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The rotational relaxation behavior of D2(1,12) in a D2–N2 mixture was investigated using coherent anti-Stokes Raman scattering (CARS) technique. The rovibrational level v = 1 and J = 12 of D2 was selectively excited through stimulated Raman pumping while monitoring the temporal evolution of population for D2(1, J ≤ 12) molecules using time-resolved CARS spectroscopy. The results demonstrate that the rotational relaxation processes of D2(1,12) encompass both multi-quantum relaxation and continuous single-quantum relaxation. When α, the molar ratio of N2, is less than 0.5, D2(1,12) predominantly undergoes a single quantum relaxation process transition. However, when α ≥ 0.5, the multi-quantum relaxation mechanism gradually predominates. The total rotational relaxation rate coefficients of D2(1,12) collisions with N2 and D2 at 295 K were determined to be 3.974 × 10−14 and 1.179 × 10−14 cm3 s−1, respectively. The temperature dependence of rotational relaxation rate of D2(1,12) was investigated within the temperature range of 295–453 K. With increasing temperature, the dominant relaxation process exhibited an accelerated behavior, while the minor relaxation process remained largely unaffected. The rotational temperature of the D2 molecule at various N2 molar ratios was determined through the utilization of Boltzmann plots. The rotational temperature undergoes a rapid decline within 2 μs, corresponding to the near-resonant rotation–vibration relaxation process of D2(1,12) collisions with N2. The system reaches a quasi-equilibrium state when the delay time is 3 μs. The findings of this study can serve as a valuable empirical basis for further validation of the kinetic theory and simulation. [ABSTRACT FROM AUTHOR]

Ultrafast optical spectroscopy is a powerful technique for studying the dynamic processes of molecular systems in condensed phases. However, in molecular systems containing many dye molecules, the spectra can become crowded and difficult to interpret owing to the presence of multiple nonlinear optical contributions. In this work, we theoretically propose time-resolved spectroscopy based on the coincidence counting of two entangled photons generated via parametric down-conversion with a monochromatic laser. We demonstrate that the use of two-photon counting detection of entangled photon pairs enables the selective elimination of the excited-state absorption signal. This selective elimination cannot be realized with classical coherent light. We anticipate that the proposed spectroscopy will help simplify the spectral interpretation of complex molecular and material systems comprising multiple molecules. [ABSTRACT FROM AUTHOR]

In this work, charge photogeneration and recombination processes of PM6:IDIC-4F and PM6:IDIC blend films were investigated by the steady-state and time-resolved spectroscopies, as well as the time-dependent density functional theory calculations. The peaks in absorption and photoluminescence (PL) spectra of IDIC and IDIC-4F solutions were assigned by combining the experiment and the simulation of UV–vis absorption and PL spectra. For neat acceptor films, the exciton diffusion length of neat IDIC and IDIC-4F films was estimated as ∼28.9 and ∼19.9 nm, respectively. For PM6-based blend films, we find that the fluorine substitution engineering on the IDIC acceptor material can increase the phase separate size of acceptor material in blend films, resulting in the reduction of dissociation efficiencies of acceptor excitons. In addition, we find that the charge recombination in PM6:IDIC-4F is dominated by bimolecular recombination, in comparison to geminate type carrier recombination in PM6:IDIC blend films. In addition, we find that thermal annealing treatment has a weak influence on carrier recombination but slightly reduces the exciton dissociation efficiency of acceptor in PM6:IDIC blend films, leading to a slightly reduced power conversion efficiency of PM6:IDIC solar cells. These results may shed light on the design of high-performance semiconductor molecules for application in solar cells. [ABSTRACT FROM AUTHOR]

The photophysics of thiobases—nucleobases in which one or more oxygen atoms are replaced with sulfur atoms— vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I− · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88 eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16 eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14 eV pulses. Excitation at 3.88 eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16 eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide–nucleobase clusters. [ABSTRACT FROM AUTHOR]

The manipulation of the ultrafast quantum dynamics of a molecular system can be achieved through the application of tailored light fields. This has been done in many ways in the past. In our present investigation, we show that it is possible to exert specific control over the nonadiabatic dynamics of a generic model system describing ultrafast charge-transfer within a condensed dissipative environment by using frequency-chirped pulses. By adjusting the external photoexcitation conditions, such as the chirp parameter, we show that the final population of the excitonic and charge-transfer states can be significantly altered, thereby influencing the elementary steps controlling the transfer process. In addition, we introduce an excitation scheme based on double-pump time-resolved fluorescence spectroscopy using chirped-pulse excitations. Here, our findings reveal that chirped excitations enhance the vibrational system dynamics as evidenced by the simulated spectra, where a substantial signal intensity dependence on the chirp is observed. Our simulations show that chirped pulses are a promising tool for steering the dynamics of the charge-transfer process toward a desired target outcome. [ABSTRACT FROM AUTHOR]

Time-resolved pump–probe and two-dimensional spectroscopy are widely used to study ultrafast chemical and biological processes in solutions. However, the corresponding signals at long times can be contaminated by molecular photothermal effects, which are caused by the nonradiative heat dissipation of photoexcited molecules to the surroundings. Additionally, molecular diffusion affects the transient spectroscopic signals because photoexcited molecules can diffuse away from the pump and probe beam focuses. Recently, a theoretical description of molecular photothermal effects on time-resolved IR spectroscopy was reported. In this work, I consider the molecular photothermal process, molecular diffusion, and sample flow to develop a generalized theoretical description of time-resolved spectroscopy. The present work can be used to interpret time-resolved spectroscopic signals of electronic or vibrational chromophores and understand the rate and mechanisms of the conversion of high-frequency molecular electronic and vibrational energy to solvent kinetic energy in condensed phases. [ABSTRACT FROM AUTHOR]

The rotational relaxation behavior of D2(1,12) in a D2–N2 mixture was investigated using coherent anti-Stokes Raman scattering (CARS) technique. The rovibrational level v = 1 and J = 12 of D2 was selectively excited through stimulated Raman pumping while monitoring the temporal evolution of population for D2(1, J ≤ 12) molecules using time-resolved CARS spectroscopy. The results demonstrate that the rotational relaxation processes of D2(1,12) encompass both multi-quantum relaxation and continuous single-quantum relaxation. When α, the molar ratio of N2, is less than 0.5, D2(1,12) predominantly undergoes a single quantum relaxation process transition. However, when α ≥ 0.5, the multi-quantum relaxation mechanism gradually predominates. The total rotational relaxation rate coefficients of D2(1,12) collisions with N2 and D2 at 295 K were determined to be 3.974 × 10−14 and 1.179 × 10−14 cm3 s−1, respectively. The temperature dependence of rotational relaxation rate of D2(1,12) was investigated within the temperature range of 295–453 K. With increasing temperature, the dominant relaxation process exhibited an accelerated behavior, while the minor relaxation process remained largely unaffected. The rotational temperature of the D2 molecule at various N2 molar ratios was determined through the utilization of Boltzmann plots. The rotational temperature undergoes a rapid decline within 2 μs, corresponding to the near-resonant rotation–vibration relaxation process of D2(1,12) collisions with N2. The system reaches a quasi-equilibrium state when the delay time is 3 μs. The findings of this study can serve as a valuable empirical basis for further validation of the kinetic theory and simulation. [ABSTRACT FROM AUTHOR]

