Room Temperature Phosphorescence Emission Research Articles

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.

Naphthyl substituted guest induce efficient room temperature phosphorescence by a triplet-triplet energy transfer mechanism

Room-temperature phosphorescent (RTP) materials have attracted more and more attention due to their long luminescence life and large Stokes displacement. Host-guest doping systems are highly regarded for their simplicity of preparation and the absence of complex synthesis processes. Strong RTP emission can be activated by the doping of a guest molecules, in particular by substituting the phenyl group in the host structure with a naphthalene group. In this study, derivatives of benzophenone were constructed as the host molecule, and used 2-Benzoylnaphthalene, a commercially available naphthyl-substituted analogue of benzophenone, as the guest molecule. The phosphorescent lifetime of the doped system can reach 335 ms and the phosphorescent quantum yield can reach 58 %, which is expected to be used in anti-counterfeiting encryption, biological imaging and other fields. This work provides a general and effective host-guest doping strategy for constructing various organic room temperature phosphorescent materials.

Water-Soluble Luminescent Polymers with Room-Temperature Phosphorescence Based on the α-Amino Acids.

Nonconventional luminophores have received increasing attention, owing to their fundamental importance, advantages in outstanding biocompatibility, easy preparation, environmental friendliness, and potential applications in sensing, imaging, and encryption. Purely organic molecules with outstanding fluorescence and room-temperature phosphorescence (RTP) have emerged as a new library of benign afterglow agents. However, the cost, toxicity, high reactivity, and poor stability of materials also limit their practical applications. Therefore, some natural products, synthetic compounds, and biomolecules have entered horizons of people. The as-designed exhibits sky blue and green fluorescence emission and green RTP emission (a lifetime of 343ms and phosphorescence quantum of 15.3%) under air condition. This study presents an organic fluorescence for biological imaging and RTP for anti-counterfeiting and encryption based on amino acids, maleic anhydride and 4-vinylbenzenesulfonic acid sodium salt hydrate. This study provides a strategy for nonconventional luminophores in designing and synthesizing pure organic RTP materials.

Visible-light-excited robust room-temperature phosphorescence of dimeric single-component luminophores in the amorphous state

Organic room temperature phosphorescence (RTP) has significant potential in various applications of information storage, anti-counterfeiting, and bio-imaging. However, achieving robust organic RTP emission of the single-component system is challenging to overcome the restriction of the crystalline state or other rigid environments with cautious treatment. Herein, we report a single-component system with robust persistent RTP emission in various aggregated forms, such as crystal, fine powder, and even amorphous states. Our experimental data reveal that the vigorous RTP emissions rely on their tight dimers based on strong and large-overlap π-π interactions between polycyclic aromatic hydrocarbon (PAH) groups. The dimer structure can offer not only excitons in low energy levels for visible-light excited red long-lived RTP but also suppression of the nonradiative decays even in an amorphous state for good resistance of RTP to heat (up to 70 °C) or water. Furthermore, we demonstrate the water-dispersible nanoparticle with persistent RTP over 600 nm and a lifetime of 0.22 s for visible-light excited cellular and in-vivo imaging, prepared through the common microemulsion approach without overcaution for nanocrystal formation.

Heavy-Atom Effect Regulating Room-Temperature Phosphorescence of Organic-Inorganic Zn-Based Halides for White-Light Emission.

Organic-inorganic metal halides (OIMHs) with room-temperature phosphorescence (RTP) properties have aroused great research enthusiasm as outstanding broadband white-light emitters. Current studies on OIMHs with white-light emission were achieved via self-trapped excitons (STEs), but the unclear mechanism of STE formation is not favorable for the design of materials. In this work, zero-dimensional OIMHs composed of organic 3,4,5-trimethoxybenzylamine (TBA) and zine halide were synthesized, which enhanced the ratio of the RTP emission to the fluorescence emission from the TBA ligand. The experimental and mechanistic analyses demonstrate that the manageable RTP is mainly caused by the heavy-atom effect. In particular, by adjusting the incorporation ratio of halogen, an obvious white-light emission with a chromaticity coordinate value of (0.31, 0.33) can be achieved. This work developed a method for regulating the RTP of OIMHs with the heavy-atom effect to realize white-light emission, providing a new idea for the design of white-light emission materials.

