Transient Lifetime Research Articles

Transient triplet differential-based photoacoustic lifetime imaging with an automatic interleaved data acquisition method for improved scanning speed and stability.

Transient triplet differential (TTD) based photoacoustic lifetime (PALT) imaging provides valuable means for background-free molecular imaging and mapping of the oxygen partial pressure (pO2) in deep tissues. However, the broad application of this method is hindered by its long scanning time, poor accuracy, and low stability. This is mainly because most PALT systems execute the three data acquisition sequences separately without automatic control and neglect the long-time fluctuation of the laser output. In this work, we have proposed a novel automatic interleaved data acquisition method for PALT. This new method not only improved the scanning efficiency but also eliminated the long-time fluctuations of laser pulse energy. Results show that this new method can significantly improve the system's stability and help reduce the scanning time. With this new method, we obtained the 3D background-free TTD images for the first time. We also observed distinct hypoxia inside the tumor due to the high metabolic rate of cancer cells, demonstrating the high reliability of our proposed method. The proposed method in this work can significantly promote the application of PALT imaging in biomedical studies.

Efficiency improvement of GaN-based micro-light-emitting diodes embedded with Ag NPs into a periodic arrangement of nano-hole channel structure by ultra close range localized surface plasmon coupling

NH-μLED, namely a micro light-emitting diode structure with nano-holes dug all the way through the active region, is designed to make silver nanoparticles in extremely close contact with the quantum wells for improving the coupling between the localized surface plasmon and the quantum wells (LSP-QWs coupling) and thus enhancing the optical properties of the μLED. The experimental results show that, thanks to this deep nanohole structure, the LSP-QWs coupling can be realized effectively, which ultimately increases the optical performance of the μLED. The internal quantum efficiency of the NH-μLED filled with silver nanoparticles is increased by 12%, and the final optical output power is also enhanced. We have further carried out a comparison study which measures the transient lifetime of two different types of μLEDs, and the results provide convincing evidence for the existence of the ultra close range LSP-QWs coupling effect.

Micrometer-Resolution X-ray Imaging Enabled by a Flexible Perovskite Screen.

Spatial resolution improvement has been keenly sought recently in the perovskite-based scintillation community. Here, micrometer resolution (∼2.0 μm) was achieved by using an X-ray imaging screen of self-assembled perovskite nanosheets. The assembly behavior of nanosheets was applicable to many substrates, including glass, metal, and polymer surfaces. The use of a polymer substrate not only eliminated the parasite absorption of X-ray but also enabled a flexible screen with robust bending stability. The assembly behavior, on the other hand, provided vicinity for an efficient energy transfer between nanosheets of varied thicknesses, as evidenced by both transient absorption and photoluminescence lifetime measurements. Importantly, the ensuing large Stokes shift (∼316 meV) significantly mitigated the reabsorption issue, leading to a comparable light yield to LYSO/Ce crystals. With the aid of the synchrotron-based collimated X-ray beam, the fine structure of two-dimensional objects, such as microchips, was clearly visualized with the flexible scintillation screen. Furthermore, those challenging biological samples were also scanned by phase-contrast imaging, whereby a three-dimensional reconstruction was obtained successfully. Despite the labile nature of the perovskite screen, this work represents the state-of-the-art spatial resolution for perovskite scintillation.

Biocompatible Chemically Fueled Transient Polymer Nanoparticles for Temporally Programmable in Vivo Imaging

Biocompatible Chemically Fueled Transient Polymer Nanoparticles for Temporally Programmable in Vivo Imaging

Investigation of excited‐state deactivation processes in benzofluorenones using time‐resolved transient absorption spectroscopy