The H atom tunneling dissociation dynamics of the S1 state of meta- or para-cresol has been investigated by using the picosecond time-resolved pump-probe spectroscopy in a state-specific manner. The S1 state lifetime (mainly due to the H atom tunneling reaction) is found to be mode-dependent whereas it quickly converges and remains constant as the rapid intramolecular vibrational energy redistribution (IVR) starts to participate in the S1 state relaxation with the increase of the S1 internal energy (Eint). The IVR rate and its change with increasing Eint have been reflected in the parent ion transients taken by tuning the total energy (hνpump + hνprobe) just above the adiabatic ionization threshold (so that the dissipation of the initial mode-character could be monitored as a function of the reaction time), indicating that the mode randomization rate into the S1 isoenergetic manifolds exceeds the tunneling rate quite early in terms of Eint for m-cresol (≤∼1200 cm−1) or p-cresol (≤∼800 cm−1) compared to the case of phenol (≤∼1800 cm−1). Though the H atom tunneling dynamics of phenol (S1) seems to be little influenced by the methyl substitution on the either m- or p-position, the IVR rate has been found to be strongly accelerated due to the sharply-increasing (S1) density of states with increasing Eint due to the pivotal role of the low-frequency CH3 torsional mode. [ABSTRACT FROM AUTHOR]

Absolute line strengths of several transitions in the ν1 fundamental band of the hydroxyl radical (OH) have been measured by simultaneous determination of hydrogen peroxide (H2O2) and OH upon laser photolysis of H2O2. Based on the well-known quantum yield for the generation of OH radicals in the 248-nm photolysis of H2O2, the line strength of the OH radicals can be accurately derived by adopting the line strength of the well-characterized transitions of H2O2 and analyzing the difference absorbance time traces of H2O2 and OH obtained upon laser photolysis. Employing a synchronized two-color dual-comb spectrometer, we measured high-resolution time-resolved absorption spectra of H2O2 near 7.9 µm and the OH radical near 2.9 µm, simultaneously, under varied conditions. In addition to the studies of the line strengths of the selected H2O2 and OH transitions, the kinetics of the reaction between OH and H2O2 were investigated. A pressure-independent rate coefficient kOH+H2O2 was determined to be [1.97 (+0.10/−0.15)] × 10−12 cm3 molecule−1 s−1 at 296 K and compared with other experimental results. By carefully analyzing both high-resolution spectra and temporal absorbance profiles of H2O2 and OH, the uncertainty of the obtained OH line strengths can be achieved down to <10% in this work. Moreover, the proposed two-color time-resolved dual-comb spectroscopy provides a new approach for directly determining the line strengths of transient free radicals and holds promise for investigations on their self-reaction kinetics as well as radical–radical reactions. [ABSTRACT FROM AUTHOR]

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil. [ABSTRACT FROM AUTHOR]

Ultrafast spectroscopy is a powerful technique that utilizes short pulses on the femtosecond time scale to generate and probe coherent responses in molecular systems. While the specific ultrafast methodologies vary, the most common data analysis tools rely on discrete Fourier transformation for recovering coherences that report on electronic or vibrational states and multi-exponential fitting for probing population dynamics, such as excited-state relaxation. These analysis tools are widely used due to their perceived reliability in estimating frequencies and decay rates. Here, we demonstrate that such "black box" methods for parameter estimation often lead to inaccurate results even in the absence of noise. To address this issue, we propose an alternative approach based on Bayes probability theory that simultaneously accounts for both population and coherence contributions to the signal. This Bayesian inference method offers accurate parameter estimations across a broad range of experimental conditions, including scenarios with high noise and data truncation. In contrast to traditional methods, Bayesian inference incorporates prior information about the measured signal and noise, leading to improved accuracy. Moreover, it provides estimator error bounds, enabling a systematic statistical framework for interpreting confidence in the results. By employing Bayesian inference, all parameters of a realistic model system may be accurately recovered, even in extremely challenging scenarios where Fourier and multi-exponential fitting methods fail. This approach offers a more reliable and comprehensive analysis tool for time-resolved coherent spectroscopy, enhancing our understanding of molecular systems and enabling a better interpretation of experimental data. [ABSTRACT FROM AUTHOR]

Quantum light is increasingly recognized as a promising resource for developing optical measurement techniques. Particular attention has been paid to enhancing the precision of the measurements beyond classical techniques by using nonclassical correlations between quantum entangled photons. Recent advances in the quantum optics technology have made it possible to manipulate spectral and temporal properties of entangled photons, and photon correlations can facilitate the extraction of matter information with relatively simple optical systems compared to conventional schemes. In these respects, the applications of entangled photons to time-resolved spectroscopy can open new avenues for unambiguously extracting information on dynamical processes in complex molecular and materials systems. Here, we propose time-resolved spectroscopy in which specific signal contributions are selectively enhanced by harnessing nonclassical correlations of entangled photons. The entanglement time characterizes the mutual delay between an entangled twin and determines the spectral distribution of photon correlations. The entanglement time plays a dual role as the knob for controlling the accessible time region of dynamical processes and the degrees of spectral selectivity. In this sense, the role of the entanglement time is substantially equivalent to the temporal width of the classical laser pulse. The results demonstrate that the application of quantum entangled photons to time-resolved spectroscopy leads to monitoring dynamical processes in complex molecular and materials systems by selectively extracting desired signal contributions from congested spectra. We anticipate that more elaborately engineered photon states would broaden the availability of quantum light spectroscopy. [ABSTRACT FROM AUTHOR]

Energetic materials are extensively used as propellants in rockets demanding the understanding of their chemical and thermal stability for safe storage and transportation as well as ease of decomposition. Nitromethane (NM) is one such material with significant performance advantage over other mono propellants. In this manuscript, we report the detailed molecular-level behavior of NM under static and dynamic compression. Dynamic compression experiments were performed up to ∼6.4 GPa using a 2 J/8 ns Nd: YAG laser coupled with time-resolved Raman spectroscopy (TRRS) setup. Static compression experiments were performed up to ∼20 GPa using a diamond anvil cell. During laser-driven shock compression, NM undergoes three phase transitions at 1.1, 2.5, and 3.4 GPa. However, in the case of static compression, the corresponding phase transitions were observed at 0.3, 1.3–1.8, and 2.5 GPa. TRRS was also performed at 300 mJ (1.47 GW/cm2), 500 mJ (2.45 GW/cm2), and 800 mJ (3.9 GW/cm2) and intensity ratios of shocked and un-shocked Raman peaks were utilized to experimentally calculate the shock velocities, which were determined to be 2.66 ± 0.09, 3.58 ± 0.40, and 3.83 ± 0.60 km/s, respectively. These experimental results were corroborated with the one-dimensional (1D) radiation hydrodynamics simulations, performed to obtain shock pressure. The shock velocities at these laser intensities were calculated to be 2.98, 3.69, and 3.92 km/s, respectively, which are in reasonably close agreement with our observed results. [ABSTRACT FROM AUTHOR]

