Light-Driven Sign Inversion of Circularly Polarized Luminescence Enabled by Dichroism Modulation in Cholesteric Liquid Crystals

Multiple stimuli-responsive circularly polarized luminescent bio-composite films by coassembling cellulose nanocrystals and curcumin

Cellulose nanocrystal (CNC) -based circularly polarized luminescent (CPL) materials, which are responsive to external stimuli, have attracted increasing attention in developing smart chiral photonic materials. In this study, chiral nematic bio-composite CNC films with right-handed (R-) CPL emission and tunable dissymmetry factors (glum) were prepared by encapsulating curcumin in chiral nematic CNC films via an evaporation-induced self-assembly strategy. The CPL active bio-composite CNC films exhibit multiple responsiveness to relative humidity (RH) and pH. It is noted that the pH response of the composite films is visualized, which is reflected in the variation of film colors, fluorescence, and CPL emission wavelengths. Additionally, with a hydrophobic treatment, the bio-composite CNC films exhibit enhanced water resistance and pH-responsive CPL in acid/base aqueous solutions. Based on the responsive circular polarization information, the bio-composite CNC films were developed as optical labels for multiple anti-counterfeiting applications. The reported environmentally friendly bio-composite CNC films provide a new reference for utilizing natural polysaccharides to build multi-mode responsive CPL materials.

Engineering Organic Photochromism with Photoactivated Phosphorescence: Multifunctional Smart Devices and Enhanced Four-Channel Data Storage

The development of organic photoresponsive materials with multiple responses is essential for advancing multichannel data storage systems. In this study, interactions between photochromic and phosphorescent components are engineered by covalently linking them to obtain NMC (the compound containing naphthalimide and merocyanine units), which converted into NSP (the compound containing naphthalimide and spiropyran units) upon blue light irradiation, resulting in a maximum decrease in absorption of more than 90%, a blueshift of the fluorescent emission peaks from 605 to 490 nm, and an 84 fold enhancement in phosphorescence emission intensity. These significant optical changes across the three modes upon exposure to blue light are unprecedented. The conversion of optical signals to electrical signals enables the successful implementation of devices for remote monitoring of acid gas and blue light, as well as automatic control of blue light exposure. Furthermore, the data storage capacity of the device is significantly enhanced, increasing from 1 bit to log2(4n) bits per point in a four-channel data storage system. The design and synthesis of this compound present a promising approach for the development of sustainable, efficient, and flexible smart optoelectronic devices.

Intrinsically Luminescent Nematic Liquid Crystals Enabling High-Brightness Full-Color and White Circularly Polarized Luminescence via Chiral Coassembly

Circularly polarized luminescence (CPL) materials with simultaneous high dissymmetry factor (glum) and brightness are pivotal for advanced photonic applications but remain challenging due to inherent trade-offs betwwen glum value and photoluminescenc quantum yield (PLQY). Here, we report a supramolecular engineering strategy to construct intrinsically luminescent chiral nematic liquid crystal (N*-LC) films via coassembly of luminescent liquid crystals (LLCs) and chiral dopant. First, five intrinsic LLCs molecules (2PFQ, 2PFBQ, 2PFB, 2PFSe, and 2PFS) were synthesized by combining the biphenyl framework with dioctyl-functionalized fluorene, achieving exceptional nematic phases and high brightness with PLQY up to 99%. Then, chiral coassembly of the obtained LLCs with chiral dopants (P/M-THH) followed by rapid thermal quenching yielded Bragg reflection-free N*-LC films exhibiting high-brightness CPL with recorded glum values (up to 0.75) and PLQY (up to 71%). Full-color tunability and white CPL (CIE: 0.33, 0.33) were realized through precise compositional control. The simultaneous optimization of glum and PLQY enables high-brightness CPL with advanced anticounterfeiting capabilities, opening new avenues for developing high-brighness CPL materials for polarized photonic and optoelectronic applications.

