Dual Stimuli-Responsive High-Efficiency Circularly Polarized Luminescence from Light-Emitting Chiral Nematic Liquid Crystals

Polymeric Cholesteric Superhelix Induced by Chiral Helical Polymer for Achieving Full-Color Circularly Polarized Room-Temperature Phosphorescence with Ultra-High Dissymmetry Factor

Circularly polarized room-temperature phosphorescence (CPRTP) simultaneously featuring multiple colors and extremely high dissymmetry factor (glum) is crucial for increasing the complexity of optical characteristics and advancing further development, but such a type of CPRTP is still unprecedented. The present work develops an effective and universal strategy to achieve full-color CPRTP with ultra-high glum factors in a polymeric cholesteric superhelix network, which is constructed by cholesteric liquid crystal polymer and chiral helical polymer (CHP). Taking advantage of the high helical twisting power of CHP, the resulting polymeric cholesteric superhelix network exhibits remarkable optical activity. Significantly, by adopting a simple double-layered architectures consisting of the cholesteric superhelix film and phosphorescent films, blue-, green-, yellow-, and red-CPRTP emissions are successfully obtained, with maximum |glum| values up to 1.43, 1.39, 1.09 and 0.84, respectively. Further, a multilevel information encryption application is demonstrated based on the multidimensional optical characteristics of the full-color double-layered CPRTP architectures. This study offers new insights into fabricating polymeric cholesteric superhelix with considerable CPRTP performance in advanced photonic applications.

When quantum dots meet blue phase liquid crystal elastomers: visualized full-color and mechanically-switchable circularly polarized luminescence

Polymer-based circularly polarized luminescence (CPL) materials with the advantage of diversified structure, easy fabrication, high thermal stability, and tunable properties have garnered considerable attention. However, adequate and precise tuning over CPL in polymer-based materials remains challenging due to the difficulty in regulating chiral structures. Herein, visualized full-color CPL is achieved by doping red, green, and blue quantum dots (QDs) into reconfigurable blue phase liquid crystal elastomers (BPLCEs). In contrast to the CPL signal observed in cholesteric liquid crystal elastomers (CLCEs), the chiral 3D cubic superstructure of BPLCEs induces an opposite CPL signal. Notably, this effect is entirely independent of photonic bandgaps (PBGs) and results in a high glum value, even without matching between PBGs and the emission bands of QDs. Meanwhile, the lattice structure of the BPLCEs can be reversibly switched via mechanical stretching force, inducing on-off switching of the CPL signals, and these variations can be further fixed using dynamic disulfide bonds in the BPLCEs. Moreover, the smart polymer-based CPL systems using the BPLCEs for anti-counterfeiting and information encryption have been demonstrated, suggesting the great potential of the BPLCEs-based CPL active 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.

Stimuli-responsive luminescence from polar cyano/isocyano-derived luminophores via structural tailoring and self-assembly

Polar cyano fragments and their isomeric isocyano counterparts have attracted great attention as stimuli-responsive luminescent materials in a wide range of fields including organic light-emitting diode devices, chemical fluorescent sensors, photoelectric semiconductors, anti-counterfeit products, etc., mainly because of their typical electron-deficient activity, noncovalent recognition ability, and variable coordination capacity. The electron-deficient and polar nature of these blocks have significant effects on the properties of the cyano/isocyano-based luminophore materials, especially concerning their condensed state-dependent electronic structures. Among them, donor-acceptor (D-A) derived unimolecular and co-assembled luminophores have attracted more attention because their large delocalized structures and noncovalent interaction recognition sites can rebuild the electronic transfer character in the aggregative state, thus endowing them with outstanding stimuli-responsive luminescent behavior via intermolecular and intramolecular charge transfer in polytropic morphologies. In this perspective paper, we give a brief introduction on stimuli-responsive organic and coordinated luminophores and the documented typical design concepts and applications in recent years. It is expected that this perspective article will not only summarize the recent developments of polar cyano/isocyano-derived luminophores and their coordination compounds via structural tailoring and self-assembly but also throw light on the future of the design of more sophisticated stimuli-responsive architectures and their versatile properties.

