Showing papers by "Andreas Hauser published in 1989"

Dynamics of spin state conversion processes in the solid state

Abstract: High spin (HS) ⇌ low spin (LS) conversions in transition metal complexes are nonradiative transitions between spin states. In this contribution, we present a study of the temperature and pressure dependence of the HS ⇌ LS intersystem crossing dynamics. For some iron(II) spin-crossover complexes, the rate constants were determined by line shape analysis of57Fe Mossbauer spectra. Their temperature dependence is described by an Arrhenius equation, their pressure dependence is interpreted within absolute rate theory. HS → LS conversion rates at low temperatures were determined from the relaxation of light-induced formation of HS states, monitored by optical spectroscopy. Deviations from a simple Arrhenius behaviour due to cooperative effects were found for one complex, low temperature tunnelling is observed for another.

Thermal and light-induced spincrossover in iron(II) complexes-new perspectives in optical storage

Abstract: Recently, we have discovered a fascinating photophysical effect in spincrossover complexes of iron(I1): Light-Induced Excited Spin State Trapping (LIESST). At sufficiently low temperatures, the low spin state ('Alg) can be (quantitatively) converted to the high spin state ( T ) by irradiating the sample into the 'A14 T1 d-d absorption band (-540 nm). The metastable HS state has a practically infinite lifetime. It relaxes back to the LS state upon heating the sample. It can also be converted back to the LS state by irradiating into the 5T24 E band (-850 nm). The system behaves like an optical switch. Kinetic studies on metal-diluted crystals show that the thermal relaxation is cooperative in nature in the solid state. The relative positioning - horizontally and vertically - of the two spin state potential wells is crucial for the lifetime of the metastable HS state. 5 1 2g