As a result of the chiral supramolecular motions powered by supramolecular crystallization, the supramolecular motions are conveniently discriminated by visual CPL signal variation with an enhancement of glum value from 0 to -0.1 in real time.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

Encoding Supramolecular Chiral Self‐Assembly with Photo‐Controlled Circularly Polarized Luminescence by Overcrowded Alkene‐Based Bis‐PBI Modulators

AbstractDeveloping photoresponsive circularly polarized luminescence (CPL) materials is an essential step for biosensing and biomedical applications. However, fabricating CPL assemblies rooted in the chirality amplification and transmission of the molecular building blocks, which simultaneously show photo‐controllable CPL signals, remains challenging. Herein, a molecular building block containing an overcrowded‐alkene core and bis‐PBI (MPBI) was designed. Importantly, the enantiopure MPBI can self‐assemble into well‐organized nanofibers via π‐π stacking interactions and enable the transmission of the intrinsic chirality, providing opposite CPL signals. The photoisomerization of MPBI induced a transformation from nanofibers to discrete nanospheres, accompanied by a gradually decreased CPL signal. The results demonstrated the development of photo‐controllable CPL materials from the assembly of chiral MPBI, which provides an alternatively facile strategy to fabricate CPL‐active materials and would offer opportunities for future biosensing and biomedical applications.

Encoding Supramolecular Chiral Self-Assembly with Photo-Controlled Circularly Polarized Luminescence by Overcrowded Alkene-Based Bis-PBI Modulators.

Developing photoresponsive circularly polarized luminescence (CPL) materials is an essential step for biosensing and biomedical applications. However, fabricating CPL assemblies rooted in the chirality amplification and transmission of the molecular building blocks, which simultaneously show photo-controllable CPL signals, remains challenging. Herein, a molecular building block containing an overcrowded-alkene core and bis-PBI (MPBI) was designed. Importantly, the enantiopure MPBI can self-assemble into well-organized nanofibers via π-π stacking interactions and enable the transmission of the intrinsic chirality, providing opposite CPL signals. The photoisomerization of MPBI induced a transformation from nanofibers to discrete nanospheres, accompanied by a gradually decreased CPL signal. The results demonstrated the development of photo-controllable CPL materials from the assembly of chiral MPBI, which provides an alternatively facile strategy to fabricate CPL-active materials and would offer opportunities for future biosensing and biomedical applications.

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Circularly polarized luminescence of polymers with coil to helix transformation in water system triggered via metal coordination

Circularly polarized luminescence (CPL) of conjugated polymers is promising functional materials for a wide range application, particularly in the field of chiral optoelectronic devices. It is critical yet challenging to endow these materials against varied environment change, such as polarity of water, due to the destruction of the induced helicity of conjugated polymers by water hydrogen bonding. In this contribution, a series of aqueous phase CPL-active materials are constructed through the synergistic effect of hydrogen bonding and metal coordination. The fluorescent random coil amino acid-based poly( N -propargylamide) exhibiting obvious CD and CPL effects are induced by metal ions in aqueous solution. The conformational transition from coil to helix and the CPL performance are distinctly depicted via the CD, CPL signals and noticeably red-shifted UV–vis absorption. Moreover, the luminescence dissymmetry factor (| g lum |) values of the induced helical polymers were up to 8.07 × 10 −3 and 2.73 × 10 −2 , respectively, in aqueous solution and thin films. It was found that the successful induction of aqueous phase CPL-active polymer attribute to chiral amplification and aggregation-enhanced emission (AEE) effect of contracted cis-cisoidal helical main chain. These results indicated a general and simple approach for the construction of aqueous phase CPL materials, and a possible relationship between geometric structure of helical conformation and the CPL-activity induction of optically inactive polymers are simultaneously established. This contribution broadens practically chiroptical applications of CPL materials in water environment and enriches the synthetic types of CPL materials. • The CPL-active polymer based on cis-cisoid helix in aqueous solution and thin films states is prepared. • The | g lum | value of the prepared polymer in aqueous solution and films are as high as to 8.07 × 10 −3 and 2.73 × 10 −2 , respectively. • The successful trigger of CPL-activity attribute to chiral amplification and aggregation-enhanced emission (AEE) effect of one-handed helical structure.

Signal Inversion and Amplification of Circularly Polarized Luminescence in a Poly(phenylacetylene)-Based Composite System Assisted by Achiral PMMA.

