Mechanism Of Phosphorescence Research Articles

Temperature‐Dependent Reversible Afterglow Between Green, Orange, and Red in Dual‐Delay Organic Doped Material

AbstractAchieving a wide‐range color‐tunable and dynamically long‐afterglow emission in a single‐doped system remains a challenge. In this study, a unique host‐guest doped material, TPA‐PTPQ/TPA, exhibits dual‐delay emission at 516 and 605 nm, both with long lifetimes of up to 108 and 145 ms, which derives from thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) mechanisms, respectively. Notably, this host‐guest material demonstrates a temperature‐dependent dynamically reversible afterglow characteristic, transitioning green, orange, and red with a substantial spectra shift of ≈90 nm under different temperature conditions. This phenomenon is due to the diverse temperature effect on TADF and RTP emissions. These remarkable luminescence properties are successfully applied in security checks and anti‐counterfeiting encryption. This study provides valuable insights into the design of dynamically reversible dual‐delay‐emissive long‐afterglow luminescent materials based on a host‐guest doping system.

(Invited) Fast Room-Temperature Phosphorescence of Organic Molecules: Mechanism and Molecular Design

The mechanism and molecular design for fast and efficient room-temperature phosphorescence of organic molecules in solution will be presented.

PH-sensitive phosphorescence in penicillamine-coated Au22 nanoclusters: Theoretical and experimental insights

Penicillamine-coated Au22 nanoclusters have an intensified yet pH-adjustable red to near infrared-I (NIR-I) phosphorescence due to their unique electronic structure, which endues them a high potential for tumor imaging and detecting in nanotheranostics. This study reports a sort of engineered Au22(D-pen)18 nanoclusters with a high quantum yield 7.39% as well as pH-conditioned phosphorescence intensity and lifetime that were addressed experimentally and theoretically. Through spin-orbital coupling calculation based on time-dependent density functional theory (TD-DFT), this study ascertains that the deprotonation of carboxylic groups on the D-penicillamine gives rise to a series of changes in the electronic structure of Au22(D-pen)18 nanocluster, leading to an ensuing pH-conditioned phosphorescence from pH-dependent spin–orbit coupling matrix element during inter-system crossing. The deprotonation also alters the bonding and interaction between Au-S core of the Au22(D-pen)18 nanocluster, which compromises the structural stability and potentially generates non-radiative decay with a quenched phosphorescence. The unique in-vitro and in vivo tumor-imagingadvantage of Au22(D-pen)18 nanocluster qualifies it as an efficient tumor-targeting phosphorescence sensor with pH-sensitivity capability for bright contrast to distinguish cancer cells from normal ones. This study provides a comprehensive view on the preparation and characterization of Au22(D-pen)18 nanoclusters, as well as the underlying mechanism of pH-conditioned phosphorescence and application prospects beside uniqueness in methodology, shedding light on further investigation for rational design and engineering of surface of ligand-coated nanoclusters.

Time-dependent and clustering-induced phosphorescence, mechanochromism, structural-function relationships, and advanced information encryption based on isomeric effects and host–guest doping

To explore the intrinsic mechanism of pure organic room temperature and clustering-induced phosphorescence and investigate mechanochromism and structural-function relationships, here, 4-(2-(9H-carbazol-9-yl)phenyl)-2-amino-6-methoxypyridine-3,5-dicarbonitrile (Lo-CzAD), 4-(3-(9H-carbazol-9-yl)phenyl)-2-amino-6-methoxypyridine-3,5-dicarbonitrile (Lm-CzAD), and 4-(4-(9H-carbazol-9-yl)phenyl)-2-amino-6-methoxypyridine-3,5-dicarbonitrile (Lp-CzAD) were designed and synthesized by choosing self-made carbazole and 3, 5-dicyanopyridine (DCP) unit as electron acceptor and electron donor in sequence. Compared with crystals Lm-CzAD and Lp-CzAD, crystal Lo-CzAD shows better room temperature phosphorescence (RTP) performance, with RTP lifetimes of 187.16 ms, as well as afterglows 1s, which are attributed to twisted carbazole unit and donor–acceptor (D-A) molecular conformation, big crystal density and spin orbit coupling constant ξ (S1 → T1 and S1 → T2), as well as intermolecular H type stacking and small ξ (S0 → T1). By choosing urea and PPh3 as host materials and tuning doping ratio, four doping systems were successfully constructed, significantly improving RTP performance of Lo-CzAD and Lp-CzAD, as well as showing different fluorescence and RTP. The lifetimes and afterglows of pure organic Urea/Lo-CzAD and Urea/Lp-CzAD systems are up to 478.42 ms, 5 s, 261.66 ms and 4.5 s in turn. Moreover, Lo-CzAD and Lp-CzAD show time-dependent RTP in doping systems due to monomer and aggregate dispersion, as well as clustering-induced phosphorescence. Based on the different luminescent properties, multiple information encryptions were successfully constructed.