Controllable Circularly Polarized Luminescence with High Dissymmetry Factor via Co-Assembly of Achiral Dyes in Liquid Crystal Polymer Films

Circularly polarized luminescence (CPL) materials are highly demanded due to their great potential in optoelectronic and chiroptical elements. However, the preparation of CPL films with high luminescence dissymmetry factors (glum ) remains a formidable task, which impedes their practical application in film-based devices. Herein, a facile strategy to prepare solid CPL film with a high glum through exogenous chiral induction and amplification of liquid crystal polymers is proposed. Amplification and reversion of the CPL appear when the films are annealed at the chiral nematic liquid crystalline temperature and the maximal glum up to 0.30 due to the enhancement of selective reflection. Thermal annealing treatment at different liquid crystalline states facilitates the formation of the chiral liquid phase and adjusts the circularly polarized emission. This work not only provides a straightforward and versatile platform to construct organic films capable of exhibiting strong circularly polarized emission but also is helpful in understanding the exact mechanism for the liquid crystal enhancement of CPL performance.

A Photo- and Thermo-Driven Azoarene-Based Circularly Polarized Luminescence Molecular Switch in a Liquid Crystal Host

The development of chiral optical active materials with switchable circularly polarized luminescence (CPL) signals remains a challenge. Here an azoarene-based circularly polarized luminescence molecular switch, (S, R, S)-switch 1 and (R, R, R)-switch 2, are designed and prepared with an (R)-binaphthyl azo group as a chiral photosensitive moiety and two (S)- or (R)-binaphthyl fluorescent molecules with opposite or the same handedness as chiral fluorescent moieties. Both switches exhibit reversible trans/cis isomerization when irradiated by 365 nm UV light and 520 nm green light in solvent and liquid crystal (LC) media. In contrast with the control (R, R, R)-switch 2, when switch 1 is doped into nematic LCs, polarization inversion and switching-off of the CPL signals are achieved in the resultant helical superstructure upon irradiation with 365 nm UV and 520 nm green light, respectively. Meanwhile, the fluorescence intensity of the system is basically unchanged during this switching process. In particular, these variations of the CPL signals could be recovered after heating, realizing the true sense of CPL reversible switching. Taking advantage of the unique CPL switching, the proof-of-concept for "a dual-optical information encryption system" based on the above CPL active material is demonstrated.

Achiral Dichroic Dyes-mediated Circularly Polarized Emission Regulated by Orientational Order Parameter through Cholesteric Liquid Crystals

It is noteworthy that cholesteric liquid crystal (CLC) platforms have been witnessed in high-performance circularly polarized luminescence (CPL) behaviors through the highly organized chiral co-assembled arrangement of achiral dyes. However, most CPL-active design strategies are closely relative to the helix co-assembly structure of CLC rather than achiral dyes. Herein, we developed an intriguing regulation strategy for CPL-active CLC materials. They were regulated using the orientational order parameter (SF ) of achiral dichroic dyes as an incisive probe for the order arrangement degree of achiral dyes in CLC media. The I-shaped phenothiazine derivative PHECN dye (SF =0.30) emitted a strong CPL signal (|glum |=0.47). In contrast, the T-shaped derivative (PHEBen) dye (SF =0.09) showed a weak circular polarization level (|glum |=0.07) at similar CLC textures. Most interestingly, this kind of dichroic PHECN dye with a higher SF could greatly improve the contrast ratio of CPL (Δglum =0.47) and emission intensity (ΔFL=46.0 %) at direct-current electric field compared with the T-shaped PHEBen (Δglum =0.07 and ΔFL=1.0 %) in CLC. This work demonstrates that an induced CPL emission can be mediated using achiral dichroic dye, which will open a new avenue for developing excellent CPL-active display materials.

Asymmetric Synthesis of Tetraphenylethylene Helicates and Their Full-Color CPL Emission with High glum and High Fluorescence Quantum Yield

Tetraphenylethylene (TPE) helicates with single helical handedness not only owe high fluorescence quantum yield but also possess good helical chirality, showing an excellent circularly polarized luminescence active material. In this work, a new method for directly obtaining single-handed TPE helicates has been developed. By using chiral p-phenylenediamine derivatives as an intramolecular cyclization reagent of TPE, the single-handed propeller-like conformation and stable helical chirality of the TPE unit were obtained, avoiding complicated and expensive HPLC chiral column separation. The as-prepared chiral TPE helicates displayed strong emission with an almost quantitative fluorescence quantum yield (Φf) and strong circularly polarized luminescence (CPL). In addition, the chirality and CPL signals of the TPE helicates could be significantly magnified by the helical arrangement together with 4'-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal molecules. Moreover, full-color CPL emissions with both a high absolute CPL dissymmetrical factor up to 0.43 and high Φf were afforded.

