Phosphorescent Color Research Articles

Altering central atoms and bromination sites of phosphorescence units to control ultralong organic room temperature phosphorescence

We report two strategies to expand the library of Phosphorescence Units, including altering the central atom and bromination. Directed by these two strategies, numerous new Phosphorescence Units can be designed. Due to the limitation of organic synthesis and commercial availability, eight organic units (BCz, NBF, BNT, BrBCz-1, BrBCz-2, BrBCz-3, BrBCz-4 and BrBNT) were obtained to verify our proposed methods and study the impact of central atoms and bromination sites on organic room temperature phosphorescence. Considering BCz, NBF and BNT (Group Ⅰ) together, when the central atom is N or S, the room temperature phosphorescence is on as BCz and BNT have higher ISC (Intersystem Crossing) efficiency than NBF; from N to S, phosphorescence wavelength red shifts because the T1 energy level is closely related to the central atom and the lifetime shortens due to different ISC efficiency. Considering BCz, BrBCz-1, BrBCz-2 and BrBCz-3 (Group Ⅱ), bromination and different bromination sites on the benzene ring matters much to ISC efficiency but little to the intrinsic T1 energy level, leading to dramatical increase of phosphorescence intensity, sharp drop of phosphorescence lifetime and subtle change of phosphorescence wavelength (color). Considering BrBCz-4 and BrBNT (Group Ⅲ), bromination on the naphthalene moiety greatly affects both ISC efficiency and the intrinsic T1 energy level, resulting in dramatical increase of phosphorescence intensity, sharp drop of phosphorescence lifetime and significant red shift of phosphorescence color. Therefore, BNT, BrBCz-1, BrBCz-2, BrBCz-3, BrBCz-4 and BrBNT can be regarded as new Phosphorescence Units while NBF cannot be. To our best knowledge, this work for the first time gives design suggestions of organic room temperature materials from the atomic level. This work may give a deep insight into organic phosphorescence from the perspective of Phosphorescence Units and lay foundation for their future applications.

Stimulus-responsive room-temperature phosphorescence with tunable color for time-resolved advanced dynamic anti-counterfeiting

Multi-stimuli responsive multicolored room-temperature phosphorescent (RTP) carbon quantum dots (CQDs) have recently attracted considerable attention, owing to their potential applications in advanced dynamic anti-counterfeiting. The design and development of carbon dots that exhibit both stimulus response characteristics and multicolor RTP emission remains a significant challenge in the field. In this work, we present a novel approach to control the dynamic phosphorescence color and stimulus response properties of CQDs coated on paper by fine-tuning the surface functional groups of the CQDs. Specifically, histidine and 2,4,6-triaminopyrimidine was separately used to prepare N, O co-doped CQDs (NOCQDs) and N-doped CQDs (NCQDs), respectively. These CQDs were further coated on filter paper substrates to achieve water and heating cascade stimulus–response RTP. These stimuli-responsive properties of NOCQDs can be modulated by deprotonating their surface oxygen-containing groups. Eventually, we achieved time-resolved multicolor dynamic anti-counterfeiting by exploiting the stimuli-response properties and lifetimes differences between NOCQDs and NCQDs, realizing the 5D information encryption in all five stimulus-, pattern-, time-, and color-dependent codes. These findings highlight the potential of NOCQDs as advanced anti-counterfeiting materials and lay a foundation for further exploration into the synthesis and properties of CQDs with tunable stimuli-response features and RTP emission.

