- 标题
- 摘要
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- 实验方案
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Ratiometric Fluorescence Sensing of Cu(II): Elucidation of FRET Mechanism and Bio‐Imaging Application
摘要： Rhodamine-formylaniline conjugate RFA has been developed as a Cu2+-selective ratiometric fluorescent probe. The probe shows high selectivity towards Cu2+ ion through both its absorption and emission properties; and has been characterized by 1H NMR, FTIR, ESI-MS spectroscopy. Sensing of Cu2+ proceed through FRET process which is nicely depicted from steady-state and fluorescence lifetime studies. From the measurement of fluorescence lifetime, the FRET mechanism has been established undoubtedly. The important parameters regarding FRET, namely the energy transfer efficiency (ΦEt) and the F?rster distance (R0) have also been calculated by fluorescence measurement. The origin of different emission bands has been distinguished by recording excitation spectra. The lowest detection limit (DL) for Cu2+ ion was 4.2 × 10?7 M in Tris-HCl buffered MeCN: H2O (10 mM, 1:1 v/v).
关键词： Time-resolved experiment,Confocal Bioimaging,Energy Transfer Efficiency,FRET,Fluorescent probes
更新于2025-09-09 09:28:46
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Time-Stretched Spectroscopy by the Quantum Zeno Effect: The Case of Auger Decay
摘要： A tenet of time-resolved spectroscopy is “faster laser pulses for shorter timescales”. Here, we suggest turning this paradigm around, and slowing down the system dynamics via repeated measurements, to do spectroscopy on longer timescales. This is the principle of the quantum Zeno effect. We exemplify our approach with the Auger process, and find that repeated measurements increase the core-hole lifetime, redistribute the kinetic energy of Auger electrons, and alter entanglement formation. We further provide an explicit experimental protocol for atomic Li, to make our proposal concrete.
关键词： quantum Zeno effect,entanglement formation,time-resolved spectroscopy,atomic Li,Auger decay
更新于2025-09-09 09:28:46
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Characterization of ultrafast plasmon dynamics in individual gold bowtie by time-resolved photoemission electron microscopy
摘要： We report on the investigation of ultrafast dynamics of the plasmonic field in individual gold bowtie nanostructure by combining interferometric time-resolved photoemission electron microscopy with a damped harmonic oscillator model. We experimentally obtain different plasmon dephasing times in the tips of the bowtie nanostructure. In the meantime, we demonstrate that the experimental time-resolved photoemission signal can be used to directly compare resonance frequency and dephasing time of different hot spots. In addition, we find that the plasmon field, which is extracted from the photoemission signal, initially oscillates at the laser field frequency, and finally develops into its eigenfrequency after experiencing a few periods of frequency fluctuation due to the competition between forced and autonomous oscillation of the plasmons.
关键词： ultrafast plasmon dynamics,gold bowtie,resonance frequency,plasmon dephasing times,time-resolved photoemission electron microscopy
更新于2025-09-09 09:28:46
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Probing the upper band gap of atomic rhenium disulfide layers
摘要： Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13 nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57 eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden d–d intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38 eV) with wavelength-variant SHG probes (2.60–2.82 eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05 eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5 eV) using modified DFT calculations.
关键词： density functional theory,ReS2,time-resolved spectroscopy,ultrafast carrier dynamics,second harmonic generation
更新于2025-09-09 09:28:46
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Probing Exciton Delocalization in Organic Semiconductors: Insight from Time-Resolved Electron Paramagnetic Resonance and Magnetophotoselection Experiments
摘要： Delocalization of excited states of organic semiconductors is directly related to their e?ciency in devices. Time-resolved electron paramagnetic resonance spectroscopy provides unique capabilities in this respect because of its high spectral resolution and capability to probe the geometry and extent of excitons. Using magnetophotoselection experiments, the mode of exciton delocalization, along the backbone or parallel to the π?π stacking direction of the conjugated polymers, can be revealed. We demonstrate the robustness of this approach by applying it to building blocks of a prototypical conjugated polymer showing a symmetry of their excited states being far from ideal for this experiment. This renders magnetophotoselection superior to other approaches because it is applicable to a wealth of other organic semiconductors. The insight gained into exciton delocalization is crucial to the structure?function relationship of organic semiconductors and directly relevant for developing highly e?cient materials.
关键词： time-resolved electron paramagnetic resonance,conjugated polymers,exciton delocalization,organic semiconductors,magnetophotoselection
更新于2025-09-09 09:28:46
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Insights into the Efficient Intersystem Crossing of Bodipy-Anthracene Compact Dyads with Steady State and Time-Resolved Optical/Magnetic Spectroscopies and Observation of the Delayed Fluorescence
摘要： Spin-orbit charge transfer induced intersystem crossing (SOCT-ISC) is of particular interest for preparation of heavy atom-free triplet photosensitizers. Up to now examples for SOCT-ISC dyads are limited and electron donor/acceptor SOCT-ISC dyads showing strong visible light-harvesting are rare. Herein we studied the photophysics of a series of Bodipy-anthracene (BDP-An) compact dyads, especially the triplet state electron spin dynamics with the time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The electronic coupling matrix elements (VDA*) between the 1CT (charge transfer) state and 1LE (locally excited) state are in the range 773 cm?1 – 1545 cm?1. For one dyad, we observed three triplet states simultaneously with TREPR, i.e. the triplet states confined on the anthracene (3An) and the Bodipy (3BDP) moieties, as well as a 3CT state. Based on the electron spin polarization (ESP) of these three triplet states and the optical experiments, the SOCT-ISC mechanism is confirmed and the RP-ISC mechanism as the main ISC channel was excluded. Triplet-triplet annihilation (TTA) induced delayed fluorescence was observed for the dyads, which is rare for Bodipy fluorophores.
