Showing papers on "Excited state published in 2003"
TL;DR: Applications involving a range of intrinsic molecules and molecular assemblies that enable direct visualization of tissue morphology, cell metabolism, and disease states such as Alzheimer's disease and cancer are compiled and demonstrated.
Abstract: Multicolor nonlinear microscopy of living tissue using two- and three-photon-excited intrinsic fluorescence combined with second harmonic generation by supermolecular structures produces images with the resolution and detail of standard histology without the use of exogenous stains. Imaging of intrinsic indicators within tissue, such as nicotinamide adenine dinucleotide, retinol, indoleamines, and collagen provides crucial information for physiology and pathology. The efficient application of multiphoton microscopy to intrinsic imaging requires knowledge of the nonlinear optical properties of specific cell and tissue components. Here we compile and demonstrate applications involving a range of intrinsic molecules and molecular assemblies that enable direct visualization of tissue morphology, cell metabolism, and disease states such as Alzheimer's disease and cancer.
1,730 citations
TL;DR: In this paper, the electrostatic attraction between the separated charges in long-range excited charge-transfer states originates from the non-local Hartree-Fock exchange potential and is a nonlocal property.
Abstract: The electrostatic attraction between the separated charges in long-range excited charge-transfer states originates from the non-local Hartree-Fock exchange potential and is, thus, a non-local property. Present-day time-dependent density functional theory employing local exchange-correlation functionals does not capture this effect and therefore fails to describe charge-transfer excited states correctly. A hybrid method that is qualitatively correct is described.
1,455 citations
TL;DR: In this article, the experimental techniques of single-molecule fluorescence spectroscopy and microscopy with emphasis on studies at room temperature where the same single molecule is studied for an extended period.
Abstract: Optical spectroscopy at the ultimate limit of a single molecule has grown over the past dozen years into a powerful technique for exploring the individual nanoscale behavior of molecules in complex local environments. Observing a single molecule removes the usual ensemble average, allowing the exploration of hidden heterogeneity in complex condensed phases as well as direct observation of dynamical state changes arising from photophysics and photochemistry, without synchronization. This article reviews the experimental techniques of single-molecule fluorescence spectroscopy and microscopy with emphasis on studies at room temperature where the same single molecule is studied for an extended period. Key to successful single-molecule detection is the need to optimize signal-to-noise ratio, and the physical parameters affecting both signal and noise are described in detail. Four successful microscopic methods including the wide-field techniques of epifluorescence and total internal reflection, as well as confocal and near-field optical scanning microscopies are described. In order to extract the maximum amount of information from an experiment, a wide array of properties of the emission can be recorded, such as polarization, spectrum, degree of energy transfer, and spatial position. Whatever variable is measured, the time dependence of the parameter can yield information about excited state lifetimes, photochemistry, local environmental fluctuations, enzymatic activity, quantum optics, and many other dynamical effects. Due to the breadth of applications now appearing, single-molecule spectroscopy and microscopy may be viewed as useful new tools for the study of dynamics in complex systems, especially where ensemble averaging or lack of synchronization may obscure the details of the process under study.
863 citations
TL;DR: In this article, the central role of the Ag femtosecond radiative lifetime and the spatial distribution of the excited Ag electrons, in the near field and far field optical properties is discussed.
Abstract: Molecular surface enhanced Raman scattering (SERS) in compact clusters of 30−70 nm Ag nanocrystals has shown single molecule Raman scattering cross sections that are orders of magnitude larger than free space single molecule luminescence cross sections. We analyze certain aspects of this phenomenon with new numerical electromagnetic calculations, and we also present new spectral depolarization data for single molecule rhodamine 6G scattering. We stress the central role of the Ag femtosecond radiative lifetime, and the spatial distribution of the excited Ag electrons, in the near field and far field optical properties. The fundamental nature of the Ag plasmon excited-electronic-state changes from a volume excitation to a surface junction excitation as two particles approach each other within 1 nm. Adsorbed molecules in the junction interact directly with the metallic excited-state wave function, showing electron-transfer-initiated photochemistry as well as enhanced Raman scattering. Depolarization studies ...
816 citations
TL;DR: In this paper, accurate quantum Monte Carlo calculations of ground states and low-lying excited states of light p-shell nuclei are now possible for realistic nuclear Hamiltonians that fit nucleon-nucleon scattering data.