Liquid Crystals Doped with Chiral Fluorescent Polymer: Multi-Color Circularly Polarized Fluorescence and Room-Temperature Phosphorescence with High Dissymmetry Factor and Anti-Counterfeiting Application

Chiral nematic liquid crystals (N*-LCs) can tremendously amplify circularly polarized luminescence (CPL) signals. Doped emissive N*-LCs have been substantially explored. However, their CPL performances still need to be improved, mainly due to the unsatisfying helical twisting power (HTP) of commonly used chiral fluorescent dopants. Chiral fluorescent helical polymers (CFHPs) have outstanding optical activity and CPL performance. The present contribution reports the first success in constructing emissive N*-LCs by doping CFHP into nematic liquid crystals (5CB, N-LCs). The helical assembly structures of N*-LCs effectively amplify the CPL signals of the CFHP. Owing to the high HTP of CFHP, the selective reflection band of N*-LC can be adjusted to fully cover its emission band. A nearly pure CPL with a dissymmetry factor (glum ) up to -1.87 is realized at 9 wt% doping concentration. Taking advantage of the selective reflection mechanism, multi-color CPL-active N*-LCs with high glum are fabricated via further adding achiral fluorophores. Also noticeably, circularly polarized room-temperature phosphorescence with glum up to -1.57 is achieved. Anti-counterfeiting application is demonstrated by exploiting multi-mode optical characteristics of the created N*-LCs. The established strategy for constructing emissive N*-LCs provides a platform for future exploring of CPL-active N*-LCs.

Helical Polymer Working as a Chirality Amplifier to Generate and Modulate Multicolor Circularly Polarized Luminescence in Small Molecular Fluorophore/Polymer Composite Films

In-depth studies of chirality and circularly polarized luminescence (CPL) have become indispensable in the process of learning human nature. Small molecules with CPL activity are one of the research hotspots. However, the CPL properties of such materials are generally not satisfying. Here, we synthesized a series of chiral small molecular fluorophores that cannot demonstrate CPL emission themselves. By introducing an optically inactive helical polymer, chirality transfer and chirality amplification efficiently occur, thereby generating intense CPL emission. Through combining different chiralized fluorophores, multicolor CPL-active films with emission wavelength centered at 463, 525, and 556 nm were fabricated, with the maximum luminescence dissymmetry factor (g_lum) being up to -0.028. Then, benefiting from the strong CPL emission and appropriate energy donor-acceptor system, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the CPL-active films work as a donor emitting circularly polarized fluorescence to excite an achiral fluorophore (Nile red) as the acceptor, producing red CPL with g_lum of up to -0.011 at around 605 nm.

Photo-triggered full-color circularly polarized luminescence based on photonic capsules for multilevel information encryption

Materials with phototunable full-color circularly polarized luminescence (CPL) have a large storage density, high-security level, and enormous prospects in the field of information encryption and decryption. In this work, device-friendly solid films with color tunability are prepared by constructing Förster resonance energy transfer (FRET) platforms with chiral donors and achiral molecular switches in liquid crystal photonic capsules (LCPCs). These LCPCs exhibit photoswitchable CPL from initial blue emission to RGB trichromatic signals under UV irradiation due to the synergistic effect of energy and chirality transfer and show strong time dependence because of the different FRET efficiencies at each time node. Based on these phototunable CPL and time response characteristics, the concept of multilevel data encryption by using LCPC films is demonstrated.

Asymmetric Ruthenium Catalysis Enables Fluorophores with Point Chirality Displaying CPL Properties

A novel enantiopure π-allylruthenium(IV) precatalyst allowed the enantioselective and stereospecific allylations of indoles and gave access to indolin-3-ones, containing vicinal stereogenic centers. Facile separation of diastereoisomers exhibiting opposite circularly polarized luminescence (CPL) activities in diverse solvents, including water, demonstrated the potential of these sustainable transformations and of the newly prepared molecules.

