With the aid of laser-flash photolysis, the one-electron oxidation of conformationally mobile tetramethoxyclibenzobicyclo[4 4 1]undecane (1), using photoexcited chloranil as an oxidant, allows us to show that extended 1(+) undergoes a conformational transformation to pi-stacked folded 1(+) on a microsecond time scale (tau approximate to 1 mu s), which is at least six times longer than that found for the conformationally locked model compound