Three benzofluorenone derivatives, benzo[a]fluorenone (BFA), benzo[b]fluorenone (BFB), and benzo[c]fluorenone (BFC), were studied spectroscopically in comparison with 9-fluorenone (9-FL) in solvents of various polarities to better understand the solvatochromism and excited-state deactivation processes in these molecules. Time-resolved transient absorption, steady-state absorption, emission, and fluorescence lifetimes were utilized in this endeavor. Differences in the excited-state deactivation processes are observed which can be attributed to the varied characters of the singlet and triplet excited states in these molecules which arise from structural differences and solvatochromism. The main deactivation pathway in all of the studied molecules was internal conversion (IC). Ignoring IC, the competition between intersystem crossing (ISC) and fluorescence is highly dependent on the molecule-solvent system. BFA was found to decay mainly via a triplet state in cyclohexane but via fluorescence in ethyl acetate and acetonitrile. BFB was found to decay via both ISC to a triplet state and emission from the singlet state in cyclohexane but only via ISC in ethyl acetate and acetonitrile. Only emission from the singlet state was observed in BFC in all solvents.

The influence of the internal interface energy barrier and the device dimensions on the transient electroluminescence lifetime of bi-layer OLEDs

Unexpected asymmetric dependence of the transient EL lifetime in bilayer OLEDs on the device dimensions is observed. It is associated with an asymmetric energy barrier at the HTL:ETL interface, and verified by a “Marburg model” based simulation.

Confinement of all-inorganic perovskite quantum dots assembled in metal-organic frameworks for ultrafast scintillator application.

Nucleation and growth of quantum dots (QDs) are thermodynamic processes driven by the total Gibbs free energy change (ΔG). We discuss the nucleation and growth theory of perovskite quantum dots (PeQDs) inside a metal-organic framework (MOF) as a strong constraint framework, which can effectively confine the size of QDs below 3 nm and achieve a scintillator with an ultra-fast transient lifetime of fluorescence. Therefore, based on the requirements for the optical properties of ultra-fast scintillation materials, two kinds of suitable MOFs (UiO-67-bpy and MIL-101(Cr)) were selected for synthesis. The method of 'ship-in-bottle' was adopted to embed perovskite quantum dots CsPbBrCl2 into MOF cages to form PeQDs@MOF composite materials, which is different from the one-pot method. In order to further improve the stability of PeQDs@MOF, polystyrene was used to cure the composite scintillator, which can resist exposure to UV light and withstand the ISO level 4 test, with the fastest transient lifetime of 2.13 ns and a fluorescence emission wavelength of 445 nm.

Alkene Difunctionalization Triggered by a Stabilized Allenyl Radical: Concomitant Installation of Two Unsaturated C−C Bonds

AbstractRadical‐mediated difunctionalization of alkenes provides a promising approach to introduce one alkenyl or alkynyl group to target compounds. However, simultaneous installation of two unsaturated C−C bonds via alkene difunctionalization remains elusive, attributable to the high instability and transient lifetimes of alkenyl and alkynyl radicals. Herein, we report the photocatalytic 1,2‐alkynylalkenylation and 1,2‐enynylalkenylation of alkenes for the first time, triggered by the intermolecular addition of a stabilized allenyl radical to an alkene. A portfolio of strategically designed, easily accessible dual‐function reagents are applied to a radical docking‐migration cascade. The protocol has broad substrate scope and efficiently increases the degree of unsaturation.

Alkene Difunctionalization Triggered by a Stabilized Allenyl Radical: Concomitant Installation of Two Unsaturated C-C Bonds.

Radical-mediated difunctionalization of alkenes provides a promising approach to introduce one alkenyl or alkynyl group to target compounds. However, simultaneous installation of two unsaturated C-C bonds via alkene difunctionalization remains elusive, attributable to the high instability and transient lifetimes of alkenyl and alkynyl radicals. Herein, we report the photocatalytic 1,2-alkynylalkenylation and 1,2-enynylalkenylation of alkenes for the first time, triggered by the intermolecular addition of a stabilized allenyl radical to an alkene. A portfolio of strategically designed, easily accessible dual-function reagents are applied to a radical docking-migration cascade. The protocol has broad substrate scope and efficiently increases the degree of unsaturation.