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed. [ABSTRACT FROM AUTHOR]

The non-adiabatic relaxation processes and the fragmentation dynamics of Rydberg-excited N,N,N′,N′-tetramethylmethylenediamine (TMMDA) are investigated using femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. Excitation at 208 nm populates TMMDA in a charge-localized 3p state. Rapid internal conversion (IC) to 3s produces two charge-delocalized conformers with independent time constants and distinct population ratios. As the system explores the 3s potential surface, the structural evolution continues on a 1.55 ps timescale, followed by a slower (12.1 ps) relaxation to the ground state. A thorough comparison of the time-dependent mass and photoelectron spectra suggests that ionization out of the 3p state ends up with the parent ion, the vibrational energy of which is insufficient for the bond cleavage. On the contrary, by virtue of the additional energy acquired by IC from 3p, the internal energy deposited in 3s is available to break the C–N bond, leading to the fragment ion. The fragmentation is found to occur on the ion surface instead of the Rydberg surface. [ABSTRACT FROM AUTHOR]

Controlled thinning of wide bandgap semiconductors by chemo-mechanical polishing (CMP) and/or reactive ion etching (RIE) has been one of the versatile methods for various optoelectronic applications. The influences of CMP and subsequent wet chemical etching, as well as independent RIE, on the room-temperature photoluminescence lifetime for the near-band-edge emission [ τ PL NBE (RT) ] of O-polarity c-plane ZnO single crystals were examined by using time-resolved photoluminescence measurements. τ PL NBE (RT) decreased from a nanosecond range to a few picoseconds (ps) by a conventional CMP, indicating a generation of high-concentration midgap recombination centers, such as nonradiative recombination centers and deep radiative recombination centers. τ PL NBE (RT) was progressively regained up to 600 ps by a subsequent etching using HCl aqueous solution. However, the recovery saturated at the etching depth of about 200 nm and τ PL NBE (RT) was not restored even after etching by 350 nm. The results indicate the introduction of certain structural deformations during the CMP. Because x-ray diffraction measurement revealed the presence of incoherent surface domains right after the CMP and the HCl etching gave rise to inhomogeneously etched canyons, nonradiative recombination centers, such as dislocations and vacancy clusters, are likely generated by mechanical shear stresses. τ PL NBE (RT) also decreased by the RIE. However, the degradation was less significant than the case for the CMP, because RIE scarcely gives mechanical stresses. Interestingly, τ PL NBE (RT) for the samples etched under higher plasma power was longer than the lower power cases. From the results of x-ray photoelectron spectroscopy measurements, unintentionally deposited oxide films containing Si are proposed to act as an attenuating layer for the introduction of nonradiative recombination centers. [ABSTRACT FROM AUTHOR]

This work describes the plume chemistry of laser-ablated carbon–carbon (C–C) composite samples in vacuum, a range of air pressures, and in pure oxygen. Time-resolved spectra were measured from a plasma plume generated by laser-ablation at 248 nm. The focus of this work was on the detection of three chemical species, C2, CN, and CO in pressures from near vacuum (10−7 Torr) to air at atmospheric pressure (760 Torr). Emission from atomic carbon C I was predominant at 10−7 Torr, while molecular C2 Swan Band emission was observed at 10−7 Torr, at all air pressures, as well as in pure oxygen. Emission from the CN violet bands was observed only when ablating in air, but not in vacuum or pure O2, indicating that CN was the product of a chemical reaction between an ablated carbon species and N2 present in air, and not intrinsically present in the C–C composite targets. High-resolution emission spectra from C2 and CN were measured and fitted to vibrational and rotational temperatures. Time-resolved emission measurements of both these molecules were used to estimate their respective velocities as a function of pressure. No emission from excited state CO could be detected from 180–900 nm, even in pure O2. However, neutral and ground state CO and CO2 were both detected by measuring FTIR absorption spectra following the ablation of a composite target at 248 nm, in dry air at atmospheric pressure. The HITRAN database was used to calculate the concentrations of CO and CO2 produced per laser pulse. [ABSTRACT FROM AUTHOR]

Time-resolved spectroscopy is commonly used to study diverse phenomena in chemistry, biology, and physics. Pump–probe experiments and coherent two-dimensional (2D) spectroscopy have resolved site-to-site energy transfer, visualized electronic couplings, and much more. In both techniques, the lowest-order signal, in a perturbative expansion of the polarization, is of third order in the electric field, which we call a one-quantum (1Q) signal because in 2D spectroscopy it oscillates in the coherence time with the excitation frequency. There is also a two-quantum (2Q) signal that oscillates in the coherence time at twice the fundamental frequency and is fifth order in the electric field. We demonstrate that the appearance of the 2Q signal guarantees that the 1Q signal is contaminated by non-negligible fifth-order interactions. We derive an analytical connection between an nQ signal and (2n + 1)th-order contaminations of an rQ (with r < n) signal by studying Feynman diagrams of all contributions. We demonstrate that by performing partial integrations along the excitation axis in 2D spectra, we can obtain clean rQ signals free of higher-order artifacts. We exemplify the technique using optical 2D spectroscopy on squaraine oligomers, showing clean extraction of the third-order signal. We further demonstrate the analytical connection with higher-order pump–probe spectroscopy and compare both techniques experimentally. Our approach demonstrates the full power of higher-order pump–probe and 2D spectroscopy to investigate multi-particle interactions in coupled systems. [ABSTRACT FROM AUTHOR]

Time-resolved photoionization measurements were performed on o-nitrophenol pumped with UV laser pulses at a central wavelength of 255 nm (4.9 eV) and probed with vacuum ultraviolet (VUV) pulses at 153 nm (8.1 eV). The photoelectron spectrum and time of flight mass spectrum for ions were recorded at each pump–probe delay. The measurements are interpreted with the aid of electronic structure calculations for both the neutral and ionic states. Evidence is found for the formation of a bicyclic intermediate followed by NO dissociation through a process of internal conversion and intersystem crossing. The combination of photoelectron and photoion spectroscopy, together with computational results, provides strong evidence of intersystem crossing that is difficult to establish with only a single technique. [ABSTRACT FROM AUTHOR]

Revealing the coaction effect of radiative and non-radiative damping on the lifetime of the localized surface plasmon resonance (LSPR) mode is a prerequisite for the applications of LSPR. Here, we systematically investigated the coaction effect of radiative and non-radiative damping on the lifetime of the super-radiant and sub-radiant LSPR modes of gold nanorods using time-resolved photoemission electron microscopy (TR-PEEM). The results show that the lifetime of the LSPR mode depends on the length of the gold nanorod, and the different variation behavior of an LSPR mode lifetime exists between the super-radiative mode and the sub-radiative one with the increase of nanorod length (volume). Surprisingly, it is found that the lifetime of the super-radiant LSPR mode can be comparable to or even longer than that of the sub-radiant LSPR mode, instead of the usual claim that a sub-radiant LSPR mode has a longer life than the super-radiant mode. Those TR-PEEM experimental results are supported by finite-difference time-domain simulations and are well explained by the coaction effect with the calculation of the radiative and non-radiative damping rate with the increase of the nanorod volume. We believe that this study is beneficial to build a low-threshold nano-laser and ultrasensitive molecular spectroscopy system. [ABSTRACT FROM AUTHOR]

