Greatness in Simplicity: Efficient Red Room-Temperature Phosphorescence from Simple Halogenated Maleimides with a 2D Layered Structure

Multiple stimulus modulated organic crystal polymorphs with tunable luminescence behavior

Polymorphism is defined as the ability of a substance to exist in two or more crystalline forms, which provide a unique platform for revealing the relationship between its spatial structure and properties. However, organic crystal polymorphism can be commonly obtained by growing crystals in different solvents or at different temperatures. This study reports a compound named p-An-Br containing carbazole and anthracene chromophores with three multiple stimulus modulated crystal polymorphs with green, yellow and red fluorescence, respectively. Interestingly, switching of p-An-Br between crystal G, crystal Y and crystal R can be achieved through the uptake and release of methanol using different stimuli, which shows dynamically adjustable luminescent colors. Significantly, structure-property investigations via the in-depth analysis of molecular conformations and frameworks of the polymorphic crystals demonstrate that the diverse conformations and abundant noncovalent interactions have a predominant impact on emission behavior. Consequently, the crystals R can be used for the highly sensitive and specific sensing of methanol with a detection limit of 39.35 ppm. This study not only provides a new strategy for crystal polymorphism, but also develops an effective method for the detection of methanol.

Lantern-Shaped Structure Induced by Racemic Ligands in Red-Light-Emitting Metal Halide with Near 100 % Quantum Yield and Multiple-Stimulus Response

Organic-inorganic metal halides (OIMHs) have become a research hotspot in recent years due to their excellent luminescent properties and tunable emission wavelengths. However, the development of efficient red-light-emitting OIMHs remains a significant challenge. This work reports three Mn-based OIMHs derived from 1-methyl-1,2,3,4-tetrahydroisoquinoline hydrobromide: racemic one (Rac-TBM) and chiral ones (R-TBM and S-TBM). As a result of the synergism of chiral organic ligands inducing a unique lantern-shaped hybrid structure containing both tetrahedra and octahedra, Rac-TBM exhibits red-light emission with near-unity luminescence quantum yield. In comparison, the chiral counterparts R/S-TBM display strong green emission and circularly polarized luminescence (CPL) with a glum value up to ±2.5×10-2. Interestingly, a mixture of R- and S-TBM can transform into Rac-TBM, successfully achieving a sensitive and reversible switch between red light of octahedra and green light of tetrahedra under external stimuli. The outstanding luminescent properties allow Rac-TBM to be utilized not only for X-ray radioluminescence with a detection limit down to 46.29 nGys-1, but also for advanced information encryption systems to achieve leak-proof decryption.

Visible-light-excited organic room temperature phosphorescence

Purely organic room temperature phosphorescence (RTP) materials have evoked considerable attention owing to their fantastic optical properties and broad application prospects. However, most of the reported organic RTP materials can be only excited by UV light, leading to accelerated photoaging of organic phosphors and severe lesions of organisms under excitation. In contrast to UV light, visible light (380-780 nm) has much lower phototoxicity, deeper penetrability and easier accessibility, which make visible-light-excited RTP materials more favorable for practical uses, especially for life-related applications. Although it remains greatly challenging to construct visible-light-excited RTP materials, impressive progress has been made with the rapid development of this field. Herein, we systematically outline the significant progress achieved in visible-light-excited RTP materials, including the design and construction strategies, unique properties, underlying mechanisms and their vital applications. In the final section, we highlight the current challenges and research perspectives for suggesting future studies of visible-light-excited RTP materials.

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.

Anionic Hydrogen-Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone

Tautomers coexisting in an equilibrium system have significant potential for regulating luminescent properties because of their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this study, it is found that hydrogen-bonded organic frameworks (HOFs) composed of Br- anions can effectively separate and stabilize two proton-transfer tautomers of triarylformamidinium bromide: namely, the nitrogen cation (BA-N) and carbon cation (BA-C). The BA-N crystal consisting of a dense anionic HOF and parallelly aligned organic cations exhibits green thermally activated delayed fluorescence and red room-temperature phosphorescence (RTP). The BA-C crystal contains acetone molecules that induce an antiparallel arrangement of the organic cations to form a loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, switching of the HOFs between BA-N and BA-C can be achieved through the uptake and release of acetone, thereby dynamically adjusting multiple luminescent properties. Consequently, the HOF crystals can be used for the highly sensitive and specific sensing of acetone with a detection limit of 66.74 ppm. This study not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with a sensitive response to a stimulus.

Ultralong Red Room-Temperature Phosphorescence of 2D Organic-Inorganic Metal Halide Perovskites for Afterglow Red LEDs and X-ray Scintillation Applications

Organic-inorganic metal hybrid perovskites (OIHPs) have emerged as a promising class of materials for next-generation optoelectronic applications. However, the realization of red and near-infrared (NIR) room-temperature phosphorescence (RTP) in these materials remains limited. In this study, a very strong red RTP emission centered at 610 nm is achieved by doping Mn2+ ions into Cd-based 2D OIHPs. Notably, the optimized B-EACC:Mn2+ exhibited a high quantum yield of 44.11%, an ultralong lifetime of up to 378 ms, and excellent stability against high temperatures and various solvents, surpassing most reported counterparts of 2D OIHPs. Moreover, the B-EACC:Mn2+ can be used as a red emitter for coating an ultraviolet light-emitting diode chip, exhibiting an observable afterglow to the naked eye for approximately 4 s. In addition, the B-EACC:Mn2+ demonstrates interesting characteristics under X-ray excitation, exhibiting X-ray response at radiation doses in the range of 34.75-278 μGy s-1. This work suggests the infinite possibility of doping guest ions to realize red RTP in 2D OIHPs, promoting the development of long-persistent phosphorescent emitters for multifunctional light-emitting applications.