Deciphering the luminescence mechanism: Investigating ESIPT-attributed HPI2C molecule with coupled thermally activated delayed fluorescence and phosphorescence properties

Long persistent luminescence (LPL) including thermally activated delayed fluorescence (TADF) and phosphorescence is widely applied in luminogens. Recently, Pan et al. pioneered the discovery of TADF and phosphorescence in the HPI2C molecule by manipulating temperature in line with the excited-state intramolecular proton transfer (ESIPT) dynamics (J. Am. Chem. Soc. 2022, 144, 2726). They blazed a new trail to explore the switching mechanism between TADF and phosphorescence in single molecule. Nevertheless, luminescence mechanism for HPI2C cannot be explained solely through experimental means. Theoretically, we demonstrate that the ESIPT and photocyclization channel induced conical intersection processes facilitate the fluorescence quenching of the Enol* state. Moreover, we prove the cruciality of the T2 state in the TADF phenomenon involved in Keto* state and reconsider the mechanism of the dual phosphorescence. Our investigation is favorable to provide theoretical support for the design of the LPL materials based on the ESIPT-attributed molecules.

Achieving Visible-Light-Excitable Blue TADF-Type Afterglow via Delicate Control of Excited States in Difluoroboron β-Diketonate Systems.

Blue afterglow constitutes of one of the primary afterglow colors and can convert into other afterglow colors through energy transfer. The reported studies show the fabrication of blue afterglow emitters, but most of them are formed by room-temperature phosphorescence mechanism and require UVB lights as excitation source (these high-energy lights may damage organic systems). Here we report visible-light-excitable blue thermally activated delayed fluorescence type (TADF-type) afterglow materials via delicate control of excited states in difluoroboron β-diketonate (BF2bdk) systems. Tiny change of the substituents in BF2bdk system has been found to pose significant influence on excited state energy levels and consequently narrow the singlet-triplet splitting energy of the system. As a result, both forward and reverse intersystem crossing have been accelerated, leading to the emergence of BF2bdk's TADF-type organic afterglow in rigid crystalline matrices. The resultant TADF-type afterglow materials exhibit emission lifetimes of several hundred milliseconds, photoluminescence quantum yield (PLQY) of 24.7 % and display temperature responsive property.

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.

Enhanced afterglow properties in reddish-orange Ca2SnO4:Sm3+ phosphors by NH4Cl or CaCl2 flux

Red long persistent phosphors are the key to achieving full-spectrum afterglow luminescence. However, their low initial brightness and short afterglow time are currently urgent problems to be solved. In this study, the reddish-orange long persistent phosphor Ca2SnO4:Sm3+ was successfully prepared via the high-temperature solid-state reaction method using NH4Cl and CaCl2 as the flux, respectively. It was proved that CaCl2 lowered the decomposition temperature of CaCO3 and form a liquid phase, accelerating the formation of the Ca2SnO4 phase. The afterglow time of Ca2SnO4:Sm3+ with 5 wt% NH4Cl or 5 wt% CaCl2 was respectively 12 or 24 times longer than that without any flux. 5 wt% CaCl2 addition exhibited the longest afterglow time, lasting over 83 min. It concluded that CaCl2 induced the increase in shallow trap concentration was the main reason for extending afterglow time. In addition, a phosphorescent mechanism model was proposed that the electron trap (Sm. Ca) and the hole trap (V″ Ca) played a crucial role in the energy storage of Ca2SnO4:Sm3+. Ca2SnO4:Sm3+ as a red long persistent phosphor has the potential to make full-spectrum afterglow luminescence a reality.

