Delayed Fluorescence Lifetime Research Articles

Gold Coordination-Accelerated Multi-Resonance TADF Emission for Efficient Solution-Processible Ultrapure Deep-Blue OLEDs.

Multi-resonance (MR) type emitters have emerged as highly promising candidates for high-resolution organic light-emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIEy close to 0.046 and an emission peak > 440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold-coordinated MR molecules to achieve efficient and short-lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep-blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparing with 60.6 μs for the organic analogue. Solution-processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, Commission International de l'Éclairage (CIE) coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8%.

Sandwich-type thermally activated delayed fluorescence molecules with through-space charge transfer excited state for red OLEDs

Exploring through-space charge transfer (TSCT) excited state for the design of thermally activated delayed fluorescence (TADF) emitters has been receiving increasing interest for organic light-emitting diodes (OLEDs). In this work, we developed two TSCT-TADF molecules, namely 2DPXZ-QX and 2DPXZ-DFQX, which have sandwich-type donor-acceptor-donor (D-A-D) structures supported by two carbazole bridges. Dibenzo[a,c]phenazine (QX) and its fluorinated derivative (DFQX) were used as the acceptors and O-bridged triphenylamine (DPXZ) was used as the donor. The two donors and acceptor in each molecule are aligned in a face-to-face orientation and thus result in the presence of intramolecular π–π interactions, as revealed by their single crystal X-ray structures. The emission maxima (λPL) of 2DPXZ-QX and 2DPXZ-DFQX in doped 1,3-bis(N-carbazolyl)benzene films are 595 and 600 nm with photoluminescence quantum yields of 67 % and 54 %, respectively. The delayed fluorescence lifetimes are 8.8 and 6.7 μs. OLEDs based on the new sandwich-type emitters show maximum external quantum efficiencies of up to 19.1 %.

Application of the Heavy-Atom Effect for (Sub)microsecond Thermally Activated Delayed Fluorescence and an All-Organic Light-Emitting Device with Low-Efficiency Roll-off.

The feature of abundant and environmentally friendly heavy atoms (HAs) like bromine to accelerate spin-forbidden transitions in organic molecules has been known for years. In combination with the easiness of incorporation, bromine derivatives of organic emitters showing thermally activated delayed fluorescence (TADF) emerge as a cheap and efficient solution for the slow reverse intersystem crossing (rISC) problem in such emitters and strong efficiency roll-off of all-organic light-emitting diodes (OLEDs). Here, we present a comprehensive photophysical study of a tri-PXZ-TRZ emitter reported previously and its hexabromo derivative showing a remarkable enhancement of rISC of up to 9 times and a short lifetime of delayed fluorescence of 2 μs. Analysis of the key molecular vibrations and TADF mechanism indicates almost compete blockage of the spin-flip transition between the charge-transfer states of different multiplicity 3CT → 1CT. In such a case, rISC as well as its enhancement by the HA is realized via the 3LE → 1CT transition, where 3LE is the triplet state localized on the same brominated phenoxazine donor involved in the formation of the 1CT state. Interestingly, the spin-orbit coupling (SOC) with two other 3LE states is negligible because they are localized on different donors and not involved in 1CT. We consider this as an example of an additional "localization" criterion that completes the well-known El Sayed rule on the different nature of states for nonzero SOC. The applicative potential of such a hexabromo emitter is tested in a "hyperfluorescent" system containing a red fluorescent dopant (tetraphenyldibenzoperiflanthene, DBP) as an acceptor of Förster resonance energy transfer, affording a narrow-band red-emitting system, with most of the emission in the submicrosecond domain. In fact, the fabricated red OLED devices show remarkable improvement of efficiency roll-off from 2-4 times depending on the luminance, mostly because of the increase of the rISC constant rate and the decrease of the overall delayed fluorescence lifetime thanks to the HA effect.

