Dresden 2003 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 21: POSTER B
CPP 21.5: Poster
Dienstag, 25. März 2003, 19:00–21:00, ZEU/250
PHOTO-CIDNP STUDIES OF INTRAMOLECULAR CHARGE TRANSFER REACTIONS IN RIGID DONOR-SPACER-ACCEPTOR COMPLEXES — •Hans-Martin Vieth1, Michael Onnen1, Karsten Miesel1, Anna M. Oliver2, and Michael N. Paddon-Row2 — 1Department of Physics, Free University of Berlin, D-14195 Berlin, Germany — 2School of Chemistry, University of New South Wales, Sydney 2052, Australia
The importance and complexity of biological light induced charge transfer reactions has stimulated numerous studies of similar processes in model compounds. Here we present investigations on a series of bichromophoric molecules, where electron donor and acceptor are interconnected by a rigid hydrocarbon bridge that is varied in well-defined increments. Charge recombination occurs either to the singlet ground state or to a local donor triplet state. Singlet-triplet intersystem crossing in the charge separated ion pair leads to nuclear polarization (CIDNP) mainly due to electron-nuclear spin flip-flop transitions. Polarization efficiency depends on the external magnetic field and is strongest in regions of level crossing between singlet and triplet spin states thus allowing determination of the exchange coupling constant J. By fast field cycling the CIDNP field dependence is mapped out between 0.05mT and 7T. Various solvents are compared, and temperature is varied, hence No-dqthrough-bondNo-dq, No-dqthrough-spaceNo-dq and No-dqthrough-solventNo-dq contributions to J can be differentiated. The close correlation between exchange interaction and CIDNP field dependence makes field cycling experiments a well suited method for determination of J without having to rely on vague model assumptions.