Abstract: ▪ Abstract Accurate quantum Monte Carlo calculations of ground states and low-lying excited states of light p-shell nuclei are now possible for realistic nuclear Hamiltonians that fit nucleon-nucleon scattering data. Results for more than 30 different (Jπ;T) states, plus isobaric analogs, in A ≤ 8 nuclei have been obtained with an excellent reproduction of the experimental energy spectrum. These microscopic calculations show that nuclear structure, including both single-particle and clustering aspects, can be explained starting from elementary two- and three-nucleon interactions. Various density and momentum distributions, electromagnetic form factors, and spectroscopic factors have also been computed, as well as electroweak capture reactions of astrophysical interest.
520 citations
473 citations
TL;DR: The calculated energy changes indicate that there may be significant contributions to inter-pigment energy interactions from molecular displacements and these may be of importance to photosynthetic energy transfer.
462 citations
TL;DR: Initial observations in the application of femtosecond time-resolved absorption techniques to the study of the photophysics of transition metal complexes are described and examples detailing these dynamics as they occur in the charge-transfer excited states of transition-metal polypyridyl chromophores are included.
Abstract: Our research is concerned with the application of femtosecond time-resolved absorption techniques to the study of the photophysics of transition metal complexes. The focus is to understand the events that characterize the process of excited-state evolution from the time a photon is absorbed by a molecule to the formation of the lowest-energy excited state of the system. This Account describes our initial observations in this area and includes examples detailing these dynamics as they occur in the charge-transfer excited states of transition-metal polypyridyl chromophores.
379 citations
TL;DR: In this paper, the derivation and implementation of excited state gradients are reported for the approximate coupled-cluster singles and doubles model CC2 employing the resolution-of-the-identity approximation for electron repulsion integrals.
Abstract: The derivation and implementation of excited state gradients is reported for the approximate coupled-cluster singles and doubles model CC2 employing the resolution-of-the-identity approximation for electron repulsion integrals. The implementation is profiled for a set of examples with up to 1348 basis functions and exhibits no I/O bottlenecks. A test set of sample molecules is used to assess the performance of the CC2 model for adiabatic excitation energies, excited state structure constants and vibrational frequencies. We find very promising results, especially for adiabatic excitation energies, though the need of a single-reference ground state and a single-replacement dominated excited state puts some limits on the applicability of the method. Its reliability, however, can always be tested on grounds of diagnostic measures. As an example application, we present calculations on the π*←π excited state of trans-azobenzene.
369 citations
TL;DR: An experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals confirms unambiguously the theoretically predicted gapless Goldstone mode characteristic of the Bose–Einstein condensation of the triplet states.
Abstract: Bose–Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled1 to form a dimer in a crystalline network: the dimer ground state is a spin singlet (total spin zero), separated by an energy gap from the excited triplet state (total spin one). In these dimer compounds, Bose–Einstein condensation becomes theoretically possible2. At a critical external magnetic field, the energy of one of the Zeeman split triplet components (a type of boson) intersects the ground-state singlet, resulting in long-range magnetic order; this transition represents a quantum critical point at which Bose–Einstein condensation occurs. Here we report an experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals. We verify unambiguously the theoretically predicted3 gapless Goldstone mode characteristic of the Bose–Einstein condensation of the triplet states.
365 citations
TL;DR: In this paper, the mechanism of the photodissociation process in the infrared and how multiphoton techniques or rare gas tagging can be employed to facilitate dissociation processes in strongly bound complexes are discussed.
Abstract: Vibrational spectroscopy measurements are described for mass-selected metal cation-molecular complexes using the technique of infrared resonance-enhanced photodissociation (REPD) spectroscopy. We discuss the mechanism of the REPD process in the infrared and how multiphoton techniques or rare gas tagging can be employed to facilitate dissociation processes in strongly bound complexes. Spectra are reported for Fe+(CO2)n complexes that demonstrate the formation of coordination spheres around the metal cation and for Mg+(CO2)n complexes, where the interaction with theory makes it possible to obtain structures for small clusters. Both of these studies investigate the asymmetric stretch region of CO2. Ni+(C2H2)n complexes are studied in the C-H stretch region, demonstrating evidence for intracluster cyclization reactions. Finally, experiments are described for metal ion-benzene (M = V, Al) complexes excited in the benzene ring distortions and C-H bending region. These experiments confirm the ~ -bonded configura...