Thermal Activated Reversible Phosphorescence Behavior of Solid Supramolecule Mediated by β‐Cyclodextrin

AbstractA reversible solid thermally responsive deep‐blue pure organic room temperature phosphorescent material is constructed by terephthalic acid (PPA), β‐cyclodextrin (β‐CD), and poly(vinylalcohol) (PVA). Attributed to the host‐guest interaction of β‐CD to isolate PPA chromophore and the rigid environment offered by hydrogen bonds to suppress the nonradiative decays, amorphous supramolecular assembly PPA‐CD/PVA not only induces a deep‐blue phosphorescence at 410 nm that differing from traditional PPA derivatives with green emission but also enhances the quantum yield up to 30.52%. Uncommonly, this film exhibits a unique reversible thermal stimulation response property with blue and cyan phosphorescence color transitions because heating can destroy the binding behavior between β‐CD and PPA, resulting in redshift phosphorescence emission from PPA stacking. Additionally, with the incorporation of Rhodamine B (RhB) or Sulforhodamine 101 (SR101) into the supramolecular film, color‐tunable phosphorescence from blue to white, yellow, and red relying on the thermal stimulation is realized through triplet‐to‐singlet Förster resonance energy transfer (TS‐FRET) platform. These thermochromic phosphorescence materials are successfully applied in multilevel anticounterfeiting and information encryption, which provides a new simple approach for temperature‐responsive TS‐FRET multicolor luminescence supramolecular materials.

Abnormal thermally-stimulated dynamic organic phosphorescence

Dynamic luminescence behavior by external stimuli, such as light, thermal field, electricity, mechanical force, etc., endows the materials with great promise in optoelectronic applications. Upon thermal stimulus, the emission is inevitably quenched due to intensive non-radiative transition, especially for phosphorescence at high temperature. Herein, we report an abnormal thermally-stimulated phosphorescence behavior in a series of organic phosphors. As temperature changes from 198 to 343 K, the phosphorescence at around 479 nm gradually enhances for the model phosphor, of which the phosphorescent colors are tuned from yellow to cyan-blue. Furthermore, we demonstrate the potential applications of such dynamic emission for smart dyes and colorful afterglow displays. Our results would initiate the exploration of dynamic high-temperature phosphorescence for applications in smart optoelectronics. This finding not only contributes to an in-depth understanding of the thermally-stimulated phosphorescence, but also paves the way toward the development of smart materials for applications in optoelectronics.

One‐Step Fabrication of New PCPNs with Unique Optical Responses for Ultra‐Stable Anti‐Counterfeiting Labels

AbstractConstructing a library of stable phosphors with unconventional fluorescence (FL) and room temperature phosphorescence (RTP) color combination is an effective approach to enhance anti‐counterfeiting strength, but remains a challenge. Herein, a one‐step strategy is proposed to fabricate ultra‐stable CsPbX3/carbon dots (CDs) @NH4AlP2O7 (X = Cl, Br, and I) nanocomposites (PCPNs) with full‐spectrum FL emission and constant short‐wavelength blue RTP emission, breaking the conventional luminescent properties that RTP generally exhibit obvious wavelength red‐shifts compared with FL. The enhanced full‐color (457–612 nm) FL emissions are implemented by adjusting halogen compositions, which is attributed to CsPbX3 as the dominant FL center. Owing to the RTP emission of CDs, constant long‐lived blue RTP emission lasting 12 s is observed from PCPNs. Additionally, the PCPNs exhibit remarkable tolerance to prolonged ultraviolet irradiation and erosion by solutions with various pH and solvents, supported by NH4AlP2O7 inert shell stabilizing the perovskite structure and triplet state. When the anti‐counterfeiting ink based on PCPNs is printed on various substrates, fine anti‐counterfeiting labels with unconventional emission combinations of FL and RTP are formed and show excellent solvent resistance and mechanical stability. This study provides fresh perspectives on the development of anti‐counterfeiting labels with enhanced security strength and long‐term effects.

Ultralong sodium alginate-based room temperature phosphorescence materials with advantages of color tunability, flexibility and facile large-area fabrication