Multichannel regulable circularly polarized luminescence (CPL) is fascinating because of its fundamental and application interest. There are few reports on helical sense (P-/M-helix) modulation and chiral signal amplification of polyacetylenes with the assistance of achiral polymers and further applications in precisely and conveniently regulating CPL handedness and magnitude. Herein, a helical poly(phenylacetylene)-based CPL-active system was constructed, in which CPL inversion occurred by adding achiral PMMA into a helical poly(phenylacetylene)-CHCl3 solution. Significantly, there is almost 10 times magnification of luminescence dissymmetry factor values (|glum|) during this process. The above phenomena could be ascribed to the PMMA-assisted polyene backbone elongation and the formation of a more ordered helical structure for the poly(phenylacetylene)s. More interestingly, the CPL signal can be facilely inverted and switched by simply changing the thickness of the PPhAD/PMMA layer. The temperature-driven dynamic CPL handedness inversion and magnitude modulation can also be achieved. Based on the multiple regulations for CPL, logic operations were developed, and the practical application is further facilitated by designing various CPL patterns. This study establishes effective and convenient strategies to switch the handedness, magnitude, and wavelength of CPL, which may generate a breakthrough in the manufacturing of CPL-active smart materials and devices with promising application potential.

Circularly Polarized Luminescence Active Supramolecular Nanotubes Based on PtII Complexes That Undergo Dynamic Morphological Transformation and Helicity Inversion.

Circularly polarized luminescence (CPL) with tunable chirality is currently a challenging issue in the development of supramolecular nanomaterials. We herein report the formation of helical nanoribbons which grow into helical tubes through dynamic helicity inversion. For this, chiral PtII complexes of terpyridine derivatives, namely S-trans-1 and R-trans-1, with respective S- and R-alanine subunits and incorporating trans-double bonds in the alkyl chain were prepared. In DMSO/H2 O (5 : 1 v/v), S-trans-1 initially forms a fibrous self-assembled product, which then undergoes dynamic transformation into helical tubes (left-handed or M-type) through helical ribbons (right-handed or P-type). Interestingly, both helical supramolecular architectures are capable of emitting CPL signals. The metastable helical ribbons show CPL signals (glum =±4.7×10-2 ) at 570 nm. Meanwhile, the nanotubes, which are the thermodynamic products, show intense CPL signals (glum =±5.6×10-2 ) at 610 nm accompanied by helicity inversion. This study provides an efficient way to develop highly dissymmetric CPL nanomaterials by regulating the morphology of metallosupramolecular architectures.

Structural Origin of Enhanced Circularly Polarized Luminescence in Hybrid Manganese Bromides

AbstractChiral hybrid metal halides with a high dissymmetry factor (glum) and a superior photoluminescence quantum yield (PLQY) are promising candidates for circularly polarized luminescence (CPL) light sources. Here, we report eight new chiral hybrid manganese halides, crystallizing in the non‐centrosymmetric space group P212121 and showing intense CPL emissions. Oppositely‐signed circular dichroism (CD) and CPL signals are detected according to the R‐ and S‐configurations of the chiral alkanolammonium cations. Time‐resolved PL spectra show long averaged decay lifetimes up to 1 ms for (R‐3‐quinuclidinol)MnBr3 (R‐1). The glum of polycrystalline samples for coordinated structures (23×10−3) is more than doubled compared with the non‐coordinated ones (8.5×10−3), due to the structural variations. R‐1 exhibit both a high glum and a high PLQY (50.2 %). The effective chirality transfer mechanism through coordination bonds, with strongly emissive MnII centers, enables a new class of high‐performance CPL materials.

Structural Origin of Enhanced Circularly Polarized Luminescence in Hybrid Manganese Bromides.

Chiral hybrid metal halides with a high dissymmetry factor (glum ) and a superior photoluminescence quantum yield (PLQY) are promising candidates for circularly polarized luminescence (CPL) light sources. Here, we report eight new chiral hybrid manganese halides, crystallizing in the non-centrosymmetric space group P21 21 21 and showing intense CPL emissions. Oppositely-signed circular dichroism (CD) and CPL signals are detected according to the R- and S-configurations of the chiral alkanolammonium cations. Time-resolved PL spectra show long averaged decay lifetimes up to 1 ms for (R-3-quinuclidinol)MnBr3 (R-1). The glum of polycrystalline samples for coordinated structures (23×10-3 ) is more than doubled compared with the non-coordinated ones (8.5×10-3 ), due to the structural variations. R-1 exhibit both a high glum and a high PLQY (50.2 %). The effective chirality transfer mechanism through coordination bonds, with strongly emissive MnII centers, enables a new class of high-performance CPL materials.