Solid‐state room‐temperature phosphorescence activated by the end‐capping strategy of cyano groups

AbstractAvoiding the tedious process of crystal cultivation and directly obtaining organic crystals with desirable phosphorescent performance is of great significance for studying their structure and properties. Herein, a set of benzophenone‐cored phosphors with bright green afterglow are obtained on a large scale through in‐situ generation via an end‐capping strategy to suppress non‐radiative triplet excitons and reinforce the intermolecular interactions. The ordered arrangement of phosphors with alkyl‐cyano groups as regulators is crucial for the enhancement of room‐temperature phosphorescence (RTP) emission, which has been further verified by the attenuated lifetimes in isolated states through the formation of inclusion complexes upon binding with pillar[5]arenes. Moreover, the hierarchical interactions of phosphors, including hydrogen bonding, π‐π stacking interactions, and van der Waals forces, are quantified by crystal structures and theoretical calculation to deeply interpret the origins of RTP emission. With this study, we provide a potential strategy for the direct acquisition of crystalline organic phosphors and modulation of RTP.

Controllable Blue Shift and Enhancement Emission during the Gradually Increasing Molecular Weight of Polyacrylamide.

Nonconventional luminescent polymers have become research hotspots due to their advantages such as persistent room temperature phosphorescence (p-RTP) emission and strong film-forming properties. It is proven that the molecular weight (MW) of such luminescent polymers has a significant impact on their emission over a large range, generally with a red shift as the MW increases. Herein, four controllable MW polyacrylamides are prepared via reversible addition-fragmentation chain transfer polymerization (RAFT), and their photoluminescence quantum yield and p-RTP lifetimes gradually increase with the increasing MW. The emission of p-RTP gradually shifts blue with increasing MW, which is likely due to the gradually changing interactions between the electron-rich portion in RAFT reagent and the increasing acrylamide (AM) units in the molecular chain. These can be reasonably explained through small angle X-ray scattering, the clustering-triggered emission (CTE) mechanism, and supported by theoretical calculations. Powder with controllable p-RTP capability has the potential for strategic anti-counterfeiting encryption. The above results not only promote the development of the CTE mechanism toward more precise explanations but also provide new ideas for the preparation of nonconventional luminescent polymers with controllable p-RTP emission performance.

Responsive organic room-temperature phosphorescence materials for spatial-time-resolved anti-counterfeiting

Stimulus-responsive room-temperature phosphorescence (RTP) materials have gained significant attention for their important optoelectronic application prospects. However, the fabrication strategy and underlying mechanism of stimulus-responsive RTP materials remain less explored. Herein, we present a reliable strategy for achieving pH-responsive RTP materials by integrating poly(vinyl alcohol) (PVA) with carboxylic acid or amino group functionalized terpyridine (Tpy) derivatives. The resulting Tpy derivatives-based RTP materials displayed reversible changes in emission color, intensity, and lifetime of both prompt and delayed emission. Notably, the RTP emission undergoes a significant diminish upon exposure to acid due to the protonation of Tpy units. Taking advantage of the decent RTP emission and pH-responsiveness of these RTP films, a spatial-time-resolved anti-counterfeiting application is demonstrated as a proof-of-concept for largely enhancing the security level. This study not only provides new prospects for developing smart RTP materials but also promotes the advancement of optical anti-counterfeiting applications.

