MAGNETIC-FIELD DEPENDENT REACTION YIELDS FROM RADICAL-ION PAIRS LINKED BY A PARTIALLY RIGID ALIPHATIC CHAIN

The electron donor-acceptor compound pyrene-(CH2) 3-cyclohexane-(CH2) 3-dimethylaniline, abbreviated as Py3(C6)3DMA, has been investigated. Photoinduced electron transfer leads to the singlet radical ion pair P y-3(C6)3DMA+. An extraordinary large and distinct magnetic field effec t is observed in the yield of the locally excited triplet state of the pyrene moiety, the recombination product of the triplet radical ion p air. The half-width of the ''J-resonance'' maximum in the magnetic fie ld dependent triplet yield curve is just 66 G, corresponding to 7.7 X 10(-7) eV or 6.2 X 10(-3) cm-1. This is due to the influence of the ri gid trans-cyclohexane part in the aliphatic chain, which leads to a re duced intramolecular mobility and to a narrow probability distribution of the radical ion pair distance, as predicted by Monte-Carlo compute r simulations. The magnetic field dependence of the triplet generation is further transmitted to secondary reactions like triplet-triplet an nihilation, thus leading to a magnetic field dependent delayed fluores cence and to a delayed excimer fluorescence.