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148 nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62–150.45 nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0–10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62 nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band. [ABSTRACT FROM AUTHOR]

Time-resolved X-ray photoelectron spectroscopy (TR-XPS) is used in a simulation study to monitor the excited state intramolecular proton transfer between oxygen and nitrogen atoms in 2-(iminomethyl)phenol. Real-time monitoring of the chemical bond breaking and forming processes is obtained through the time evolution of excitedstate chemical shifts. By employing individual atomic probes of the proton donor and acceptor atoms, we predict distinct signals with opposite chemical shifts of the donor and acceptor groups during proton transfer. Details of the ultrafast bond breaking and forming dynamics are revealed by extending the classical electron spectroscopy chemical analysis to real time. Through a comparison with simulated time-resolved photoelectron spectroscopy at the valence level, the distinct advantage of TR-XPS is demonstrated thanks to its atom specificity. [ABSTRACT FROM AUTHOR]

Recently, the incorporation of transition‐metal ions into lead‐free double perovskite has garnered considerable attention for improving the lattice environment and enhancing photoluminescence (PL) to achieve white light emission. Here, Sb/X (Mn, Er, Ho) co‐doped Cs2NaInCl6 (CNIC) microcrystals (MCs) synthesized by conventional hydrothermal method are developed for single‐component white light emission with various photoinduced transition mechanisms. Sb doping in CNIC MCs causes the breaking of non‐parity forbidden transition under 360 nm laser excitation and results in blue emission; Sb/X co‐doping for CNIC MCs successfully broadens the spectrum with multi‐peak emission, which consists of unique X‐peak emission and blue emission peaked at 445 nm. The energy transfer channels from both free excitons state of CNIC and self‐trapping excitons (STEs) state of [SbCl6]3− to X ion are proved and studied by use of steady‐state and time‐resolved PL spectroscopy. Among them, Sb/Er co‐doped CNIC MCs show unique dual‐mode PL under 360 and 980 nm laser excitation. Single‐component white light emitting diode is successfully fabricated by adjusting the composition of Sb/X co‐doped CNIC MCs, which provides an alternative path for realizing single‐component white light illumination. [ABSTRACT FROM AUTHOR]

Due to the low‐lying Pd(4d)‐orbitals, luminescent palladium(II) complexes usually show 3IL phosphorescence (IL = intraligand) with excited state lifetimes in the range of hundreds of microseconds, which limits their application in blue organic light‐emitting diodes (OLEDs). Here, a molecular design strategy for the development of strongly luminescent Pd(II)‐based thermally activated delayed fluorescence (TADF) emitters with fast radiative decay rate constants and reverse intersystem crossing rate (kRISC) constants is presented. The synthesized tetradentate [Pd(N*C*C^N)] TADF emitters show sky‐blue to yellow (λmax = 484–565 nm) emission with excited state lifetimes in the range of 0.9−8.7 µs and high photoluminescence quantum yield of up to 77% in CH2Cl2 solution. In 5 wt.% 2,8‐bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) thin films, these [Pd(N*C*C^N)] TADF complexes display blue to sky‐blue (476−496 nm) emission with quantum yields close to unity. Variable‐temperature emission lifetime measurements, femtosecond time‐resolved spectroscopy, and density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations together reveal ultrafast kRISC rate constants of these [Pd(N*C*C^N)] TADF emitters. Using these Pd(II)‐TADF emitters as dopants, sky‐blue TADF and blue TADF‐sensitized OLEDs with small efficiency roll‐offs achieved high maximum external quantum efficiencies (EQEs) of 24.8% and 23.1%, respectively. [ABSTRACT FROM AUTHOR]

A time-resolved laser fluorescence spectroscopy (TRLFS) study was carried out to investigate the Eu(III)- SO4 complexation at room temperature over a wide range of Na2SO4 concentrations (0-2 mol kg-1). Spectroscopic observations confirm the step-wise formation of the aqueous complexes Eu(SO4)+, Eu(SO4)2- and Eu(SO4)33- over the investigated Na2SO4 concentrations. Combining TRLFS data obtained in this study and solubility data reported in Part I of this work for the Eu2(SO4)3-Na2SO4-H2O and Eu2(SO4)3-MgSO4-H2O systems, thermodynamic and activity models were derived based on the SIT and Pitzer formalisms. A combination of the geochemical calculation codes PhreeqC (SIT), PhreeSCALE (Pitzer) and the parameter estimation code PEST was used to determine the solubility products (K°s;0) of Eu2(SO4)3·8H2O(cr) and Na2Eu2(SO4)4·2H2O(cr), stability constants of the Eu(III)-SO4 complexes (β0i), and the specific binary and ternary interaction parameters (εij, β(0)ij, β(1)ij, Cϕij, θik, Ψijk) for both activity models. The thermodynamic constants determined in this work are discussed with reference to values available in the literature. [ABSTRACT FROM AUTHOR]

The effects of backbone amine functionalization in three new homoleptic C^N^C type ruthenium(II) complexes bearing a tridentate bis‐imidazole‐2‐ylidene pyridine ligand framework are characterized and studied by single crystal diffraction, electrochemistry, optical spectroscopy and transient absorption spectroscopy in combination with ab initio DFT calculations. Functionalization by dimethylamine groups in 4‐position of the pyridine backbone significantly influences the properties of the complexes as revealed by comparison with the unfunctionalized references. As a result of the amine functionalization, a higher molar absorption coefficient of the MLCT bands, a decreased photoluminescence quantum yield at room temperature together with a shortened excited state lifetime but an improved photostability is observed. Introduction of electron donating and withdrawing groups at the NHC unit modifies the electronic and optical properties, such as the oxidation potential, absorption and emission properties, and the lifetimes of the excited states. [ABSTRACT FROM AUTHOR]

Psoralens are eponymous for PUVA (psoralen plus UV-A radiation) therapy, which inter alia can be used to treat various skin diseases. Based on the same underlying mechanism of action, the synthetic psoralen amotosalen (AMO) is utilized in the pathogen reduction technology of the INTERCEPT® Blood System to inactivate pathogens in plasma and platelet components. The photophysical behavior of AMO in the absence of DNA is remarkably similar to that of the recently studied psoralen 4′-aminomethyl-4,5′,8-trimethylpsoralen (AMT). By means of steady-state and time-resolved spectroscopy, intercalation and photochemistry of AMO and synthetic DNA were studied. AMO intercalates with a higher affinity into A,T-only DNA (KD = 8.9 × 10−5 M) than into G,C-only DNA (KD = 6.9 × 10−4 M). AMO covalently photobinds to A,T-only DNA with a reaction quantum yield of ΦR = 0.11. Like AMT, it does not photoreact following intercalation into G,C-only DNA. Femto- and nanosecond transient absorption spectroscopy reveals the characteristic pattern of photobinding to A,T-only DNA. For AMO and G,C-only DNA, signatures of a photoinduced electron transfer are recorded. [ABSTRACT FROM AUTHOR]