Stimulus responsive luminescence and application of rotor type 1,1'-([2,2'-bithiophene]-3,3'-diyl)bis(ethan-1-one) and 3'-acetyl-[2,2'-bithiophene]-3-carbaldehyde as molecular rotors

Two dithiophene aldehyde/ketone derivatives are designed as luminescence molecular rotors, i.e., 1,1'-([2,2'-bithiophene]-3,3'-diyl)bis(ethan-1-one) (BTBE) and 3'-acetyl-[2,2'-bithiophene]-3-carbaldehyde (BTAC). Their absorption and luminescence properties, as well as the stimulus responsive luminescence characteristics of water spikes are studied in detail. In order to further explore relationship of luminescence and molecular structure, three reference compounds are also synthesized, named 1-(2-methylthiophen-3-yl)ethanone (MTE), 2-methylthiophene-3-carbaldehyde (MTC) and 4H-cyclohepta[1,2-b:7,6-b']dithiophen-4-one (CDTO). BTBE and BTAC have two obvious absorption bands in the short wavelength region with peak wavelengths of about 212 nm and 260 nm, respectively, while there is a weak trailing type absorption band in the range of about 300-400 nm. Their fluorescence spectra show two luminescence bands in the range of 280-350 nm and 400-600 nm, respectively, and the latter is stronger. Compared with the absorption and luminescence spectra of the reference compounds, it is determined that two absorption bands of BTBE and BTAC in shorter wavelength region are derived from the single thiophene ring carbonyl planar unit, while the absorption band in longer region are derived from the integrated structure of dithiophene carbonyl. The fluorescence bands with peaks of about 300 nm and 470 nm originate respectively from the localized F-C vertical excited states (LE), i.e., the excited state from single planar thienyl-carbonyl unit, and integrated excited state (IE), i.e., the excited state from integrated di-thienyl-carbonyl rings linked covalently with less dihedral angle and greater degree of conjugation at excited state. The crystal structure data show that two thiophene rings possess larger dihedral angles in crystal states, 86.9° for BTBE and 60.8° for BTAC, respectively. However, theoretical calculation results prove the conformational stabilization energy changes little, less than 1.5 kcal/mol, as dihedral angle changes from 50° to 100°. Hydrogen bonding is sufficient to overcome the energy required for this conformational change. Therefore, both BTBE and BTAC can produce water stimulation response luminescence behavior. This stimulating response behavior of BTBE and BTAC can be applied to the preparation of water writable film materials.

Programming and Dynamic Control of the Circular Polarization of Luminescence from an Achiral Fluorescent Dye in a Liquid Crystal Host by Molecular Motors

Circular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light-driven molecular motors as photo-controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non-invasively by light, opening possibilities for pixilated displays with externally addressable polarization.

A Flexible Circularly Polarized Luminescence Switching Device Based on Proton-Coupled Electron Transfer

Flexible circularly polarized luminescence (CPL) switching devices have been long-awaited due to their promising potential application in wearable optoelectronic devices. However, on account of the few materials and complicated design of manufacturing systems, how to fabricate a flexible electric-field-driven CPL-switching device is still a serious challenge. Herein, a flexible device with multiple optical switching properties (CPL, circular dichroism (CD), fluorescence, color) is designed and prepared efficiently based on proton-coupled electron transfer (PCET) mechanism by optimizing the chiral structure of switching molecule. More importantly, this device can maintain the switching performance even after 300 bending-unbending cycles. It has a remarkable comprehensive performance containing bistable property, low open voltage, and good cycling stability. Then, prototype devices with designed patterns have been fabricated, which opens a new application pattern of CPL-switching materials.

