"Through Space" Triplet Energy Transfer: Movement of Electrons through the Hemicarcerand Skeleton

Electrochemistry of Encapsulated Guests: Ferrocene inside Cram's Hemicarcerands

“…Furthermore, Farran et al have investigated the isomerization of cis-piperylene sensitized by free and encapsulated acetophenone. [20] It may be inferred from their triplet energy transfer data that the hemicarcerand skeleton is involved in the simultaneous exchange of electrons between the HOMO and LUMO of the donor ± acceptor pair. This suggests that the hemicarcerand aromatic structure may mediate the electronic coupling between the encapsulated ferrocene center and the electrode surface, but further electrochemical experimentation with other hemicarceplexes is needed to verify this point.…”

“…In this regard, Cram and his co-workers have demonstrated that cyclobutadiene is stabilized inside these hosts, [15] proton-transfer equilibria are strongly affected by encapsulation, [16] and encapsulated guests can undergo chemical oxidation or reduction reactions. [17] Very recently, Balzani and co-workers [18,19] as well as Farran et al [20,21] have investigated the photophysical properties of encapsulated guests. Here we report, for the first time, the electrochemical behavior of ferrocene encapsulated inside these intriguing molecular containers.…”

Electrochemistry of encapsulated redox centers

“…We must note here that Deshayes and coworkers 28 have investigated the triplet energy transfer between acetophenone encapsulated inside a related hemicarcerand and external acceptors. Their results suggest that the presence of the hemicarcerand shell causes only a modest decrease in the rate of triplet energy transfer, leading these authors to postulate an electron exchange mechanism involving the hemicarcerand skeleton.…”

Reactions Inside Carcerands

“…As a consequence of a strong distance dependence, 111b,114 ET and PET are substantially slower than diffusion, which has made observation of the inverted region possible in these systems 96,110,115 In their seminal work on through space triplet ET, Deshayes and co -workers studied acetophenone (AC) hemicarceplex 14 ᭪ Ac and probed through -shell triplet ET chemically via the isomerization of cis -piperylene to trans -piperylene (Figure 9.36 ). 116 From a Stern -Volmer analysis and the lifetimes of free and incarcerated triplet acetophenone, Deshayes determined a 2.7 -fold slower triplet ET rate for 14 ᭪ Ac compared to free acetophenone. This corresponds to an almost diffusion controlled rate for 14 ᭪ Ac.…”