PHOTOINDUCED ELECTRON-TRANSFER IN LINKED RUTHENIUM(II) DIIMINE DIQUAT COMPLEXES - LINKAGE DEPENDENCE

Intramolecular photoinduced electron transfer in a series of linked ruthenium(II) diimine donor-diquat acceptor complexes was examined as a function of the nature of the bridge between the donor and acceptor centers. Bridging groups include polymethylene chains (-(CH2)n-, n = 2-7, 12) and phenyl- or cyclohexyl-containing spacers (p-(-CH2-Ph-CH2-), p-(-CH2-trans-cyclohexyl-CH2-), and p-(-CH2-cis-cyclohexyl-CH2-)). The rate constant for electron transfer decreases sharply as the number of methylenes separating the donor and acceptor increases in straight chain alkyl bridged complexes. An odd-even alternation in the electron-transfer rate constant is observed in the straight chain series. Rate constants for electron transfer in the series of complexes bridged by the cyclic spacers having a fixed number of bonds but differing steric environments varied by only a factor of 2. Results are discussed in terms of possible through-space and through-bond interactions. The combined results suggest that the bridging ligands may serve to mediate the electron transfer in these systems.