Stabilization of the (E)-1-ferrocenyl-2-(1-methyl-4-pyridinium)ethylene cation by inclusion in cucurbit[7]uril

The (F)-l-ferrocenyl-2-(l-methyl-4-pyridinium)ethylene cation, (E)-FcMPE(+), forms a very stable guest-host complex (K-CB7 = (1.3 +/- 0.5) x 10(12) M-1) in aqueous solution with cucurbit[7]uril (CB[7]). The H-1 NMR, ES-MS, and UV-visible spectra are consistent with 1:1 {(E)-FcMPE(.)CB[7]}(+) species formation, in which the CB[7] encapsulates the ferrocenylethylene portion of the guest. The reduction potential of the (E)-FcMPE(2+/+) couple increases slightly (+0.03 V) in the presence of CB[7], while the rate constant for the oxidation of (E)-FcMPE(+) by Co(dipic)(2)(-) (dipic(2-) = 2,6-pyridinedicarboxylate) decreases significantly. UV-visible spectra of (E-)-Fc-MPE+ in the absence and in the presence of CB[7] during photoirradiation demonstrate that the photoisomerization to (Z)-FcMPE(+) is fully inhibited and photostabilization of (E)-FcMPE(+) is dramatically enhanced upon inclusion in CB[7].