Persistent Room-temperature Phosphorescence Research Articles

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow.

Highly efficient persistent (lifetime > 0.1 s) room-temperature phosphorescence (pRTP) chromophores are important for futuristic high-resolution afterglow imaging for state-of-the-art security, analytical, and bioimaging applications. Suppression of the radiationless transition from the lowest triplet excited state (T1) of the chromophores is a critical factor to access the high RTP yield and RTP lifetime for desirable pRTP. Logical explanations for factor suppression based on chemical structures have not been reported. Here we clarify a strategy to reduce the radiationless transition from T1 based on chemical backbones and yield a simultaneous high RTP yield and high RTP lifetime. Yellow phosphorescence chromophores that contain a coronene backbone were synthesized and compared with yellow phosphorescent naphthalene. One of the designed coronene derivatives reached a RTP yield of 35%, which is the best value for chromophores with a RTP lifetime of 2 s. The optically measured rate constant of a radiationless transition from T1 was correlated precisely with a multiplication of vibrational spin–orbit coupling (SOC) at a T1 geometry and with the Franck–Condon chromophore factor. The agreement between the experimental and theoretical results confirmed that the extended two-dimensional fused structure in the coronene backbone contributes to a decrease in vibrational SOC and Franck–Condon factor between T1 and the ground state to decrease the radiationless transition. A resolution-tunable afterglow that depends on excitation intensity for anticounterfeit technology was demonstrated, and the resultant chromophores with a high RTP yield and high RTP lifetime were ideal for largely changing the resolution using weak excitation light.

Achieving Purely Organic Room-Temperature Phosphorescence Mediated by a Host-Guest Charge Transfer State.

Strategies for developing purely organic materials exhibiting both high efficiency and persistent room-temperature phosphorescence (RTP) have remained ambiguous and challenging. Herein, we propose that introducing an intermediate charge transfer (CT) state into the donor-acceptor binary molecular system holds promise for accomplishing this goal. Guest materials showing gradient ionization potentials were selected to fine-tune the intermolecularly formed CT state when doped into the same host material with a large electron affiliation potential. Such a CT intermediate state accelerates the population of the triplet exciton to benefit phosphorescent emission and decreases the phosphorescence lifetime via quenching the long-lived triplet excitons. As a result, a "trade-off" between a long phosphorescence lifetime (595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained by tuning the host-guest energy gap offset. This finding highlights the key role of CT in RTP emission and provides new guidance for developing novel RTP systems.

Realize efficient organic afterglow from simple halogenated acridan derivatives

Organic molecules with persistent room-temperature phosphorescence (RTP) have attracted considerable attention due to their broad applications, but typically suffered from low emission intensity and short lifetime. In this contribution, a twisted donor-acceptor (D-A) system by simple conjugation of acridan and aryl halide is proposed to construct efficient and ultralong RTP luminogens. The photophysical measurements and theoretical predictions demonstrate the halogenation renders simultaneous realization of large spin-orbital coupling (SOC), small energy gap between singlet/triplet excited states, and restrained non-radiative decay channel, which benefit for RTP properties. Correspondingly, the acridan derivatives realized phosphorescence quantum efficiency up to 3.2% with lifetime up to 372 ms in its crystalline state, and also exhibited distinct afterglow in heavily grinded samples. To demonstrate the potential applications, these materials were furtherly explored in information encryption and fingerprint identification. This study not only provides rare examples of efficient and long-lived phosphors based on acridan building block, but also sheds light on the inherent photophysical mechanism of RTP materials and paves a way to design highly promising RTP luminogens with a simplified structure.

Bromine heavy-atom induced persistent room temperature phosphorescence of [ZnBr2] based coordination polymer

Molecule-based room temperature phosphorescence (RTP) materials have attracted considerable attention owing to their extensive applications in the optoelectronic and biological field. In this paper, two isostructural coordination polymers [Zn3(TIB)2X6] (X ​= ​Cl, 1-Cl; X ​= ​Br, 1-Br) have been synthesised and characterized by the assemble of triangular D-A-D ligand 1,3,5-tri(1H-imidazol-1-yl)benzene (TIB) and ZnX2 salts. The incorporation of halogen atoms play significant role in the formation of abundant C-H···X hydrogen-bonding interactions and dense structures, enable high thermal stability of the two complexes. 1-Br shows phosphorescence lifetime three order of magnitude longer than that of 1-Cl, and obviously phosphorescence emission recognized by naked eyes. The theory calculations reveal complete separation of molecular orbitals between halogen atoms and TIB ligand. Photoelectron response performance have also been studied. This work provides an efficient way to achieve long-last RTP by the incorporation of metal-bromide units in the coordination polymers.