Cascading Photoelectric Detecting and Chemiresistive Gas-Sensing Properties of Pb5 S2 I6 Nanowire Mesh for Multi-Factor Accurate Fire Alarm

Accurate fire warning is very important for people's life and property safety. The most commonly used fire alarm is based on the detection of a single factor of gases, smoke particles, or temperature, which easily causes false alarm due to complex environmental conditions. A facile multi-factor route for fabricating an accurate analog fire alarm using a Pb₅ S₂ I₆ nanowire mesh based on its photoelectric and gas-sensing dual function is presented. The Pb₅ S₂ I₆ nanowire mesh presents excellent photoelectric detection capabilities and is sensitive to ppm-level NO₂ at room temperature. Under the "two-step verification" circuit of light and gas factors, the bimodal simulation fire alarm based on this Pb₅ S₂ I₆ nanowire mesh can resist the interference of complex environmental factors and effectively reduce the false alarm rate.

The preparation and properties of circularly polarized luminescent liquid crystal physical gels with self-supporting performance

In recent years, great progress has been made in the preparation methods and performance regulation of host-guest doped CPL liquid crystal materials. However, there still exist some basic problems to be solved, such as complex packaging and unstable CPL properties. With the consideration of the above problems, in this study, we introduced gelators into the host-guest doped CPL liquid crystal materials to prepare CPL liquid crystal physical gels. The gelators can be assembled to form a nanofiber physical gel network, which limits the movement of the liquid crystals and enhances the stability of the CPL properties. Meanwhile, liquid crystal physical gels show self-supporting ability and the gel-sol phase transition temperature can reach 136 °C. The amplification of the g_lum value is achieved by self-assembly of chiral liquid crystals, and the g_lum value can reach -0.31. The phase structure changes with electric field and temperature, and the CPL properties can be regulated by changing the temperature and electric field. With the increasing applied voltage or the temperature, the g_lum value decreases. Therefore, we have successfully prepared a new type of CPL liquid crystal physical gels with self-supporting performance, stimulus response performance and large g_lum values.

Turn-On Mode Circularly Polarized Luminescence in Self-Organized Cholesteric Superstructure for Active Photonic Applications

Developing circularly polarized luminescence (CPL)-active materials with a large luminescence dissymmetry factor (g_lum) or stimulus responses has evoked a lot of interest in the past few years; however, the light-controllable "on/off" CPL still remains a challenge. Here, a novel diarylethene-based chiral fluorescent photoswitch featuring "turn-on" CPL characteristic is developed, designated as (S,S)-switch 6, which can undergo reversible photocyclization/cycloreversion upon irradiation with UV and visible light. (S,S)-Switch 6 shows completely reversible "off-on-off"-responsive CPL behavior in solution. By doping (S,S)-switch 6 into nematic liquid crystals (LCs), the consequent luminescent cholesteric LCs (CLCs) exhibit a larger g_lum value enhanced 2 orders of magnitude when irradiated with UV light, which can be attributed to the highly ordered helical arrangement of CLCs. The potentials of this turn-on type CPL material for anticounterfeiting and information encryption are illustrated. Furthermore, the visualization of circularly polarized (CP) fluorescent patterns can be successfully achieved by constructing the double-layer CPL system consisting of a CP luminescent layer and a polymer cholesteric reflective layer. The proposed concept establishes a light-controlled off-on-off CPL platform that is of tremendous potential for applications in multi-informational data storage and encryption devices.

Dynamic Circularly Polarized Luminescence with Tunable Handedness and Intensity Enabled by Achiral Dichroic Dyes in Cholesteric Liquid Crystal Medium

Cholesteric liquid crystals (CLCs) are chiral supramolecular systems that self-assemble into a highly regular helical arrangement in a liquid crystal (LC) medium. Such an arrangement is highly beneficial for the chiral enlargement effect on circularly polarized luminescence (CPL) signals. Dichroic dyes with rod-like molecular structures can exhibit fluorescence anisotropy along both the long and short molecular axes owing to their transition dipole moment (TDM) vectors. In this work, a pair of donor-accepter (D-A) achiral dichroic dyes is prepared, namely, 3,4-ethylenedioxythiophene derivative (P1, whose TDM vector is parallel to the long axis of the molecule, i.e., F_||  > F_⊥ ) and anthraquinone derivative (N1, whose TDM vector is perpendicular to the long axis of the molecule, i.e., F_||  < F_⊥ ). CLCs can be fabricated by doping P1 or N1 together with chiral 1,1'-binaphthyl-derived inducers into SLC1717 medium. Dynamic CPL with tunable handedness and intensity is achieved by changing the N1:P1 mass ratio, and the luminescence dissymmetry factor (g_em ) value reaches |0.71|. This work describes the first observation of dynamic CPL with tunable handedness and intensity enabled by TDM regulation of achiral dichroic dyes in a CLC medium.