Summary: Excited molecules Converting light into charge carriers and transporting them to electrical contacts are the main tasks of organic semiconductors in information technology and photovoltaic components. However, little is known about the mutual influence of both processes. Time‐resolved photoelectron spectroscopy with ultrashort pulses in the extreme UV range provides insights into the coupling of optical and transport properties in organic semiconductors. [ABSTRACT FROM AUTHOR]

Exit from mitosis is brought about by dramatic changes in the phosphoproteome landscape. A drop in Cyclin-dependent kinase (Cdk) activity, the master regulatory kinase, and activation of counteracting phosphatases such as Cdc14 in budding yeast, results in ordered substrate dephosphorylation, allowing entry into a new cell cycle and replication licensing. In meiosis however, two cell divisions have to be executed without intermediate DNA replication, implying that global phosphorylation and dephosphorylation have to be adapted to the challenges of meiosis. Using a global time-resolved phosphoproteomics approach in budding yeast, we compared the phosphoproteome landscape between mitotic exit and the transition from meiosis I to meiosis II. We found that unlike exit from mitosis, Cdk phosphomotifs remain mostly stably phosphorylated at the end of meiosis I, whereas a majority of Cdk-unrelated motifs are reset by dephosphorylation. However, inducing an artificial drop of Cdk at metaphase of meiosis I leads to ordered substrate dephosphorylation, comparable to mitosis, indicating that phosphoregulation of substrates at the end of meiosis I is thus mainly qualitatively rather than quantitatively ordered. Synopsis: The two consecutive meiotic nuclear divisions without intervening replication necessitate adaptations to the phosphoproteome regulation occurring at mitotic exit. Here, time-resolved mass spectrometry analyses of the meiosis I-to-meiosis II transition in budding yeast reveal how variations in CDK activity define the meiotic phosphoproteome landscape. Global phosphoproteome analysis describes the meiosis I-to-meiosis II transition in high temporal resolution. Dephosphorylation resets CDK-dependent phosphorylation events at mitotic exit, but not after meiosis I. A mitotic-like dephosphorylation pattern can be implemented in meiosis by inhibiting Cdk activity. Phosphoregulation of substrates at the end of meiosis I is ordered qualitatively, rather than quantitatively. Time-resolved mass spectrometry analyses show how variations in CDK activity define the phosphoproteome at the exit from meiosis I as compared to exit from mitosis. [ABSTRACT FROM AUTHOR]

We conducted an analysis of 45 bursts observed from 4U 1636−53. To investigate the mechanism behind the light-curve profiles and the impact of thermonuclear X-ray bursts on the accretion environment in accreting neutron star low-mass X-ray binaries. This analysis employed both light-curve and time-resolved spectroscopy methodologies, with data collected by the Insight - Hard X-ray Modulation Telescope instrument. We found that 30 bursts exhibited similar light-curve profiles and were predominantly in the hard state, and two photospheric radius expansion (PRE) bursts were in the soft state. The light curves of most bursts did not follow a single exponential decay but displayed a dual-exponential behaviour. The initial exponent had a duration of approximately 6 s. We utilized both the standard method and the ' f a' method to fit the burst spectra. The majority of the ' f a' values exceeded 1, indicating an enhancement of the persistent emission during the burst. Under the two Comptonization components assumption, we suggest that the scattering of burst photons by the inner corona may mainly contribute to the persistent emission enhancement. We also observed an inverse correlation between the maximum f a and the persistent emission flux in the non-PRE burst. This anticorrelation suggests that when the accretion rate is lower, there is a greater enhancement of persistent emission during the burst peak. The prediction based on Poynting–Robertson drag (P–R drag) aligns with this observed anticorrelation. [ABSTRACT FROM AUTHOR]

Aim: To investigate cerebral blood volume (CBV) in preterm neonates using time‐resolved near‐infrared spectroscopy. Methods: In this prospective observational study, time‐resolved near‐infrared spectroscopy measurements of CBV using tNIRS‐1 were performed in 70 preterm neonates. For measurements, a sensor was placed for a duration of 1 min, followed by four further reapplications of the sensor, overall five measurements. Results: In this study, 70 preterm neonates with a mean ± SD gestational age of 33.4 ± 1.7 weeks and a birthweight of 1931 ± 398 g were included with a postnatal age of 4.7 ± 2.0 days. Altogether, 2383 CBV values were obtained with an overall mean of 1.85 ± 0.30 mL/100 g brain. A total of 95% of the measured CBV values varied in a range from −0.31 to 0.33 from the overall individual mean. Taking the deviation of the mean of each single application for each patient, this range reduced from −0.07 to 0.07. The precision of the measurement defined as within‐variation in CBV was 0.24 mL/100 g brain. Conclusion: The overall mean CBV in stable preterm neonates was 1.85 ± 0.30 mL/100 g brain. The within‐variation in CBV was 0.24 mL/100 g brain. Based on the precision obtained by our data, CBV of 1.85 ± 0.30 mL/100 g brain may be assumed as normal value for this cohort. [ABSTRACT FROM AUTHOR]

The selective separation of ions from aqueous systems, and even in the human body, is a crucial to overall environmental management and health. Nanoporous materials are widely known for their selective removal of cations from aqueous media, and therefore have been targeted for use as a pharmaceutical to treat hyperkalemia. This study investigated the detailed crystallographic molecular mechanisms that control the potassium ion selectivity in the nanoporous cubic zirconium silicate (CZS) related materials. Using time-resolved in situ Raman spectroscopy and time-resolved in situ X-ray diffraction, the selectivity mechanisms were determined to involve a synchronous cation-cation repulsion process that serves to open a favorable coordination bonding environment for potassium, not unlike the ion selectivity filter process found in potassium ion channels in proteins. Enhancement of ion exchange was observed when the CZS material was in a partial protonated state (≈3:1 Na:H), causing an expansion of the unit-cell volume, enlargement of the 7 member-ring window, and distortion of framework polyhedra, which allowed increased accessibility to the cage structures and resulted in rapid irreversible potassium ion exchange. [ABSTRACT FROM AUTHOR]