TL;DR: The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N=C=N-coordinating ligand cyclometalated at C2 of the benzene ring, have been investigated and the emission is attributed to an excited state of primarily (3)pi-pi character.
Abstract: The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N∧C∧N-coordinating ligand cyclometalated at C2 of the benzene ring ([PtL1Cl]), have been investigated, together with those of two new 5-substituted analogues [PtL2Cl] and [PtL3Cl] {HL2 = methyl-3,5-di(2-pyridyl)benzoate; HL3 = 3,5-di(2-pyridyl)toluene}. All three complexes are intense emitters in degassed solution at 298 K (λmax 480−580 nm; φlum = 0.60, 0.58, and 0.68 in CH2Cl2), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 μs). On the basis of the very small Stokes shift, the highly structured profiles, and the relatively long lifetimes, the emission is attributed to an excited state of primarily 3π−π* character. At concentrations >1 × 10-5 M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL2Cl] is also reported.
TL;DR: In this article, the femtogram-level mass sensitivity was achieved by using gold-coated silicon cantilevers with resonance frequencies in the range of 1 to 10 MHz, characteristic thickness of 50-100 nm, and force constants of about 0.1 N/m.
Abstract: Nanomechanical devices with very small mass and size have the potential for mass sensing at the level of individual molecules. In the present study, we designed nanomechanical mass sensors, demonstrated their operation under ambient pressure and temperature, and achieved femtogram-level mass sensitivity. Our nanomechanical resonators were gold-coated silicon cantilevers with resonance frequencies in the range of 1 to 10 MHz, characteristic thicknesses of 50–100 nm, and force constants of about 0.1 N/m. Using a cantilever with a resonant frequency of 2.2 MHz that was excited photothermally, we measured a mass change of 5.5 fg upon chemisorption of 11-mercaptoundecanoic acid. Our analysis indicates that, by decreasing the mass of the cantilever and increasing the excitation amplitude, even higher mass sensitivity can be realized in an easily accessible frequency range (<100 MHz).
TL;DR: In this paper, the authors used very high signal-to-noise, medium resolution archive optical spectra of I Zw 1 to build a template for the spectrum of a bright narrow-line Seyfert 1 galaxy.
Abstract: Most Seyfert 1s show strong Fe II lines in their spectrum having the velocity and width of the broad emission lines. To remove the Fe II contribution in these objects, an accurate template is necessary. We used very high signal-to-noise, medium resolution archive optical spectra of I Zw 1 to build such a template.
I Zw 1 is a bright narrow-line Seyfert 1 galaxy. As such it is well suited for a detailed analysis of its emission line spectrum. Furthermore it is known to have a very peculiar spectrum with, in addition to the usual broad and narrow line regions, two emission regions emitting broad and blue shifted [O III] lines making it a peculiarly interesting object. While analysing the spectra, we found that the narrow-line region is, unlike the NLR of most Seyfert 1 galaxies, a very low excitation region dominated by both permitted and forbidden Fe II lines. It is very similar to the emission spectrum of a blob in $\eta$ Carinae which is a low temperature (T$_{\rm e}\sim$6 500 K), relatively high density (N$_{\it e}$=10$^{6}$ cm$^{-3}$) cloud. The Fe II lines in this cloud are mainly due to pumping via the stellar continuum radiation field (Verner et al. \cite{verner02}). We did not succeed in modelling the spectrum of the broad-line region, and we suggest that a non radiative heating mechanism increases the temperature in the excited H I region, thus providing the necessary additional excitation of the Fe II lines. For the low-excitation narrow-line region, we are able to settle boundaries to the physical conditions accounting for the forbidden and permitted Fe II lines (10$^{6}$$<$N$_{\rm e}$$<10^{7}$ cm$^{-3}$; 10$^{-6}$$<$U$<10^{-5}$).
TL;DR: The relaxation time, T1, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit) is measured and a lower bound on T1 is found of 50 micros at 7.5 T, only limited by the signal-to-noise ratio.
Abstract: We have measured the relaxation time, ${T}_{1}$, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit). In a magnetic field, applied parallel to the two-dimensional electron gas in which the quantum dot is defined, Zeeman splitting of the orbital states is directly observed by measurements of electron transport through the dot. By applying short voltage pulses, we can populate the excited spin state with one electron and monitor relaxation of the spin. We find a lower bound on ${T}_{1}$ of $50\text{ }\ensuremath{\mu}\mathrm{s}$ at 7.5 T, only limited by our signal-to-noise ratio. A continuous measurement of the charge on the dot has no observable effect on the spin relaxation.
