Phosphorescence Lifetime Research Articles

Developing Bright Afterglow Materials via Manipulation of Higher Triplet Excited States and Relay Synthesis in Difluoroboron β‐Diketonate Systems

AbstractAfterglow brightness represents one of the most important characteristics in the application of afterglow materials. High molar absorption coefficient, high afterglow efficiency, and long afterglow lifetimes are required to achieve intense afterglow. However, current strategies cannot simultaneously fulfill these requirements due to specific intrinsic problems. Here, based on the understanding of difluoroboron β‐diketonate systems, the manipulation of higher triplet excited states is conceived to selectively enhance intersystem crossing with phosphorescence lifetimes remaining long. Aromatic substrates, which possess specific HOMO levels and T1 levels, are selected for relay synthesis to form difluoroboron β‐diketonate compounds with very close‐lying S1 and T2 levels; according to the energy gap law, such systems exhibit strong intersystem crossing. Upon doping into rigid matrices, the resultant difluoroboron β‐diketonate systems display the brightest ambient afterglow that has ever been observed.

Synthesis and properties of long-lived room-temperature phosphorescent liquid crystal polymers based on “Jacketing” effect

Polymerization is one of the most widely used strategies to achiever RTP. To date, various polymer-based RTP materials have been reported. However, how to improve the phosphorescence lifetime of polymer-based RTP materials still needs to be further researched. In this article, we proposed a new strategy to realize long-lived room-temperature phosphorescence by utilizing the “jacketing” effect of mesogen-jacketed liquid crystal polymers. Two polymers PMJ0DFM and PMJ6DFM with different flexible spacer length were synthesized, and their liquid crystal phase structures and photo-physical properties were systematically investigated. PMJ0DFM formed columnar nematic phase while PMJ6DFM formed a more ordered hexagonal columnar phase liquid crystal. For PMJ0DFM without spacer length, due to the strong “Jacketing” effect, the thermal motion of the chromophore was suppressed, and it was also more conducive to the aggregation and planarization of the chromophores. Therefore, PMJ0DFM film showed longer phosphorescence lifetime and more red-shifted phosphorescence spectrum than PMJ6DFM film. The phosphorescence lifetimes of PMJ0DFM and PMJ6DFM were 355 ms and 247 ms, respectively. In addition, we also explored their application in linearly polarized luminescent materials. When oriented, PMJ0DFM and PMJ6DFM film could emit efficient linearly polarized room temperature phosphorescence.

Naphthalimide-Modified Tridentate Platinum(II) Complexes: Synthesis, Characterization, and Application in Singlet Oxygen Generation

Singlet oxygen (1O2), representing an important reactive oxygen species, has promising applications in biomedical, material, and environmental sciences. Photosensitized production of 1O2 using organic dyes is highly desirable and the exploration of highly efficient photosensitizers has received considerable attention. Herein, two tridentate Pt(II) complexes, i.e., cationic 1(PF6) and neutral 2, modified with the ethynylnaphthalimide chromophore, were designed and prepared for the application in 1O2 generation. Spectroscopic studies and computational results suggest that 1(PF6) and 2 display the lowest-energy absorption bands centered at 435–465 nm with the molar extinction coefficients of 0.6–3.2 × 104 M−1 cm−1, originating from the singlet ligand-to-ligand charge transfer (1LLCT) and a mixture of 1LLCT and singlet ligand-centered (LC) transitions, respectively. Moreover, they show similar phosphorescence at 620–640 nm assigned to the Pt-perturbed triplet LC emission of the ethynylnaphthalimide moiety. Thanks to the relatively long phosphorescence lifetimes, these complexes exhibit O2-dependent phosphorescence intensities with good reversibility and stability. They are able to behave as efficient triplet photosensitizers to promote the 1O2 generation with high quantum yields (84–89%). This work indicates that the combination of an organic chromophore with Pt(II) complexes provides an effective method to obtain photosensitizers for 1O2 generation.

An iridium complex-based probe for phosphorescent lifetime-elongated imaging of nitroreductase in living cells

Nitroreductase (NTR) is an important biomarker and often overexpressed in hypoxia tumors, thus the selective and precise detection of NTR is of great importance in the early diagnosis of tumors. Although various analytical methods have been constructed for NTR detection, there is still a lack of an effective photoluminescence probe for NTR using photoluminescence lifetime imaging (PLIM) within living cells. In this study, an iridium-based probe (Ir-NO2) decorated with p-nitrophenyl group has been designed and investigated for detection and imaging of NTR. Upon addition of NTR and nicotinamide adenine dinucleotide (NADH), the p-nitrophenyl group of Ir-NO2 underwent reduction and elimination, leading to generation of Ir-NH2. This transformation effectively blocked photoinduced electron transfer, resulting in an observable enhancement of phosphorescence intensity and an extension of phosphorescence lifetime during the detection process. The capability of Ir-NO2 to detect NTR at the cellular level was confirmed through PLIM analysis of hypoxia A549 cells.