Comprehensive Summary The problem of molecular diffusion in the soup of chemical reactions attracts mounting interest across fields ranging from chemistry to biophysics to material science. Chemical reactions involve bond breakup and formation, whose time scale is typically on the orders of fs to ps, while molecular diffusion occurs at time scales of μs to ms. The two processes are often considered orthogonal, given the vastly different scales. The serial results show that the enzyme's diffusion is enhanced in a substrate‐dependent manner, which was further extended to small molecule reaction systems, challenging this classical paradigm. However, the results from different groups using different techniques do not quantitatively agree, and a general mechanism is yet to be understood. We summarize experimental studies on diffusion problems and seek to reconcile the interpretation with understanding the limits of measurement tools and the chemical nature of reaction systems. Understanding molecular diffusion in chemical reactions will provide fresh thoughts in designing chemical systems such as molecular machines that harvest work at the nanoscale in a controllable manner. [ABSTRACT FROM AUTHOR]

Understanding electron and ion dynamics is an important task for improving modern energy materials, such as photovoltaic perovskites. These materials usually have delicate nano‐ and microstructures that influence the device parameters. To resolve detailed structure–function relationships on the relevant micro‐ and nanometer length scales, the current macroscopic and microscopic measurement techniques are often not sufficient. Here, nanoscale surface photovoltage spectroscopy (nano‐SPV) and nanoscale ideality factor mapping (nano‐IFM) via time‐resolved Kelvin probe force microscopy are introduced. These methods can map nanoscale variations in charge carrier recombination, ion migration, and defects. To show the potential of nano‐SPV and nano‐IFM, these methods are applied to perovskite samples with different morphologies. The results clearly show an improved uniformity of the SPV and SPV decay distribution within the perovskite films upon passivation and increasing the grain size. Nevertheless, nano‐SPV and nano‐IFM can still detect local variations in the defect density on these optimized samples, guiding the way for further optimization. [ABSTRACT FROM AUTHOR]

Halide perovskite colloidal nanocrystals (NCs) have enabled considerable progress in light conversion applications. However, the presence of unavoidable defect states and phase transition effects can accelerate undesirable rapid charge recombination of the photogenerated charge carriers. To address this issue, chromophores with an anchoring moiety are often used to modify the surface of the NCs, promoting prolonged charge separation through electron or energy transfer processes for optoelectronic applications. Here, steady‐state and time‐resolved spectroscopy methods are combined with density functional theory (DFT) calculations to explore and decipher the excited‐state interaction in colloidal CsPbX3 (X = Br, I) NCs with a rhodamine 6G (Rh6G) hybrid assembly. The results show that Rh6G dimerizes even at low concentrations, as evidenced by DFT calculations. The binding of Rh6G on the NC surface is confirmed by FTIR and NMR spectroscopy techniques. In addition, transient absorption spectroscopy reveals directional sub‐ps electron transfer from Rh6G to CsPbI3 NCs, whereas energy transfer occurs from CsPbBr3 to Rh6G, which ultimately recombines in the µs time regime. The findings highlight the simplest and most practical approaches for studying and tailoring the excited‐state interaction in colloidal perovskite NCs and chromophore assembly. [ABSTRACT FROM AUTHOR]

Since its discovery in 1992, GRS 1915 + 105 has been among the brightest sources in the X-ray sky. However, in early 2018, it dimmed significantly and has stayed in this faint state ever since. We report on AstroSat and NuSTAR observation of GRS 1915 + 105 in its unusual low/hard state during 2019 May. We performed time-resolved spectroscopy of the X-ray flares observed in this state and found that the spectra can be fitted well using highly ionized absorption models. We further show that the spectra can also be fitted using a highly relativistic reflection dominated model, where for the lamp post geometry, the X-ray emitting source is always very close to the central black hole. For both interpretations, the flare can be attributed to a change in the intrinsic flux, rather than dramatic variation in the absorption or geometry. These reflection dominated spectra are very similar to the reflection dominated spectra reported for active galactic nuclei in their low flux states. [ABSTRACT FROM AUTHOR]

Designing efficient antimicrobials for the rapid disinfection of water is increasingly critical owing to the rising threat of pathogenic microorganisms. In this study, direct Z-scheme Bi 2 WO 6 /TiO 2 heterojunctions were constructed using a simple in situ hydrothermal method. The optimal Bi 2 WO 6 /TiO 2 Z-scheme heterojunction inhibited 98.80 % of Escherichia coli (5 × 108 CFU mL−1) at 0.35 mg mL−1 and 99.33 % of Staphylococcus aureus (5 × 108 CFU mL−1) at 0.5 mg mL−1 after 10 min of light-emitting diode (LED) light irradiation. Furthermore, in antibiotic degradation experiments, Bi 2 WO 6 /TiO 2 had a 92.91 % removal rate for ciprofloxacin with a pseudo-second-order degradation rate constant (k) of 0.056 min−1 after 240 min of irradiation. The antibacterial mechanism of Bi 2 WO 6 /TiO 2 was systematically investigated and confirmed to occur by LED light-driven surface activation and efficient charge transfer. The surface and interfacial structures of the Bi 2 WO 6 /TiO 2 samples were studied by high-resolution transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The antibacterial mechanism was studied by controlled experiments and electron spin resonance analyses, which revealed that the primary antibacterial mechanism of Bi 2 WO 6 /TiO 2 is oxidative sterilisation via generated reactive oxygen species. Time-resolved fluorescence spectroscopy was used to analyse the charge-transfer pathway in Bi 2 WO 6 /TiO 2 , which demonstrated that the spatial separation of the redox-active sites extended the lifetimes of the photogenerated carriers, enhancing the oxidative destruction of bacteria. This comprehensive understanding paves the way for the design of new Z-type heterojunction photocatalytic materials for antimicrobial applications. [ABSTRACT FROM AUTHOR]

In this study, we, for the first time, compiled all publicly available annually or biannually resolved 14 C records, which fully covers 7 grand solar minima at an annual and bi-annual resolution. Our results from 7 grand solar minima showed a clear relationship between the rate of increase (decrease) in solar activity levels and how long the onset (termination) of the grand solar minima will last. Additionally, we show a weaker relationship between the durations of onsets and terminations and between the rate of increase and decrease of solar activity levels. Our results also suggest there might be two or more types of grand solar minima. [ABSTRACT FROM AUTHOR]

A supramolecular photovoltaic strategy is applied to enhance power conversion efficiencies (PCE) of photoelectrochemical devices by suppressing electron–hole recombination after photoinduced electron transfer (PET). Here, the author exploit supramolecular localization of the redox mediator—in close proximity to the dye—through a rotaxane topology, reducing electron–hole recombination in p‐type dye‐sensitized solar cells (p‐DSSCs). Dye PRotaxane features 1,5‐dioxynaphthalene recognition sites (DNP‐arms) with a mechanically‐interlocked macrocyclic redox mediator naphthalene diimide macrocycle (3‐NDI‐ring), stoppering synthetically via click chemistry. The control molecule PStopper has stoppered DNP‐arms, preventing rotaxane formation with the 3‐NDI‐ring. Transient absorption and time‐resolved fluorescence spectroscopy studies show ultrafast (211 ± 7 fs and 2.92 ± 0.05 ps) PET from the dye‐moiety of PRotaxane to its mechanically interlocked 3‐NDI‐ring‐acceptor, slowing down the electron–hole recombination on NiO surfaces compared to the analogue. p‐DSSCs employing PRotaxane (PCE = 0.07%) demonstrate a 30% PCE increase compared to PStopper (PCE = 0.05%) devices, combining enhancements in both open‐circuit voltages (VOC = 0.43 vs 0.36 V) and short‐circuit photocurrent density (JSC = −0.39 vs −0.34 mA cm−2). Electrochemical impedance spectroscopy shows that PRotaxane devices exhibit hole lifetimes (τh) approaching 1 s, a 16‐fold improvement compared to traditional I−/I3−‐based systems (τh = 50 ms), demonstrating the benefits obtained upon nanoengineering of interfacial dye‐regeneration at the photocathode. [ABSTRACT FROM AUTHOR]

