A facile and green strategy to obtain organic room-temperature phosphorescence from natural lignin

Bio-Based Thermoplastic Room Temperature Phosphorescent Materials with Closed-Loop Recyclability

Producing thermoplastic room temperature phosphorescent (RTP) materials with closed-loop recyclability from natural sources is an attractive approach but hard to achieve. Here, the study develops such RTP materials, Poly(TA)/Cell, by thermally polymerizing thioctic acid in the presence of cellulose. Specifically, polymerized thioctic acid poly(TA) forms strong hydrogen bonding interactions with CNF, promoting formation of molecular clusters between the oxygen-containing units. The as-formed clusters generate humidity- and excitation-sensitive green RTP emission. Red afterglow emission is also obtained by integrating Poly(TA)/Cell together with Rhodamine B (RhB) via an energy transfer process. Attributed to the thermoplastic properties, the as-obtained Poly(TA)/Cell can be thermally molded into flexible shapes with uncompromised RTP performance. Moreover, owing to the alkali-cleavable properties of the disulfide bond in Poly(TA)/Cell, thioctic acid and cellulose can be successfully recycled from Poly(TA)/Cell with a yield of 92.3% and 81.5%, respectively. As a demonstrator for potential utility, Poly(TA)/Cell is used to fabricate materials for information encryption.

Frontier in Advanced Luminescent Biomass Nanocomposites for Surface Anticounterfeiting

Biomass-based luminescent nanocomposites have garnered significant attention due to their renewable, biocompatible, and environmentally sustainable characteristics for ensuring information encryption and security. Nanomaterials are central to this development, as their high surface area, tunable optical properties, and nanoscale structural advantages enable enhanced luminescent efficiency, stability, and adaptability in diverse conditions. This review delves into the principles of luminescence, focusing on the inherent bioluminescent properties of natural materials, the utilization of biomass as precursors for carbon dots (CDs) and aggregation-induced emission (AIE)-enhanced substances, and the structural and functional optimization of luminescent materials. The role of cellulose nanocrystals (CNC), lignin, and chitosan as key biomass-derived nanomaterials will be highlighted, alongside surface and interfacial engineering strategies that further improve material performance. Recent advancements in the synthesis of biomass carbon dots and their integration into luminescent anticounterfeiting systems are discussed in detail. Furthermore, the integration of advanced artificial intelligence (AI) technologies is explored, emphasizing their potential to revolutionize luminescent anticounterfeiting. Current challenges, including scalability, waste minimization, and performance optimization, are critically examined. Finally, the review outlines future research directions, including the application of AI-driven methodologies and the exploration of unconventional luminescent biomass materials, to accelerate the development of high-performance, eco-friendly anticounterfeiting solutions.

Unique Organic Crystal Skeleton Based on N-Phenyl-Carbazole Derivatives with Adjustable Room Temperature Phosphorescence and Highly Stable Inclusion Ability to Dichloromethane

Monosubstituted 9-(2-bromophenyl)-carbazole (1Br1CZ) and disubstituted 9,9'-(2,4-dibromo-1,3-phenylene) bis(9H-carbazole) (2Br2CZ) are synthesized by introducing bromine into ortho-phenyl position of 9-phenyl-carbazole (PhCZ). The decomposition temperature with 5% mass loss and melting point of 2Br2CZ crystal are 360 and 230 °C. The highest occupied molecular orbital energy level of PhCZ is the highest, and that of 2Br2CZ is the lowest. The crystals of PhCZ, 1Br1CZ, and 2Br2CZ are monoclinic, orthorhombic, and triclinic system, which exhibit room temperature phosphorescence with lifetimes of 171.81, 37.15, and 28.77 ms, and their corresponding phosphorescence quantum yields are 0.83%, 0.16%, and 4.58%. It theoretically reveals that six triplet energy levels (T1-T6) exist under S1 in 2Br2CZ crystal, and the spin orbit coupling constants between S1 and Tn in 2Br2CZ are also greater than those in PhCZ and 1Br1CZ, which promotes the intersystem crossing. Meanwhile, through crystal structure and Hirshfeld surface analysis, the torsion angles between the carbazole unit of 2Br2CZ and the central phenyl group reached 85.28°. The 2Br2CZ crystal exhibits the richest intermolecular interactions. A cavity of 4.498 Å is formed within the crystal skeleton of 2Br2CZ, which can precisely fixe dichloromethane with a record-high desorption temperature over 145 °C.

Photoactivated room temperature phosphorescence from lignin

Sustainable photoactivated room temperature phosphorescent materials exhibit great potential but are difficult to obtain. Here, we develop photoactivated room temperature phosphorescent materials by covalently attaching lignin to polylactic acid, where lignin and polylactic acid are the chromophore and matrix, respectively. Initially the phosphorescence of the lignin is quenched by residual O2. However, the phosphorescence is switched on when the residual oxygen is consumed by the triplet excitons of lignin under continuous UV light irradiation. As such, the lifetime increases from 3.0 ms to 221.1 ms after 20 s of UV activation. Interestingly, the phosphorescence is quenched again after being kept under an atmosphere of air for 2 h in the absence of UV irradiation due to the diffusion of oxygen into the materials. Using these properties, as-developed material is successfully used as a smart anti-counterfeiting logo for a medicine bottle and for information recording.