Bromine indirubin FLIM/PLIM sensors to measure oxygen in normoxic and hypoxic PDT conditions

BackgroundThe induction of phototoxicity during photodynamic therapy (PDT) is dependent on oxygen availability. For this reason, the development of sensors to measure oxygen and oxygen consumption is extremely important. ApproachIn this project we have used Fluorescence Lifetime imaging (FLIM) and Phosphorescence Lifetime Imaging/ delayed Fluorescence Lifetime Imaging (PLIM/dFLIM) to investigate the ability of bromine indirubin derivatives as oxygen sensors. ResultsThe oxygen sensitivity of bromine indirubins was detected through PLIM/dFLIM. Moreover, we have observed, by measuring nicotinamide adenine dinucleotide (NADH) FLIM, that bromine indirubin has a significant impact on cellular metabolism by shifting the SCC-4 Cells metabolism from oxidative phosphorylation (OXPHOS) to glycolysis. ConclusionsIn conclusion, this study successfully achieves its goals and provides important insights into the use of indirubin as a potential oxygen consumption sensor with the capability to identify and differentiate between normoxic and hypoxic regions within the cells.

Borylation and rearrangement reactions of azasilaanthracenes to afford B,N-doped nanographenes.

An air-stable B3,N3-containing dibenzobisanthene (8) was prepared in 29% yield by heating a 1,3,5-tri(azasilaanthryl)benzene (5) with BBr3 (180 °C). Under these conditions, the reaction does not stop after threefold SiMe2/BBr exchange but proceeds further via two rearrangement and two intramolecular C-H borylation steps. Some mechanistic details were unveiled by using smaller model systems and applying lower reaction temperatures. According to X-ray crystallography, compound 8 has a helically distorted scaffold. Due to its multiple resonance structure, it shows a narrow-band blue-green emission (λem = 493 nm; ΦPL = 84%; FWHM = 0.20 eV; THF); samples measured in PMMA gave prompt and delayed fluorescence lifetimes of 10.7 ns and 136 μs, respectively. The optical properties of 8 and of structurally related species were also investigated by quantum-chemical means: most of these compounds exhibit a small energy gap ΔEST between the lowest excited singlet (S1) and triplet (T1) states and a non-negligible spin-orbit coupling (SOC) between S1 and T1/T2, demonstrating their potential as thermally activated delayed fluorescence (TADF) emitters.

Efficient orange and red thermally activated delayed fluorescence materials based on 1,8-naphthalimide derivatives.

Thermally activated delayed fluorescence (TADF) molecules have emerged as a promising class of third-generation organic light-emitting diode (OLED) emitters that can achieve 100% internal quantum efficiency without the use of noble metals. However, the design of high-efficiency red TADF materials has been challenging due to limitations imposed by the energy-gap law. To overcome this challenge, two new TADF emitters, namely, 6-(4-(diphenylamino)phenyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (NI-TPA) and 6-(10H-phenothiazin-10-yl)-2-phenyl-1H-benzo[de]-isoquinoline-1,3(2H)-dione (NI-Pz), have been synthesized and characterized. These compounds exhibit strong TADF characteristics with a small energy gap (ΔEST) between the lowest excited singlet and triplet states, short delayed fluorescence lifetimes, high thermal stability, and high photoluminescence quantum yields. The OLED devices fabricated using NI-TPA and NI-Pz as emitters show orange and red electroluminescence with emission peaks at 593 nm and 665 nm, respectively, and maximum external quantum efficiencies (EQEs) of 11.3% and 7.6%, respectively. Furthermore, applying NI-TPA to cell imaging yielded excellent imaging results, indicating the potential of red TADF materials in the field of biological imaging.

Efficient energy levels and lifetimes regulation of excited states for narrowband thermally activated delayed fluorescence

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials attract much attention owing to their 100 % exciton utilization, high photoluminescence quantum yield (PLQY) and narrowband emission with high color purity. However, how to regulate the energy levels and lifetimes of excited states for long-wavelength and short delayed fluorescence lifetime MR-TADF materials is still a challenge. Herein, an electron acceptor unit of pyrimidine derivative is introduced with steric-hinerance effect. The emission spectrum of BN-DPP is red shifted with 15 nm and the full width at half maximum (FWHM) is even narrower of 20 nm compared with that of DtCZB. A yellow-green MR-TADF material, called BN-DPBQ, is fabricated by extended the conjugation. Moreover, the delayed fluorescence lifetime of BN-DPBQ is half of that of BN-DPP. The BN-DPP based devices exhibit greenish blue emission with peak locating at 494 nm and maximum external quantum efficiency (EQE) of 23.6 %. BN-DPBQ based ones show much red shifted spectrum with emission peak at 538 nm and maximum EQE of 20.3 %. The results indicate that introducing electron acceptor units with steric-hinerance effect and extending the conjugation of resonance skeleton are effective ways to regulate energy levels and lifetimes of excited states for MR-TADF.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Color-Tunable Dual-Mode Organic Afterglow for White-Light Emission and Information Encryption Based on Carbazole Doping.