TL;DR: Two near-degenerate pipi* excited states, S2 and S3,4, were identified in a region hitherto associated with only one excited state, which helps to explain contradictory reports about the photoisomerization mechanism and the wavelength dependence of the quantum yield.
Abstract: The excited-state dynamics of trans-azobenzene were investigated by femtosecond time-resolved photoelectron spectroscopy and ab initio molecular dynamics. Two near-degenerate ππ* excited states, S2 and S3,4, were identified in a region hitherto associated with only one excited state. These results help to explain contradictory reports about the photoisomerization mechanism and the wavelength dependence of the quantum yield. A new model for the isomerization mechanism is proposed.
TL;DR: In this article, the luminescence properties of colloidal YVO4:Eu nanoparticles (8 nm in diameter) are investigated and compared to those of the bulk materials.
Abstract: The luminescence properties of colloidal YVO4:Eu nanoparticles (8 nm in diameter) are investigated and compared to those of the bulk materials. The emission quantum yield of nanoparticles is improved after the transfer of the colloidal particles into D2O, showing that surface OH groups act as efficient quenchers of the Eu3+ emission. The growth of a silicate shell around the nanoparticles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate groups. Nanoparticles also exhibit structural distortions directly related to the small size of the particles. No clear evidence is found concerning the influence of these distortions on the energy-transfer processes, since the improvement of the emission properties observed after thermal annealing of both crude and silicated powders seems to result mainly from the elimination of Eu3+ and vanadate quenchers from the surface. This latter effect is greatly e...
TL;DR: In this paper, the authors used TDDFT to estimate the excitation energies of polycyclic aromatic hydrocarbons (PAH) with up to 28 π-electrons.
TL;DR: In this paper, the upconversion properties of nanocrystalline and bulk Y2O3:Er3+ as a function of the erbium concentration (1, 2, 5, 10, 25, and 35 mol %) were investigated.
Abstract: We investigated the upconversion properties of nanocrystalline and bulk Y2O3:Er3+ as a function of the erbium concentration (1, 2, 5, 10, 25, and 35 mol %). Following excitation with 980 nm, upconverted emission is observed from the 2H11/2, 4S3/2, and 4F9/2 excited states to the 4I15/2 ground state centered at 525, 550, and 660 nm, respectively. As the dopant concentration is increased, the upconverted luminescence revealed not only an overall increase in intensity but also an enhancement of the red (4F9/2 → 4I15/2) emission with respect to the green (2H11/2, 4S3/2 → 4I15/2) emission. A cross-relaxation process is involved in populating the 4F9/2 state, which bypasses the green-emitting states. Blue upconversion, observed in bulk Y2O3:Er3+ only, also showed a concentration dependence. The population of the 2P3/2 state was achieved through a three-step phonon-assisted energy-transfer process.
TL;DR: A simple electroluminescent device, based on a semiconducting polymer combined with a phosphorescent complex, that shows fully reversible voltage-dependent switching between green and red light emission.
Abstract: Research on new materials for organic electroluminescence has recently focused strongly on phosphorescent emitters, with the aim of increasing the emission efficiency and stability Here we report the fabrication of a simple electroluminescent device, based on a semiconducting polymer combined with a phosphorescent complex, that shows fully reversible voltage-dependent switching between green and red light emission The active material is made of a polyphenylenevinylene (PPV) derivative molecularly doped with a homogeneously dispersed dinuclear ruthenium complex, which fulfils the dual roles of triplet emitter and electron transfer mediator At forward bias (+4 V), the excited state of the ruthenium compound is populated, and the characteristic red emission of the complex is observed On reversing the bias (-4 V), the lowest excited singlet state of the polymer host is populated, with subsequent emission of green light The mechanism for the formation of the excited state of the PPV derivative involves the ruthenium dinuclear complex in a stepwise electron transfer process that finally leads to efficient charge recombination reaction on the polymer
TL;DR: The results confirm the previously proposed "exciplex" structure of the MLCT state in Lewis basic solvents and indicate that the amount of charge transferred from copper to the dmp ligand upon photoexcitation is similar to the charge difference at the copper center between the ground-state copper(I) and copper(II) complexes.
