Publications de Majed Chergui | EPFL Graph Search

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It is known that excitation by visible light of the singlet metal-to-ligand charge-transfer (1MLCT) states of Fe(II) complexes leads to population of the lowest-lying high-spin quintet state (T-5) with unity quantum yield. Here we investigate this so-calle ...

We report broadband transient absorption measurements of adenine strands in the deep-UV (250-370 nm). By varying the strand length we resolve the interplay between inter-base stacking and exciton formation and dynamics in DNA oligomers. ...

Picosecond X-ray absorption spectroscopy (XAS) is used to investigate the electronic and structural dynamics initiated by plasmon excitation of 1.8 nm diameter Au nanoparticles (NPs) functionalised with 1-hexanethiol. We show that 100 ps after photoexcitat ...

Absorption and photoluminescence excitation (PLE) spectra were recorded for colloidal CdSe quantum dots of different sizes. No significant deviation between the PLE and the absorption spectra, provided appropriate corrections and sample treatment are made were found. This implies that there is no intrinsic wavelength dependence of the luminescence quantum yield, in line with the ultrafast intraband relaxation processes reported in the literature. Probably a possible source for the deviations reported in the

We review our recent studies of excited state structures and dynamics of chemical and biological systems with pico- and femtosecond X-ray absorption spectroscopy in the liquid phase. ...

The ultrafast spectral evolution of the fluorescence of the all-trans protonated Schiff base of retinal (PSBR) in alcs. with different polarity was studied using the fluorescence up-conversion technique in a "polychromatic mode". Results reveal that vibrational cooling is the dominant contribution to the total Stokes shift of PSBR's in alcs. The total Stokes shifts are very large: 7.9 +- 100/cm for PSBR/methanol and 6.87 +- 100/cm for octanol. Another striking observation is the .apprx.30% smaller width o

We analyze the structures of the low-spin (LS) ground state and the high-spin (HS) lowest excited state of the iron-(II)-tris bipyridine complex ([Fe(bpy)3]2+) using density functional theory PBE methods, modeling the solvent interactions with conductor-li ...

We present the extension of time-resolved optical pump/x-ray absorption spectroscopy (XAS) probe experiments towards data collection atMHz repetition rates. The use of a high-power picosecond laser operating at an integer fraction of the repetition rate of ...

Titanium dioxide (TiO2) is the most popular material for applications in solar-energy conversion and photocatalysis, both of which rely on the creation, transport, and trapping of charges (holes and electrons). The nature and lifetime of electron traps at ...

Femtosecond broadband photoluminescence studies are presented for Ir(ppy)(3) (Ir1), Ir(ppy)(2)(pic) (Ir2), Ir(ppy)(2)(bpy)(PF6) (Ir3), Ir(ppz)(3) (Ir4), and Ir(ppz)(2)dipy (Ir5) (where ppy = 2-phenylpyridine, pic = picolinate, bpy = 2,2'-bipyridine, ppz = ...

We present a new setup for resonant inelastic hard x-ray scattering at the Bernina beamline of SwissFEL with energy, momentum, and temporal resolution. The compact R = 0.5 m Johann-type spectrometer can be equipped with up to three crystal analyzers and al ...

Photodissocn. of H2O (D2O) and Cl2 trapped in rare gas matrixes was studied in relation to the cage effect. Barrier energies for the exit of the fragments from the matrix cage were detd., together with the excess kinetic energy dependence of the photodissocn. quantum efficiency. Simple anal. models and classical mol. dynamics simulations are used to discuss the results. [on SciFinder (R)]

We report the results of ultrafast transient absorption studies of tetrakis(l-pyrophosphito) diplatinate(II), Pt-2(mu-P(2)O(5)H2)(4) (Pt(pop)) and its perfluoroborated derivative Pt-2(mu-P2O5(BF2)(4) (Pt(pop-BF2)) in water and acetonitrile upon e ...