Dual-mode emission materials, combining phosphorescence and delayed fluorescence, offer promising opportunities for white-light afterglow. However, the delayed fluorescence lifetime is usually significantly shorter than that of phosphorescence, limiting the duration of white-light emission. In this study, a carbazole-based host-guest system that can be activated by both ultraviolet (UV) and visible light is reported to achieve balanced phosphorescence and delayed fluorescence, resulting in a long-lived white-light afterglow. Our study demonstrated the critical role of a charge transfer state in the afterglow mechanism, where the charge separation and recombination process directly determined the lifetime of afterglow. Simultaneously, an efficient reversed intersystem crossing process was obtained between the singlet and triplet charge transfer states, which further boosted the delayed fluorescence properties of the doping system. As a result, delayed fluorescence lifetime was successfully prolonged to approach that of phosphorescence. This work presents a delayed fluorescence lifetime improvement strategy via doping method to realize durable white-light afterglow.

Color‐Tunable Dual‐Mode Organic Afterglow for White‐Light Emission and Information Encryption Based on Carbazole Doping

AbstractDual‐mode emission materials, combining phosphorescence and delayed fluorescence, offer promising opportunities for white‐light afterglow. However, the delayed fluorescence lifetime is usually significantly shorter than that of phosphorescence, limiting the duration of white‐light emission. In this study, a carbazole‐based host–guest system that can be activated by both ultraviolet (UV) and visible light is reported to achieve balanced phosphorescence and delayed fluorescence, resulting in a long‐lived white‐light afterglow. Our study demonstrated the critical role of a charge transfer state in the afterglow mechanism, where the charge separation and recombination process directly determined the lifetime of afterglow. Simultaneously, an efficient reversed intersystem crossing process was obtained between the singlet and triplet charge transfer states, which facilitating the delayed fluorescence properties of host–guest system. As a result, delayed fluorescence lifetime was successfully prolonged to approach that of phosphorescence. This work presents a delayed fluorescence lifetime improvement strategy via doping method to realize durable white‐light afterglow.

Efficient and stable green organic light-emitting diode utilizing an asymmetric butterfly-shaped chromophore with enhanced reverse intersystem crossing and suppressed exciton annihilation

Intermolecular electron-exchange interactions involving long-lived triplet state excitons dominate the quenching process of the films. In this work, a butterfly-shaped thermally activated delayed fluorescence (TADF) emitter 10,10′-(5-((3,5-di(9H-carbazol-9-yl)phenyl)sulfonyl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (BCZ-DPS-BAD) with diphenylsulfone skeleton is constructed by modulating the rigid steric hindrance on the electron donor fragment to weaken intermolecular electron-exchange interactions. Analysis of the ground and excited state properties, crystal structure, steady-state and transient photophysical characteristics reveals that BCZ-DPS-BAD exhibits loose intermolecular arrangements with no direct facing close packing and weak π–π interactions of 4.18 Å and 4.67 Å. The triplet state excitons can swiftly return to the single exciton state in accordance with a short delayed fluorescence lifetime (2.3 μs) and a quick reverse intersystem crossing rate (1.85 × 106 s−1), obstructing the way for the triplet state to lose energy. A remarkable maximum external quantum efficiency of 21.8 %, maximum current efficiency of 56.8 cd/A and exciton utilization rate of 82 % is achieved for BCZ-DPS-BAD-based green non-doped OLED, concomitant with Commission Internationale d'Eclairage (CIE) coordinates of (0.30, 0.50). Notably, BCZ-DPS-BAD behaves stable non-doped OLED performance with efficiency roll-off of 4 % at 1000 cd m−2.