A novel group of N,N-diaryl-1,2-benzenediamine room temperature phosphors based on structural engineering

Room temperature phosphorescence (RTP) has gained new momentum as a long-term topic along with the appearance of novel phosphors with versatile application potentials. Compared to traditional RTP materials, innovative pure organic phosphors have become promising alternatives due to their superiority in cost and processibility. However, the development of single-component organic phosphors with ultralong emission lifetimes and simple structures is still ongoing. Despite several kinds of organic phosphors being developed, the ones utilizing arylamine skeletons are barely reported. In this paper, we present a novel family of N,N-diaryl-1,2-benzenediamine phosphors with varying numbers of methyl substituents on terminal phenyl rings based on structural engineering. These molecules exhibited bright phosphorescence in the region of green to yellow light with a remarkably long lifetime up to 684 ms in crystalline states under ambient conditions. Comprehensive experimental and theoretical studies revealed that diverse intermolecular interactions and weak intramolecular hydrogen bonds co-contribute to the long-lived RTP emission. An encryption QR code was constructed, which displayed great potential in anti-counterfeiting applications. This work offered a novel structural motif for ultralong RTP material design and is constructive for material pool expansion.

Hydrogen‐Bonded Organic Frameworks Enabling Highly Robust Aqueous Phase Ultralong Room‐Temperature Phosphorescence

AbstractAqueous phase room‐temperature phosphorescence (RTP) materials are attracting increasing interest owing to their unique optical properties and promising applications. However, the realization of ultralong aqueous state RTP remains a formidable challenge due to severe quenching of triplet excitons in aqueous medium. In this study, a universal strategy is presented to achieve aqueous RTP materials through the encapsulation of organic phosphors within rigid hydrogen‐bonded organic frameworks (HOFs) by in situ self‐assembly. Benefiting from the compact and rigid microenvironments provided by HOFs, the nonradiative dissipations are immensely suppressed and populated triplet excitons are greatly stabilized by geometrical confinement and isolating organic phosphors from quenchers. As a result, the assembled HOFs‐based materials reveal robust RTP emission with an ultralong phosphorescence lifetime of up to 493.1 ms and exhibit long‐term optical and structural stability in water and even in harsh conditions (acid and base) for more than 10 days. Moreover, a fluorescent dye is introduced to finely tune the afterglow performance based on triplet‐to‐singlet Förster resonance energy transfer (TS‐FRET), facilitating advanced information encryption and anticounterfeiting applications. This study provides a reliable and universal method to design and prepare robust RTP materials and expands their applications in advanced information encryption.

Room-Temperature Phosphorescence Materials Featuring Triplet Hybrid Local Charge Transfer Emission.

Room-temperature phosphorescence materials have found important applications in dissolved oxygen sensing, temperature monitoring, anticounterfeiting, etc., because of their prolonged phosphorescence lifetime. However, the known systems mainly utilize the triplet local excited state emission, which is generally less sensitive to microenvironment perturbation. In this work, we designed a series of 4-phenyl-1,8-naphthalimide (NMI) derivatives containing different numbers of carbazole (Cz) units (denoted as NMI-Cz, NMI-2Cz, and NMI-3Cz). Steady state and time-resolved spectroscopy studies determined that the compounds undergo intramolecular through-space charge transfer in solution, yielding a triplet hybrid local charge transfer state. Room-temperature phosphorescence emission was observed in compound-doped poly(methyl methacrylate) thin films upon ammonia treatment. Interestingly, emission from different films exhibited different persistence times. We believe a film-based, time-resolved luminescent ammonia sensor could be developed by making a device of the emissive films as fabricated.

Stable and ultralong room-temperature phosphorescent copolymers with excellent adhesion, resistance, and toughness.

Developing stable room-temperature phosphorescence (RTP) emission without being affected by moisture and mechanical force remains a great challenge for purely organic systems, due to their triplet states sensitive to the infinitesimal motion of phosphors and the oxygen quencher. We report a kind of highly robust phosphorescent systems, by doping a rigid phosphor into a copolymer (polyvinyl butyral resin) matrix with a balance of mutually exclusive features, including a rigidly hydrophilic hydrogen bond network and elastically hydrophobic constituent. Impressively, these RTP polymeric films have superior adhesive ability on various surfaces and showed reversible photoactivated RTP with lifetimes up to 5.82 seconds, which can be used as in situ modulated anticounterfeit labels. They can maintain a bright afterglow for over 25.0 seconds under various practical conditions, such as storage in refrigerators, soaking in natural water for a month, or even being subjected to strong collisions and impacts. These findings provide deep insights for developing stable ultralong RTP materials with desirable comprehensive performance.

