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The investigation of a new fast timing system based on DRS4 waveform sampling system
摘要： In the study of nuclear structure, the fast timing technique can be used to measure the lifetime of excited states. In the paper, we have developed a new fast timing system, which is made up of two LaBr3:Ce detectors and a set of waveform sampling system. The sampling system based on domino ring sampler version 4 chip (DRS4) can digitize and store the waveform information of detector signal, with a smaller volume and higher timing accuracy, and the waveform data are performed by means of digital waveform analysis methods. The coincidence time resolution of the fast timing system for two annihilation 511 keV g photon is 200ps (FWHM), the energy resolution is 3.5%@511 keV, and the energy linear response in the large dynamic range is perfect. Meanwhile, to verify the fast timing performance of the system, the t 152Gd-21 decay of 152Eu source is measured. The measured lifetime is 45.3(±5.0)ps, very close to the value of the National Nuclear Data Center (NNDC: 46.2((±3.9)ps). The experimental results indicate that the fast timing system is capable of measuring the lifetime of dozens of ps. Therefore, the system can be widely used in the research of the fast timing technology.
关键词： Waveform sampling system,Excited state lifetime,LaBr3:Ce scintilator,Fast timing technique
更新于2025-09-23 15:22:29
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Exploring the spectral features and quantum chemical computations of a novel biologically active heterocyclic class of compound 2MEFPBA dye: Experimental and theoretical approach
摘要： Here we report, experimental and theoretical determination of ground and excited state dipole moments of the class of heterocyclic compound namely 2-Methoxy-5-fluoro phenyl boronic acid (2MEFPBA) dye. Bathochromic shift with increasing solvent polarity is observed indicating π →π* transition due to intermolecular charge transfer interactions. The ground and excited state dipole moments are found to be parallel to each other. The molecular structure, Frontier molecular orbital (FMO), Natural bond orbital (NBO) analysis and Nonlinear optical (NLO) properties of 2MEFPBA have been investigated using the Density Functional Theory with B3LYP/6?31 ++ g(d, p) basis set. Chemical reactivity and kinetic stability of 2MEFPBA are analyzed using F M O energy. Polarizability and hyperpolarizability computations are used to determine the NLO properties, whereas Natural bond orbital (NBO) analysis showed the proton transfer within the selected donor-acceptor depicting large energy of stabilization for the compound under study.
关键词： MEP,NBO,FMO,Solvatochromic ground and excited state dipole moments,and NLO.
更新于2025-09-23 15:22:29
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Heteroleptic Ir(III)N6 Complexes with Long-Lived Triplet Excited States and In Vitro Photobiological Activities
摘要： A series of cationic heteroleptic iridium(III) complexes bearing tris-diimine ligands [Ir(phen)2(R-phen)]3+ (R-phen = phenanthroline (1), 3,8-diphenylphenanthroline (2), 3,8-dipyrenylphenanthroline (3), 3-phenylphenanthroline (4), 3-pyrenylphenanthroline (5), and 3,8-diphenylethynylphenanthroline (6)) were synthesized and characterized. These complexes possessed phen ligand-localized 1π,π* transitions below 300 nm, and charge transfer (1CT) and/or 1π,π* transitions between 300 and 520 nm. In 1, 2, 4, and 6, the low-energy bands were mixed 1CT/1π,π*. However, the increased π-donating ability of the pyrenyl substituent(s) in 3 and 5 split the low-energy bands into a pyrene-based 1π,π* transition at 300-380 nm and an intraligand charge transfer (1ILCT) transition at 380-520 nm. All complexes were emissive at room temperature in CH3CN, but the parentage of the emitting state varied depending on the R substituent(s). Complex 1 exhibited predominantly phen ligand-localized 3π,π* emission mixed with metal-to-ligand charge transfer (3MLCT) character, while the emission of 2, 4, and 6 was predominantly from the excited-state with 3π,π*/3ILCT/3MLCT character. The emission from 3 and 5 was dominated by pyrene-based 3π,π* states mixed with 3ILCT character. The different natures of the lowest triplet excited states were also reflected by the different spectral features and lifetimes of the triplet transient absorption of these complexes. Complexes 3 and 5 had singlet oxygen quantum yields as high as 81 and 72%, respectively. Both gave submicromolar phototoxicities toward cancer cells (SK-MEL-28 human melanoma) and bacteria (S. aureus and S. mutans) with visible light activation (and marginal to no photobiological activity with red light). Their visible-light phototherapeutic indices (PIs) toward SK-MEL-28 cells were 248 for 3 and >435 for 5; PIs were lower in bacteria (≤62) due to their inherent antimicrobial activities. Both complexes were shown to produce substantial amounts of intracellular reactive oxygen species (ROS), which may account for their photobiological activities.