Strongly Entangled Triplet Acyl-Alkyl Radical Pairs in Crystals of Photostable Diphenylmethyl Adamantyl Ketones.

Radical pairs generated in crystalline solids by bond cleavage reactions of triplet ketones offer the unique opportunity to explore a frontier of spin dynamics where rigid radicals are highly entangled as the result of short inter-radical distances, large singlet-triplet energy gaps (ΔEST), and limited spin-lattice relaxation mechanisms. Here we report the pulsed laser generation and detection of strongly entangled triplet acyl-alkyl radical pairs generated in nanocrystalline suspensions of 1,1-diphenylmethyl 2-ketones with various 3-admantyl substituents. The sought-after triplet acyl-alkyl radical pairs could be studied for the first time in the solid state by taking advantage of the efficient triplet excited state α-cleavage reactions of 1,1-diphenylmethyl ketones and the slow rate of CO loss from the acyl radicals, which would have to generate highly unstable phenyl and primary alkyl radicals or relatively unstable secondary and tertiary alkyl radicals. With the loss of CO prevented, the lifetime of the triplet acyl-alkyl radical pair intermediates is determined by intersystem crossing to the singlet radical pair state, which is followed by immediate bond formation to the ground state starting ketone. Experimental results revealed biexponential kinetics with long-lived components that account for ca. 87-92% of the transient population and lifetimes that extend to the range of 53-63 μs, the longest reported so far for this type of radical pair. Structural information inferred from the starting ketone will make it possible to analyze the affects of proximity and orientation of the singly occupied orbitals and potentially help set a path for the use of triplet radical pairs as qubits in quantum information technologies.

Highly Stable Acid-Induced Emission-Enhancing Cd-MOFs: Synthesis, Characterization, and Detection of Glutamic Acid in Water and Fe Ions in Acid

Two novel 3D fluorescent metal-organic frameworks (MOFs), [Cd(L)(bbibp)]n (1) and [Cd(L)(bbibp)0.5]n (2), where H2L = 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoic acid and bbibp = 4,4'-bis(benzoimidaz-1-yl)biphenyl, were acquired through a conventional method and characterized via IR spectra, single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction (PXRD), scanning electron microscopy, N2 adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The crystal framework of Cd-MOF 1 remained stable in the range of pH = 1.0-12.0. Interestingly, the emission peak of 1 showed a red shift and exhibited a fluorescence turn-on effect in an acidic environment. X-ray diffraction measurement revealed that the crystal structure of 1 remained unchanged after immersion in a pH = 1.0 solution. In addition, Cd-MOFs 1 and 2 displayed fluorescent quenching to l-glutamic acid with high sensitivity and selectivity. Meanwhile, 1 showed high selectivity in recognizing Fe3+ under acidic conditions, which made 1 capable of detecting Fe3+ in acidic industrial wastewater. Finally, the fluorescent sensing mechanism was carefully studied by PXRD, transient fluorescence lifetime, XPS, and UV spectroscopy.

Carrier engineering of carbon nitride boosts visible-light photocatalytic hydrogen evolution

Carbon nitride, as one of the metal-free photocatalysts, has aroused wide attention due to its low cost, easy preparation, and excellent optical response. However, challenges of the high recombination rate of electron-hole pair hindered their potential applications. Here, boron-doped carbon nitride nanotubes were designed and prepared by a simple hydrothermal and calcination route. Compared with the bulk carbon nitride, the control strategy forms the ordered nanotube structure, which greatly improved their specific surface area, exposed more active sites, and enhanced the graphitization degree. The transient fluorescence lifetime of tubular carbon nitride is twice as long as that of pure carbon nitride. Furthermore, boron doping carbon nitride nanotubes exhibited a 1.5-fold increase in a lifetime over tubular carbon nitride, which acts a synergistic role with nanotube architecture to further increases the carrier concentration and hinder the recombination of photogenerated electron-hole. Under the irradiation of visible light, the amount of hydrogen evolution of the optimum photocatalyst has achieved 22.1 mmol g−1 h−1, which was 64 times that of the bulk carbon nitride and exhibited excellent stability. This work provides a promising strategy for the development of non-metallic doped carbon nitride nanotube photocatalysts for hydrogen evolution.