Colorful Room‐Temperature Phosphorescence Including White Afterglow from Mechanical Robust Transparent Wood for Time Delay Lighting

The preparation of mechanical robust organic room‐temperature phosphorescence (RTP) materials especially with white afterglow is attractive but rarely reported. Herein, a method to produce mechanical robust colorful RTP transparent wood (PTW) by infiltrating delignified wood with poly (vinyl alcohol) solutions containing arylboronic acids with various π conjugations is reported. The doubly rigid environment provided by the B─O covalent bonds and hydrogen bonds can stabilize the triplet excitons, leading to a ultralong lifetime of up to 2.13 s and excellent RTP emission stability (without obviously quenching over a month) of the target PTW. Besides, as a promising structural material for optical applications, the PTW shows combined advantages of multicolored persistent luminescence (from blue to green and then to red), good optical transmittance (≈90%), and striking mechanical strength (≈154 MPa). More importantly, by introducing appropriate amount of fluorescent dye rhodamine 6 G to the PTW with blue afterglow, white afterglow with a lifetime of 1.85 s is successfully achieve through triplet‐to‐singlet Förster resonance energy transfer. The PTW can function as afterglow window, anticounterfeiting label, and time delay lighting. This success paves the way for the development of mechanical robust, ecofriendly, and practical RTP materials.

Targeting Compact and Ordered Emitters by Supramolecular Dynamic Interactions for High-performance Organic Ambient Phosphorescence.

Purely organic room-temperature phosphorescence (RTP) materials have received intense attention due to their fascinating optical properties and advanced optoelectronic applications. The promotion of intersystem crossing (ISC) and minimalization of nonradiative dissipation under ambient conditions are key prerequisites for realizing high-performance organic RTP; However, the ISC process is generally inefficient for organic fluorogens and the populated triplet excitons are always too susceptible to be well stabilized by conventional means. Particularly, organizing organic fluorophores into compact and ordered entities by supramolecular dynamic interactions has proven to be a newly-emerged strategy to boost the ISC process greatly and suppress the non-radiative relaxations immensely, facilitating the population and stabilization of triplet excitons to access high-performance organic RTP. Consequently, well-defined organic emitters enable robust RTP emission even in the solution state, thus greatly extending the applications. Here, this review is focused on a timely and brief introduction to recent progress in tailoring ordered high-performance RTP emitters by supramolecular dynamic interactions. Their typical preparation strategies, optoelectronic properties, and applications are thoroughly summarized. In the summary section, key challenges and perspectives of this field are highlighted to suggest potential directions for future study.

Mechanical Stretch α-Cyclodextrin Pseudopolyrotaxane Elastomer with Reversible Phosphorescence Behavior.

Polyethylene glycol chains in two terminals of the naphthalene functional group are threaded into α-cyclodextrin cavities to form the pseudopolyrotaxane (NPR), which not only effectively induces the phosphorescence of the naphthalene functional group by the cyclodextrin macrocycle confinement, but also provides interfacial hydrogen bonding assembly function between polyhydroxy groups of cyclodextrin and waterborne polyurethane (WPU) chains to construct elastomers. The introduction of NPR endows the elastomer with enhanced mechanical properties and excellent room temperature phosphorescent(RTP) emission (phosphorescence remains in water, acid, alkali, and organic solvents, even at 160 °C high temperatures). Especially, the reversible mechanically responsive room temperature phosphorescence behavior (phosphorescence intensity increased three times under 200% strain) can be observed in the mechanical stretch and recover process, owing to strain-induced microstructural changes further inhibiting the non-radiative transition and the vibration of NPR. Therefore, changing the phosphorescence behavior of supramolecular elastomers through mechanical stretching provides a new approach for supramolecular luminescent 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.