Organic room temperature phosphorescence (RTP) has promising applications in diverse fields, whereas a formidable challenge remains in the development of flexible organic RTP materials, especially environmentally friendly RTP materials. In this work, natural polymer sodium alginate (SA)-based RTP materials have been facilely developed by doping phenylboronic acid (PBA) and its derivatives into SA matrices. 4-carboxyphenylboric acid doped system SA-CPBA exhibits the best RTP performance with an ultralong phosphorescence lifetime of up to 231 ms. Interestingly, SA-CPBA shows excitation-dependent phosphorescence color tunability by water vapor fumigation and heating, and the afterglow color change has good reversibility upon alternating treatment of water vapor fumigation and heating. Amazingly, flexible and transparent RTP films are obtained through adding a certain amount of glycerol (G) into SA-CPBA matrices, and SA-CPBA-G also possesses excellent excitation-dependent phosphorescence color tunability. Furthermore, the flexible SA-CPBA-G film can be conveniently fabricated on a large area. These excellent features enable the prepared SA-based RTP materials to be successfully applied in the fields of flexible display and information encryption. This work provides a guideline for the preparation of environmentally friendly flexible polymer-based color-tunable RTP materials and expands the application range of SA-based materials to the field of flexible displays.

Molecular Engineering Enables Multi‐Color Room Temperature Phosphorescence of Carbon Dots Composites Derived In Situ, Facilitating their Utilization for Advanced Information Encryption

AbstractLong‐life room temperature phosphorescent (RTP) materials hold significant potential in the fields of optoelectronic devices, information encryption, and bio‐imaging due to their excellent optical properties. However, achieving multi‐color tunable RTP materials has proven challenging. In this study, molecular engineering strategies are employed to select precursor molecules with varying degrees of conjugation such as phthalic anhydride (PA), naphtho[2,3‐c] furan‐1,3‐dione (23NA), and naphthalic anhydride (NA). By combining these guest molecules with a host boric acid matrix through a one‐step microwave method, carbon dots (CDs)composites (PA@BA, 23NA@BA and NA@BA) exhibiting excellent RTP properties are successfully prepared. As the degree of precursor conjugation increased gradually, the phosphorescence color modulation of the composites demonstrates satisfactory transitions from blue to yellow. Notably, CDs are derived in situ within the boric acid matrix while covalent and hydrogen bonds formed between CDs and borate matrix effectively suppress nonradiative leaps and facilitate composite RTP activation. Furthermore, the boric acid matrix acts as insulation against oxygen diffusion and prevents quenching of triplet excitons by external factors. The rationality behind phosphorescence emission mechanism and wavelength modulation is further conformed by density functional theory (DFT) calculations. Finally, CDs composites are successfully applied for advanced message encryption of text and images.

Circularly Polarized Phosphorescence of Benzils Achieved by Chiral Supramolecular Polymerization.

In current approaches for circularly polarized phosphorescent materials, the crystallization of chiral phosphors suffers from poor processability, while integrating them into an amorphous polymer matrix results in unsatisfactory chiroptical signals due to the absence of chirality communication. Here, we have developed an innovative strategy through chiral supramolecular polymerization of benzil phosphors facilitated by intermolecular hydrogen bonds. The inherent film-forming capabilities of non-covalent supramolecular polymers obviate the need for an external polymer matrix. The pronounced helical asymmetry of benzil phosphors resulting from chiral supramolecular polymerization leads to enhanced circularly polarized phosphorescence compared to their non-hydrogen-bonded counterparts. The circularly polarized phosphorescent signals can be further modulated by varying the location of stereogenic centers or introducing halogen bonding to benzils. Incorporation of platinum(II) phosphor into the benzil supramolecular polymers induces both chirality and triplet-to-triplet energy transfer, leading to a change in circularly polarized phosphorescent color from yellow to red. In summary, chiral supramolecular polymerization of phosphors represents a novel and effective approach to circularly polarized phosphorescent materials.

Circularly Polarized Phosphorescence of Benzils Achieved by Chiral Supramolecular Polymerization

AbstractIn current approaches for circularly polarized phosphorescent materials, the crystallization of chiral phosphors suffers from poor processability, while integrating them into an amorphous polymer matrix results in unsatisfactory chiroptical signals due to the absence of chirality communication. Here, we have developed an innovative strategy through chiral supramolecular polymerization of benzil phosphors facilitated by intermolecular hydrogen bonds. The inherent film‐forming capabilities of non‐covalent supramolecular polymers obviate the need for an external polymer matrix. The pronounced helical asymmetry of benzil phosphors resulting from chiral supramolecular polymerization leads to enhanced circularly polarized phosphorescence compared to their non‐hydrogen‐bonded counterparts. The circularly polarized phosphorescent signals can be further modulated by varying the location of stereogenic centers or introducing halogen bonding to benzils. Incorporation of platinum(II) phosphor into the benzil supramolecular polymers induces both chirality and triplet‐to‐triplet energy transfer, leading to a change in circularly polarized phosphorescent color from yellow to red. In summary, chiral supramolecular polymerization of phosphors represents a novel and effective approach to circularly polarized phosphorescent materials.