Monoanionic Phosphorus‐Supported Air Stable Cu(I)8, Ag(I)7, and Ag(I)5 Nanoclusters Exhibiting TADF: A Novel Photocatalyst for Stereoselective Carbene Transfer Reactions

AbstractApplications of structurally well‐defined coinage‐metal nanoclusters (NCs) as optoelectronic materials and homogeneous catalysts have been restricted due to their inherent lower stability. Herein, the syntheses, structural characterizations, and photoluminescence properties of three novel air‐stable coinage‐metal(I) NCs‐supported by carbene‐anchored monoanionic phosphorus (cAAC=P−) with molecular formulae [(Cy‐cAACP)4(Cu)4(CuCl)4] (4), [(Cy‐cAACP)4(Ag)4(AgOTf)3] (5), and [(Cy‐cAACP)4(Ag)5]NTf2 (6) (cAAC = cyclic alkyl(amino) carbene; Tf = CF3SO2) exhibiting thermally activated delayed fluorescence (TADF) are reported. Apart from attractive metallophilic interactions [M─M; M ═ Cu, Ag], the enhanced kinetic and thermodynamic stability of 4–6 can be attributed to the excellent π‐accepting ability of cAAC=P− surrounding the metallic cores. cAAC=P− anion is generated either in situ by anion‐induced cleavage of P−Sb/B bonds of corresponding stibanyl/boryl phosphaalkenes in the presence of coinage‐metal(I)‐Cl/OTf/NTf2 salts or by directly introducing alkali‐metal phosphinidenide. The TADF properties of 4–6 are established by smaller energy gaps between the lowest singlet excited state and triplet excited state. In solid‐state, the delayed fluorescence lifetimes of 4–6 are found to be in the microsecond range with absolute photoluminescence quantum yields up to 20%. The redox‐active Cu(I)8 NC 4 is successfully exploited as an efficient photo‐catalyst for the selective carbene transfer reaction at ambient conditions, affording cyclopropanated indoles/styrenes with excellent yields and diastereoselectivity.

Facile Functionalization of Ambipolar, Nitrogen-Doped PAHs toward Highly Efficient TADF OLED Emitters.

Despite promising optoelectronic features of N-doped polycyclic aromatic hydrocarbons (PAHs), their use as functional materials remains underdeveloped due to their limited post-functionalization. Facing this challenge, a novel design of N-doped PAHs with D-A-D electronic structure for thermally activated delayed fluorescence (TADF) emitters was performed. Implementing a set of auxiliary donors at the meta position of the protruding phenyl ring of quinoxaline triggers an increase in the charge-transfer property simultaneously decreasing the delayed fluorescence lifetime. This, in turn, contributes to a narrow (0.04-0.28 eV) singlet-triplet exchange energy split (ΔEST) and promotes a reverse intersystem crossing transition that is pivotal for an efficient TADF process. Boosting the electron-donating ability of our N-PAH scaffold leads to excellent photoluminescence quantum yield that was found in a solid-state matrix up to 96% (for phenoxazine-substituted derivatives, under air) with yellow or orange-red emission, depending on the specific compound. Organic light-emitting diodes (OLEDs) utilizing six, (D-A)-D, N-PAH emitters demonstrate a significant throughput with a maximum external quantum efficiency of 21.9% which is accompanied by remarkable luminance values which were found for all investigated devices in the range of 20,000-30,100 cd/m2 which is the highest reported to date for N-doped PAHs investigated in the OLED domain.

Long Lifetime Delayed Fluorescent Materials with Water and Temperature Tolerability Based on Charge Separation States

AbstractLong lifetime delayed fluorescent materials have great potential applications in bioimaging, anti‐counterfeiting encryption, lighting, and other fields. However, the preparation of functionalized long lifetime fluorescent materials with simple chemical structure and tunable luminescent behavior still poses significant challenges. In this article, a simple and effective method to prepare a series of long lifetime delayed fluorescent copolymers with temperature and humidity tolerance is presented. This method involves the copolymerization of 2‐bromo‐5‐hydroxybenzaldehyde derivative monomer (M1), which contains electron‐withdrawing groups, with naphthalimide derivative fluorescent monomer (M2), which contains electron‐donating groups. The results demonstrate that long‐range charge transfer occurs between the two components in copolymers, forming charge‐separated states that emit long lifetime delayed fluorescence after exciton recombination. The delayed luminescent behavior of the copolymer is directly influenced by the content of the M2 component. The maximum delayed fluorescence lifetime can reach 13.7 ms, and the fluorescence quantum yield is 39%. Interestingly, the polymer film of P3 can emit a maximum afterglow of 1.00 s after photoactivation. Even after being immersed in water for 49 days, the afterglow remains unchanged. Besides, the afterglow of P3 can exist for ≈0.43 s at 323 K. Even at 373 K, the afterglow for 0.2 s can still be observed.

The effect of dark states on the intersystem crossing and thermally activated delayed fluorescence of naphthalimide-phenothiazine dyads.