Given the high toxicity and easy availability of fluoride ions in surface as well as ground water, an on–off–on fluorescence process-based fluoride ion sensor is developed by using highly fluorescent carbon quantum dots (CQDs) derived from coal washery rejects/waste coal (CWRs). The chemical properties of the fabricated CQDs are evaluated by using high resolution-transmission electron microscopy (HR-TEM), Fourier transform-infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) studies. The as-synthesized CQDs/Fe3+ was validated to be an excellent nanoprobe in aqueous conditions based on fluorescence quenching with high sensitivity towards F− ions. The "turn off" fluorescence mechanism of the developed sensor (i.e., CQDs/Fe3+) was investigated by using fluorescence quenching, TRPL (time resolved photoluminescence spectroscopy), XPS, and HR-TEM analysis. The developed CQDs/Fe3+ sensor was found to have promising applications in estimating trace F− ions in real water samples with the working range of 0–20 ppm with a detection limit of as low as 0.3 ppm. The nanoprobe also shows high sensitivity of F− ion detection in the presence of various anions, and was found to be non-toxic, environmentally benign, cheap, rapid, efficient, and most significantly selective. Furthermore, the nanoprobe was satisfactorily employed as a simple and alternative typical laboratory-based fluoride monitoring technique by using a smartphone based on image processing and machine learning approaches. In addition to that, CQDs used in the nanoprobe are considered to be bio-compatible and eco-friendly provided its safety against normal cells with an average cell viability of more than 80% (500 μg ml−1) and as such no apparent DNA fragmentation in the treated cells was observed at a concentration of 500 μg ml−1. CQDs will not only serve a significant role in fluoride diagnostic tools, but they are also safer and less hazardous than other conventional nanomaterials. [ABSTRACT FROM AUTHOR]

Spectroelectrochemical methods are employed to systematically investigate the impacts of external charge filling in three pure wurtzite CdSe/CdS core/shell nanocrystals (NCs) with different shell thicknesses. We observed that electrons can penetrate the thick CdS shell and inject into the conduction band with an abnormal brightening, while holes are blocked. The formed negative trions result in a different spectral shift according to the size of the NCs, with a redshift of 3.7 nm for 12.5 nm NCs and almost no movement for 23.4 nm NCs. Meanwhile, due to the formation of biexcitons, a variational spectral blueshift with the NCs' size can be determined in time-resolved photoluminescence spectroscopy. This indicates that the binding energy of both biexcitons and negatively charged excitons can be regulated by controlling the shell thickness. Extra charges can also be used to activate/passivate trap states, thereby confirming that the 12.5 nm sample has better surface/interface quality. [ABSTRACT FROM AUTHOR]

We present the development of a versatile apparatus for 6.2 eV laser-based time and angle-resolved photoemission spectroscopy with micrometer spatial resolution (time-resolved μ-ARPES). With a combination of tunable spatial resolution down to ∼11 μm, high energy resolution (∼11 meV), near-transform-limited temporal resolution (∼280 fs), and tunable 1.55 eV pump fluence up to 3 mJ/cm2, this time-resolved μ-ARPES system enables the measurement of ultrafast electron dynamics in exfoliated and inhomogeneous materials. We demonstrate the performance of our system by correlating the spectral broadening of the topological surface state of Bi2Se3 with the spatial dimension of the probe pulse, as well as resolving the spatial inhomogeneity contribution to the observed spectral broadening. Finally, after in situ exfoliation, we performed time-resolved μ-ARPES on a ∼30 μm flake of transition metal dichalcogenide WTe2, thus demonstrating the ability to access ultrafast electron dynamics with momentum resolution on micro-exfoliated materials. [ABSTRACT FROM AUTHOR]

Parametric superfluorescence (PSF), which originated from the optical amplification of vacuum quantum noise, is the primary noise source of femtosecond fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS). It severely affects the detection limit of FNOPAS to collect the femtosecond time-resolved spectra of extremely weak fluorescence. Here, we report the development of femtosecond fluorescence conical optical parametric amplification spectroscopy (FCOPAS), aimed at effectively suppressing the noise fluctuation from the PSF background. In contrast to traditional FNOPAS configurations utilizing lateral fluorescence collection and dot-like parametric amplification, FCOPAS employs an innovative conical fluorescence collection and ring-like amplification setup. This design enables effective cancellation of noise fluctuation across the entire PSF ring, resulting in an approximate order of magnitude reduction in PSF noise compared to prior FNOPAS outcomes. This advancement enables the resolution of transient fluorescence spectra of 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecules in ethanol, even at an optically dilute concentration of 10−6 mol/l, with significantly enhanced signal-to-noise ratios. This improvement will be significant for extremely weak fluorescence detection on the femtosecond time scale. [ABSTRACT FROM AUTHOR]

A noncollinear optical parametric amplifier (NOPA) can produce few-cycle femtosecond laser pulses that are ideally suited for time-resolved optical spectroscopy measurements. However, the nonlinear-optical process giving rise to ultrabroadband pulses is susceptible to spatiotemporal dispersion problems. Here, we detail refinements, including chirped-pulse amplification (CPA) and pulse-front matching (PFM), that minimize spatiotemporal dispersion and thereby improve the properties of ultrabroadband pulses produced by a NOPA. The description includes a rationale behind the choices of optical and optomechanical components, as well as assessment protocols. We demonstrate these techniques using a 1 kHz, second-harmonic Ti:sapphire pump configuration, which produces ∼5-fs duration pulses that span from about 500 to 800 nm with a bandwidth of about 200 THz. To demonstrate the utility of the CPA-PFM-NOPA, we measure vibrational quantum beats in the transient–absorption spectrum of methylene blue, a dye molecule that serves as a reference standard. [ABSTRACT FROM AUTHOR]

The photoinduced relaxation dynamics of nucleobases and their thionated analogs have been investigated extensively over the past decades motivated by their crucial role in organisms and their application in medical and biochemical research and treatment. Most of these studies focused on the spectroscopy of valence electrons and fragmentation. The advent of ultrashort x‐ray laser sources such as free‐electron lasers, however, opens new opportunities for studying the ultrafast molecular relaxation dynamics utilizing the site‐ and element‐selectivity of x‐rays. In this review, we want to summarize ultrafast experiments on thymine and 2‐thiouracil performed at free‐electron lasers. We performed time‐resolved x‐ray absorption spectroscopy at the oxygen K‐edge after UV excitation of thymine. In addition, we investigated the excited state dynamics of 2‐tUra via x‐ray photoelectron spectroscopy at sulfur. For these methods, we show a strong sensitivity to the electronic state or charge distribution, respectively. We also performed time‐resolved Auger–Meitner spectroscopy, which shows spectral shifts associated with internuclear distances close to the probed site. We discuss the complementary aspects of time‐resolved x‐ray spectroscopy techniques compared to optical and UV spectroscopy for the investigation of ultrafast relaxation processes. [ABSTRACT FROM AUTHOR]