Achieving the conversion from Room-Temperature phosphorescence to photothermal properties by Carbon-Regulated bandgap

Bandgap tunability plays an important role in controlling the photophysical properties of semiconductor material. In this work, we propose a powerful carbon component engineering strategy for regulating the optical bandgap of scandium/cysteine functional materials (Sc/Cys-FMs) that are synthesized by a facile one-pot hydrothermal method. The band structure of Sc/Cys-FMs is closely related to the Cys ligands. As Cys amount rises, the obtained Sc/Cys-FMs exhibit the red-shifted room-temperature phosphorescence (RTP) emission from Sc/Cys-FMs-50 (3.01 eV) to Sc/Cys-FMs-150 (2.14 eV), accompanied by a decrease in quantum efficiency and an increase in lifetime. Meanwhile, the Sc/Cys-FMs show a unique time-dependent phosphorescence color (TDPC) phenomenon, with a dynamic transition of RTP color from yellow to green as the decay time prolongs because of the emission-dependent lifetime. As the amount of Cys further increases, the bandgap can be continuously reduced to 1.88 eV (Sc/Cys-FMs-300) and 1.56 eV (Sc/Cys-FMs-600), causing the quenching of RTP emission and significantly enhanced photothermal properties. The continuously decreasing bandgap has been proven to be directly ascribed to the increase of carbon component in Sc/Cys-FMs. Considering the TDPC properties, Sc/Cys-FMs can be well used for dynamic phosphorescent anti-counterfeiting. This work not only develops a scalable method for preparing functional materials with superior RTP and photothermal properties, but also proposes the carbon component engineering strategy to achieve bandgap tunability of materials.

Time-dependent room temperature phosphorescent colors from a sulfur-doped carbon dot-based composite for advanced information encryption and anti-counterfeiting applications

Sulfur doping regulates the bandgap of the carbon dots, and time-dependent afterglow color emission is realized in a carbon dot-based composite via the multiple triplet emissions with distinct lifetimes.

Time-dependent phosphorescence color of carbon dots in boric acid matrix for dynamic information encryption

CDs and CDs-X (X = F, Cl, Br, or I) synthesis and applications in advanced information encryption.

Correction: Time-dependent phosphorescence color of carbon dots in boric acid matrix for dynamic information encryption

Correction for ‘Time-dependent phosphorescence color of carbon dots in boric acid matrix for dynamic information encryption’ by Xiaopeng Wang et al., J. Mater. Chem. C, 2024, 12, 5849–5855, https://doi.org/10.1039/D4TC00431K.

Confinement-Modulated Clusterization-Triggered Time-Dependent Phosphorescence Color from Xylan-Carbonized Polymer Dots.

Achieving time-dependent phosphorescence color (TDPC) in organic materials is attractive but extremely challenging due to the nonradiative decay and modulation puzzle of triplet state. Herein, xylan, a hemicellulose waste from the paper mill, was used to construct carbonized polymer dots (CPDs) with clusterization-triggered room-temperature phosphorescence (RTP). CPDs were endowed with tuneable triplet energy levels by through-space conjugation of heteroatom groups, which could be confined in silica to simultaneously activate surface oxide-related low-energy and cross-linked core N-related high-energy emissive centers. Thus, the blue emissive center with a lifetime of 425.6 ms and green emissive center with a longer lifetime of 1506 ms coexisted in the confined CPDs; the former was the dominant contribution to RTP at first, and the latter became dominant over time, leading to a typical TDPC evolution with large color contrast from blue to blue-green and then to green. Meanwhile, the TDPC could remain unobstructed after the confined CPDs were soaked in water for more than a month. The CPDs were successfully applied in location and deformation imaging of hydrogel and advanced dynamic information encryption and anticounterfeiting. The work may shed new light on the design of TDPC materials and broaden the high-value use of paper-mill waste xylan.