A series of 1,8-naphthalimide (NI)-phenothiazine (PTZ) electron donor-acceptor dyads were prepared to study the thermally activated delayed fluorescence (TADF) properties of the dyads, from a point of view of detection of the various transient species. The photophysical properties of the dyads were tuned by changing the electron-donating and the electron-withdrawing capability of the PTZ and NI moieties, respectively, by oxidation of the PTZ unit, or by using different aryl substituents attached to the NI unit. This tuning effect was manifested in the UV-vis absorption and fluorescence emission spectra, e.g., in the change of the charge transfer absorption bands. TADF was observed for the dyads containing the native PTZ unit, and the prompt and delayed fluorescence lifetimes changed with different aryl substituents on the imide part. In polar solvents, no TADF was observed. For the dyads with the PTZ unit oxidized, no TADF was observed as well. Femtosecond transient absorption spectra showed that the charge separation takes ca. 0.6 ps, and admixtures of locally excited (3LE) state and charge separated (1CS/3CS) states formed (in n-hexane). The subsequent charge recombination from the 1CS state takes ca. 7.92 ns. Upon oxidation of the PTZ unit, the beginning of charge separation is at 178 fs and formation of 3LE state takes 4.53 ns. Nanosecond transient absorption (ns-TA) spectra showed that both 3CS and 3LE states were observed for the dyads showing TADF, whereas only 3LE or 3CS states were observed for the systems lacking TADF. This is a rare but unambiguous experimental evidence that the spin-vibronic coupling of 3CS/3LE states is crucial for TADF. Without the mediating effect of the 3LE state, no TADF is resulted, even if the long-lived 3CS state is populated (lifetime τCS ≈ 140 ns). This experimental result confirms the 3CS → 1CS reverse intersystem crossing (rISC) is slow, without coupling with an approximate 3LE state. These studies are useful for an in-depth understanding of the photophysical mechanisms of the TADF emitters, as well as for molecular structure design of new electron donor-acceptor TADF emitters.

Observation of Long-Lived Charge-Separated States in Anthraquinone-Phenothiazine Electron Donor-Acceptor Dyads: Transient Optical and Electron Paramagnetic Resonance Spectroscopic Studies.

We prepared a series of phenothiazine (PTZ)-anthraquinone (AQ) electron donor-acceptor dyads to study the relationship between molecular structures and the possibility of charge transfer (CT) and intersystem crossing (ISC). As compared to the previously reported PTZ-AQ dyad with a direct connection of two units via a C-N single bond, the PTZ and AQ units are connected via a p-phenylene or p-biphenylene linker. Conformation restriction is imposed by attaching ortho-methyl groups on the phenylene linker. UV-vis absorption spectra indicate electronic coupling between the PTZ and AQ units in the dyads without conformation restriction. Different from the previously reported PTZ-AQ, thermally activated delayed fluorescence (TADF) is observed for the dyads containing one phenylene linker (PTZ-Ph-AQ and PTZ-PhMe-AQ). The prompt fluorescence lifetime in cyclohexane is exceptionally long (τPF = 62.0 ns, population ratio: 99.2%) and 245.0 ns (93.5%) for PTZ-Ph-AQ and PTZ-PhMe-AQ, respectively (normally τPF <20 ns); the delayed fluorescence lifetimes for these two dyads were determined as τDF = 2.4 μs (6.5%) and 7.6 μs (0.8%), respectively. For the dyad containing a biphenylene linker (PTZ-Ph2Me-AQ), no TADF was observed. Charge-separated (CS) states were observed for PTZ-Ph-AQ and PTZ-PhMe-AQ, and the lifetimes were determined as 7.0 and 1.3 μs, respectively, indicating the triplet spin multiplicity of the CS state. The 3CS state lifetimes are shortened to 100 ns and 440 ns for the two dyads, respectively, in the polar solvent acetonitrile. For dyads with a longer linker, i.e., PTZ-Ph2Me-AQ, the CS state lifetime is not sensitive to solvent polarity (τCS = 1.8 and 1.3 μs in cyclohexane and acetonitrile, respectively). In reference dyads, where the PTZ unit is oxidized to sulfoxide, no CT absorption band and TADF were observed, which is attributed to the increased CS state energy (>3 eV) becoming higher than that of the AQ triplet (3AQ*) state (ca. 2.7 eV). These experimental evidence show that the presence of 1CS, 3CS, and 3LE (LE: locally excited) states sharing similar energy is essential for the occurrence of TADF. Population of the long-lived 3CS state (with a lifetime of a few μs) does not produce by itself TADF, because the ISC process of 1CS→3CS is nonsufficient. Femtosecond transient absorption spectra show that charge separation (CS) occurs readily (<5 ps) for most dyads, even in nonpolar solvents. Nanosecond pulsed laser-excited time-resolved electron paramagnetic resonance (TREPR) spectra show that either a spin correlated radical pair (SCRP) is formed, with the electron exchange energy 2J = +2.14 mT, or radical pairs with stronger interaction, |2J| > 6.57 mT. These studies are useful for in-depth understanding of the CS and ISC in compact electron donor-acceptor dyads and for design of efficient TADF emitters.