Abstract: The molecular structure and dynamics of the photoexcited metal-to-ligand-charge-transfer (MLCT) state of [CuI(dmp)2]+, where dmp is 2,9-dimethyl-1,10-phenanthroline, in acetonitrile have been investigated by time-domain pump-probe X-ray absorption spectroscopy, femtosecond optical transient spectroscopy, and density functional theory (DFT). The time resolution for the excited state structural determination was 100 ps, provided by single X-ray pulses from a third generation synchrotron source. The copper ion in the thermally equilibrated MLCT state has the same oxidation state as the corresponding copper(II) complex in the ground state and was found to be penta-coordinate with an average nearest neighbor Cu−N distance 0.04 A shorter than that of the ground state [CuI(dmp)2]+. The results confirm the previously proposed “exciplex” structure of the MLCT state in Lewis basic solvents. The evolution from the photoexcited Franck-Condon MLCT state to the thermally equilibrated MLCT state was followed by femtosec...
TL;DR: Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)(3)(N-N)(btpz)], where N-N = 2,2'-bipyridine and 1,10-phenanathroline, and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods,
Abstract: Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)3(N-N)(btpz)] where N-N = 2,2‘-bipyridine (1) and 1,10-phenanathroline (2), and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods, and single-crystal X-ray diffraction study. Ground and excited state properties of these complexes were investigated by steady-state and time-resolved spectroscopies. Complexes 1 and 2 show photoluminescent emission in both solution and solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition with strong overlapping of intraligand π → π* transitions. The long-lived excited state lifetimes of complexes 1 and 2, which are on the order of microseconds, indicate the presence of phosphorescent emission. As these complexes hold the potential to serve as phosphors for organic light-emitting diodes (OLEDs), their electroluminescent performances were evaluated by employing them as dopant...
TL;DR: In this article, the authors applied the momentum space version of the density-matrix renormalization-group method (k-DMRG) in quantum chemistry in order to study the accuracy of the algorithm in this new context.
Abstract: We have applied the momentum space version of the density-matrix renormalization-group method (k-DMRG) in quantum chemistry in order to study the accuracy of the algorithm in this new context. We have shown numerically that it is possible to determine the desired accuracy of the method in advance of the calculations by dynamically controlling the truncation error and the number of block states using a novel protocol that we dubbed dynamical block state selection protocol. The relationship between the real error and truncation error has been studied as a function of the number of orbitals and the fraction of filled orbitals. We have calculated the ground state of the molecules CH 2 , H 2 O, and F 2 as well as the first excited state of CH 2 . Our largest calculations were carried out with 57 orbitals, the largest number of block states was 1500-2000, and the largest dimensions of the Hilbert space of the superblock configuration was 800 0000-1 200 000.
TL;DR: The advantages of the molecular ionization continuum as the final state in polyatomic wavepacket experiments are discussed and how the electronic structure of the continuum can be used to disentangle electronic from vibrational dynamics are shown.
Abstract: ▪ Abstract Femtosecond time-resolved photoelectron spectroscopy is emerging as a useful technique for investigating excited state dynamics in isolated polyatomic molecules. The sensitivity of photoelectron spectroscopy to both electronic configurations and vibrational dynamics makes it well suited to the study of ultrafast nonadiabatic processes. We review the conceptual interpretation of wavepacket dynamics experiments, emphasizing the role of the final state. We discuss the advantages of the molecular ionization continuum as the final state in polyatomic wavepacket experiments and show how the electronic structure of the continuum can be used to disentangle electronic from vibrational dynamics. We illustrate these methods with examples from diatomic wavepacket dynamics, internal conversion in polyenes and polyaromatic hydrocarbons, excited state intramolecular proton transfer, and azobenzene photoiosomerization dynamics.
TL;DR: Computational evidence at the CASPT2 level supports that the lowest excited state pipi* contributes to the S1/S0 crossing responsible for the ultrafast decay of singlet excited cytosine.
Abstract: Computational evidence at the CASPT2 level supports that the lowest excited state pipi* contributes to the S1/S0 crossing responsible for the ultrafast decay of singlet excited cytosine. The computed radiative lifetime, 33 ns, is consistent with the experimentally derived value, 40 ns. The nOpi* state does not play a direct role in the rapid repopulation of the ground state; it is involved in a S2/S1 crossing. Alternative mechanisms through excited states pisigma* or nNpi* are not competitive in cytosine.
