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

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.

Fluorescent Materials Based on Spiropyran for Advanced Anti-Counterfeiting and Information Encryption

In daily life, counterfeit and substandard products, particularly currency, medicine, food, and confidential documents, are capable of bringing about very serious consequences. The development of anti-counterfeiting and authentication technologies with multilevel securities is a powerful means to overcome this challenge. Among various anti-counterfeiting technologies, fluorescent anti-counterfeiting technology is well-known and commonly used to fight counterfeiters due to its wide material source, low cost, simple usage, good concealment, and simple response mechanism. Spiropyran is favored by scientists in the fields of anti-counterfeiting and information encryption due to its reversible photochromic property. Here, we summarize the current available spiropyran-based fluorescent materials from design to anti-counterfeiting applications. This review will be help scientists to design and develop fluorescent anti-counterfeiting materials with high security, high performance, quick response, and high anti-counterfeiting level.

Polymers with Circularly Polarized Luminescent Properties: Design, Synthesis, and Prospects

Chiral materials with circularly polarized luminescence (CPL) have garnered significant attention owing to their distinctive luminescent properties and wide array of applications. CPL enables the selective emission of left and right circularly polarized light. The fluorescence quantum yield and dissymmetry factor play pivotal roles in the generation of CPL. Helical polymers exhibit immense promise as CPL materials due to their inherent chirality, structural versatility, modifiability, and capacity to incorporate diverse chromophores. This Review provides a brief review of the synthesis of CPL materials based on helical polymers. The CPL can be realized by aggregation-induced CPL of non-emissive helical polymers, and helices bearing chromophores on the pendants and on the chain end. Furthermore, future challenges and potential applications of CPL materials are summarized and discussed.

Precise Modulation of Circularly Polarized Luminescence via Polymer Chiral Co-assembly and Contactless Dynamic Chiral Communication

Circularly polarized luminescence (CPL) plays a pivotal role in cutting-edge display and information technologies. Currently achieving precise color control and dynamic signal regulation in CPL still remains challenging due to the elusory relationship between fluorescence and chirality. Inspired by the natural mechanisms governing color formation and chiral interaction, we proposed an addition-subtraction principle theory to address this issue. Three fluorene-based polymers synthesized by Suzuki polycondensation with different electron-deficient monomers exhibit similar structures and UV/Vis absorption, but distinct fluorescence emissions due to intramolecular charge transfer. Based on this, precise-color CPL-active films are obtained through quantitative supramolecular co-assembly directed by addition principle. Particularly, an ideal white-emitting CPL film (CIE coordinates: (0.33, 0.33)) is facilely fabricated with a high quantum yield of 80.8 % and a dissymmetry factor (glum) of 1.4×10-2. Structural analysis reveals that the ordered stacking orientation favors higher glum. Furthermore, to address the dynamically regulated challenge, the comparable subtraction principle is proposed, involving a contactless chiral communication between excited and ground states. The representative system consisting of as-prepared fluorene-based polymers and chirality-selective absorption azobenzene (Azo)-containing polymers is constructed, achieving CPL weakening, reversal, and enhancement. Finally, a switchable quick response code is realized based on trans-cis isomerization of Azo moiety.

"Matching Rule" for Generation, Modulation and Amplification of Circularly Polarized Luminescence

ConspectusCircularly polarized luminescence (CPL) generated by chiral luminescent systems has sparked enormous attention in multidisciplinary field as it brings infinite potential for applications, such as 3D optical displays, biological probes, and chiroptical sensors. Satisfying both the conditions of chirality and luminescence (including fluorescence or phosphorescence) is a prerequisite for constructing CPL materials. In this regard, whether in organic, inorganic, or hybrid systems, chiral and luminescent components generally involve effective coupling through covalent or noncovalent bonds. For covalent interactions, such as the copolymerization of chiral and luminescent monomers, although covalent bonds provide high stability for the system, they inevitably involve tedious preparation procedures that connect chirality and luminescence together. For noncovalent bonds, take supramolecular assembly as an example, chiral elements and achiral light-emitting units are chiral transferred through intermolecular interactions, and their advantages include the diversity of luminescent and chiral building blocks, the stimuli responsiveness brought by noncovalent bonds, as well as the potential amplification of CPL signals by coassembly. However, the stability of the assembly system may be poor, and the assembly chiroptical performance and morphology are difficult to predict. Gratifyingly, matching rule that do not rely on covalent together with noncovalent interactions allows for the effortless construction, modulation, as well as amplification of CPL systems.In this Account, we overview different strategies based on matching rule, including fluorescence-selective absorption, circularly polarized reflection, and circularly polarized fluorescence energy transfer (CPF-ET). Examples of these strategies are illustrated with a focus on helical polymers in light of their appealing structures and wide uses. For instance, for fluorescence-selective absorption, chiral helical polymers can convert racemic fluorescence light into a circularly polarized one with specific handedness by simply overlapping the helical polymer's circular dichroism (CD) spectra with the luminophore's emission spectra. For circularly polarized reflection, employing the selective reflection of certain handedness's circularly polarized light, the high helical twisting power (HTP) of the helical polymer in the cholesteric liquid crystals (N*-LCs) gives the system high glum. Additionally, for CPF-ET, only the emission spectrum of the donor and the absorption (or excitation) spectrum of the achiral acceptor are required to overlap, and no covalent or noncovalent interactions between the two are required. An outlook for the CPL materials related to matching rule which will avail the optimization and extension of this intriguing approach concludes the Account. We hope that the Account will offer insightful inspiration for the flourishing progress of chiroptical systems and present exciting opportunities.