Solvent-Dependent Chirality Transmission and Amplification from Cellulose Derivative to Achiral Helical Polymer for Achieving Full-Color and White Circularly Polarized Luminescence

Cellulose derivatives represent a promising natural chiral platform for creating circularly polarized luminescence (CPL) materials owing to their excellent processability and structural diversity. However, achieving full-color and white CPL emissions based on cellulose derivatives remains challenging. The present work reports the first success in achieving full-color and white CPL emissions leveraging chirality transmission and amplification from cellulose derivative to achiral helical polymer. Importantly, such chirality transfer displays a dependence on the hydrogen bond accepting ability of solvent, making it effortless to precisely regulate chiral intensity by single or combined solvents. Moreover, the induced chirality in helical polymer is further transferred to the introduced racemic fluorescent dyes, resulting in full-color and white-light CPL emissions with a maximum luminescence dissymmetry factor (glum) and photoluminescence quantum yield (PLQY) up to 1.5×10-2 and 62.9 %, respectively. Further spatially separating the chiral and fluorescent components allows inversion of CPL handedness and precise modulation of CPL intensity. Notably, circularly polarized white organic light-emitting diodes and chiral logic gate with multiple information outputs are successfully developed. This work gives an impetus to construct cellulosic chiroptical materials, offering more insights into chirality transfer between biomacromolecules and synthetic helical polymers.

Gradient-Metasurface-Contact Photodetector for Visible-to-Near-Infrared Spin Light

Spin light detection is a rapidly advancing field with significant impact on diverse applications in biology, medicine, and photonics. Developing integrated circularly polarized light (CPL) detectors is pivotal for next-generation compact polarimeters. However, previous compact CPL detectors, based on natural materials or artificial resonant nanostructures, exhibit intrinsically weak CPL polarization sensitivity, are susceptible to other polarization states, and suffer from limited bandwidths. A gradient-metasurface-contact CPL photodetector is demonstrated operating at zero-bias with a high discrimination ratio (≈1.6 ✗ 104), broadband response (500-1100 nm), and immunity to non-CPL field components. The photodetector integrates InSe flakes with CPL-selective metasurface contacts, forming an asymmetric junction interface driven by CPL-dependent unidirectional propagating surface plasmon waves, generating zero-bias vectorial photocurrents. Furthermore, it is implemented the developed CPL photodetector in a multivalued logic system and demonstrated the optical decoding of CPL-encrypted communication signals. This metasurface contact engineering represents a new paradigm in light property detection, paving the way for future integrated optoelectronic systems for on-chip polarization detection.

MAPbBr3 Quantum Dots Encapsulated Within Lanthanide-MOFs for Time-Resolved Multicolor Dynamic Anticounterfeiting

Multicolor dynamic optical materials exhibit significant potential in the realms of anticounterfeiting and information encryption, benefitting from their capacity for generating unpredictable optical information that changes over time. Herein, a novel approach is presented utilizing quantum-confinement effect of MAPbBr3 quantum dots (QDs) embedded within lanthanide-metal organic frameworks (Ln-MOFs) for time-resolved multicolor dynamic anticounterfeiting applications. The dimensions of MAPbBr3 QDs undergo temporal variations during in situ growth, resulting in dynamic alterations in luminescent color due to the quantum-confinement effect. Furthermore, the emission colors of MAPbBr3@Eu-MOFs can be modulated by varying UV excitation wavelengths, thereby conferring a spatially distinguishable anticounterfeiting dimension. The time-resolved unpredictability of these dynamic color changes coupled with sustained luminescent intensity and multi-dimensional anticounterfeiting, render them suitable system for advanced graphical coding. These findings pave the way for the advancement of intelligent multicolor dynamic optical anticounterfeiting.