关键词： photophysics,photodynamic therapy,long-lived triplet excited state,antimicrobial,photobiological activities,reactive oxygen species,heteroleptic Ir(III) trisdiimine complexes
更新于2025-09-23 15:22:29
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Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode
摘要： The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employing high concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N2, 20% and 100% O2 atmospheres. Dimerization of Trp was a major pathway under the N2 atmosphere, though this occurred with a low yield (DφTrp = 5.9 x 10-3), probably as a result of extensive back electron transfer reactions between RF●- and Trp(H)●+. The presence of O2 decreased the extent of this back electron transfer reaction, and the extent of Trp dimerization. This difference is attributed to the formation of O2●- (generated via electron transfer from RF●- to O2) which reacts rapidly with Trp● leading to extensive consumption of the parent amino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols, diols) of Trp, as detected by LC-MS. Thus, it appears that the first step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the amino acid and 3RF, with the presence of O2 modulating the subsequent reactions and the products formed, as a result of O2●- formation. These data have potential biological significance as LED systems and RF-based treatments have been proposed for the treatment of pathological myopia and keratitis.
关键词： type 1/type 2 mechanisms,dimers,LED,N-formylkynurenine,trimers,riboflavin,photo-oxidation,electron transfer,photobleaching,tryptophan,triplet excited state
更新于2025-09-23 15:21:21
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Reducing Anomalous Hysteresis in Perovskite Solar Cells by Suppressing Interfacial Ferroelectric Order
摘要： Despite booming researches in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of the hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI3 (FAPbI3)/TiO2 and MAPbI3/PCBM heterostructures, and explore the correlations between the interfacial ferroelectricity and the hysteresis from the perspective of nonadiabatic electronic dynamics. It is found that ferroelectric order develops at the MAPbI3/TiO2 interface owing to the interaction between the polar MA ions and TiO2. The polarization switching of the MA ions under an applied gate field would result in drastically different rates in interfacial photoelectron injection and electron-hole recombination, contributing to the undesirable hysteresis. In a sharp contrast, ferroelectricity is suppressed at the FAPbI3/TiO2 and MAPbI3/PCBM interfaces, thanks to elimination of the interfacial electric field between perovskite and TiO2 via substitution of strong polar MA (dipole moment: 2.29 Debye) by weak polar FA ions (dipole moment: 0.29 Debye) and interface passivation, leading to consistent interfacial electronic dynamics and the absence of the hysteresis. The present work sheds light to the physical cause for hysteresis and points to the direction to which the hysteresis could be mitigated in PSCs.
关键词： Ferroelectricity,Hysteresis,Perovskite Solar Cells,Excited-state Electronic Dynamics,Electron-Hole Recombination,Orientation Selectivity
更新于2025-09-23 15:21:01
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Excited-state proton transfer in protonated adrenaline revealed by cryogenic UV photodissociation spectroscopy
摘要： We report a comprehensive study of the structures and deactivation processes of protonated adrenaline through cryogenic UV photodissociation spectroscopy. Single UV and double-resonance UV-UV hole burning spectroscopies have been performed and compared to coupled-cluster SCS-CC2 calculations done on the ground and first electronic states. Three conformers were assigned, the two lowest energy gauche conformers along with a higher energy conformer with an extended structure which is indeed the global minimum in solution. This demonstrates the kinetic trapping of this high energy gas phase conformer during the electrospray process. At the band origin of all conformers, the main fragmentation channel is the Cα-Cβ bond cleavage, triggered by an excited state proton transfer to the catechol ring. Internal conversion leading to the water loss channel competes with the direct dissociation and tends to prevail with the increase of excess energy brought by the UV laser. Picosecond time-resolved pump-probe spectroscopy was achieved to measure the excited state lifetimes of the three conformers of AdH+, which decay with the increase of excess in the ππ* state from 2 ns at the band origin down to few hundreds of picosecond 0.5 eV to the blue. Finally, about 0.8 eV above the band origin, the πσ* state is directly reached leading to the opening of the H-loss channel.
关键词： excited-state proton transfer,SCS-CC2 calculations,cryogenic UV photodissociation spectroscopy,protonated adrenaline,conformer assignment
更新于2025-09-23 15:21:01
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Aggregation-Induced Emission-Based Polymer Materials: Ratiometric Fluorescence Responses Controlled by Hydrostatic Pressure
摘要： Dual fluorescence materials that exhibit controllable ratiometric changes in response to various external stimuli have attracted much attention from the viewpoints of applied material science and sensing/imaging technologies in interfaces. In the present study, we found fluorescence polymers based on aggregation-induced emission (AIE) characters. The functional AIE polymers can be converted to ratiometric fluorophores upon electronic excitation, and subsequently, their optical/photophysical properties can also be regulated by hydrostatic pressure or isotropic mechanical force. The degree of substitution (DS) of AIE branches on the polymer backbone plays critical roles in influencing the pressure-induced ratiometric fluorescence responses. The present study provides significant guidelines for developing AIE-based smart applied materials to response in hydrostatic pressure.
