Metastable Excited State Research Articles

Structural Evolution of Photoexcited Methylcobalamin toward a CarH-like Metastable State: Evidence from Time-Resolved X-ray Absorption and X-ray Emission.

CarH is a protein photoreceptor that uses a form of B12, adenosylcobalamin (AdoCbl), to sense light via formation of a metastable excited state. Aside from AdoCbl bound to CarH, methylcobalamin (MeCbl) is the only other example─to date─of photoexcited cobalamins forming metastable excited states with lifetimes of nanoseconds or longer. The UV-visible spectra of the excited states of MeCbl and AdoCbl bound to CarH are similar. We have used transient Co K-edge X-ray absorption and X-ray emission spectroscopies in conjunction with transient absorption spectroscopy in the UV-visible region to characterize the excited states of MeCbl. These data show that the metastable excited state of MeCbl has a slightly expanded corrin ring and increased electron density on the cobalt, but only small changes in the axial bond lengths.

High-accuracy optical clocks with sensitivity to the fine-structure constant variation based on Sm[formula omitted]

We identify two metastable excited states in Sm10+ highly charged ion as candidates for high accuracy optical clocks. Several atomic properties relevant to optical clock development are calculated using relativistic many-body methods. This includes energy levels, transition amplitudes, lifetimes, scalar polarizabilities, black body radiation shift, and the sensitivity to the fine structure constant variation. We found that the clock transitions are not sensitive to perturbation, e.g., relative black body radiation shifts are ∼10−19. The enhancement factor for the α variation is ∼ 0.8 for one clock transition and ∼ 16 for another.

Modeling Photoassociative Spectra of Ultracold NaK + K.

A model for photoassociation of ultracold atoms and molecules is presented and applied to the case of 39K and 23Na39K bosonic particles. The model relies on the assumption that photoassociation is dominated by long-range atom-molecule interactions well outside the chemical bond region. The frequency of the photoassociation laser is chosen close to a bound-bound rovibronic transition from the X1Σ+ ground state toward the metastable b3Π lowest excited state of 23Na39K, allowing us to neglect any other excitation, which could hinder the photoassociation detection. The energy level structure of the long-range 39K···23Na39K excited super-dimer is computed in the space-fixed frame by solving coupled-channel equations, involving the coupling between the 23Na39K internal rotation and the mechanical rotation of the super-dimer complex. A quite rich structure is obtained, and the corresponding photoassociation rates are presented. Other possible photoassociation transitions are discussed in the context of the proposed model.

One/Two-Photon-Excited ESIPT-Attributed Coordination Polymers with Wide Temperature Range and Color-Tunable Long Persistent Luminescence.

The multiple metastable excited states provided by excited-state intramolecular proton transfer (ESIPT) molecules are beneficial to bring temperature-dependent and color-tunable long persistent luminescence (LPL). Meanwhile, ESIPT molecules are intrinsically suitable to be modulated as D-π-A structure to obtain both one/two-photon excitation and LPL emission simultaneously. Herein, we report the rational design of a dynamic CdII coordination polymer (LIFM-106) from ESIPT ligand to achieve the above goals. By comparing LIFM-106 with the counterparts, we established a temperature-regulated competitive relationship between singlet excimer and triplet LPL emission. The optimization of ligand aggregation mode effectively boost the competitiveness of the latter. In result, LIFM-106 shows outstanding one/two-photon excited LPL performance with wide temperature range (100-380 K) and tunable color (green to red). The multichannel radiation process was further elucidated by transient absorption and theoretical calculations, benefiting for the application in anti-counterfeiting systems.

