Conformational dynamics of semiflexibly bridged electron donor-acceptor systems comprising long aliphatic tails

In continuation of our previous work on the conformational dynamics (harpoo ning mechanism) of semiflexibly bridged electron donor-acceptor systems we have studied a derivative with two long aliphatic chains tethered to the do nor and acceptor moieties, respectively. The fitting of the time- and wavel ength-resolved fluorescence curves required three components whose lifetime s varied smoothly with pressure (solvent viscosity). It is concluded that t hese three components correspond to three distinct conformations of the cha rge transfer state. Consequently, the previously established reaction schem e must be expanded by introducing an additional conformer termed the interm ediate charge transfer (ICT) state, which differs from the previously defin ed extended charge transfer (ECT) state by rotation around the single bond connecting the acceptor to the bridge. Due to the enlarged hydrodynamic vol ume, this rotation is slowed down sufficiently to be easily detectable (1.7 x10(8)less than or equal tok(rot)/s(-1)less than or equal to 16x10(8)). The rate of the folding process of the bridge leading from the ICT to the comp act (CCT) conformational state is also reduced by a factor of 5 compared to the parent compound (5x10(7)less than or equal tok(fold)/s(-1)less than or equal to 40x10(7)).