Tunable Circularly Polarized Luminescence with a High Dissymmetry Factor Emitted from Luminogen-Bonded and Electrically Controlled Polymer-Stabilized Cholesteric Liquid Crystals

Circularly polarized luminescence (CPL)-active materials with high dissymmetry factor (g_lum) values show great potential in photonic devices. In this study, electric-field-driven systems with tunable CPL signals are successfully fabricated based on polymer-stabilized cholesteric liquid crystal (PSChLC) doping by fluorescent molecules. By constructing a gradient helical superstructure of PSChLCs, distinctive CPL emission from two sides of a single sample is realized, in which the |g_lum| values were measured to be 0.6 and 1.5, respectively. Herein, we discussed the possible mechanism of this phenomenon. In addition, an applied electric field could broaden the reflection bandwidth of PSChLCs from 150 to 500 nm, covering the whole visible light region. Furthermore, this electric field-induced behavior leads to the variation of CPL signals and corresponding g_lum values, indicating the potential of the novel materials in the design and preparation of CPL-emitting devices with electrically tunable CPL intensity and g_lum.

Cholesteric Liquid Crystalline Polyether with Broad Tunable Circularly Polarized Luminescence

Strong circularly polarized luminescence (CPL) with high purity and broad tunability was achieved in a new type of polyether-based cholesteric liquid crystalline (CLC) copolymers comprising chiral cholesteryl, nematic mesogens, and cross-linkable moieties. The phase boundary diagram of the copolymers was constructed, wherein the CLC phase in a wide composition and temperature window down to room temperature was achieved. Furthermore, reflection colors across the infrared and visible light regions can be continuously tuned by altering composition or temperature, which can be further fixed in the flexible CLC elastomer by photo-cross-linking. Introducing achiral dyes in the CLC thin films can generate strong CPL with distinct handedness and high dissymmetry factors (g_lum). Particularly, the left-handed full-color CPL is obtained by selective circularly polarized scattering in the spectral region outside the band gap of the CLC thin film, and the right-handed CPL with g_lum up to -1.05 is achieved within the band gap of the CLC thin film following the selective circularly polarized reflection mechanism. This type of CPL active material is expected to have potential applications in liquid crystal display and photonics.

Stimuli-Responsive Self-Assembly of π-Conjugated Liquids Triggers Circularly Polarized Luminescence

We developed novel room-temperature stimuli-responsive N-heteroacene-based liquid materials bearing a chiral alkyl chain. When these liquid materials were exposed to HCl vapor as an external stimulus, a disordered-ordered state change occurred immediately to yield self-assembled solid states from fluidic liquids. The self-assembly mechanism during this state change was evaluated by experimental in situ observations and molecular dynamics simulations over various spatiotemporal scales. These self-assembled structures led to supramolecular chirality through the influence of the chiral alkyl chain. As a result, circularly polarized luminescence (CPL) was triggered in the solid state, which was absent in the precursor liquid, thereby rendering this the first report on a stimuli-responsive CPL on/off liquid material. In addition, the initial state was recovered by exposure to air or upon heating. Moreover, the synergy between the experimental and the theoretical studies opens a new avenue to develop a novel class of stimuli-responsive materials and to discover novel phenomena in such materials.

Brightening up Circularly Polarized Luminescence of Monosubstituted Polyacetylene by Conformation Control: Mechanism, Switching, and Sensing

The first example of luminescent monosubstituted polyacetylenes (mono-PAs) is presented, based on a contracted cis-cisoid polyene backbone. It has an excellent circularly polarized luminescence (CPL) performance with a high dissymmetric factor (up to the order of 10^-1 ). The luminescence stems from the helical cis-cisoid PA backbone, which is tightly fixed by the strong intramolecular hydrogen bonds, thereby reversing the energy order of excited states and enabling an emissive energy dissipation. CPL switches are facilely achieved by the solvent and temperature through reversible conformational transition. By taking advantages of fast response and high sensitivity, the thin film of mono-PAs could be used as a CPL-based probe for quantitative detection of trifluoroacetic acid with a wider linear dynamic range than those of photoluminescence and circular dichroism. This work opens a new avenue to develop novel smart CPL materials through modulating conformational transition.