Achieving Dual Emission of Fluorescence and Phosphorescence from Anti-Kasha's Metal-Organic Halides for Information Encryption

Luminescent materials typically emit their fluorescence or phosphorescence at a specific wavelength with different excitation energies via the so-called Kasha's rule. If fluorescence or phosphorescence emission via anti-Kasha's rule could be achieved, it will hold great promise for applications in many fields. In this work, we report the synthesis and characterization of new metal-organic halide materials with dual emission of efficient room-temperature phosphorescence and fluorescence, which obey anti-Kasha's rule. Here, three emitting metal-organic halides with formula [ZnX2(bidpe)] (X = Cl for 1, X = Br for 2, X = I for 3, bidpe = 4,4'-bis(imidazol-1-yl)diphenyl ether) were prepared and their photophysical properties were investigated. The complexes exhibit dual emission of fluorescence and phosphorescence via anti-Kasha's rule, and their RTP properties of resultant products are modulated by halide substitution synthesis. DFT calculations indicate that the singlet states exhibit a halide-ligand charge transfer (XLCT) character while the triplet states are dominated by the intraligand π-π* transitions. Furthermore, the multilevel information encryption and anticounterfeiting applications are developed by virtue of anti-Kasha's rule emission.

Room-temperature phosphorescent materials derived from natural resources

Room-temperature phosphorescent (RTP) materials have enormous potential in many different areas. Additionally, the conversion of natural resources to RTP materials has attracted considerable attention. Owing to their inherent luminescent properties, natural materials can be efficiently converted into sustainable RTP materials. However, to date, only a few reviews have focused on this area of endeavour. Motivated by this lack of coverage, in this Review, we address this shortcoming and introduce the types of natural resource available for the preparation of RTP materials. We mainly focus on the inherent advantages of natural resources for RTP materials, strategies for activating and enhancing the RTP properties of the natural resources as well as the potential applications of these RTP materials. In addition, we discuss future challenges and opportunities in this area of research.

Room temperature phosphorescence from natural wood activated by external chloride anion treatment

Producing afterglow room temperature phosphorescence (RTP) from natural sources is an attractive approach to sustainable RTP materials. However, converting natural resources to RTP materials often requires toxic reagents or complex processing. Here we report that natural wood may be converted into a viable RTP material by treating with magnesium chloride. Specifically, immersing natural wood into an aqueous MgCl₂ solution at room temperature produces so-called C-wood containing chloride anions that act to promote spin orbit coupling (SOC) and increase the RTP lifetime. Produced in this manner, C-wood exhibits an intense RTP emission with a lifetime of ~ 297 ms (vs. the ca. 17.5 ms seen for natural wood). As a demonstration of potential utility, an afterglow wood sculpture is prepared in situ by simply spraying the original sculpture with a MgCl₂ solution. C-wood was also mixed with polypropylene (PP) to generate printable afterglow fibers suitable for the fabrication of luminescent plastics via 3D printing. We anticipate that the present study will facilitate the development of sustainable RTP materials.

Coordinate Anchoring of Mixed Luminophores in Two Isostructural Hybrid Layers to Achieve Tunable Room-Temperature Phosphorescence

Room-temperature phosphorescence (RTP) materials have widespread applications in biological imaging, anticounterfeiting, and optoelectronic devices. Because of the predesignability of metal-organic complexes (MOCs), the RTP materials based on MOC systems have received huge attention from researchers. The coordinate anchoring of luminophores to enhance the rigidity of organic molecules and restrict the nonradiative transition offers opportunities for generating MOC materials with captivating RTP performance. Hitherto, most of the MOC-based RTP materials feature a single luminophore ligand. The development of new MOC systems with RTP functionality is still challenging. Herein, we use the mixed-ligand synthetic strategy to produce isostructural MOCs, [Zn(TIMB)(X₂-TPA)]·H₂O (1, X = Cl; 2, X = Br; TIMB = 1,3,5-tris(2-methyl-1H-imidazol-1-yl)benzene; H₂-X₂-TPA = 2,5-dichloroterephthalic and 2,5-dibromoterephthalic acid), and modulate the RTP properties of resultant products via the synergy of coordinate anchoring and substitution synthesis. 1 and 2 feature similar coordination layers composed of neutral TIMB and anionic X₂-TPA^2- ligands, which provide a good structural model to tune the RTP performances of final products via substitution synthesis. Different from the reported RTP materials based on MOC systems, our study provides a general way to build and modulate MOC-based RTP materials with the assistance of coordinate anchoring and substitution synthesis strategies.