One/Two‐Photon‐Excited ESIPT‐Attributed Coordination Polymers with Wide Temperature Range and Color‐Tunable Long Persistent Luminescence

AbstractThe multiple metastable excited states provided by excited‐state intramolecular proton transfer (ESIPT) molecules are beneficial to bring temperature‐dependent and color‐tunable long persistent luminescence (LPL). Meanwhile, ESIPT molecules are intrinsically suitable to be modulated as D‐π‐A structure to obtain both one/two‐photon excitation and LPL emission simultaneously. Herein, we report the rational design of a dynamic CdII coordination polymer (LIFM‐106) from ESIPT ligand to achieve the above goals. By comparing LIFM‐106 with the counterparts, we established a temperature‐regulated competitive relationship between singlet excimer and triplet LPL emission. The optimization of ligand aggregation mode effectively boost the competitiveness of the latter. In result, LIFM‐106 shows outstanding one/two‐photon excited LPL performance with wide temperature range (100–380 K) and tunable color (green to red). The multichannel radiation process was further elucidated by transient absorption and theoretical calculations, benefiting for the application in anti‐counterfeiting systems.

Many-body correlations in one-dimensional optical lattices with alkaline-earth(-like) atoms

We explore the rich nature of correlations in the ground state of ultracold atoms trapped in state-dependent optical lattices. In particular, we consider interacting fermionic ytterbium or strontium atoms, realizing a two-orbital Hubbard model with two spin components. We analyze the model in one-dimensional setting with the experimentally relevant hierarchy of tunneling and interaction amplitudes by means of exact diagonalization and matrix product states approaches, and study the correlation functions in density, spin, and orbital sectors as functions of variable densities of atoms in the ground and metastable excited states. We show that in certain ranges of densities these atomic systems demonstrate strong density-wave, ferro- and antiferromagnetic, as well as antiferroorbital correlations.

Excited-state intramolecular proton transfer emitter for efficient violet-blue organic light-emitting diodes with hybridized local/charge transfer channel

Excited-state intramolecular proton transfer (ESIPT) materials have attracted much interest, attributed to their metastable excited states which provide suitable platforms for efficient intersystem crossing (ISC) and reverse intersystem crossing (rISC). However, the studies on the utilization of ESIPT to achieve effective hybridized local/charge transfer (HLCT) emitters are rarely reported, due to their ubiquitous issue of low photoluminescence quantum yields (ΦPLs). In this research, a novel ESIPT molecule with HLCT characteristic, 4′-(diphenylamino)-4-(1,4,5- triphenyl-1H-imidazol-2-yl)-[1,1′-biphenyl]-3-ol (HIT-TPA), is designed and synthesized. The hydrogen atom in this molecule can transfer on the way of an intramolecular hydrogen bond from a proton-donating part (–OH/–NH–) to the accepting one (CO/CN–). The HLCT and /or color-tuned fluorescence are observed by the irradiation of specific wavelength, which followed the guidance of ESIPT. It is consistent with the results of transient absorption and time-resolved photoluminescent spectroscopy. By the synergistic interaction of ESIPT and HLCT, the film based on the target molecule presents a high ΦPL value of ∼75.5%. After employing HIT-TPA as the emitter for doped/undoped organic light-emitting diodes (OLEDs), a maximum external quantum efficiency of ∼10.08% is achieved, which proves the efficient triplet harvesting in the ESIPT-based HLCT material. Noticeably, the device exhibits a violet-blue emission with the CIE(x,y) of (0.152, 0.051). It is among the highest reported EQE values on the ESIPT-HLCT materials for violet-blue devices. These results not only open a novel pathway to design effective ESIPT attributed HLCT materials, but also provide a strategy to efficiently utilize ESIPT emitters in achieving high-performance OLEDs.

Singlet Molecular Oxygen: from COIL Lasers to Photodynamic Cancer Therapy.

Translation of experimental techniques from one scientific discipline to another is often difficult but rewarding. Knowledge gained from the new area can lead to long lasting and fruitful collaborations with concomitant development of new ideas and studies. In this Review Article, we describe how early work on the chemically pumped atomic iodine laser (COIL) led to the development of a key diagnostic for a promising cancer treatment known as photodynamic therapy (PDT). The highly metastable excited state of molecular oxygen, a1Δg, also known as singlet oxygen, is the link between these disparate fields. It powers the COIL laser and is the active species that kills cancer cells during PDT. We describe the fundamentals of both COIL and PDT and trace the development path of an ultrasensitive dosimeter for singlet oxygen. The path from COIL lasers to cancer research was relatively long and required medical and engineering expertise from numerous collaborations. As we show below, the knowledge gained in the COIL research, combined with these extensive collaborations, has resulted in our being able to show a strong correlation between cancer cell death and the singlet oxygen measured during PDT treatments of mice. This progress is a key step in the eventual development of a singlet oxygen dosimeter that could be used to guide PDT treatments and improve outcomes.