Irradiation-Wavelength Directing Circularly Polarized Luminescence in Self-Organized Helical Superstructures Enabled by Hydrogen-Bonded Chiral Fluorescent Molecular Switches

Two light-driven chiral fluorescent molecular switches, (R,S,R)-switch 1 and (R,S,R)-switch 2, are prepared by means of hydrogen-bonded (H-bonded) assembly of a photoresponsive (S) chiral fluorescent molecule, respectively with a cyano substitution at different positions as an H-bond acceptor and an opposite (R) chiral molecule as an H-bond donor. The resulting two switches exhibit tunable and reversible Z/E photoisomerization irradiated with 450 nm blue and 365 nm UV light. When doped into an achiral liquid crystal, both switches are found to be able to form a CPL tunable luminescent helical superstructure. In contrast to the tunable CPL characteristics of the system incorporating switch 2, exposure of the system incorporating switch 1 to 365 nm and 450 nm radiation can lead to controllable different photostationary CPL behavior, including switching-off and polarization inversion. In addition, optical information coding is demonstrated using the system containing switch 1.

Generating circularly polarized luminescence from clusterization-triggered emission using solid phase molecular self-assembly

Purely-organic clusterization-triggered emission (CTE) has displayed promising abilities in bioimaging, chemical sensing, and multicolor luminescence. However, it remains absent in the field of circularly polarized luminescence (CPL) due to the difficulties in well-aligning the nonconventional luminogens. We report a case of CPL generated with CTE using the solid phase molecular self-assembly (SPMSA) of poly-L-lysine (PLL) and oleate ion (OL), that is, the macroscopic CPL supramolecular film self-assembled by the electrostatic complex of PLL/OL under mechanical pressure. Well-defined interface charge distribution, given by lamellar mesophases of OL ions, forces the PLL chains to fold regularly as a requirement of optimal electrostatic interactions. Further facilitated by hydrogen bonding, the through-space conjugation (TSC) of orderly aligned electron-rich O and N atoms leads to CTE-based CPL, which is capable of transferring energy to an acceptor via a Förster resonance energy transfer (FRET) process, making it possible to develop environmentally friendly and economic CPL from sustainable and renewable materials.

Switchable Circularly Polarized Luminescence in Supramolecular Gels through Photomodulated FRET

While the tremendous deal of efforts has been dedicated to the design and fabrication of materials with circularly polarized luminescence (CPL), the development of the chiroptical switch between different CPL signals is one of the important routes toward its application. Here, we prepared a supramolecular gel from the coassemblies containing a chiral gelator (9-fluoren-methoxycarbonyl-functionalized glutamate derivatives, FLG), a fluorescent molecule [(rhodamine B, RhB) or (2',7'-dichlorofluorescein sodium salt, DCF)], and a photochromic molecule [1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene, DAE], thus constructing photomodulated switchable CPL soft materials. It was found that FLG could form supramolecular gel in ethanol and self-assemble into left-handed twisted nanostructures. During the formation of a co-gel with RhB (or DCF) and DAE, the chirality of FLG could be effectively transferred to both the fluorescent and photochromic components, which induced them with chiroptical properties including CPL and circular dichroism (CD). DAE undergoes a reversible transition between the achromatous open state and the dark purple closed state in the co-gel under alternating irradiation with UV and visible light. During such a process, an intermolecular Förster resonance energy transfer (FRET) behavior from fluorescent RhB to ring-closed DAE caused the emission quenching of RhB, which led to CPL silence of RhB in the co-gel. Subsequent irradiation with visible light caused the restoration of the emission and CPL activity with the restored open state. These changes could be repeated many times upon alternate UV and visible irradiation. Therefore, a reversible CPL switch was fabricated in supramolecular gels through the photomodulated FRET process.

Side-chain chiral fluorescent liquid crystal polymers with highly efficient circularly polarized luminescence emission in a glassy-state SmC* film

A series of high-efficiency CPL-active homopolymer materials in solid films with modulated properties were fabricated.