Transient chaos in time-delayed systems subjected to parameter drift

External and internal factors may cause a system’s parameter to vary with time before it stabilizes. This drift induces a regime shift when the parameter crosses a bifurcation. Here, we study the case of an infinite dimensional system: a time-delayed oscillator whose time delay varies at a small but non-negligible rate. Our research shows that due to this parameter drift, trajectories from a chaotic attractor tip to other states with a certain probability. This causes the appearance of the phenomenon of transient chaos. By using an ensemble approach, we find a gamma distribution of transient lifetimes, unlike in other non-delayed systems where normal distributions have been found to govern the process. Furthermore, we analyze how the parameter change rate influences the tipping probability, and we derive a scaling law relating the parameter value for which the tipping takes place and the lifetime of the transient chaos with the parameter change rate.

Relating transient electroluminescence lifetime and bulk transit time in OLED during switch-off

The EL decay is attributed to the transit time, and it originates from the radiative recombination of newly formed singlet excitons during the discharge of the space-charge regions.

Efficient and stable organic light-emitting devices employing phosphorescent molecular aggregates

Stable and efficient organic light-emitting diodes (OLEDs) operating at high brightness are desirable for future high-resolution displays and lighting products. Here, we report a tetradentate Pd(ii) complex called Pd3O8-P, which has attractive optoelectronics properties. At room temperature, aggregates of Pd3O8-P exhibited a close-to-unity photoluminescent quantum yield and a short transient lifetime of 0.62 μs. A host-free Pd3O8-P yellow-orange OLED emitted light with a peak at 588 nm, a half-bandwidth of 84 nm and CIE coordinates of (0.52, 0.47), and achieved a peak external quantum efficiency (EQE) of 34.8%. The device had reduced efficiency roll-off, retaining high EQEs of 33.5% at 1,000 cd m−2 and 29.5% at 10,000 cd m−2. The estimated operational half-lifetime was 9.59 million hours at 1,000 cd m−2. The fact that the tetradentate metal complex has a triplet in the blue-emitting region may also assist the development of efficient and long-lived blue OLEDs in the future. A tetradentate Pd(ii) complex with near unity photoluminescent quantum yield is the basis of bright, long-lifetime organic LEDs.

Search for extreme electromagnetic fields through measurements of charm mesons flow harmonics in PbPb collisions at 5.02 TeV with the CMS detector

In ultrarelativistic heavy-ion collisions, a very strong (on the order of 1016 T) and transient (lifetime on the order of 10−1 fm/c) electromagnetic (EM) field is expected to be generated inside the medium formed in the collision. This EM field, generated by the collision participants and spectators, is predicted to produce a difference in the νn harmonics for positive-and negative-charged particles, with the magnetic field mainly responsible for a splitting in rapidity-odd directed flow (ν1), and the Coulomb electric field leading to a charge-dependent splitting in the ν2 and average pT values of emitted particles. Due to the large mass, charm quarks are expected to be created very early in the collision, and thus have more chance of interacting with this strong EM field than light flavor hadrons. In this contribution, measurements of D0 (u‾c) and D‾0uc‾) mesons flow harmonics (ν2 and ν3) are presented as functions of rapidity (y), transverse momentum, and collision centrality for PbPb collisions at 5.02 TeV, using the large data samples collected by the CMS experiment during the LHC Run 2. The wide rapidity coverage (|y| < 2) of these new charm mesons measurements allow for a better understanding of the 3-dimensional evolution of the medium formed in heavy-ion collisions.