Isocytosine, having important applications in antivirus and drug development, is among the building blocks of Hachimoji nucleic acids. In this report, we present an investigation of the excited state dynamics of isocytosine in both protic and aprotic solvents, which was conducted by a combination of methods including steady‐state spectroscopy, femtosecond broadband time‐resolved fluorescence, and transient absorption. These methods were coupled with density functional and time‐dependent density functional theory calculations. The results of our study provide the first direct evidence for a highly efficient nonradiative mechanism achieved through internal conversion from the ππ* state of the isocytosine keto‐N(3)H form occurring within subpicoseconds and picoseconds following photo‐excitation. Our study also unveils a crucial role of solvent, particularly solute–solvent hydrogen bonding, in determining the tautomeric composition and regulating the pathways and dynamics of the deactivation processes. The deactivation processes of isocytosine in the solvents examined are found to be distinct from those of cytosine and the case known for isocytosine in the gas phase mainly due to different tautomeric forms involved. Overall, our findings demonstrate the high photo‐stability of isocytosine in the solution and showcase the remarkable effect of covalent modification in altering the spectral character and excited state dynamics of nucleobases. [ABSTRACT FROM AUTHOR]

Guanine quadruplexes (GQs) are four‐stranded DNA/RNA structures exhibiting an important polymorphism. During the past two decades, their study by time‐resolved spectroscopy, from femtoseconds to milliseconds, associated to computational methods, shed light on the primary processes occurring when they absorb UV radiation. Quite recently, their utilization in label‐free and dye‐free biosensors was explored by a few groups. In view of such developments, this review discusses the outcomes of the fundamental studies that could contribute to the design of future optoelectronic biosensors using fluorescence or charge carriers stemming directly from GQs, without mediation of other molecules, as it is the currently the case. It explains how the excited state relaxation influences both the fluorescence intensity and the efficiency of low‐energy photoionization, occurring via a complex mechanism. The corresponding quantum yields, determined with excitation at 266/267 nm, fall in the range of (3.0–9.5) × 10−4 and (3.2–9.2) × 10−3, respectively. These values, significantly higher than the corresponding values found for duplexes, depend strongly on certain structural factors (molecularity, metal cations, peripheral bases, number of tetrads ...) which intervene in the relaxation process. Accordingly, these features can be tuned to optimize the desired signal. [ABSTRACT FROM AUTHOR]

Merocyanines (MC) usually adopt ring opened zwitterionic structures that are interconvertible with their ring‐closed spiropyran photoisomers. By methylating the phenolate oxygen, and thereby blocking the ring‐closure reaction, a cis/trans‐only MC photoswitch was obtained, yielding a perfect candidate for a detailed examination of the cis/trans isomerization mechanism for this class of compounds. This photoswitch displays outstanding properties including excellent photoreaction quantum yields and photoswitching turnovers. Due to the central polymethine bridge of MC, in principle eight cis (C)/trans/(T) isomers are possible. Density Functional Theory (DFT) calculations revealed the CCT and TTT‐isomers of the studied compound as most stable cis and trans ground state isomers, respectively. UV/vis transient absorption studies combined with conical intersection computations with the complete active space self‐consistent field (CASSCF) method show that both trans/cis‐ and cis/trans‐photoisomerizations are initiated by a rotation of the central doubled bond fragment. A hot ground state species is then formed, which undergoes a second isomerization. Thus, the cis/trans reaction proceeds via a CCT‐CTT‐TTT sequence and the reverse reaction via TTT‐TCT‐CCT. [ABSTRACT FROM AUTHOR]

Two different hybrid nanosystems are prepared by loading highly crystalline, monodisperse magnetite nanocubes (MNCs) with phosphorescent Pt(II) complexes (PtCxs). One involves the encapsulation of the hydrophobic PtCx1 within an amphiphilic comb polymer (MNC@poly(maleic anhydride‐alt‐1‐octadecene) [PMAO]–PtCx1), whereas the other involves the direct binding of the hydrophilic PtCx2 to the surface of the MNC mediated by a ligand‐exchange procedure (MNC@OH–PtCx2). Both systems are evaluated as potential candidates for multimodal imaging in magnetic resonance imaging (MRI) and photoluminescence lifetime imaging micro(spectro)scopy (PLIM). PLIM measurements on agarose phantoms demonstrate significantly longer excited‐state lifetimes compared to the short‐lived autofluorescence of biological background. Additionally, both nanosystems perform as effective MRI contrast agents (CAs): the r2* values are 3–4 times higher than for the commercial CA ferucarbotran. MNC@PMAO–PtCx1 particles also cause significant increases in r2. While the ligand exchange procedure efficiently anchors PtCxs to the MNC surface, the polymeric encapsulation ensures higher colloidal stability, contributing to differences in PLIM and MRI outcomes. In these results, the successful integration of two complementary noninvasive imaging modalities within a single nanosystem is confirmed, serving as the impetus for further investigation of such systems as advanced multimodal–multiscale imaging agents with dual orthogonal readouts. [ABSTRACT FROM AUTHOR]

Latent fingerprints were successfully visualized using fluorescence lifetime imaging (FLIM) on paper which emits strong fluorescence with a lifetime close to that of fingerprints and thus from which it is difficult for time‐resolved spectroscopy to visualize fingerprints. Latent fingerprint samples on paper were excited using a 450 nm or 532 nm nanosecond pulsed‐laser, and time‐resolved fluorescence images were obtained at a delay time of 6–16 ns in intervals of 1 ns, to the excitation pulse. The excitation beam was expanded using a lens, and the fluorescence from the fingerprints was captured using an intensified CCD camera. Because of the large fluorescence intensity of the background paper of approximately two to four orders of magnitude larger than that of the fingerprint, the fingerprint was not visualized on each fluorescence image by time‐resolved spectroscopy. However, the fingerprint was visualized in a FLIM image constructed using a series of the fluorescence images for the case with the fluorescence intensity of the background paper being four orders of magnitude larger than that of the fingerprint. The difference in fluorescence lifetime in the FLIM image of the visualized fingerprint and background paper was in the order of 0.1 ns, which was an order of magnitude smaller than the inherent fluorescence lifetime of a few nanoseconds for the fingerprints and paper. It was demonstrated that, at a background fluorescence intensity with a certain order of magnitude larger than that of fingerprints, FLIM has the potential to visualize latent fingerprints which cannot be visualized by time‐resolved spectroscopy. [ABSTRACT FROM AUTHOR]