Achieving pure room temperature phosphorescence (RTP) in phenoselenazine-based organic emitters through synergism among heavy atom effect, enhanced n → π* transitions and magnified electron coupling by the A–D–A molecular configuration

Synergism among heavy atom effect, enhanced n → π* transitions and magnified electron coupling to promote pure RTP emission.

Multi-colour room-temperature phosphorescence from fused-ring compounds for dynamic anti-counterfeiting applications.

We present a facile strategy to achieve purely organic multi-colour room-temperature phosphorescence (RTP) films by doping typical fused-ring compounds into a poly(vinyl alcohol) matrix. Such RTP films demonstrate inherent RTP emission ranging from green to red with a long lifetime and high quantum yield (QY) (lifetime: ∼0.56 ms, QY: ∼35.4%). We further exploit such high-performance RTP films for dynamic information encryption.

Construction and fine tuning of host-guest doping systems and the underlying mechanism of room temperature phosphorescence

To obtain ultralong and efficient pure organic room temperature phosphorescent materials, as well as explore the intrinsic mechanisms affecting the phosphorescence performance of host-guest doping systems, two carbazole derivatives with the same molecular structure, named as L-CzIPCN and CzIPCN, were prepared by using carbazole synthesized in the laboratory and commercial carbazole. By choosing L-CzIPCN/CzIPCN and polymethyl methacrylate (PMMA)/polyvinyl alcohol (PVA)/benzophenone derivatives (BP, F-BP, Br-BP, and DF-BP) as the guest and host respectively, a series of new doping systems were constructed, and optimized by tuning doping ratios between host and guest materials. Among of them, F-BP/L-CzIPCN shows the longest room temperature phosphorescence (RTP) lifetime (501.23 ms), with RTP quantum yield of 31.19 %, followed by 0.2 % L-CzIPCN@PVA film (221.66 ms, 5.86 %) and 0.2 % L-CzIPCN@PMMA film (102.73 ms, 4.28 %) respectively. Moreover, L-CzIPCN displays different RTP spectra in diverse hosts, with dual-band RTP emission at 550 nm and 600 nm in benzophenone derivatives, but single RTP emission maxima in PMMA films, as well as a main emission peak at 470–510 nm and a shoulder peak at 550–590 nm in PVA films. The UV–Vis absorption spectra, fluorescence and phosphorescence spectra, and theoretical calculations indicate that RTP comes from the guest monomers in benzophenone derivatives/L-CzIPCN doping systems, with local triple characteristics, and host materials with large dipole moment, appropriate T1 energy level, and small energy gap between S1 and T1 contribute to improving RTP performance of the doping systems. Based on the excellent luminescence and different RTP lifetimes of the doping systems, some high-level anti-counterfeiting, and information encryption patterns were successfully constructed.

Triplet-triplet energy transfer between host and guest induced strong phosphorescence in the organic doped system

Recently, purely organic room-temperature phosphorescence (RTP) from guest-host-doped systems has grown exponentially due to their high modulation flexibility. Benzophenone has been found as a preferred host matrix thanks to its low melting point, minimal biological toxicity, remarkable stability, and cost-effectiveness. However, the precise role of benzophenone remains elusive and has been debated within the scientific community concerning mechanistic elucidations. Here, five indole derivatives were designed and synthesized as guest molecules while retaining benzophenone as the host to construct doped materials exhibiting outstanding RTP properties. Our experimental findings unequivocally establish that the host benzophenone initially absorbs excitation energy, subsequently intersystem crossing into triplet exciton, facilitating the exciton transfer to guest molecule through the triplet energy transfer and culminating in guest RTP emission. Mechanistic investigation corroborates the superiority of benzophenone in possessing a large spin-orbit coupling constant and quantitatively triplet energy transfer. Collectively, this work provides compelling evidence deciphering energy transfer between host and guest entities for the manifestation of phosphorescence performance in benzophenone-hosted doped materials.