TL;DR: In this article, the Time Dependent Density Functional Theory (TD-DFT) method implemented in the ADF program has been extended to treat core electrons excitations, where the complete one-electron excited configurations space is reduced to the subspace where only the core electrons are excited.
TL;DR: For doubly deuterated methane (CD2H2), this article showed that the reaction probability with two quanta of excitation in one C-H bond was greater (by as much as a factor of 5) than with one quantum in each of two c-H bonds.
Abstract: The dissociation of methane on a nickel catalyst is a key step in steam reforming of natural gas for hydrogen production. Despite substantial effort in both experiment and theory, there is still no atomic-scale description of this important gas-surface reaction. We report quantum state-resolved studies, using pulsed laser and molecular beam techniques, of vibrationally excited methane reacting on the nickel (100) surface. For doubly deuterated methane (CD2H2), we observed that the reaction probability with two quanta of excitation in one C-H bond was greater (by as much as a factor of 5) than with one quantum in each of two C-H bonds. These results clearly exclude the possibility of statistical models correctly describing the mechanism of this process and attest to the importance of full-dimensional calculations of the reaction dynamics.
TL;DR: In this paper, a Franck−Condon simulation of the neutral oxygen states was performed to determine the potential energy curves of O2 and O2- in its ground state and two excited states, in both the electronically bound and unbound regions.
Abstract: The ultraviolet photoelectron spectrum of O2- exhibits 29 resolved vibronic transitions to the three low-lying electronic states of neutral O2 (X 3Σg-, a 1Δg, b 1Σg+) from the X 2ΠJ (J = 3/2 and 1/2) spin−orbit states of the anion. A Franck−Condon simulation, using the established molecular constants of the neutral oxygen states, matches every observed feature in the spectrum. The 0−0 origin transition is unambiguously assigned, yielding the electron affinity EA0(O2) = 0.448 ± 0.006 eV. The derived bond dissociation energy is D0(O2-) = 395.9 ± 0.6 kJ/mol. Coupled-cluster theory at the CCSD(T)/aug-cc-pVTZ level is used to determine the potential energy curves of O2 and of O2- in its ground state and two excited states, in both the electronically bound and unbound regions. Stabilization methods are employed to characterize the anion curves at bond lengths where their electronic energies lie above that of the ground-state neutral. The calculations confirm that the O2- X 2Πg ground state is adiabatically stab...
TL;DR: In this article, the damage threshold of deuterated potassium dihydrogen phosphate (DKDP) from the near ultraviolet into the visible was measured using an OPO (optical parametric oscillator) laser.
Abstract: A novel experimental approach is employed to understand the mechanisms of laser induced damage. Using an OPO (optical parametric oscillator) laser, we have measured the damage thresholds of deuterated potassium dihydrogen phosphate (DKDP) from the near ultraviolet into the visible. Distinct steps, whose width is of the order of ${k}_{B}T$, are observed in the damage threshold at photon energies associated with the number of photons ($3\ensuremath{\rightarrow}2$ or $4\ensuremath{\rightarrow}3$) needed to promote a ground state electron across the energy gap. The wavelength dependence of the damage threshold suggests that a primary mechanism for damage initiation in DKDP is a multiphoton process in which the order is reduced through excited defect state absorption.
TL;DR: In this article, the excited state interaction between CdSe nanocrystals and a hole acceptor, p-phenylenediamine (PPD), was probed using emission and transient absorption spectroscopies.
Abstract: The excited state interaction between CdSe nanocrystals and a hole acceptor, p-phenylenediamine (PPD), is probed using emission and transient absorption spectroscopies. The changes in the photophysical properties of CdSe nanocrystals arising from the interaction with PPD are compared with an aliphatic amine, n-butylamine (n-BA). At low concentrations (<0.5 mM) n-butylamine enhances the emission of CdSe quantum dots whereas PPD effectively quenches the emission at similar concentrations. The low oxidation potential of PPD (E° = 0.26 V vs NHE) enables it to act as an effective scavenger for photogenerated holes. A surface bound complexation equilibrium model has been proposed to explain the quenching phenomenon. The transient absorption measurements confirm the formation of PPD cation radical and subsequent formation of coupling product. Formation of such charged species at the surface extends the bleaching recovery over several microseconds.