Theoretical exploration of the bromine substitution effect and hydrostatic pressure responsive mechanism for room temperature phosphorescence.

Stimulus-responsive organic room temperature phosphorescence (RTP) materials with long lifetimes, high efficiencies and tunable emission properties have broad applications. However, the amounts and species of efficient RTP materials are far from meeting the requirements and the inner stimulus-responsive mechanisms are unclear. Therefore, developing efficient stimulus-responsive RTP materials is highly desired and the relationship between the molecular structures and luminescent properties of RTP materials needs to be clarified. Based on this point, the influences of different substitution sites of Br on the luminescent properties of RTP molecules are studied by the combined quantum mechanics and molecular mechanics (QM/MM) coupled with thermal vibration correlation function (TVCF) theory. Moreover, the hydrostatic pressure effect on the efficiencies and lifetimes is explored and the inner mechanism is illustrated. The results show that, for the exciton conversion process, the o-substitution molecule possesses the largest spin-orbit coupling (SOC) value (〈S1|Ĥso|T1〉) in the intersystem crossing (ISC) process and this is conducive to the accumulation of triplet excitons. However, for the energy consumption process, the large SOC value (〈S0|Ĥso|T1〉) for the p-substitution molecule brings a fast non-radiative decay rate, and the small SOC value for the m-substitution molecule generates a decreased non-radiative decay rate which is helpful for realizing long lifetime emission. Keeping with this perspective, the conflict between high exciton utilization and long RTP emission needs to be balanced rather than enhancing the SOC effect by simply adding heavy atoms in RTP systems. Through regulating the molecular stacking modes by the hydrostatic pressure effect, the inner stimulus-responsive mechanism is revealed. The data of 〈S1|Ĥso|T1〉 in the ISC process remain almost unchanged, while 〈S0|Ĥso|T1〉 values and transition dipole moments are sensitive to the hydrostatic pressure. Under 1 GPa, the RTP molecule achieves a maximum efficiency (81.17%) and long lifetime (2.72 ms) with the smallest SOC and decreased non-radiative decay rate. To our knowledge, this is the first time that the hydrostatic pressure responsive mechanism for RTP molecules is revealed from a theoretical perspective, and the relationships between molecular structures and luminescent properties are detected. Our work could facilitate the development of high performance RTP molecules and expand their applications in multilevel information encryption.

Rational molecular and doping strategies to obtain organic polymers with ultralong RTP.

Organic-doped polymers and room-temperature phosphorescence (RTP) mechanisms have been widely reported. However, RTP lifetimes >3 s are rare and RTP-enhancing strategies are incompletely understood. Herein, we demonstrate a rational molecular doping strategy to obtain ultralong-lived, yet bright RTP polymers. The n-π* transitions of boron- and nitrogen-containing heterocyclic compounds can promote a triplet-state population, and the grafting of boronic acid onto polyvinyl alcohol can inhibit molecular thermal deactivation. However, excellent RTP properties were achieved by grafting 1-0.1% (N-phenylcarbazol-2-yl)-boronic acid rather than (2-/3-/4-(carbazol-9-yl)phenyl)boronic acids to afford record-breaking ultralong RTP lifetimes up to 3.517-4.444 s. These results showed that regulation of the interacting position between the dopant and matrix molecules to directly confine the triplet chromophore could more effectively stabilize triplet excitons, disclosing a rational molecular-doping strategy for achieving polymers with ultralong RTP. Based on the energy-donor function of blue RTP, an ultralong red fluorescent afterglow was demonstrated by co-doping with an organic dye.

Highly efficient and robust multi-color afterglow of ZnO nanoparticles.

Room temperature phosphorescence (RTP) materials are widely used in various fields. However, the realization of multicolor RTP via facile approaches still remains a great challenge. In this study, we propose an in situ hydrolysis method using different solvents to synthesize blue, green, and yellow phosphorescence ZnO/SiO2 composites. By investigating the photoluminescence (PL) and phosphorescence mechanisms of ZnO/SiO2 composites, it is discovered that the solvents not only introduce impurities to ZnO but also affect the position of defect energy levels, leading to the variation in luminescent performance. Meanwhile, the as-synthesized ZnO/SiO2 composites exhibit stable PL and phosphorescence under extreme conditions. Specifically, the PL and phosphorescence properties of the composites are well maintained at high temperature (523 K) or underwater. Owing to the multicolor phosphorescence properties of these ZnO/SiO2 products, herein, we demonstrate that ZnO/SiO2 composites can act as new smart materials for information encryption, fingerprint identification, and white light-emitting diodes (WLEDs).