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

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

Room Temperature Phosphorescence in Chiral 0D Zn(II) Metal Halide Crystals for Multiple Anti‐Counterfeiting

AbstractThe development of metal halides that enable multiple information storage and cryptographic security is highly desirable but remains a challenge. Here, a pair of 0D Zn(II) metal halide enantiomers ZnCl2·R/S‐2‐MP with excitation wavelength‐dependent emission and room temperature phosphorescence properties are reported. Organic ligands via N─H···Cl hydrogen bonding induce structural chirality. In order to stabilize the triplet state exciton and achieve excellent photophysical properties, the organic ligands combine with halogens to promote emission. The differences between the photophysical properties of ZnCl2·R‐2‐MP and ZnCl2·S‐2‐MP are analyzed in depth. Furthermore, combined with femtosecond transient absorption (fs‐TA) results, the long phosphorescence lifetimes may originate from the triplet state emission due to the synergistic effect between the organic components and the inorganic metal halides. The design strategy of advanced multiple anticounterfeiting technology is further extended.

Stepwise taming of triplet excitons via multiple confinements in intrinsic polymers for long-lived room-temperature phosphorescence

Polymeric materials exhibiting room temperature phosphorescence (RTP) show a promising application potential. However, the conventional ways of preparing such materials are mainly focused on doping, which may suffer from phase separation, poor compatibility, and lack of effective methods to promote intersystem crossing and suppress the nonradiative deactivation rates. Herein, we present an intrinsically polymeric RTP system producing long-lived phosphorescence, high quantum yields and multiple colors by stepwise structural confinement to tame triplet excitons. In this strategy, the performance of the materials is improved in two aspects simultaneously: the phosphorescence lifetime of one polymer (9VA-B) increased more than 4 orders of magnitude, and the maximum phosphorescence quantum yield reached 16.04% in halogen-free polymers. Moreover, crack detection is realized by penetrating steam through the materials exposed to humid surroundings as a special quenching effect, and the information storage is carried out by employing the Morse code and the variations in lifetimes. This study provides a different strategy for constructing intrinsically polymeric RTP materials toward targeted applications.

Evolution of organic phosphor through precision regulation of nonradiative decay.

Development of single-component organic phosphor attracts increasing interest due to its wide applications in optoelectronic technologies. Theoretically, activating efficient intersystem crossing (ISC) via 1(π, π*) to 3(π, π*) transitions, rather than 1(n, π*) → 3(π, π*) transitions, is an alternative access to purely organic phosphors but remains challenging. Herein, we designed and successfully synthesized the sila-8-membered ring fused biaryl benzoskeleton by transition metal catalysis, which served as a new organic phosphor with efficient 1(π, π*) to 3(π, π*) ISC. We first found that such a compound exhibits a record-long phosphorescence lifetime of 6.5 s at low temperature for single-component organic systems. Then, we developed two strategies to tune their decay channels to evolve such nonemissive molecules into bright phosphors with elongated lifetimes at room temperature: 1) Physic-based design, where quantitative analyses of electron-phonon coupling led us to reveal and hinder the major nonradiative channels, thus lighted up room temperature phosphorescence (RTP) with a lifetime of 480 ms at 298 K; 2) chemical geometry-driven molecular engineering, where a geometry-based descriptor ΔΘT1-S0/ΘS0 was developed for rational screening RTP candidates and further improved the RTP lifetime to 794 ms. This study clearly shows the power of interdiscipline among synthetic methodology, physics-based rational design, and computational modeling, which represents a paradigm for the development of an organic emitter.

Multi‐Color Pure Organic Room Temperature Phosphorescent Materials with Long Lifetime and High Efficiency

AbstractOrganic room temperature phosphorescent (ORTP) materials have garnered significant interest in the fields of anti‐counterfeiting, optical display, and bio‐imaging owing to their distinctive optical properties. However, a major drawback of most existing ORTP materials is their short phosphorescence lifetime and low quantum yields (QYs), which greatly limit their applicability across multiple fields. In this paper, a covalently assisted host‐guest doping strategy that involves embedding three aminobenzoic acids with different carboxylate substitution positions into a cyanuric acid (CA) matrix through covalent bonding using microwave heating is proposed. All three prepared ORTP materials exhibit long phosphorescence lifetime exceeding 600 ms and high phosphorescence quantum yields (PhQYs) surpassing 20%. Among them, the composite of 2‐aminoterephthalic acid (2‐A) anuric acid stands out with its unique blue phosphorescence, boasting an exceptional absolute photoluminescence quantum yield (PLQY) of 98.95% and remarkable phosphorescence quantum yield (PhQY) of 76.42%, along with a long lifetime of 800 ms. Importantly, these high‐performance ORTP materials have been successfully utilized in anti‐counterfeiting and display applications.