Stimuli-Responsive Circularly Polarized Luminescence of Gold Clusters Based on Hydrogen-Bond Driven Intercluster Coupling

Stimuli-responsive circularly polarized luminescence (CPL) metal clusters hold significant potential in high-security encryption and sensing applications, yet the exploration of hydrogen-bond-driven CPL-active metal clusters remains limited. Here, we report the synthesis of an enantiomeric pair of rhomboid Au4 clusters utilizing chiral R/S-4-hydroxymethyl-5-methyloxazole-2-thione (R/S-HMMT) ligands. Two enantiomeric pairs of self-assembled metal clusters R/S-Au4(HMMT)4-blue and R/S-Au4(HMMT)4-red were obtained, by constructing distinct intercluster hydrogen bonds through the use of different crystalline solvents. In R/S-Au4(HMMT)4-blue, 1,4-dioxane guest molecules were observed to form a hydrogen-bond network with the hydroxyl groups of the cluster surface ligands. In contrast, a different hydrogen-bond network involving the hydroxyl groups of the surface ligands was identified in R/S-Au4(HMMT)4-red, resulting in a distinct stacking pattern. The unique intercluster couplings mediated by hydrogen bonds result in R/S-Au4(HMMT)4-blue exhibiting a blue CPL emission at 466 nm, while R/S-Au4(HMMT)4-red shows a dual CPL emission at 446 and 727 nm. Theoretical calculations reveal that hydrogen-bond driven intercluster couplings in R-Au4(HMMT)4-red are significantly stronger than in R-Au4(HMMT)4-blue. Additionally, both solid R/S-Au4(HMMT)4-blue and R/S-Au4(HMMT)4-red undergo reversible CPL transformations in response to organic vapors, temperature, or mechanical stimuli, due to the destruction and reconstruction of hydrogen-bond networks. These characteristics make them promising materials for information encryption applications.

Chiral Cross-Linked Covalent Organic Framework Films for Highly Sensitive Circularly Polarized Luminescence Probing

The development of covalent organic framework (COF) films featuring circular polarization luminescence (CPL) probing remains a formidable challenge. Herein, we developed a chiral cross-linked COF film to obtain uniform and dense chiral COF films (chirCOFilm) possessing highly sensitive CPL probing for enantiomers. The axial chiral cross-linkers (R-/S-BBNA) are initially introduced into the channels of a COF film (COFilm/R-BBNA or COFilm/S-BBNA) by the vapor-assisted epitaxial method. Then, olefin groups in R-/S-BBNA and COF layers undergo a chiral cross-linking reaction under UV irradiation, forming a chirCOFilm. The obtained chirCOFilms have strong chirality with mirror images, fluorescence discoloration, and intense CPL properties. A multitude of rich chiral photopatterns and chirCOFilm/PDMS flexible films are prepared taking advantage of the photochromic properties of the chirCOFilms during UV illumination, showing the potential application of advanced anticounterfeiting. More importantly, the chirCOFilms realize highly sensitive CPL probing of phenethylamine enantiomers at 5% concentration, which can hardly be achieved from their corresponding fluorescence probing. This study not only provides a new strategy for preparing chiral COF films using chiral cross-linking reaction but also opens a new avenue for achieving highly sensitive probing of enantiomers though CPL.

Excitation-Dependent Circularly Polarized Luminescence Inversion Driven by Dichroic Competition of Achiral Dyes in Cholesteric Liquid Crystals

The development of stimuli-responsive chiral cholesteric liquid crystals (CLCs) materials holds significant potential for achieving three-dimensional (3D) anti-counterfeiting and multi-level information encryption. However, constructing phototunable CLCs systems with easy fabrication and fast response remains a great challenge. Herein, we exploit an excitation-dependent CLCs (ExD-CLCs) material by establishing dynamically photoresponsive dichroic competition between two achiral dyes: a negative dichroic dye (SP-COOH) and a positive dichroic dye (Nile Red, NR) within a CLCs medium. The ExD-CLCs exhibits a negative circularly polarized luminescence (CPL) signal (glum=-0.16) at 625 nm when excited at 365 nm. Remarkably, under excitation at 430 nm, the CPL signal is inverted, and the glum value increases to +0.26. Notably, the helical superstructure and handedness of the ExD-CLCs remain unchanged during this reversal process. The CPL signal reversal is driven by the dichroic competition between the SP-COOH dimer, which displays strong negative dichroism in its open-ring isomer form and silent negative dichroism in its closed-ring isomer form, and the NR dye, which exhibits static positive dichroism. Leveraging these excitation-dependent CPL properties, the quadruplex numerical anti-counterfeiting using ExD-CLCs is achieved.