Boosting Room Temperature Phosphorescence Performance by Alkyl Modification for Intravital Orthotopic Lung Tumor Imaging.

Pure organic persistent room temperature phosphorescence (RTP) materials have attracted wide attention owing to their great potential in various applications, particularly in bioimaging. However, it is still a challenge to manufacture organic RTP materials possessing quite high efficiency and long lifetime, owing to the high requirements for triplet excitons. In this study, a series of keto derivatives with efficient RTP in crystals are developed through the regulation of molecular aggregation states by simple alkyl groups, resulting in impressive luminescence performance with a longer lifetime and higher efficiency of up to 868ms and 51.59%, respectively. All the alkyl-substituted derivatives exhibit bright RTP intensities after heavy grinding with a pestle, indicating their robust RTP features, which are suitable for many fields. Encouraged by the excellent RTP performance of these luminogens in the crystalline state, successful orthotopic lung tumor imaging with a high signal-to-background ratio (SBR) of 65 is demonstrated in this study to provide the promise of pure organic RTP materials for disease diagnosis, which hold the advantages of low autofluorescence interference and high signal-to-background ratio.

5,5-Dioxoyphenothiazine-based D-A-D type AIE molecules enabling persistent room temperature phosphorescence, white light emission and dual-mode mechanochromism

Novel heavy atom free 5,5-dioxoyphenothiazine-based “D–A–D” emitters with aggregation-induced emission (AIE), room-temperature phosphorescence (RTP), white light emission and dual-mode mechanochromic luminescence (MCL) characteristics have been designed and synthesized. Impressively, DCzCs and DCzCs-Et showed persistent RTP (pRTP) in the crystalline state with lifetimes of 528 ms and 137 ms in air, respectively. DCzCs-Ac exhibited white light emission with a CIE coordinate of (0.25, 0.26), due to the dual emission of fluorescence and phosphorescence. Detailed studies have shown that through simply functional group modification on the acceptor skeleton to modulate the molecular structure and intermolecular interactions, we fine-tuned the optical properties of the luminogens and realized white light emission. The dense crystal packing was proved to be closely related to the phosphorescence of the system and the special dual-mode MCL behavior was attributed to the conversion of crystalline-amorphous state under external force.

Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D4-A Conjugates and Data Security Application.

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor(D4)–acceptor(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (ΦP = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π···π interactions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π···π interactions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (−OEt) groups that enables spin–orbit coupling caused by strong lone pair (O)···π interactions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly(methyl methacrylate).

Boosting purely organic room-temperature phosphorescence performance through a host-guest strategy.

The host–guest doping system has aroused great attention due to its promising advantage in stimulating bright and persistent room-temperature phosphorescence (RTP). Currently, exploration of the explicit structure–property relationship of bicomponent systems has encountered obstacles. In this work, two sets of heterocyclic isomers showing promising RTP emissions in the solid state were designed and synthesized. By encapsulating these phosphors into a robust phosphorus-containing host, several host–guest cocrystalline systems were further developed, achieving highly efficient RTP performance with a phosphorescence quantum efficiency (ϕP) of ∼26% and lifetime (τP) of ∼32 ms. Detailed photophysical characterization and molecular dynamics (MD) simulation were conducted to reveal the structure–property relationships in such bicomponent systems. It was verified that other than restricting the molecular configuration, the host matrix could also dilute the guest to avoid concentration quenching and provide an external heavy atom effect for the population of triplet excitons, thus boosting the RTP performance of the guest.

Persistent room-temperature phosphorescence or high-contrast phosphorescent mechanochromism: polymorphism-dependent different emission characteristics from a single gold(i) complex

Luminophores with persistent room-temperature phosphorescence (p-RTP) or effective phosphorescent mechanochromism features have significant potential applications in the field of optoelectronic materials. Until now, p-RTP and remarkable phosphorescent mechanochromism phenomena have been observed in some luminescent molecules with different molecular structures. However, separately realizing p-RTP and high-contrast phosphorescent mechanochromism in different polymorphs from a single luminophore is still a valuable and challenging topic. In this work, two polymorphs 1B and 1YG of a new gold(i) complex with blue and yellow-green luminescence, respectively, are reported. Interestingly, 1B exhibits high-contrast phosphorescent mechanochromic behavior, while 1YG exhibits a persistent room-temperature phosphorescence effect. This is the first example of simultaneously obtaining double-purpose crystalline materials with a high-contrast phosphorescent mechanochromism or persistent room-temperature phosphorescence feature from a single luminophore.