Overview of Seniority Isomers

Nuclear isomers are the metastable excited states of nuclei. The isomers can be categorized into a few classes including spin, seniority, K, shape and fission isomers depending upon the hindrance mechanisms. In this paper, we aim to present an overview of seniority isomers, which is a category related to the seniority quantum number. The discussion is mainly based on the concepts of seniority and generalized seniority. Various aspects of seniority isomers and their whereabouts have been covered along with the situations where seniority mixing prevents the isomerism.

Visualizing the transiently populated closed-state of human HSP90 ATP binding domain

HSP90 are abundant molecular chaperones, assisting the folding of several hundred client proteins, including substrates involved in tumor growth or neurodegenerative diseases. A complex set of large ATP-driven structural changes occurs during HSP90 functional cycle. However, the existence of such structural rearrangements in apo HSP90 has remained unclear. Here, we identify a metastable excited state in the isolated human HSP90α ATP binding domain. We use solution NMR and mutagenesis to characterize structures of both ground and excited states. We demonstrate that in solution the HSP90α ATP binding domain transiently samples a functionally relevant ATP-lid closed state, distant by more than 30 Å from the ground state. NMR relaxation enables to derive information on the kinetics and thermodynamics of this interconversion, while molecular dynamics simulations establish that the ATP-lid in closed conformation is a metastable exited state. The precise description of the dynamics and structures sampled by human HSP90α ATP binding domain provides information for the future design of new therapeutic ligands.

Atomic clocks highly sensitive to the variation of the fine-structure constant based on Hf ii, Hf iv, and W vi ions

We demonstrate that several metastable excited states in Hf ii, Hf iv, and W vi ions may be good clock states since they are sufficiently long-living and are not sensitive to the perturbations. The cooling electric dipole ($E1$) transition is available for Hf ii, while sympathetic cooling is possible for Hf iv and W vi using ${\mathrm{Ca}}^{+}$ or ${\mathrm{Sr}}^{+}$ ions. Energy levels; Land\'e $g$ factors; transition amplitudes for electric dipole ($E1$), electric quadrupole ($E2$), and magnetic dipole ($M1$) transitions; lifetimes; and electric quadrupole moments for Hf ii, Hf iv, and W vi ions are investigated using a combination of several methods of relativistic many-body calculations including the configuration interaction (CI), linearized coupled-cluster single-doubles (SD), and many-body perturbation theory ($\mathrm{CI}+\mathrm{SD}$), and also the configuration interaction with perturbation theory (CIPT). Scalar polarizabilities of the ground states and the clock states have been calculated to determine the blackbody radiation (BBR) shifts. We have found that the relative BBR shifts for these transitions range between ${10}^{\ensuremath{-}16}$ and ${10}^{\ensuremath{-}18}$. A linear combination of two clock transition frequencies allows one to further suppress BBR. Several $5d\text{\ensuremath{-}}6s$ single-electron clock transitions ensure high sensitivity of the transition frequencies to the variation of the fine-structure constant $\ensuremath{\alpha}$ and may be used to search for dark matter producing this variation of $\ensuremath{\alpha}$. The enhancement coefficient for the $\ensuremath{\alpha}$ variation reaches $K=8.3$. Six stable isotopes of Hf and five stable isotopes in W allow one to make King plots and study its nonlinearities in order to put limits on the new interactions mediated by scalar particles or other mechanisms.

Defects in hafnium-doped lutetium oxide and the corresponding electron traps: a meta-generalized gradient approximation study.