Sign Inversion of Circularly Polarized Luminescence in Cholesteric Liquid Crystals Induced by Mercury Ions through Binaphthyl Dopants' Conjugation Control

Stimuli-responsive circularly polarized luminescence (CPL) materials based on cholesteric liquid crystal (CLC) platforms show great promise for applications in information encryption and anticounterfeiting. In this study, we constructed a mercury ion-responsive CPL system in CLCs by controlling the conjugation degree of axially chiral binaphthyl derivatives. Two chiral binaphthyl derivatives (R/S-1 and R/S-2) were initially used as chiral dopants to demonstrate that CPL inversion (glum values from 0.5/-0.44 to -0.53/0.48) in CLCs could be achieved by modulating the conjugation degree of the chiral binaphthyls. Based on this concept, the thioacetal binaphthyl R-2S was developed and used as a mercury-responsive chiral dopant in CLCs. Under Hg ion treatment, the CPL sign inverted (glum value changed from 0.22 to -0.29) due to the transformation of the thioacetal into an aldehyde group. Additionally, the mercury ion-responsive CPL material was applied in information encryption.

Three-Level Chirality Transfer and Amplification in Liquid Crystal Supramolecular Assembly for Achieving Full-Color and White Circularly Polarized Luminescence

Chiral liquid crystal supramolecular assembly provides an ideal strategy for constructing excellent circularly polarized luminescence (CPL) materials. However, the chirality transfer in chiral liquid crystals normally occurs at two levels from the configurational chirality to the supramolecular phase chirality. The more precise and more levels of chirality transmission are fascinating but remain challenging. The present work reports the first success of three-level chirality transfer and amplification from configurationally point chirality of small molecules to conformationally helical chirality of helical polymers and finally to supramolecular phase chirality of cholesteric liquid crystals composed of chiral nonfluorescent polymers (P46) and nematic liquid crystals. Noticeably, the helical twisting power of P46 is five-fold larger than its monomer. Full-color and white CPL with maximum luminescence dissymmetry factor up to 1.54 and photoluminescence quantum yield up to 63.8% are realized utilizing helical supramolecular assembly combined with selective reflection mechanism. Also significantly, the electrically stimuli-responsive CPL switching device as well as anti-counterfeiting security, information encryption, and chiral logic gate applications are developed. This study deepens the understanding of chirality transfer and amplification across different hierarchical levels.

Reversible Circularly Polarized Luminescence Inversion and Emission Color Switching in Photo-Modulated Supramolecular Polymer for Multi-Modal Information Encryption

Constructing circularly polarized luminescence (CPL) materials that exhibit dynamic handedness inversion and emissive color modulation for multimodal information encryption presents both a significant challenge and a compelling opportunity. Here, we have developed a pyridinethiazole acrylonitrile-cholesterol derivative (Z-PTC) that exhibits wavelength-dependent photoisomerization and photocyclization, enabling dynamic handedness inversion and emissive color modulation in supramolecular assemblies with decent CPL activity. Coordination with Ag+ ions form the Z-PTC Ag supramolecular polymer (SP1), which assembles into nanotubes displaying enhanced positive yellow-green CPL. Irradiation at 454 nm transforms SP1 into nanospheres of a mixture supramolecular polymer (SP2) of Z/E-PTC Ag, displaying inverted supramolecular chirality and emitting negative orange-yellow CPL. Reheating SP2 to 343 K restores the original nanotube structure via excellent reversible photoisomerization. Exposure to 365 nm light also induces CPL inversion from positive to negative and triggers morphological changes from SP1 to SP2. Prolonged irradiation causes further transformation into irregular supramolecular aggregate, shifting the emission color to blue and eliminating CPL. These dynamic properties of the multicolor CPL system, including reversible handedness inversion, can also be realized in the semisolid state, exhibiting promising potential for multimodal information encryption applications with enhanced security and complexity.

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.

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.