Dynamic Room Temperature Phosphorescence of Silane-Functionalized Carbon Dots Confining within Silica for Anti-Counterfeiting Applications.

Room temperature phosphorescent (RTP) materials with long-lived, excitation-dependent, and time-dependent phosphorescence are highly desirable but very hard to achieve. Herein, this work reports a rational strategy of multiple wavelength excitation and time-dependent dynamic RTP color by confining silane-functionalized carbon dots (CDs) in a silica matrix (Si-CDs@SiO2). The Si-CDs@SiO2 possesses unique green-light-excitation and a change in phosphorescence color from yellow to green. A slow-decaying phosphorescence at 500nm with a lifetime of 1.28 s and a fast-decaying phosphorescence at 580nm with a lifetime of 0.90 s are observed under 365nm of irradiation, which originated from multiple surface triplet states of the Si-CDs@SiO2. Given the unique dynamic RTP properties, the Si-CDs@SiO2 are demonstrated for applications in fingerprint recognition and multidimensional dynamic information encryption. These findings will open an avenue to explore dynamic phosphorescent materials and significantly broaden their applications.

Enabling Carbonized Polymer Dots with Color‐tunable Time‐dependent Room Temperature Phosphorescence through Confining Carboxyl Dimer Association

AbstractDeveloping a facile strategy to realize fine‐tuning of phosphorescence color in time‐dependent room temperature phosphorescence (RTP) materials is essential but both theoretically and practically rarely exploited. Through simultaneously confining carboxyl dimer association and isolated carboxyl into the particle via a simple hydrothermal treatment of polyacrylic acid, a dual‐peak emission of red phosphorescence (645 nm) and green phosphorescence (550 nm) was observed from carbonized polymer dots (CPDs). The ratio of the two luminescent species can be well regulated by hydrochloric acid inhibiting the dissociation of carboxyl to promote hydrogen bond. Due to comparable but different lifetimes, color‐tunable time‐dependent RTP with color changing from yellow to green or orange to green were obtained. Based on the crosslinking enhanced emission effect, the phosphorescence visible time was even extended to 7 s through introducing polyethylenimide. This study not only proposes a novel and facile method for developing CPDs with color‐tunable time‐dependent RTP, but also provides a bran‐new non‐conjugated red phosphorescence unit and its definite structure.

Enabling Carbonized Polymer Dots with Color-tunable Time-dependent Room Temperature Phosphorescence through Confining Carboxyl Dimer Association.

Developing a facile strategy to realize fine-tuning of phosphorescence color in time-dependent room temperature phosphorescence (RTP) materials is essential but both theoretically and practically rarely exploited. Through simultaneously confining carboxyl dimer association and isolated carboxyl into the particle via a simple hydrothermal treatment of polyacrylic acid, a dual-peak emission of red phosphorescence (645 nm) and green phosphorescence (550 nm) was observed from carbonized polymer dots (CPDs). The ratio of the two luminescent species can be well regulated by hydrochloric acid inhibiting the dissociation of carboxyl to promote hydrogen bond. Due to comparable but different lifetimes, color-tunable time-dependent RTP with color changing from yellow to green or orange to green were obtained. Based on the crosslinking enhanced emission effect, the phosphorescence visible time was even extended to 7 s through introducing polyethylenimide. This study not only proposes a novel and facile method for developing CPDs with color-tunable time-dependent RTP, but also provides a bran-new non-conjugated red phosphorescence unit and its definite structure.

