Density dependent study of In-Cage reactions of a diazene

ARAMENDIA, PEDRO FRANCISCO; GARCÍA-GARIBAY, MIGUEL ANGEL; HOIJEMBERG, PABLO ARIEL; JAPAS, MARÍA LAURA; KARLEN, STEVE; SANRAMÉ, CARLOS NORBERTO; SCHROEDER, JÖRG; ZERBS, JOCHEN

Praga

Workshop; Vth Workshop of PhotoInduced Molecular Processes (PIMoP); 2006

Czech Tecnical University; Georg-August-Universität, Göttingen; Max-Planck Institute of Biophysical Chemistry in Göttingen

The aim of the project is the study of the ´cage effect´ in radical reactions that initiate photochemically from the singlet state. The experiments, performed in reaction media that span from low density supercritical fluids to high density matrices, i.e. solids, will show how the environment influences the fate of the reaction products and will also let us obtain structural and dynamic information of the systems under study. Photolysis of asymmetric diazenes provides an efficient and irreversible way to produce a pair of geminate radicals from the first singlet excited state. The precursor (1-biphenyl-4-yl-1-methyl-ethyl)-tert-butyl-diazene and its expected photolysis products have been synthesized. Computational calculations aid in the analysis and understanding of the reaction. The recombination inside the solvent cage with respect to escape and non-geminate recombination in this type of experiments is evaluated by the distribution of reaction products, measured by HPLC. High amounts of disproportionation products are observed after photolysis in the solid state. Solid state photolysis over a wide temperature range has been conducted. The comparison of behavior in supercritical carbon dioxide and in an inert compressed gas (argon or nitrogen) will let us appreciate the real difference between the plain effect of pressure (through its normal effect on density and viscosity) and the critical phenomenon. The reaction kinetics is now being investigated by means of pump probe absorption spectroscopy with a time resolution of a few hundreds femtoseconds. Preliminary anisotropy experiments in various solvents led to an assignment of the transient absorption to the isopropylbiphenyl radical.