- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Ultrafast dynamics in van der Waals heterostructures
摘要： Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two-dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer-to-layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited-state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long-lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.
关键词： spin and valley polarization,charge transfer,valleytronic,transition metal dichalcogenide,Van der Waals heterostructures,excited-state dynamics,spintronic devices,interlayer excitons,optoelectronic
更新于2025-09-23 15:21:01
-
Luminescent Radical-Excimer: Excited-State Dynamics of Luminescent Radical in the Doped Host Crystals
摘要： The excited dynamics of a photostable luminescent organic radical (PyBTM) doped in the host crystal was investigated by using the optically detected magnetic resonance (ODMR) time-resolved emission spectroscopies. In the radical system, the unpaired electron can be used as the probe for the electronic-state and the dynamics. The mixed crystal with high concentration of the radical showed excimer emission, together with the monomer emission. The ODMR signals were observed with opposite signs for monitoring the monomer and the excimer emissions. Based on their temperature and concentration dependencies, the excited-state dynamics on the doped crystal and the mechanism of the excimer formation and the ODMR signal generation are discussed with the help of the quantum mechanical simulation of the excited-state spin dynamics. The initial process of excimer formation has been clarified for the first time from the viewpoint of the spin-dynamics.
关键词： Luminescent Radical,Time-Resolved Spectroscopy,ODMR,Excimer,Excited-State Dynamics
更新于2025-09-23 15:19:57
-
Sub-Femtosecond Stark Control of Molecular Photoexcitation With Near Single-Cycle Pulses
摘要： Electric fields can tailor molecular potential energy surfaces by interaction with the electronic state-dependent molecular dipole moment. Recent developments in optics have enabled the creation of ultra-short few-cycle optical pulses with precise control of the carrier envelope phase (CEP) that determines the offset of the maxima in the field and the pulse envelope. This opens news ways of controlling ultrafast molecular dynamics by exploiting the CEP. In this work, we show that the photoabsorption efficiency of oriented H2CSO (sulfine) can be controlled by tuning the CEP. We further show that this control emanates from a resonance condition related to Stark shifting of the electronic energy levels.
关键词： ultrafast photochemistry,Ab initio multiple spawning (AIMS),few-cycle pulse,Stark effect,excited state dynamics
更新于2025-09-19 17:15:36
-
First-principles study of electron dynamics with explicit treatment of momentum dispersion on Si nanowires along different directions
摘要： In this research, ground-state electronic structure and optical properties along with photoinduced electron dynamics of Si nanowires oriented in various directions are reviewed. These nanowires are significant functional units of future nano-electronic devices. All observables are computed for a distribution of wave vectors at ambient temperature. Optical properties are computed under the approximation of momentum conservation. The total absorption is composed of partial contributions from fixed values of momentum. The on-the-fly non-adiabatic couplings obtained along the ab initio molecular dynamics nuclear trajectories are used as parameters for Redfield density matrix equation of motion. The main outcomes of this study are transition energies, light absorption spectra, electron and hole relaxation rates, and electron transport properties. The results of these calculations would contribute to the understanding of the mechanism of electron transfer process on the Si nanowires for optoelectronic applications.
关键词： nanowires,excited state dynamics,nonadiabatic,Momentum dispersion,silicon
更新于2025-09-19 17:15:36
-
Singly, Doubly, and Triply Linked Corrole Oligomers: Synthesis, Structures, and Linking Position Dependent Properties
摘要： Direct covalent connections of porphyrinoids have been demonstrated as an effective way to expand their π-electronic networks and perturb their optical and electrochemical properties. Covalent connections are also useful for studies on the precise electronic interaction between two porphyrinoid units. However, the chemistry of covalently linked corrole oligomers lags far behind that of the porphyrin counterparts in spite of the importance of corrole as a ring-contracted porphyrinoid. The lower symmetry of corroles naturally leads to many possible corrole dimers, which have been found to display different optical and electrochemical properties depending on the linking position. In this review, we summarize the synthesis, structures, and properties of corrole oligomers such as singly linked oligomers and fused dimers as well as their metal complexes with a particular focus on their linking position dependent electronic properties.
关键词： excited-state dynamics,oxidation,oligomers,corroles,metal complexes
更新于2025-09-19 17:15:36
-
Intramolecular Charge Transfer in 5-Halogen Cytidines Revealed by Femtosecond Time-resolved Spectroscopy
摘要： Ultraviolet radiation induced damage to DNA/RNA can lead to chemical modifications to the nucleosides and understanding the excited states involved is the key to reveal the mechanism of those reactions. 5-Halogen cytidines are metabolized DNA/RNA nucleoside byproducts that exhibit very important biological functions in the process of nucleic acid methylation as well as DNA/RNA damage repairing. However, despite the accumulation of knowledge about their biological functions, effect of halogen substitution on the excited states of canonical nucleoside have not received much attention. In this work, excited-state dynamics of 5-fluorocytidine, 5-chlorocytidine and 5-bromocytidine is investigated. Excitation at 295 nm results a bifurcation event that leads to sub-picosecond decay to ground state and population of intramolecular charge transfer states which have several to tens of picosecond lifetimes. The results elucidate the general excited state relaxation pathways in 5-halogen cytidines and the intrinsic charge transfer state may affect the halogen bonding that stabilizes DNA and protein structures when 5-halogen cytidines are excited.