Effect of annealing on the room temperature luminescence of coumarin 106 in PVA films

We studied the effect of annealing on the luminescence of Coumarin 106 (C106) in poly (vinyl alcohol) films (PVA films). The samples and reference polymer films were treated at temperatures between 100 °C and 150 °C (212 F and 302 F) for various times. After cooling and smoothing, the samples and references were measured at room temperature. We observed that the PVA polymer (reference films) changes its optical properties with annealing at higher temperatures, affecting the baselines in absorption and the backgrounds in emission measurements. This requires precise background subtractions and control of the signal-to-noise ratio. Whereas the fluorescence intensity of C106 in PVA films modestly decreases with annealing, the phosphorescence depends dramatically and progressively increases by many folds. The fluorescence quantum yields and lifetimes decrease with the annealing, which suggests an increase in the non-radiative processes in the singlet excited state S1. The increase in the phosphorescence intensities results from increased intersystem crossing (ISC), which also decreases fluorescence. We also studied the effect of annealing on phosphorescence with the directly excited triplet state of C106. In this case, two processes are affected by annealing, S0→T1 absorption and T1→S0 phosphorescence. The long-wavelength excitation (475 nm) avoids PVA polymer excitation. The phosphorescence lifetime decreases with annealing while the phosphorescence intensity increases. These changes suggest that the radiative rate of T1 → S0 increases with annealing.

Analysis of tumour oxygenation in model animals on a phosphorescence lifetime based macro-imager

Monitoring of tissue O2 is essential for cancer development and treatment, as hypoxic tumour regions develop resistance to radio- and chemotherapy. We describe a minimally invasive technique for the monitoring of tissue oxygenation in developing grafted tumours, which uses the new phosphorescence lifetime based Tpx3Cam imager. CT26 cells stained with a near-infrared emitting nanoparticulate O2 probe NanO2-IR were injected into mice to produce grafted tumours with characteristic phosphorescence. The tumours were allowed to develop for 3, 7, 10 and 17 days, with O2 imaging experiments performed on live and euthanised animals at different time points. Despite a marked trend towards decreased O2 in dead animals, their tumour areas produced phosphorescence lifetime values between 44 and 47 µs, which corresponded to hypoxic tissue with 5–20 μM O2. After the O2 imaging in animals, confocal Phosphorescence Lifetime Imaging Microscopy was conducted to examine the distribution of NanO2-IR probe in the tumours, which were excised, fixed and sliced for the purpose. The probe remained visible as bright and discrete ‘islands’ embedded in the tumour tissue until day 17 of tumour growth. Overall, this O2 macro-imaging method using NanO2-IR holds promise for long-term studies with grafted tumours in live animal models, providing quantitative 2D mapping of tissue O2.

Regulating isolated-molecular and aggregated state phosphorescence for multi-color afterglow by photo-activation.

Ultralong organic phosphorescence (UOP) materials have attracted considerable attention in recent years. Herein, a new type of flexible films was fabricated by doping amphipathic pyrene tetra sulfonic acid sodium salts into amorphous poly(vinyl alcohol) matrix, which enabled the realization of color-tunable UOP spanning from orange-red to green after excitation light switched off. Interestingly, we demonstrated precise control of the proportion of isolated-molecular and aggregated state phosphorescence for colorful afterglow using photo-activation. A 2.19-fold increase in the dynamic phosphorescence lifetime of isolated molecules was observedfrom 752.94 to 1650.46 ms following an 8-minute irradiation under ambient conditions. This flexible and processable film exhibited versatile applications in multi-color afterglow displays, ultraviolet detection, multilevel information encryption, etc. Our study not only provides a strategy for the rational regulation of UOP colors but also expands the application potential of color-tunable UOP materials. This article is protected by copyright. All rights reserved.