Regulating excited state of sulfone-locked triphenylamine heteroaromatics for high-efficiency ultralong room-temperature phosphorescence

• Organic RTP of ultralong lifetime and high quantum efficiency was presented. • Phosphorescence mechanism based on the excited states regualtion was proposed. • Multilevel information encryption based on liftetimes and colors was shown. Organic room-temperature phosphorescence (RTP) with ultralong lifetime and high quantum efficiency is of interest but challenging. Few phosphor systems in the monomer state demonstrate lifetimes over 0.1 s with quantum efficiencies exceeding 10% due to the lack of molecular design principle and qualified molecular system. Here we present a novel class of phosphors based on heteroaromatic sulfone-locked triphenylamine core BTPO with rational subunit modification that displays ultralong RTP in a doped polymer matrix with lifetimes up to 818 ms and quantum efficiencies over 20% simultaneously. The co-win situation is attributed to an efficient and multichannel intersystem crossing (ISC) process arising from narrower singlet-triplet exchange energy and strong spin-orbital coupling interaction between the lowest singlet state (S 1 ) and high-lying triplet states that facilitate numerous triplet excitons generation, as well as a relatively pure (π, π*) configuration for the lowest triplet state (T 1 ), ensuring the small radiative rate of phosphorescence ( k p ) and consequently ultralong lifetime. Taking advantage of RTP features with the multicolor and diverse lifetime of this phosphor family, the primary application in information encryption is well demonstrated versatilely.

Polymer-Based TADF-Type Organic Afterglow

Polymer-based organic afterglow materials exhibit excellent flexibility and mechanical properties, whereas their afterglow mainly follows a phosphorescence mechanism with limited afterglow efficiency. Here, we report polymer-based TADF-type afterglow materials, which feature a moderate rate of reverse intersystem crossing of 1–10 s–1 to harvest triplet energies and consequently possess an afterglow efficiency of >80%. By doping a specific difluoroboron diketonate dye into polymer matrices, various polymer-based afterglow materials have been obtained. In particular, afterglow elastomers, which have been rarely reported, have also been achieved with a high efficiency of 50% and a long lifetime of 0.19 s. Variable temperature-delayed emission studies and TD-DFT calculations have been performed to support the TADF afterglow mechanism. This study would pave the way for highly efficient polymer-based organic afterglow materials and their promising applications in diverse areas.

Recent Advances in Organic Room-Temperature Phosphorescence of Heteroatom (B/S/P)-Containing Chromophores

Recent Advances in Organic Room-Temperature Phosphorescence of Heteroatom (B/S/P)-Containing Chromophores

A review on carbon quantum dots: Synthesis, photoluminescence mechanisms and applications.

Carbon quantum dots (CQDs), having outstanding biocompatibility, attractive catalytic performance, excellent optical properties, and valuable environment friendliness, are emerging as a new paradigm to design luminescent devices and show great potential in application fields such as biomedical sensors, optical and photonic devices. Furthermore, CQDs are known as one of the most promising carbon-based nanomaterials in the 21st century. Therefore, they have attracted a lot of attention since they were first discovered in 2004. In this review, we explain the accepted photoluminescence mechanism of CQDs, including fluorescence and phosphorescence. There are two main types of synthesis strategies: top-down approach and bottom-up approach. At the same time, the main application fields, including ion detection, anti-counterfeiting, biological imaging, food safety, sensors, lubrication additives, are reviewed. Finally, the existing bottlenecks, pending problems and prospects for the future of CQDs are discussed.

Thermochromic Phosphors Based on One‐Dimensional Ionic Copper‐Iodine Chains Showing Solid‐State Photoluminescence Efficiency Exceeding 99 %

AbstractThermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor.