A number of Lu2O3-based materials were reported to present efficient capability of trapping excited charge carriers in metastable excited states formed either by specific dopants or naturally occurring defects. Over the years, abundant experimental data have been collected, which were taken as a solid ground to treat the problem using computational chemistry. Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Individual ions of dopant and nearest-neighbor dopant ion pairs were considered. The effects of interstitial anions such as O2- and Cl- were analyzed. In most of the analyzed cases the additional electron charge is localized at the dopant site. However, in many of the studied cases, the dopant/defect states overlap with the conduction band and cannot correspond to electron trapping. The Hf3+ ion in the Lu site of C3i local symmetry ({\rm Hf}^{\times}_{{\rm Lu}-C_{\rm 3i}}) corresponds to a moderate trap depth of 0.8-0.9 eV. Several composite defects corresponding to deeper (1.1-1.4 eV) traps also exist. Unambiguous deep traps (1.5-1.8 eV) correspond to systems with Hf dopant in the cationic void, accompanied by two interstitial oxygen atoms. The results thus indicate that basic `Hf-substitutes-Lu' doping is unlikely to correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf andLu2O3:Pr,Hf and more complex defects must be involved.

Thermal neutron activation of a CeBr[formula omitted] gamma-ray sensor

We observed significant activation of a CeBr3 gamma-ray sensor following exposure to thermal neutrons with a fluence of 105 cm−2 over a 40-minute-long period. Following irradiation, the intrinsic background rate increased from 30 to 18,100 counts s−1. Pulse height spectra of the activated detector were collected over a 45-minute-long period following neutron irradiation, and the spectra showed evidence for radioactive decay products produced via both β decay and gamma decay of meta-stable excited states (isomeric transitions). The decay energies and half lives revealed the presence of 80Br (t1/2=17 min), 80Br* (t1/2=4.4 h), 82Br (t1/2=6.1 min), and 139Ce (t1/2=55 s). The presence of additional, longer-lived radioisotopes cannot be ruled out by our measurements. All of the observed activation products were formed via neutron capture on primary detector elements, and thus would be expected for any CeBr3 sensor exposed to similar (or higher) thermal neutron flux environments. Given the dramatic increase in intrinsic count rates that we observed following the relatively modest neutron exposure, we propose that CeBr3-based gamma-ray sensors may not be suitable for use in environments with high thermal neutron fluxes without the inclusion of a thermal neutron shield surrounding the sensor.

Measurement of the lifetime of a metastable excited state in Bi−

The lifetime of the $^{3}P_{0}$ state of ${\mathrm{Bi}}^{\ensuremath{-}}$ has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of $16.0\ifmmode\pm\else\textpm\fi{}0.5$ s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.

Analytical Solving a Nonlinear Model of the Glow Discharge

A nonlinear model has been introduced for the positive column of DC glow discharge in apure sealed, or low flow, gas media by including the diffusion, recombination, attachment, detachment,process and having the two-step ionization process of the metastable excited states, too. By thecombination of the system of the nonlinear continuity equations of the system, using some physicalestimations, and degrading the resulted nonlinear PDE in polar and rectangular systems of coordinatethe steady-state nonlinear ODE have been derived. Using a series-based solution, an innovativenonlinear recursion relation has been proposed for calculating the sentence of series. Using the stateof elimination of free charge on the outer boundary of the discharge vessel, the universal equation ofthe characteristic energy of the electrons versus the similarity variable, using the maximum degree ofionization as the parameter, has been derived.

Optical Tweezer Arrays with Ytterbium Atoms for Studying Quantum Phenomena

A neutral Rydberg atom tweezer array is a promising platform for quantum computation. In this study, featuring its metastable excited state, an array of single ytterbium atoms trapped in micro-optical tweezers was constructed. This overcomes many problems in conventional systems using alkali atoms.

Singlet oxygen quenching as a probe for cytochrome c molten globule state formation.