Time-Dependent Afterglow from a Single Component Organic Luminogen.

Pure organic luminogens with long-persistent luminescence have been extensively studied, on account of their fundamental research significance and diverse utilizations in anticounterfeiting, bioimaging, encryption, organic light-emitting diodes, chemo-sensing, etc. However, time-dependent color-tunable afterglow is rarely reported, especially for single-component materials. In this work, we reported an organic luminogen with time-dependent afterglow, namely, benzoyleneurea (BEU), with multiple persistent room-temperature phosphorescence (p-RTP) and thermally activated delayed fluorescence (TADF) in single crystals. While the lifetime of TADF is relatively short (~1.2 ms), those for p-RTP are as long as around 369~754 ms. The comparable but different decay rates of diversified p-RTP emissions endow BEU crystals with obvious time-dependent afterglow. The existence of multiple emissions can be reasonably illustrated by the clustering-triggered emission (CTE) mechanism. Single-crystal structure illustrates that the combination of benzene ring and nonconventional chromophores of ureide helps facilitate divergent intermolecular interactions, which contribute to the formation of varying emissive species. Moreover, its methyl- and chloro-substituted derivatives show similar multiple p-RTP emissions. However, no time-dependent afterglows are observed in their crystals, due to the highly approaching lifetimes. The afterglow color variation of BEU crystals grants its applications in advanced anticounterfeiting field and information encryption.

Persistent room temperature blue phosphorescence from racemic crystals of 1,1-diphenylmethanol derivatives

Among the six alkyldiphenylmethanol derivatives assessed in this study, five showed persistent room temperature phosphorescence (pRTP), whereas the original diphenylmethanol (DPhHOH) did not. pRTP is a unique luminescence phenomenon that appears only in the crystalline state and is different from the luminescence produced by dispersed molecules, such as those in a glassy solvent matrix at 77 K or a polymeric matrix. The data also suggest that pRTP appears in conjunction with a specific crystal structure. The present work demonstrates that various crystal structures show pRTP regardless of the presence or absence of weak hydrogen bonds. However, nonradiative deactivation is suppressed by both intermolecular interactions and steric regulation in the crystal, such that the emission quantum yield is dependent on the crystal structure. In addition, although the molecular structure in the crystalline state necessary for the appearance of pRTP was not fully elucidated, intermolecular interactions between face-to-face and face-to-edge benzene rings appear to play a major role. Density functional theory calculations indicate that intersystem crossing is promoted in the crystalline state because the number of paths that allow this intersystem crossing is greater in a structure having weak interactions between molecules as compared to a dispersed state. DPhHOH did not show pRTP and is considered to have a structure based on the column-like stacking of multiple molecules. In contrast, the crystals that exhibited pRTP had pseudo racemic conformation in their crystals even though each molecule was achiral. In these racemic crystals, the interactions between pairs of molecules were important to the generation of pRTP.

Effective Internal and External Modulation of Nontraditional Intrinsic Luminescence.

The rational modulation of the nontraditional intrinsic luminescence (NTIL) of nonconventional luminophores remains difficult, on account of the limited understanding on the structure-property relationships and emission mechanisms. Herein, the effective modulation of NTIL is demonstrated based on a group of nonaromatic anhydrides and imides. Mutual bridging of isolated subgroups effectively promotes intramolecular through-space conjugation (TSC), leading to red-shifted emission, enhanced efficiency, and prolonged persistent room-temperature phosphorescence (p-RTP). The substitution of heteroatoms from oxygen to nitrogen drastically changes the TSC and enhances intermolecular interactions, resulting in enhanced emission efficiency. In addition, upon freezing, compression, or embedding into polymer matrices, the emission intensity and color remain well regulated. These results shed new light on the rational modulation of the NTIL and p-RTP of nonconventional luminophores.

High contrast temperature-responsive luminescence materials from purely organic molecule with persistent room-temperature phosphorescence

Organic materials with temperature-responsive luminescence (TRL) generally exhibit step-change of luminescent intensity during temperature variation. The persistent room-temperature phosphorescence (pRTP) materials have significant advantages in long-lived triplet excitons, which are promising new type of TRL materials. Here, a D-A type benzophenone derivative, namely BrBDBF, has been designed and synthesized. Interestingly, two crystals (BrBDBF-Y and BrBDBF-W) with different pRTP properties are found for BrBDBF. In addition, the bright crystal BrBDBF-Y presented a temperature-induced tunable emission color-switching from bluish-green to yellow. While the crystal BrBDBF-W with very weak emission exhibited high contrast “turn-on” luminescence which increased about 40 times as the temperature dropping. These results demonstrate that BrBDBF is a new type of TRL material and provides opportunities for the advanced application of organic pRTP materials.

