Interpretations of High-Order Transient Absorption Spectroscopies

Transient absorption (TA) spectroscopy has long been an invaluable tool for determining the energetics and dynamics of excited states in atomic, molecular, and solid-state systems. When pump pulse intensities are sufficiently high, the resulting TA spectra include both the generally desired third-order response of the studied material as well as responses that are higher order in the electric field amplitudes of the pulses. It has recently been shown that pump-intensity-dependent TA measurements allow separating the various orders of response of the TA signal, but the information content available in those higher orders has not been described. We give a general framework, intuition, and nomenclature for understanding the information contained in high-order TA spectra. Standard TA spectra are generally interpreted in terms of three fundamental processes: ground-state bleach (GSB), stimulated emission (SE), and excited state absorption (ESA), and we extend those concepts to higher order. Each order introduces two new processes: SE and ESA from highly excited states that were not accessible in lower orders. In addition, each order contain negations of lower-order processes, just as GSB is a negation of the linear absorption. We show the new spectral and dynamical information that is introduced at each order and show how the relative signs of the signals in different orders can be used to identify which processes are dominant.Comment: 15 pages, 7 figure

High pressure behavior of CsC8 graphite intercalation compound

International audienceThe high pressure phase diagram of CsC8 graphite intercalated compound has been investigated at ambient temperature up to 32 GPa. Combining X-ray and neutron diffraction, Raman and X- ray absorption spectroscopies, we report for the first time that CsC8, when pressurized, undergoes phase transitions around 2.0, 4.8 and 8 GPa. Possible candidate lattice structures and the transition mechanism involved are proposed. We show that the observed transitions involve the structural re- arrangement in the Cs sub-network while the distance between the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8 GPa, important modifications of signatures of the electronic structure measured by Raman and X-ray absorption spectroscopies evidence the onset of a new transition

X-ray structures of dinuclear copper(I) and polynuclear copper(II) complexes with the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion

From the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion (2,4-NCNsq2−), two copper complexes [Cu2(PPh3)4(PhCN)2(μ-2,4-NCNsq)] · PhCN (1) and [Cu(dien)(μ-2,4-NCNsq) · H2O]n (2) have been synthesized and characterized by IR and electronic absorption spectroscopies. Their structures have been determined by X-ray crystallography. Complex 1 is a dinuclear copper(I) compound with a 2,4-NCNsq2− ligand bridging two copper atoms through the nitrile nitrogen atoms. Complex 2 appears as a 3D network constituted of copper(II) atoms bridged by 2,4-NCNsq2− dianions. This complex presents an unexpected coordination mode of the bis(cyanamido) ligands which are both coordinated via the nitrile functions and via the amido nitrogen atoms of the NCN groups

Photoexcitation spectroscopy of polythiophene

Journal ArticleRadiative recombination in polythiophene is studied by cw photoluminescence and photoinduced absorption spectroscopies and by photoluminescence-detected magnetic resonance. The fast-recombination centers are assigned to intrachain excitons in defect-free chains, while the slow recombination is due to intrachain excitons bound to spin- 1/2 defects

Intermolecular interaction of photoexcited Cu(TMpy-P4) with water studied by transient resonance Raman and picosecond absorption spectroscopies

photoinduced complex between Cu(TMpy-P4) and water molecules, reversibly axially coordinated to the central metal, was observed in picosecond transient absorption and nanosecond resonance Raman experiments. This complex is rapidly created (τ1 = 15 ± 5 ps) in the excited triplet (π, π*) state of Cu-porphyrin, and the subsequent relaxation is proposed to proceed via two parallel pathways. One is fast and efficient (≥90% of molecules), and presumably involves a (π, d) charge-transfer state. The second pathway is slow (τ2 >> 1 ns), has a low quantum yield (≤10%) and involves the excited (d, d) state which is responsible for transient Raman features at ≈ 1553 cm−1 (ν2*) and ≈ 1347 cm−1 (ν4*), and for low-intensity long-lived transient absorption features

Bioinspired catalysts: Synthesis, characterisation and some applications

Our recent work concerning the synthesis, characterisation and some applications of bioinspired electron-transfer catalysts is reviewed in this contribution. The catalysts were various mono- or heterobimetallic complexes having either Cu(II) or Cu(II) and Zn(II) as central ions and amino acids, their derivatives or various N-containing organic molecules as ligands. Emphasis was based upon the solid support immobilised versions of these complexes. They were built or anchored onto various kinds of supports (silica gel, montmorillonite, Merrifield’s resin) with different methods (adsorption, ion exchange, covalent grafting). The resulting materials were characterised by a variety of instrumental (FT-IR, Raman, EPR [electron paramagnetic resonance] and atomic absorption spectroscopies, thermogravimetry) as well as computational methods. Their superoxide dismutase, catecholase and catalase activities were tested and some of them were found to be promising candidates as durable electron-transfer catalysts being close to the efficiency of the mimicking enzymes

Bandgap and effective mass of epitaxial cadmium oxide

The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02 eV and 0.21±0.01m0 respectively