关键词： Excited-state dynamics,Femtosecond Time-resolved Spectroscopy,DNA/RNA damage,5-Halogen Cytidines,Intramolecular Charge Transfer
更新于2025-09-19 17:13:59
-
Excited state structural dynamics of 4-cyano-4′-hydroxystilbene: deciphering the signatures of proton-coupled electron transfer using ultrafast Raman loss spectroscopy
摘要： The photo-initiated proton-coupled electron transfer (PCET) process plays a crucial role in the context of light harvesting in various biological and chemical systems. Molecular model systems are typically employed to understand the mechanisms underlying the functioning of complex biological systems. Some molecular dyads based on the PCET property have been particularly designed to achieve efficient sunlight-to-fuel production. Organic photoacids are potential sources for such applications since they exhibit an enhancement in their acidity upon photoexcitation, facilitating the mimicking of some of the biological processes. p-Hydroxybenzylideneimidazolinone (p-HBI), an organic photoacid, is a key chromophore in green fluorescent protein, which exhibits green emission due to excited state proton transfer. Herein, we investigate the structural changes and dynamics of 4-cyano-40-hydroxystilbene (CHSB), an analogue of p-HBI, in the presence of an external base, t-butylamine (TBA), using the techniques of ultrafast transient absorption, emission and ultrafast Raman loss spectroscopy.
关键词： excited state dynamics,Raman loss spectroscopy,proton-coupled electron transfer,photoacids,ultrafast spectroscopy
更新于2025-09-12 10:27:22
-
Enhanced quantum yields and efficiency in a quantum dot photocell modeled by a multi-level system
摘要： An ultraviolet energy dissipation mechanism plays a critical role in the photoprotection effect of sunscreens. In this work, we discovered substitution dependent UV energy dissipation mechanisms of model plant sunscreen methyl sinapate (MS). We found that the initially populated V(ππ*) states of MS and p-OMeMS relax to the ground state nonradiatively along an ultrafast trans?cis photoisomerization in tens of picoseconds. However, for p-HMS, an internal conversion from V(ππ*) to a relative dark V′(ππ*) state occurs in less than 1 ps, leading to a branching of the excited-state relaxations. The V(ππ*) state still relaxes nonradiatively as in the case of MS and p-OMeMS. In contrast, the V′(ππ*) state decays to the ground state mainly by emitting photons, exhibiting a lifetime as long as 5 ns. It is the first time to definitely distinguish the dynamics between V(ππ*) and V′(ππ*) states in the study of sinapates and cinnamates. These results indicate the anticipation of the V′(ππ*) state should be avoided when designing sunscreens.
关键词： excited-state dynamics,methyl sinapate,plant sunscreens,ultraviolet energy dissipation,photoisomerization
更新于2025-09-11 14:15:04
-
Strong-field- versus weak-field-ionization pump-probe spectroscopy
摘要： Ionization can serve as a universal probe of excited-state dynamics in molecules, such as internal conversion, dissociation, and isomerization. These processes are of fundamental importance to a wide array of dynamics in biology, chemistry, and physics. In recent years, there has been significant debate about the relative merits of strong-field ionization (SFI), which involves multiphoton absorption, versus weak-field ionization (WFI), where a single photon is absorbed, as probes of these dynamics. SFI is advantageous because it uses wavelengths that are relatively easy to generate, and one can always ionize the molecule with sufficient intensity. However, for SFI it is difficult to calculate observables, such as the time-dependent ion yield, since the calculation of the ionization dynamics including multiphoton processes is computationally expensive and difficult to carry out for many molecular geometries. WFI has the advantage that calculations of observables are tractable. However, the generation and implementation of the appropriate wavelengths (photon energies) can be challenging, and the fixed energy of the probe can lead to technical complications in following the dynamics from excited states back down to the ground state. Here we present a quantitative comparison of the two approaches for following the excited-state dynamics of two molecules, diiodomethane and uracil. The combination of internal conversion and dissociation in these molecules provides an ideal comparison of WFI and SFI as a probe. We compare the measurements with calculations of the dynamics. Our work indicates that while SFI and WFI provide qualitatively similar information about the excited-state dynamics, only WFI results can be compared quantitatively with present-day calculations.
关键词： strong-field ionization,diiodomethane,uracil,weak-field ionization,excited-state dynamics
更新于2025-09-10 09:29:36
-
3.5: Investigation of excited-state dynamics upon both photo- and electro-excitation of thermally activated delayed fluorescent molecules
摘要： Exciton dynamics is one of the core issues lies in the field of achieving high efficiency organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) molecules. The authors briefly review the host dependence of TADF dopant, and then discuess the host–guest interaction in TADF OLEDs. By the means of transient electroluminescence measurement, the dynamics of triplet and singlet excitons are studied. Results show that host material with high T1 energy levels, large spectral overlap with TADF dopant’s absorption and free of exciplex formation exhibits higher TADF character. Furthermore, the underlying reason for the efficiency roll-off of the TADF OLEDs is clarified to be attributed to deeply trapped charges.
关键词： transient,trapped charges,excited-state dynamics,electroluminescence measurement
更新于2025-09-10 09:29:36