Phosphorescence Quenching of Heavy-Atom-Free Dopant Chromophores Triggered by Thermally Activated Triplet Exciton Diffusion of a Conjugated Crystalline Host

Persistent room-temperature phosphorescence (pRTP) from aggregated molecular crystalline materials is important for stable high-resolution afterglow imaging. However, an unclear understanding conce...

Color-Tunable, Excitation-Dependent, and Time-Dependent Afterglows from Pure Organic Amorphous Polymers.

Achieving persistent room-temperature phosphorescence (p-RTP), particularly those of tunable full-colors, from pure organic amorphous polymers is attractive but challenging. Particularly, those with tunable multicolor p-RTP in response to excitation wavelength and time are highly important but both fundamentally and technically underexplored. Here, a facile and general strategy toward color-tunable p-RTP from blue to orange-red based on amidation grafting of luminophores onto sodium alginate (SA) chains, resulting in amorphous polymers with distinct p-RTP and even impressively excitation-dependent and time-dependent afterglows is reported. p-RTP is associated with the unique semi-rigidified SA chains, effective hydrogen bonding network, and oxygen barrier properties of SA, whereas excitation-dependent and time-dependent afterglows should stem from the formation of diversified p-RTP emissive species with comparable but different lifetimes. These results outline a rational strategy toward amorphous smart luminophores with colorful, excitation-dependent, and time-dependent p-RTP, excellent solution processability, and film-forming ability for versatile applications.

Persistent Room Temperature Phosphorescence from Triarylboranes: A Combined Experimental and Theoretical Study

AbstractAchieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate kisc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions.

Persistent Room Temperature Phosphorescence from Triarylboranes: A Combined Experimental and Theoretical Study.

Achieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate k isc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions.

Highly Efficient Persistent Room-Temperature Phosphorescence from Heavy Atom-Free Molecules Triggered by Hidden Long Phosphorescent Antenna.

Persistent (lifetime > 100 ms) room-temperature phosphorescence (pRTP) is important for state-of-the-art security and bioimaging applications. An unclear relationship between chromophores and physical parameters relating to pRTP has prevented obtaining an RTP yield of over 50% and a lifetime over 1 s. Here highly efficient pRTP is reported under ambient conditions from heavy atom-free chromophores. A heavy atom-free aromatic core substituted with a long-conjugated amino group considerably accelerates the phosphorescence rate independent of the intramolecular vibration-based nonradiative rate from the lowest excited triplet state. One of the designed heavy atom-free dopant chromophores presents an RTP yield of 50% with a lifetime of 1 s under ambient conditions. The afterglow brightness under strong excitation is at least 104 times stronger than that of conventional long-persistent luminescence emitters. Here it is shown that highly efficient pRTP materials allow for high-resolution gated emission with a size of the diffraction limit using small-scale and low-cost photodetectors.

Förster Resonance Energy Transfer: An Efficient Way to Develop Stimulus-Responsive Room-Temperature Phosphorescence Materials and Their Applications

Summary In this work, Forster resonance energy transfer (FRET) is utilized to construct a stimulus-responsive room-temperature phosphorescence (RTP) system. Owing to the specificity of the FRET system and its sensitivity to distance, the resultant material shows turn-on persistent RTP emission upon force or heating stimulus. Furthermore, a near-perfect compatibility with existing printing technology is demonstrated for this material, especially for thermal printing. This finding could provide a simple, efficient, and truly commercially viable construction strategy for RTP material.

An Unexpected Chromophore-Solvent Reaction Leads to Bicomponent Aggregation-Induced Phosphorescence.

Organic luminogens with persistent room-temperature phosphorescence (RTP) have found a wide range of applications. However, many RTP luminogens are prone to severe quenching in the crystalline state. Herein, we report a strategy to construct a donor-sp3 -acceptor type luminogen that exhibits aggregation-induced emission (AIE) while the donor-sp2 -acceptor counterpart structure exhibits a non-emissive solid state. Unexpectedly, it was discovered that a trace amount (0.01 %) of the structurally similar derivative, produced by a side reaction with the DMF solvent, could induce strong RTP with an absolute RTP yield up to 25.4 % and a lifetime of 48 ms, although the substance does not show RTP by itself. Single-crystal XRD-based calculations suggest that n-σ* orbital interactions as a result of structural similarity may be responsible for the strong RTP in the bicomponent system. This study provides a new insight into the design of multi-component, solid-state RTP materials from organic molecular systems.