Singlet oxygen refers to the nonradical metastable excited state of molecular oxygen that readily oxidizes various cellular components. Its behavior in different biological systems has been studied for many years. Recently, we analyzed the effect of singlet oxygen quenching by heme cofactor in cytochrome c (cyt c). Here, we have exploited this effect in the investigation of conformational differences in the molten globule states of cyt c induced by different sodium anions, namely sulfate, chloride and perchlorate. The high efficiency of heme toward quenching singlet oxygen enabled us to use this property for the analysis of the otherwise experimentally difficult-to-determine parameter of heme upon exposure to solvents as highly similar conformational states of cyt c in the molten globule states are induced by different salts at acidic pH. Our results from singlet oxygen quenching experiments correlate well with other spectroscopic methods, such as circular dichroism and fluorescence measurements, and suggest increasing availability of heme in the order: perchlorate < chloride < sulfate. Based on our findings we propose that singlet oxygen phosphorescence measurements are useful in determining the differences in the protein conformation of their heme regions, particularly regarding the relative heme exposure to the solvent.

Electronic structure of Rf+ (Z=104) from ab initio calculations

We report calculation of the energy spectrum and the spectroscopic properties of the superheavy element ion: Rf^+. We use the 4-component relativistic Dirac-Coulomb Hamiltonian and the multireference configuration interaction (MRCI) model to tackle the complex electronic structure problem that combines strong relativistic effects and electron correlation. We determine the energies of the ground and the low-lying excited states of Rf+, which originate from the 7s^26d^1, 7s^16d^2, 7s^27p^1, and 7s^16d^17p^1 configurations. The results are discussed vis-\`a-vis the lighter homologue, Hf^+ ion. We also assess the uncertainties of the predicted energy levels. The main purpose of the presented calculations is to provide a reliable prediction of the energy levels and to identify suitable metastable excited states that are good candidates for the planned ion-mobility-assisted laser spectroscopy studies.

Electron collisions with molecular nitrogen in its ground and electronically excited states using the R-matrix method

A comprehensive study of electron collisions with the X 1Σg + ground state as well as the metastable A 3Σu + and a 1Πg excited states of the N2 molecule is reported using the fixed-nucleus R-matrix method. Integral elastic scattering and electronic excitation cross sections from the X 1Σg + ground state to the eight lowest electronic states, A 3Σu +, B 3Πg, W 3Δu, B′ 3Σu −, a 1Πg, a′ 1Σu −, w 1Δu and C 3Πu, overall agree well with the available experimental and theoretical results although updates of some recommended values are suggested. Accurate electron impact electronic transition cross sections starting from the A 3Σu + and a 1Πg metastable excited states are reported. The total summed electronic transition cross sections from the a 1Πg state is dominant: an order of magnitude higher than those of the X 1Σg + ground state. The de-excitation cross sections generally show a downward trend with increasing incident electron energy, which is different from the elastic and electronic excitation cross sections which generally increase with collision energy. There is a prominent 2Πu symmetry resonance peak at 2.8 eV for electronic de-excitation scattering of a 1Πg → B 3Πg, which significantly contributes to the total summed cross sections from the a 1Πg excited state. The present results provide a new insight which will aid understanding of electron spectra in the atmosphere of the Earth and Titan.

Engineering the level structure of a giant artificial atom in waveguide quantum electrodynamics

Engineering light-matter interactions at the quantum level has been central to the pursuit of quantum optics for decades. Traditionally, this has been done by coupling emitters, typically natural atoms and ions, to quantized electromagnetic fields in optical and microwave cavities. In these systems, the emitter is approximated as an idealized dipole, as its physical size is orders of magnitude smaller than the wavelength of light. Recently, artificial atoms made from superconducting circuits have enabled new frontiers in light-matter coupling, including the study of "giant" atoms which cannot be approximated as simple dipoles. Here, we explore a new implementation of a giant artificial atom, formed from a transmon qubit coupled to propagating microwaves at multiple points along an open transmission line. The nature of this coupling allows the qubit radiation field to interfere with itself leading to some striking giant-atom effects. For instance, we observe strong frequency-dependent couplings of the qubit energy levels to the electromagnetic modes of the transmission line. Combined with the ability to in situ tune the qubit energy levels, we show that we can modify the relative coupling rates of multiple qubit transitions by more than an order of magnitude. By doing so, we engineer a metastable excited state, allowing us to operate the giant transmon as an effective lambda system where we clearly demonstrate electromagnetically induced transparency.