Vibrational progressions due to radiative decay of A1P(v' = 0,2,3,5,6,8) e3S(v' = 3,5,12), a'3S(v' = 11,14),d3D(v' = 5) to the ground state and of e3S(v' = 3,7,9,11,12), d3D(v' = 3,7,11) to the a3P state were obsd. for selective excitation of A1P(v' = 0, ..., 8). The intersystem crossing rate consts., the bottle necks, pathways and rate consts. for internal conversion in the triplet levels and the triplet-singlet radiative rate consts. are explained by an intramol. mixing of electronic states and electron-p

Single mols. that act as light-energy transducers (e.g., converting the energy of a photon into at.-level mech. motion) are examples of minimal mol. devices. Here, we focus on a mol. switch designed by merging a conformationally locked diarylidene skeleton ...

Networks of tryptophan (Trp)& horbar;an aromatic amino acid with strong fluorescence response & horbar;are ubiquitous in biological systems, forming diverse architectures in transmembrane proteins, cytoskeletal filaments, subneuronal elements, photorecepto ...

Due to their very nature, ultrafast phenomena are often accompanied by the occurrence of nonadiabatic effects. From a theoretical perspective, the treatment of nonadiabatic processes makes it necessary to go beyond the (quasi) static picture provided by th ...

Transient absorption spectra of C60 mols. trapped in cryogenic rare gas matrixes and dissolved in room temp. toluene were measured with a time resoln. of 90 fs. An absorption build-up with a characteristic rise time of 200 fs is measured, which is solvent-, temp.- and probe wavelength-independent. It is attributed to the population of an intermediate state by the decay of the initially excited singlet state(s) by vibrational and electronic relaxation. The data are discussed in the light of results from the

Emission from the valence levels B2P (v = 3-5) of NO embedded in Ne crystals following excitation of the Rydberg level A 2S+ (v = 2) by synchrotron radiation is reported. A 2-step process combining bubble formation around the Rydberg state and Rydberg->valence energy transfer is invoked in order to account for these emissions. [on SciFinder (R)]

I discuss the recent developments concerning emerging ultrafast sources of short wavelength radiation, as well as the new methods they generate. I then dwell on a few examples of recent results and the way the new sources will bring major advancements in o ...

Majed Chergui

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Sub-50-fs photoinduced spin crossover in [Fe(bpy)(3)](2+)

Exciton dynamics in DNA oligomers studied by broadband deep-UV transient absorption spectroscopy

Probing the dynamics of plasmon-excited hexanethiol-capped gold nanoparticles by picosecond X-ray absorption spectroscopy

On the Excitation Wavelength Dependence of the Luminescence Yield of Colloidal CdSe Quantum Dots

Ultrafast X-ray Absorption Studies of the Structural Dynamics of Molecular and Biological Systems in Solution

Ultrafast photophysics of the protonated Schiff base of retinal in alcohols studied by femtosecond fluorescence up-conversion

Asymmetric conformation of the high-spin state of iron(II)-tris(2,2-bipyridine): Time-resolved x-ray absorption and ultraviolet circular dichroism

A high-repetition rate scheme for synchrotron-based picosecond laser pump/x-ray probe experiments on chemical and biological systems in solution

Mapping of the Photoinduced Electron Traps in TiO2 by Picosecond X-ray Absorption Spectroscopy

Dual Luminescence, Interligand Decay, and Nonradiative Electronic Relaxation of Cyclometalated Iridium Complexes in Solution

A setup for hard x-ray time-resolved resonant inelastic x-ray scattering at SwissFEL

Cage effect on the photodissociation of small molecules in rare gas matrices

Conservation of vibrational coherence in ultrafast electronic relaxation: The case of diplatinum complexes in solution

Vibrationally hot emission and electronic relaxation of carbon monoxide in neon matrix

An artificial molecular switch that mimics the visual pigment and completes its photocycle in picoseconds

Ultraviolet Superradiance from Mega-Networks of Tryptophan in Biological Architectures

Nonadiabatic effects in electronic and nuclear dynamics

Ultrafast intramolecular relaxation of C60

Vibrationally "hot" valence luminescence of nitric oxide in neon matrixes

Emerging photon technologies for chemical dynamics