Enabling robust blue circularly polarized organic afterglow through self-confining isolated chiral chromophore

Creating circularly polarized organic afterglow system with elevated triplet energy levels, suppressed non-radiative transitions, and effective chirality, which are three critical prerequisites for achieving blue circularly polarized afterglow, has posed a formidable challenge. Herein, a straightforward approach is unveiled to attain blue circularly polarized afterglow materials by covalently self-confining isolated chiral chromophore within polymer matrix. The formation of robust hydrogen bonds within the polymer matrix confers a distinctly isolated and stabilized molecular state of chiral chromophores, endowing a blue emission band at 414 nm, lifetime of 3.0 s, and luminescent dissymmetry factor of ~ 10-2. Utilizing the synergistic afterglow and chirality energy transfer, full-color circularly polarized afterglow systems are endowed by doping colorful fluorescent molecules into designed blue polymers, empowering versatile applications. This work paves the way for the streamlined design of blue circularly polarized afterglow materials, expanding the horizons of circularly polarized afterglow materials into various domains.

Dynamically Modulating the Dissymmetry Factor of Circularly Polarized Organic Ultralong Room-Temperature Phosphorescence from Soft Helical Superstructures

Achieving circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) with a high luminescent dissymmetry factor (glum ) is crucial for diverse optoelectronic applications. In particular, dynamically controlling the dissymmetry factor of CP-OURTP can profoundly advance these applications, but it is still unprecedented. This study introduces an effective strategy to achieve photoirradiation-driven chirality regulation in a bilayered structure film, which consists of a layer of soft helical superstructure incorporated with a light-driven molecular motor and a layer of room-temperature phosphorescent (RTP) polymer. The prepared bilayered film exhibits CP-OURTP with an emission lifetime of 805 ms and a glum value up to 1.38. Remarkably, the glum value of the resulting CP-OURTP film can be reversibly controlled between 0.6 and 1.38 over 20 cycles by light irradiation, representing the first example of dynamically controlling the glum in CP-OURTP.

Clustering-Triggered Emission Liquid Crystalline Polymer Bearing Cholesterol: Tunable Circularly Polarized Luminescence and Room-Temperature Phosphorescence

Circularly polarized luminescence (CPL) materials with clustering-triggered emission (CTE) characteristic have gradually attracted attention for their unique photophysical properties. However, the majority of reported clusteroluminogens lack chirality and exhibit heterogeneity, making it challenging to achieve a well-defined helical structure necessary for efficient CPL with high dissymmetry factor (glum ). In this paper, chiral liquid crystals are constructed to obtain CTE-based CPL materials with high glum values. Side chain liquid crystal polymer PM6Chol bearing cholesterol clusteroluminogens are designed and synthesized. PM6Chol-coated film and PM6Chol thermal-treated film are also successfully prepared by different film-forming methods. Both the films inherit the CTE characteristic of cholesterol and show excitation wavelength-dependent luminescent behavior. However, the two polymer films exhibit different liquid crystal phase structures, with PM6Chol-coated film being a chiral bilayer smectic C phase and PM6Chol thermal-treated film being an achiral bilayer smectic A phase. Attributed to helical arrangement of cholesterol, PM6Chol-coated film emits efficient CPL with glum values up to 1.0 × 10-1 . For PM6Chol thermal-treated film, no CPL signal is detected due to the absence of helical structure. However, it shows obvious room-temperature phosphorescence with 2.0 s afterglow and 23.9 ms lifetime.