Rational Design of Dual‐Mode Emitting Carbon Dots to Exploit the Synergistic Effect of Matrices for High‐Efficiency WLEDs and Anti‐Counterfeiting

AbstractLong‐lived room‐temperature phosphorescence (RTP) materials have been widely applied in various fields. However, achieving high‐performance carbon dots (CDs) RTP remains a great challenge. Here, a facile synthetic strategy is rationally designed for the synthesis of high‐performance dual‐mode emitting CDs by constructing rigid structures through the synergistic effect of the matrices. The obtained CD RTP powder possesses an ultrahigh photoluminescence quantum yield (PLQY) of 70.7%, a phosphorescence lifetime of about 0.45 s, and an afterglow that lasts for 15 s to the naked eyes. Most importantly, the prepared CD RTP powder can be utilized as a commercial phosphor powder for the fabrication of a high‐performance white lighting‐emitting diode (WLED) with a CIE coordinate of (0.39, 0.39), a high color rendering index of 93.6, and a color temperature of 3805 K for warm WLED. Especially the luminous efficiency of the fabricated WLED can reach up to 66.89 lm W−1, which is much higher than the values reported for most CDs‐based WLED devices. Additionally, CD RTP can be applied to advanced invisible inks for information encryption due to its excellent water solubility and can also be exploited for advanced information anti‐counterfeiting by utilizing phosphorescent properties.

A Mitochondria-Localized Iridium(III) Complex for Simultaneous Two-Photon Phosphorescence Lifetime Imaging of Downstream Products N2O3 and ONOO- of Endogenous Nitric Oxide.

Nitric oxide (NO) serves as a ubiquitous and fundamental signaling molecule involved in intricate effects on both physiological and pathological processes. NO, biosynthesized by nitric oxide synthase (NOS) or generated from nitrite, can form nitrosation reagent N2O3 (4NO + O2 = 2N2O3) through its oxidation or quickly produce peroxynitrite anion ONOO- (NO + •O2- = ONOO-) by reacting with superoxide anion (•O2-). However, most of the existing luminescent probes for NO just focus on specificity and utilize only a single signal to distinguish products N2O3 or ONOO-. In most of the present work, they differentiate one product from another simply by fluorescence signal or fluorescence intensity, which is not enough to distinguish accurately the behavior of NO in living cells. Herein, a new mitochondria-targeted and two-photon near-infrared (NIR) phosphorescent iridium(III) complex, known as Ir-NBD, has been designed for accurate detection and simultaneous imaging of two downstream products of endogenous NO, i.e., N2O3 and ONOO-. Ir-NBD exhibits a rapid response to N2O3 and ONOO- in enhanced phosphorescence intensity, increased phosphorescence lifetime, and an exceptionally high two-photon cross-section, reaching values of 78 and 85 GM, respectively, after the reaction. Furthermore, we employed multiple imaging methods, phosphorescence intensity imaging, and phosphorescence lifetime imaging together to image even distinguish N2O3 and ONOO- by probe Ir-NBD. Thus, coupled with its excellent photometrics, Ir-NBD enabled the detection of the basal level of intracellular NO accurately by responding to N2O3 and ONOO- in the lipopolysaccharide-stimulated macrophage model in virtue of fluorescence signal and phosphorescence lifetime imaging, revealing precisely the endogenous mitochondrial NO distribution during inflammation in a cell environment.

Deep-red ultralong room temperature phosphorescence of chitosan-based nanofibrous membrane activated by carboxylic acids

Organic non-conjugated materials with room temperature phosphorescence (RTP) have attracted increasing attention due to their fundamental importance and advantages like environmental friendliness, good biocompatibility, and various processing methods. However, most non-conjugated systems often suffered from the problem with very short RTP lifetimes in ambient conditions. Here, we proposed an efficient strategy to improve the RTP performance of chitosan (CTS) by constructing a strong ionic bond network based on carboxylic acids. The CA/CTS film prepared using citric acid (CA) as a solvent was found to emit a bright afterglow of about 5 s with a phosphorescence lifetime of up to 515 ms at 530 nm. Our experimental results indicated that forming synergistic networks of ionic and hydrogen bonding was a highly efficient method for achieving persistent RTP of CTS itself. Furthermore, due to the strong ionic interaction between 1-pyrenecarboxylic acid (PCA) and CTS, the PCA@CTS nanofibrous membrane with bright deep-red afterglow was first achieved through an electrostatic spinning technique using polyethylene glycol (PEG) or polyvinyl alcohol (PVA) as a co-spinning agent. This work not only offered a new kind of persistent RTP nanofibrous membrane but also gained a deeper insight into improving the phosphorescence properties of non-conjugated materials, especially natural polysaccharide.