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Purely Organic Fluorescence Afterglow: Visible‐Light‐Excitation, Inherent Mechanism, Tunable Color, and Practical Applications with Very Low Cost

AbstractPurely organic materials with visible light excitable fluorescence afterglow are promising for applications. Herein, fluorescence afterglow with various intensity and duration was observed on fluorescent dyes once being dispersed in polymer matrix, thanks to the slow reverse intersystem crossing rate (kRISC) and long delayed fluorescence lifetime (τDF) derived from the coplanar and rigid chemical structure of the dyes. To verify the mechanism, different polymers were used to tune singlet‐triplet splitting energy based on solvent effect. And commercial acriflavine (Acf) film showed blue shifted fluorescence compared to purified one, with slower kRISC (≈100 s−1) and longer τDF (0.6 s). Via energy transfer from Acf to rhodamine B, the afterglow color was further regulated, with the largest fluorescence quantum yield of 42.4 %. It was demonstrated that the materials worked on color tunable light sources, and low‐cost ($2 for 50 000 labels) anti‐counterfeit labels recognized by white light.

Purely Organic Fluorescence Afterglow: Visible-Light-Excitation, Inherent Mechanism, Tunable Color, and Practical Applications with Very Low Cost.

Purely organic materials with visible light excitable fluorescence afterglow are promising for applications. Herein, fluorescence afterglow with various intensity and duration was observed on fluorescent dyes once being dispersed in polymer matrix, thanks to the slow reverse intersystem crossing rate (kRISC ) and long delayed fluorescence lifetime (τDF ) derived from the coplanar and rigid chemical structure of the dyes. To verify the mechanism, different polymers were used to tune singlet-triplet splitting energy based on solvent effect. And commercial acriflavine (Acf) film showed blue shifted fluorescence compared to purified one, with slower kRISC (≈100 s-1 ) and longer τDF (0.6 s). Via energy transfer from Acf to rhodamine B, the afterglow color was further regulated, with the largest fluorescence quantum yield of 42.4 %. It was demonstrated that the materials worked on color tunable light sources, and low-cost ($2 for 50 000 labels) anti-counterfeit labels recognized by white light.

In situ crosslink polymerization induced long-lived multicolor supramolecular hydrogel based on modified β-cyclodextrin

The construction of hydrogels with good mechanical properties and phosphorescent properties is full of challenges. Herein, we report a supramolecular phosphorescent hydrogel with long lifetime, high tensile strength and self-healing property, which can be easily constructed through in-situ thermal-initiated polymerization of isocyanatoethyl acrylate-modified β-cyclodextrin (β-CD-DA) and acrylate-modified adamantane (Ad-DA), acrylic acid (AA), followed by the non-covalent association with carbon dots (CNDs). The lifetime of phosphorescent hydrogel can reach 1261 ms at room temperature, and the quantum yield is 11%. Importantly, through the efficient triplet to singlet Förster resonance energy transfer (TS-FRET), the phosphorescent hydrogel shows the good phosphorescence energy transfer property for organic dyes Rhodamine B and Eosin Y with the delayed fluorescence lifetime up to 730 ms and 585 ms as well as the energy transfer efficiency (ΦET) up to 99.9% and 99.3%, respectively. Moreover, owing to the host-guest interactions between β-CD-DA and Ad-DA, the three-dimensional cross-linked network phosphorescent hydrogel can be easily stretched to 18 times of its original length, and can achieve self-healing of the cut surfaces within 30 min. These results will expand the scope of phosphorescent materials and provide new ideas and opportunities for materials science.