Thermochromic Phosphors Based on One‐Dimensional Ionic Copper‐Iodine Chains Showing Solid‐State Photoluminescence Efficiency Exceeding 99 %

Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light-emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one-dimensional Cu 4 I 6 (4-dimethylamino-1-ethylpyridinium) 2 is reported. This unique ionic copper-iodine chain-based hybrid exhibits near-unity photoluminescence efficiency owing to through-space charge-transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by first principle simulation of concerted copper atom migration in the copper-iodine chain. Furthermore, we successfully fabricate a bright thermochromic light-emitting diode using this Cu 4 I 6 (4-dimethylamino-1-ethylpyridinium) 2 thermochromic phosphor. Our reported flexible ionic copper-iodine chain-based thermochromic luminescent material represents a new type of cost-effective functional phosphor.

Tunable Photoluminescence Properties of Cotton Fiber With Gradually Changing Crystallinity.

The alkali mercerizing process of semicrystalline cotton fiber (CF) is widely used in the printing and dyeing industry. The crystallinity change in the mercerizing process has been studied and certain laws have been obtained, but there is still a certain distance between the theoretical research results and the practical applications. CF is almost composed of cellulose, combined with the photoluminescence (PL) phenomenon of cellulose; herein, the varying crystallinity is correlated with its PL behavior after being treated with different concentrations of NaOH. In line with the characteristics of nonconventional luminogens, CF enjoys excitation-dependent emission and persistent room temperature phosphorescence (p-RTP) behavior. The emission spectra of all samples under the same excitation wavelength indicate that the change of CF crystallinity has a significant impact on its fluorescence and p-RTP emission. As the concentration of NaOH increases, the varying trend of quantum efficiency (QY) is consistent with the changed crystallinity of CF. Interestingly, the lifetime of p-RTP is exactly the opposite of the crystallinity change law. Clustering-triggered emission (CTE), crystallization-Induced Phosphorescence (CIP) mechanism, and the swelling due to hydrated sodium ions can reasonably explain these interesting photophysical processes, which also can be supported by theoretical calculations. The above studies have basically clarified the inherent law between the crystalline change of CF and the PL emission behavior during the alkali treatment process, which can be used as a theoretical reference for real-time monitoring of CF crystallinity changes using the spectral method in the actual cotton mercerizing process.

Exploration of Room‐Temperature Phosphorescence and New Mechanism on Carbon Dots in a Polyacrylamide Platform and their Applications for Anti‐Counterfeiting and Information Encryption

AbstractThis is the first report of full‐color afterglow composites composed of four multicolored (blue, green, orange, and red) carbon dots (CDs) in polyacrylamide (PAM) matrix. Thus, adjustable four‐color room‐temperature phosphorescence (RTP) CDs@PAM composites are prepared on a PAM platform. The abundant amide groups in PAM are connected to the functional groups in CDs by hydrogen bonds, which promote the intersystem crossover and inhibit the non‐radiative relaxation of triple states (T1) in CDs@PAM and effectively shield the quenching agents such as oxygen. Furthermore, the rigid hydrogen bond mesh structure is beneficial to the stability of T1 in CDs@PAM. In addition, the results of electron spin resonance reveal that the afterglow of CDs@PAM composites is not caused by oxygen defects and the increase of oxygen defects hinders the emission of phosphorescence. The CDs@PAM composites display not only multi‐color fluorescence from blue to red, but also display full‐color RTP emission from blue to red with average phosphorescence lifetime in the range of 637–478.97 ms. These composites, in addition to the full‐color RTP performance, are promising for multi‐color pattern anti‐counterfeiting and information encryption.

Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Organic luminogens with room temperature phosphorescence (RTP) have been paid great attention and developed rapidly for their wide application values. Until now, the internal mechanism and source of phosphorescence are still obscure, especially for the relationship between molecular dimer and RTP emission. Hence, we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior. Dimers with strong π-π stacking (θ < 20.66°; d < 3.86 Å) lead to pure triplet excimer emission, while those with weak π-π stacking (27.02°< θ < 40.64°; 3.84 Å < d < 4.41 Å) contribute to dual RTP emissions of both monomer and triplet excimer. The valuable information of this work would promote the further development of this research field, as well as others in aggregate.