Time-resolved excited-state dynamics of star-shaped carbazole-based room temperature phosphorescent molecule by ultrafast absorption spectroscopy

Star-shaped room-temperature phosphorescent (RTP) molecules have attracted much attention due to high luminescence efficiency by inhibiting nonradiative transition of triplet excitons. In this work, the photophysical processes of 1,3,5-tri(9h-carbazol-9-phenyl)benzene (TCzP) and tri(4-carbazol-9-phenyl)amine (TCzTa), with benzene and triphenylamine (TPA) as central cores respectively and carbazole (Cz) as peripheral groups, are investigated. The excited state absorption (ESA) signal (625 nm) of TCzP reaches maximum intensity within 8.8 ps in the femtosecond (fs) transient absorption (TA) spectroscopy and then decays significantly with the enhancing of triplet-triplet absorption (TTA) signal (425 nm). These evolution processes of spectral signal and the appearance of isosbestic point at 450 nm together confirm the intersystem crossing (ISC) process within 5.1 ns. The TTA signal gradually disappears in the nanosecond (ns) TA spectroscopy with a phosphorescence lifetime (τph) of 2 μs. Compared to TCzP, TCzTa exhibits similar spectral evolution behavior with faster ISC of 2.1 ns and lower τph of 0.95 μs. The theoretical simulation shows that the nitrogen atoms in the TPA core of TCzTa leads to a significantly increased spin-orbit coupling constant of S1→Tn (0.86 cm−1) and T1→S0 (0.08 cm−1) than that of TCzP (0.25 cm−1 and 0.05 cm−1), resulting in the shorter experimental ISC rate constants (2.1 ns) and τph (0.95 μs). This work provides reasonable insights for understanding the real-time spectral signal evolution of star-shaped carbazole-based RTP molecules.

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

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

Structural Elucidation of Some Coordination Compounds With Reference Phosphorescent Metal Composite as Theranostic Anticancer Agents

This paper reveals that the phosphorescent metal composite are a new kind of multifunctional antitumor compounds that can integrate imaging and antitumor functions in a single molecule. In this minireview, we summarize the recent research progress in this field, concentrating on the theranostic applications of phosphorescent iridium(III), ruthenium(II) and rhenium(I) composite. The infinitesimal design that affords these composite with tumour- or subcellular organelle-targeting properties is elucidated. The potential of these composite to induce and monitor the dynamic behavior of subcellular organelles and the changes in microenvironment during the process of therapy is demonstrated. Moreover, the potential and advantages of applying new technologies, such as super-resolution imaging and phosphorescence lifetime imaging, are also described. Finally, the challenges faced in the development of novel theranostic metallo-anticancer composite for possible clinical translation are proposed.

Enhancing blue phosphorescence in matrix-free carbon dots through covalent crosslinking

Room temperature phosphorescence (RTP) of carbon dots (CDs) has received extensive attention due to its excellent performance and promising application. Here, a novel kind of matrix-free CDs with blue phosphorescence emission was synthesized by a simple one-step hydrothermal method of heating (3-Aminopropyl) trimethoxysilane (APTMS) and phosphoric acid in aqueous solution. The obtained CDs show a phosphorescence lifetime of 315.73 ms, and the absolute photoluminescence quantum yield (PLQY) and the phosphorescence quantum yield (PQY) can reach up to 37.8 % and 12.4 %, respectively. From the experimental results, we speculate that the generation of RTP is attributed to the restriction effect of the covalent crosslinking structure of SiOSi, SiOC, or SiC bonds formed on the CDs surface. In addition, phosphoric acid as a crosslinking agent and heteroatom dopant can promote the formation of cross-linked structures and facilitate the intersystem crossing (ISC) process, thus enhancing room temperature phosphorescence. Finally, the CDs were successfully used in information encryption and anti-counterfeiting.

Single-crystal structure and highly efficient sky-blue light-emitting devices of Ir(Fppy)2(Mepic) with a peak EQE of 14.27% achieved by exhaustively optimizing

An iridium complex, Ir(Fppy)2(Mepic), was synthesized, and its single crystal was obtained. The single-crystal structure, thermal stability, UV–vis absorption, photoluminescence, phosphorescent lifetime and electrochemistry of Ir(Fppy)2(Mepic) were thoroughly investigated. Ir(Fppy)2(Mepic) was incorporated into OLEDs by vacuum thermal deposition technique, and the performances of these devices were studied. The continuously optimized devices, with this Ir complex doped EML, demonstrate remarkable efficiencies for the sky-blue emissive device, achieving peak EQE of 14.27 %, CE of 29.79 cd/A and luminance of 16791 cd/m2.