关键词： fluorescence spectroscopy,excited-state behavior,polyethylene,hydrostatic pressure,aggregation-induced emission,luminescence materials
更新于2025-09-23 15:21:01
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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
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Cyclometalated Ir(III) Complexes Towards Blue-Emissive Dopant for Organic Light-Emitting Diodes: Fundamentals of Photophysics and Designing Strategies
摘要： The main difficulties hindering development of a deep-blue phosphorescent cyclometalated Ir(III) complex are insufficient colour purity, i.e., failure to achieve ideal Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.09), and insufficient emission efficiency and stability. The latter problem is due to the highly energetic and hot excited states of these complexes, which yield faster decomposition. Therefore, control of the excited-state properties of cyclometalated Ir(III) complexes through systematic chemical modification of the ligands is being extensively investigated, with the aim of developing efficient and stable blue phosphorescent materials. The most common strategies towards achievement of a blue phosphorescent cyclometalated Ir(III) complex involve 1) substitution of electron-withdrawing F atoms at the cyclometalating ligands that stabilise the HOMO orbitals and 2) use of a heteropeltic system with electron-rich ancillary ligands bearing a 5-membered ring heterocycle to increase the LUMO energy level. However, the C–F bonds on the cyclometalating ligands have been found to be inherently unstable during device operation; thus, other types of electron-withdrawing groups (e.g., the cyano, trifluoromethyl, and sulfonyl groups) have been applied. Along with phosphorescence colour tuning to blue, the influence of the ligand structure on the photoluminescence quantum yield (PLQY) is also being intensively investigated. Two major PLQY lowering mechanisms for blue emissive Ir(III) complexes have been identified: 1) the vibronic-coupled non-radiative decay process and 2) crossing from the emissive state to an upper non-emissive 3MC excited state. To enhance the PLQY, mechanism 1) can be suppressed by employing rigid ligand frameworks to restrict intramolecular motion, whereas mechanism 2) can be prevented by destabilising the 3MC state using strong σ donor ligands such as N-heterocyclic carbenes. This review summarises the fundamental photophysics of cyclometalated Ir(III) complexes and surveys design strategies for efficient blue phosphorescent Ir(III) complexes, to provide a guide for future research in this field.
关键词： blue phosphorescent,3MC excited state,photoluminescence quantum yield,non-radiative decay,N-heterocyclic carbenes,cyclometalated Ir(III) complexes,OLEDs
更新于2025-09-23 15:21:01
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Ultrafast Excited-State Dynamics of Hydrogen-Bonded Cytosine Microsolvated Clusters with Protic and Aprotic Polar Solvents
摘要： Microsolvation effects on the ultrafast excited-state deactivation dynamics of cytosine (Cy) were studied in hydrogen-bonded Cy clusters with protic and aprotic solvents using mass-resolved femtosecond pump-probe ionization spectroscopy. Two protic solvents, water (H2O) and methanol (MeOH), and one aprotic solvent, tetrahydrofuran (THF), were investigated, and transients of Cy·(H2O)1-6, Cy·(MeOH)1-3, and Cy·THF microsolvated clusters produced in supersonic expansions were measured. With the aid of electronic structure calculations, we assigned the observed dynamics to the low-energy isomers of various Cy clusters and discussed the microsolvation effect on the excited-state deactivation dynamics. With the protic solvents only the microsolvated clusters of Cy keto tautomer were observed. The observed decay time constants of Cy·(H2O)n are 0.5 ps for n=1 and ~0.2–0.25 ps for n=2–6. For Cy·(MeOH)n clusters, the decay time constant for n=1 cluster is similar to that of the Cy monohydrate, but for n=2 and 3 the decays are about a factor of two slower than the corresponding microhydrates. With the aprotic solvent, THF, hydrogen-bonded complexes of both keto and enol tautomers are present in the beam. The keto-Cy·THF shows a similar decay as the keto-Cy monomer, whereas the enol-Cy·THF exhibits a two-fold slower decay than the enol-Cy monomer, suggesting an increase in the barrier to excited-state deactivation upon binding of one THF molecule to the enol form of Cy.
关键词： Cytosine,Excited-state deactivation,Hydrogen-bonded clusters,Microsolvation,Ultrafast dynamics
更新于2025-09-23 15:21:01