Multicolor‐Tunable and Time‐Dependent Circularly Polarized Room‐Temperature Phosphorescence from Liquid Crystal Copolymers

AbstractCircularly polarized luminescent (CPL) materials have significant promising applications in organic light‐emitting diodes, asymmetric synthesis, and other fields. However, due to the instability of triplet‐state excitons, how to achieve an effective combination of CPL with room‐temperature phosphorescence (RTP) remains a formidable challenge. Here, a simple and feasible method for constructing polymer‐based CPRTP materials is proposed by preparing chiral phosphorescent liquid crystals through copolymerization. A series of RTP chiral liquid crystal copolymers are successfully synthesized by copolymerizing phosphorescent monomer bearing chiral cholesterol mesogen with phosphorescent monomer bearing dibenzofuran chromophore. Due to the introduction of chiral cholesterol mesogen, copolymers can form chiral smectic C‐phase liquid crystals. Utilizing their selective reflection characteristic, efficient CPRTP is achieved, with a glum value of up to −1.6 × 10−2. In addition, both components in copolymers exhibit RTP properties and show significant differences in phosphorescence color and lifetime. By changing the composition of copolymers, the regulation of their phosphorescence properties is successfully achieved. As a result, multicolor‐tunable and time‐dependent CPRTP materials are successfully prepared.

Synthesis and Properties of Room-Temperature Phosphorescent Liquid Crystal Copolymers with Linearly Polarized Luminescence Characteristic.

Room-temperature phosphorescent (RTP) liquid crystal materials have garnered considerable attention because of their significant applications in organic light emitting diodes, polarized light emitting materials, and so forth. How to efficiently synthesize pure organic RTP liquid crystals and regulate their performance is of great significance. In this article, we propose a simple and feasible method to synthesize RTP liquid crystals and manipulate their properties through copolymerization. We constructed RTP liquid crystal copolymers by copolymerizing a phosphorescent monomer bearing biphenyl mesogen with a phosphorescent monomer bearing a dibenzofuran chromophore. All the synthesized copolymers show a liquid crystal property because of the introduction of biphenyl mesogen. Meanwhile, by changing the composition of copolymers, it is possible to regulate their RTP performance, including luminescence color and lifetime. As the content of the PMDFM0C component in copolymers increases, the phosphorescence lifetime gradually increases. For poly(MDFM0C(0.46)-co-MBi18C(0.54)), the phosphorescence lifetime can reach 463.0 ms. Moreover, the phosphorescence color of the PMDFM0C component in copolymers changes with the copolymer composition, which can induce variable room-temperature phosphorescence. In addition, when oriented, liquid crystal copolymer films can emit linearly polarized fluorescence and linearly polarized phosphorescence. The linearly polarized phosphorescence dichroic ratio and polarization ratio values of the oriented poly(MDFM0C(0.46)-co-MBi18C(0.54)) film are 3.33 and 0.50, respectively.

Visible light-excited full-color phosphorescent material realized by carbon dots dispersed in polyacrylamide and applied to anti-counterfeiting

Carbon dots-based phosphorescent composites have excellent room-temperature phosphorescent properties. However, the development of carbon dots-based phosphorescent materials that are excited by visible light and have adjustable colors remains a challenge. Here, we report on phosphorescent composites based on multicolored fluorescent carbon dots (CDs) and polyacrylamide (PAM) with four phosphorescent colors (blue, green, yellow and red). The phosphorescence of CDs@PAM composites is mainly derived from the C=O bonds of CDs. Electron transition of n-π* in the C=O bonds facilitates the intersystem crossover that are necessary to generate phosphorescence. In addition, the hydrogen bond actions between the amide groups of PAM polymer and the functional groups on CDs surface also promote the intersystem crossover and inhibit the non-radiative relaxation of triple states (T1) in CDs@PAM. Meanwhile, the PAM matrix provides a rigid protective environment (hydrogen bond mesh structure) that inhibits vibrations, rotations and collisions of the CDs' luminescent clusters (C=O), avoiding the rapid decay of phosphorescence. Four kinds of CDs based phosphorescence materials can produce brilliant phosphorescence under the excitation of visible light (flashlight). Finally, their colorful phosphorescent colors were used to achieve a naked-eye observable anti-counterfeit pattern, demonstrating the potential application of these materials.