Andreas Hauser

Bio: Andreas Hauser is an academic researcher from University of Geneva. The author has contributed to research in topics: Spin crossover & Spin transition. The author has an hindex of 54, co-authored 234 publications receiving 13479 citations. Previous affiliations of Andreas Hauser include University of Mainz & Bulgarian Academy of Sciences.

Thermal and Optical Switching of Iron(II) Complexes

Abstract: Transition metal chemistry contains a class of complex compounds for which the spin state of the central atom changes from high spin to low spin when the temperature is lowered. This is accompanied by changes of the magnetic and optical properties that make the thermally induced spin transition (also called spin crossover) easy to follow. The phenomenon is found in the solid state as well as in solution. Amongst this class, iron(II) spin crossover compounds are distinguished for their great variety of spin transition behavior; it can be anything from gradual to abrupt, stepwise, or with hysteresis effects. Many examples have been thoroughly studied by Mossbauer and optical spectroscopy, measurements of the magnetic susceptibilities and the heat capacities, as well as crystal structure analysis. Cooperative interactions between the complex molecules can be satisfactorily explained from changes in the elastic properties during the spin transition, that is, from changes in molecular structure and volume. Our investigations of iron(II) spin crossover compounds have shown that green light will switch the low spin state to the high spin state, which then can have a virtually unlimited lifetime at low temperatures (this phenomenom is termed light-induced excited spin state trapping - acronym: LIESST). Red light will switch the metastable high spin state back to the low spin state. We have elucidated the mechanism of the LIESST effect and studied the deactivation kinetics in detail. It is now well understood within the theoretical context of radiationless transitions. Applications of the LIESST effect in optical information technology can be envisaged.

Light-induced spin crossover and the high-spin→low-spin relaxation

Abstract: The discovery of a light-induced spin transition at cryogenic temperatures in a series of iron(II) spin-crossover compounds in 1984 has had an enormous impact on spin-crossover research. Apart from being an interesting photophysical phenomenon in its own right, it provided the means of studying the dynamics of the intersystem crossing process between the high-spin and the low-spin state in a series of compounds and over a large temperature range. It could thus be firmly established that intersystem crossing in spin-crossover compounds is a tunnelling process, with a limiting low-temperature lifetime below 50 K and a thermally activated region above 100 K. This review begins with an elucidation of the mechanism of the light-induced spin transition, followed by an in depth discussion of the chemical and physical factors, including cooperative effects, governing the lifetimes of the light-induced metastable states.

Light-induced excited-spin-state trapping in iron(II) spin-crossover systems. Optical spectroscopic and magnetic susceptibility study

Abstract: Single-crystal optical absorption spectra of the iron(I1) sph-crossover compounds [Fe(pt~)~]@F~), (ptz = 1-propyltetrazole) and [Fe(2-pi~)~]Cl,.EtOH (2-pic = 2-(aminomethy1)pyridine) have been.measured between room temperature and 8 K. The wellestablished thermally induced spin transition high spin (?,& + low spin (lAIg) as well as the recently discovered phenomenon of 'light-induced excited-spin-state trapping (LIWT)" is followed and analyzed. A kinetic study by optical spectroscopy of the relaxation from the light-induced high-spin (HS) state to the low-spin (LS) state has been carried out for [Fe(ptz),](BF,), in the temperature range 53-61 K. The magnetic susceptibility of the light-induced HS state of this compound has also been measured.

Thermisch und optisch schaltbare Eisen(II)‐Komplexe

Abstract: In der Ubergangsmetallchemie gibt es eine Klasse von Komplexverbindungen, bei denen eine Temperaturerniedrigung einen Wechsel im Spinzustand des Zentralatoms vom High-Spin- in den Low-Spin-Zustand bewirkt. Dabei andern sich die magnetischen und optischen Eigenschaften, uber die der thermische Spinubergang (auch Spincrossover genannt) sehr gut verfolgt werden kann. Dieses Phanomen tritt sowohl in flussiger Phase als auch im Festkorper auf. Eine herausragende Stellung nehmen Eisen(II) - Spincrossover - Verbindungen ein, in denen der Spinubergang im Festkorper auf sehr unterschiedliche Weise - graduell, abrupt, mit Hysterese oder stufenweise - verlaufen kann und mit Mosbauer- und optischer Spektroskopie, mit magnetischen Suszeptibilitats- und Warmekapazitatsmessungen sowie durch Kristallstrukturanalyse intensiv untersucht worden ist. Die kooperative Wechselwirkung zwischen den einzelnen Komplexmolekulen kann befriedigend durch elastische Eigenschaften und durch die Anderung von Gestalt und Volumen der Komplexmolekule beim Spinubergang erklart werden. Bei Untersuchungen an Eisen(II)-Spincrossover-Verbindungen konnte man beobachten, das sich der Low-Spin-Zustand mit grunem Licht in den High-Spin-Zustand umschalten last, der bei tiefen Temperaturen eine nahezu unendlich lange Lebensdauer haben kann (LIESST = Light-Induced Excited Spin State Trapping). Mit rotem Licht last sich der metastabile High-Spin- wieder in den Low-Spin-Zustand zuruckschalten. Der Mechanismus des LIESST-Effekts ist aufgeklart, die Zerfallskinetik im Detail untersucht und im Rahmen der Theorie strahlungsloser Ubergange verstanden. Anwendungen des LIESST-Effekts in der optischen Informationstechnik sind denkbar.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Taking advantage of luminescent lanthanide ions

Abstract: Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.)

Engineering coordination polymers towards applications

Abstract: The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.

Highly phosphorescent bis-cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes.

Abstract: The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C∧N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C∧N2Ir(LX). The C∧N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all β-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C∧N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1−0.6), and microsecond lifetimes (e.g., 1−14 μs). The strongly allowed phosphorescence in these complexes is the result of significant spin−orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C∧N2Ir(acac) complexes is a mixture of 3MLCT and 3(π−π*) states. By choosing the appropriate C∧N ligand, C∧N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C∧N ligands, whic...