关键词： intersystem crossing,Bodipy-anthracene dyads,Spin-orbit charge transfer,time-resolved electron paramagnetic resonance,delayed fluorescence,triplet states
更新于2025-09-09 09:28:46
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Discrimination of molecular thin films by surface-sensitive time-resolved optical spectroscopy
摘要： An optical discrimination technique, tailored to nanometric-sized, low optical absorbance molecular complexes adhering to thin metal films, is proposed and demonstrated. It is based on a time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition. The present approach aims to differentiate among molecular films based on statistical methods, without using previous detailed knowledge of the physical mechanisms responsible for the detected signal. The technique is open to integration in lab-on-a-chip architectures and nanoscopy platforms for applications ranging from medical screening to material diagnostics.
关键词： time-resolved optical spectroscopy,principal value decomposition,optical discrimination technique,hierarchical cluster analysis,molecular thin films
更新于2025-09-09 09:28:46
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Photoactivation mechanism, timing of protein secondary structure dynamics and carotenoid translocation in the Orange Carotenoid Protein
摘要： The Orange Carotenoid Protein (OCP) is a two-domain photoactive protein that noncovalently binds an echinenone (ECN) carotenoid and mediates photoprotection in cyanobacteria. In the dark, OCP assumes an orange, inactive state known as OCPO; blue light illumination results in the red active state, known as OCPR. The OCPR state is characterized by large-scale structural changes that involve dissociation and separation of C-terminal and N-terminal domains accompanied by carotenoid translocation into the N-terminal domain. The mechanistic and dynamic-structural relations between photon absorption and formation of the OCPR state have remained largely unknown. Here, we employ a combination of time-resolved UV-visible and (polarized) mid-infrared spectroscopy to assess the electronic and structural dynamics of the carotenoid and the protein secondary structure, from femtoseconds to 0.5 milliseconds. We identify a hereto unidentified carotenoid excited state in OCP, the so-called S* state, which we propose to play a key role in breaking conserved hydrogen-bond interactions between carotenoid and aromatic amino acids in the binding pocket. We arrive at a comprehensive reaction model where the hydrogen-bond rupture with conserved aromatic side chains at the carotenoid β1-ring in picoseconds occurs at a low yield of <1 %, whereby the β1-ring retains a trans configuration with respect to the conjugated π-electron chain. This event initiates structural changes at the N-terminal domain in 1 μs, which allow the carotenoid to translocate into the N-terminal domain in 10 μs. We identified infrared signatures of helical elements that dock on the C-terminal domain β-sheet in the dark and unfold in the light to allow domain separation. These helical elements do not move within the experimental range of 0.5 ms, indicating that domain separation occurs on longer timescales, lagging carotenoid translocation by at least 2 decades of time.
关键词： protein secondary structure dynamics,photoactivation mechanism,Orange Carotenoid Protein,time-resolved spectroscopy,carotenoid translocation
更新于2025-09-09 09:28:46
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Ultrafast electron and spin dynamics of strongly correlated NdNiO <sub/>3</sub>
摘要： Electron and spin dynamics of strongly correlated NdNiO3 are investigated across the metal–insulator transition with ultrafast optical spectroscopy at different temperatures, pump laser fluences, and laser polarizations. Transient differential reflectivity measurements on the insulating phase NdNiO3 show two characteristic electronic decay processes. The slow decay process, strongly dependent on coherent phonon excitation, is attributed to the electron–phonon interaction, while the fast decay process, to the electron-spin interaction. The temporal evolution of Kerr rotation reveals that net spin polarization can be induced by circularly polarized light in insulating NdNiO3 via electron excitation from the Ni t?2g to e?g orbital, and two net spin polarizations with opposite directions are observed given the antiferromagnetic ordering in insulating NdNiO3. At the insulator-to-metal transition, the transient differential reflectivity reverses its sign; the metallic phase NdNiO3 also shows two characteristic electronic decay processes, a typical metallic decay processes and a slow decay process; the slow decay process is attributed to the interaction between electrons and the low frequency coherent phonons (～2.45 THz). Our experiments demonstrate that the phase transition involves several processes upon continuous heating: the electron-spin interaction disappears at 9 K below the transition temperature; at the transition temperature, NdNiO3 transitions into the metallic phase and the antiferromagnetic ordering transitions into the paramagnetic ordering; at the transition temperature, the structure of NdNiO3 changes from a monoclinic structure ( P21/n) to a high temperature orthorhombic ( Pbmn) structure. Such a structure change results in the change in phonon vibrations, and subsequently, leads to the disappearance of the electron–phonon interactions due to the insulating phase NdNiO3 and the emergence of other types of electron–phonon interactions due to the metallic phase.
关键词： time-resolved Kerr rotation measurements,electron and spin dynamics,femtosecond transient reflectivity measurement,polymer-assisted deposition,strongly correlated oxide NdNiO3
更新于2025-09-09 09:28:46
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[IEEE 2018 7th Electronic System-Integration Technology Conference (ESTC) - Dresden, Germany (2018.9.18-2018.9.21)] 2018 7th Electronic System-Integration Technology Conference (ESTC) - Ultrafast miniaturized pulsed electron gun for timeresolved surface measurements
摘要： We report the development of an ultrafast miniaturized pulsed electron gun for the implementation of time-resolved low-energy electron diffraction. This electron gun consists of a nanotip photocathode and an einzel lens for beam collimation. Assembly and electrical contacting of the gun is achieved in a multistep process involving photolithography and focused-ion-beam etching. First applications in a backscattering geometry were demonstrated with a temporal resolution of 1 ps at an electron energy of 80 eV.
关键词： Low energy electron diffraction,charge-density wave,time resolved
更新于2025-09-09 09:28:46