Synchronization within synchronization: transients and intermittency in ecological networks

Transients are fundamental to ecological systems with significant implications to management, conservation and biological control. We uncover a type of transient synchronization behavior in spatial ecological networks whose local dynamics are of the chaotic, predator–prey type. In the parameter regime where there is phase synchronization among all the patches, complete synchronization (i.e. synchronization in both phase and amplitude) can arise in certain pairs of patches as determined by the network symmetry—henceforth the phenomenon of ‘synchronization within synchronization.’ Distinct patterns of complete synchronization coexist but, due to intrinsic instability or noise, each pattern is a transient and there is random, intermittent switching among the patterns in the course of time evolution. The probability distribution of the transient time is found to follow an algebraic scaling law with a divergent average transient lifetime. Based on symmetry considerations, we develop a stability analysis to understand these phenomena. The general principle of symmetry can also be exploited to explain previously discovered, counterintuitive synchronization behaviors in ecological networks.

Triplet collection for highly efficient single-emitting-layer pure fluorescent WOLED based thermally activated delayed fluorescent host of acridine/sulfone derivative

Abstract Herein, highly efficient single-emitting-layer structure pure fluorescent white organic light-emitting diodes (WOLED) were designed by employing thermally activated delayed fluorescence emitter of mSOAD as host material to sensitize traditional fluorescent dopant of Rubrene and DCJTB, respectively. The WOLED based Rubrene dopant achieve a cool white emission with maximum current efficiency, power efficiency and external quantum efficiency of 33.0 cd/A, 34.5 l m/W and 12.2%, respectively. While a warm white emission with the efficiency of 20.9 cd/A, 20.1 lm/W and 9.0%, respectively, were realized in WOLED based DCJTB dopant. The study to energy level and photoluminescence transient decay lifetime demonstrate the sufficient confinement to charges and excitons, and efficient triplet collection by host triplet exciton reverse intersystem crossing and energy transfer to dopant are the reasons of high device efficiency and stable spectra.

Tipping point and noise-induced transients in ecological networks.

A challenging and outstanding problem in interdisciplinary research is to understand the interplay between transients and stochasticity in high-dimensional dynamical systems. Focusing on the tipping-point dynamics in complex mutualistic networks in ecology constructed from empirical data, we investigate the phenomena of noise-induced collapse and noise-induced recovery. Two types of noise are studied: environmental (Gaussian white) noise and state-dependent demographic noise. The dynamical mechanism responsible for both phenomena is a transition from one stable steady state to another driven by stochastic forcing, mediated by an unstable steady state. Exploiting a generic and effective two-dimensional reduced model for real-world mutualistic networks, we find that the average transient lifetime scales algebraically with the noise amplitude, for both environmental and demographic noise. We develop a physical understanding of the scaling laws through an analysis of the mean first passage time from one steady state to another. The phenomena of noise-induced collapse and recovery and the associated scaling laws have implications for managing high-dimensional ecological systems.

Scaling law of transient lifetime of chimera states under dimension-augmenting perturbations

Chimera states arising in the classic Kuramoto system of two-dimensional phase coupled oscillators are transient but they are "long" transients in the sense that the average transient lifetime grows exponentially with the system size. For reasonably large systems, e.g., those consisting of a few hundreds oscillators, it is infeasible to numerically calculate or experimentally measure the average lifetime, so the chimera states are practically permanent. We find that small perturbations in the third dimension, which make system "slightly" three-dimensional, will reduce dramatically the transient lifetime. In particular, under such a perturbation, the practically infinite average transient lifetime will become extremely short, because it scales with the magnitude of the perturbation only logarithmically. Physically, this means that a reduction in the perturbation strength over many orders of magnitude, insofar as it is not zero, would result in only an incremental increase in the lifetime. The uncovered type of fragility of chimera states raises concerns about their observability in physical systems.