Multiexciton Generation from a 2D Organic-Inorganic Hybrid Perovskite with Nearly 200% Quantum Yield of Red Phosphorescence

2D organic-inorganic hybrid perovskites (OIHPs) show obvious advantages in the field of optoelectronics due to their high luminescent stability and good solution processability. However, the thermal quenching and self-absorption of excitons caused by the strong interaction between the inorganic metal ions lead to a low luminescence efficiency of 2D perovskites. Herein, a 2D Cd-based OIHP phenylammonium cadmium chloride (PACC) with a weak red phosphorescence (Φ_P  < 6%) at 620 nm and a blue afterglow is reported. Interestingly, the Mn-doped PACC exhibits very strong red emission with nearly 200% quantum yield and 15 ms lifetime, thus resulting in a red afterglow. The experimental data prove that the doping of Mn²⁺ not only induces the multiexciton generation (MEG) process of the perovskite, avoiding the energy loss of inorganic excitons, but also promotes the Dexter energy transfer from organic triplet excitons to inorganic excitons, thus realizing the superefficient red-light emission of Cd²⁺ . This work suggests that guest metal ions can induce host metal ions to realize MEG in 2D bulk OIHPs, which provides a new idea for the development of optoelectronic materials and devices with ultrahigh energy utilization.

Role of halogen effects and cyclic imide groups in constructing red and near-infrared room temperature phosphorescence molecules: theoretical perspective and molecular design

Organic room temperature phosphorescence (RTP) has been widely investigated to realize long-lifetime luminescent materials and improvement in their efficiency is a key focus of research, especially for red and near-infrared (NIR) RTP molecules. However, due to the lack of systematic studies on the relationship between basic molecular structures and luminescence properties, both the species and amounts of red and NIR RTP molecules remain far from meeting the requirements of practical applications. Herein, based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, the photophysical properties of seven red and NIR RTP molecules in tetrahydrofuran (THF) and in the solid phase were theoretically studied. The excited state dynamic processes were investigated by calculating the intersystem crossing and reverse intersystem crossing rates considering the surrounding environmental effects in THF and in the solid phase using a polarizable continuum model (PCM) and quantum mechanics and molecular mechanics (QM/MM) method, respectively. The basic geometric and electronic data were obtained, Huang-Rhys factors and reorganization energies were analyzed, and natural atomic orbital was used to calculate the orbital information of the excited states. Simultaneously, the electrostatic potential distribution on molecular surfaces was analyzed. Further, intermolecular interactions were visualized using the molecular planarity binding independent gradient model based on Hirshfeld partition (IGMH). The results showed that the unique molecular configuration has the potential to achieve red and NIR RTP emission. Not only did the substitutions of halogen and sulfur make the emission wavelength red-shifted, but also linking the two cyclic imide groups could further make the emission wavelength longer. Moreover, we found that the emission characteristics of molecules in THF had a similar trend as in the solid phase. Based on this point, two new RTP molecules with long emission wavelengths (645 nm and 816 nm) are theoretically proposed and their photophysical properties are fully analyzed. Our investigation provides a wise strategy to design efficient and long-emission RTP molecules with an unconventional luminescence group.

Green Synthesis of Phosphorescent Carbon Dots for Anticounterfeiting and Information Encryption

Room-temperature phosphorescent (RTP) carbon dots (CDs) have promising applications in bioimaging, anticounterfeiting, and information encryption owing to their long lifetimes and wide Stokes shifts. Numerous researchers are interested in developing highly bright RTP CDs using environmentally friendly and safe synthesis processes (e.g., natural raw materials and zero-pollution production pathways). In this study, we successfully synthesized RTP CDs using a hydrothermal process employing natural vitamins as a raw material, ethylenediamine as a passivator, and boric acid as a phosphorescent enhancer, which is referred to as phosphorescent CD (PCD). The PCDs exhibit both bright blue fluorescence emission and green RTP emission, with a phosphorescence lifetime as long as 293 ms and an excellent green afterglow visible to the naked eye for up to 7.0 s. The total quantum yield is 12.69%. The phosphorescence quantum yield (PQY) is up to 5.15%. Based on the RTP performance, PCDs have been successfully employed for anticounterfeiting and information protection applications. The results of this study provide a green strategy for the scalable synthesis of RTP materials, which is a practical method for the fabrication of RTP materials with high efficiency and long afterglow lifetimes.

Cluster-luminescent polysiloxane nanomaterials: adjustable full-color ultralong room temperature phosphorescence and a highly sensitive response to silver ions

Non-conjugated polysiloxane nanomaterials with amino and urea groups show persistent cluster-induced phosphorescence regulated by doping different small molecules, and fluorescence/phosphorescence dual responses to Ag+ in aqueous solutions.

Construction of a unique 2-D layered vanadoborate with water-assisted proton conductivity

In the present work, a new two-dimensional layered vanadoborate Na4[V12B18O54(OH)6(H2O)]•(H2en)4•2(OH)•3H2O (1, en = ethylenediamine), based on a [V12B18O54(OH)6(H2O)]10- cluster unit, was hydrothermally obtained and characterized. In the structure, the clusters...