INFLUENCE OF SOLVENT VISCOSITY AND PERMITTIVITY ON THE HARPOONING MECHANISM IN SEMIRIGIDLY BRIDGED ELECTRON DONOR-ACCEPTOR SYSTEMS

After the photoinduced electron transfer, the donor-bridge-acceptor sy stem ''WS4'' executes a large scale motion which leads from an extende d to a compact geometry (harpooning mechanism). The rate of this foldi ng process, k(fold), was measured in three nonpolar solvents as a func tion of temperature (283 < T < 343 K) and hydrostatic pressure (0.1 < P < 350 MPa) and successfully fitted by the expression k(fold) = B.(A/ eta)(0.7)exp[-(E-ster - E'/epsilon(r) + E ''/epsilon(r)(2))/RT], This implies that the effect of friction on the folding kinetics of WS4 is modeled best by the same stretched exponential, in contrast to the pre viously studied structurally related systems WS2 and WS3 where no fric tion dependence was observed.