Molecular pedal

Figure 94 Schematic representation of photoisomerization of a 1 1 complex of molecular pedal host with a rotary guest. (Reproduced from Ref. 157. Royal Society of Chemistry, 2007.)...

Several years ago, we found that the isomerization of n-butylammonium ( Z,Z)-muconate produces the corresponding EE-isomer in a high yield in the crystalline state under photoirradiation [41]. This solid-state photoisomerization was re e e< t0 he a one-way reaction and no EZ-isomer was formed during the reaction, unsaturated compounds such as olefins, polyenes, and azo compounds generally undergo reversible one-bonded photoisomerization to form a mixture of omers. Previously, we pointed out the possibility that the isomerization of the but thni(i er Va ves the s°hd state f°ll°ws the bicycle-pedal reaction mechanism, et al [4 eta s °ffhe molecular dynamics ofthe reaction had not been clarified. Saltiel react an< fl have independently discussed volume-conserving... 

The hula twist mechanism (HT, Fig. 2.3B), first validated with carotenoids, is not consistent with the time-scale of photoisomerization of chromoproteins since CTI of the retinal chromophore, which is inserted deep inside the protein, necessitates a major reorganization of the peptide molecular framework. Therefore, a new volume-conserving mechanism, called bicyclic pedal (BP, Fig. 2.3C), was proposed. In fact, all these mechanisms are still a topic of discussion since chromoprotein photo-intermediates highlighted by recent studies do not confirm this hypothesis. In particular, several photo-products of the retinal Schiff base in the... 

Although the transformation demonstrated here involves large structural change and seems difficult to take place in a crystal, it can easily occur through the motion of a pair of benzene rings analogous to the pedal motion of a bicycle, which is extensively studied in the thermochromism of azobenzenes containing similar molecular skeletons to those of salicylideneanilines [33]. 

Another interesting example of guest-triggered reversible pedal motion in a pillared-layer structure 49, with unusual isomers of paddle wheel SBUs, " was reported by Park et al (Figure 42). The understanding of such molecular motion offers to explain various dynamic aspects of molecules besides being potentially useful in fabricating molecular devices. 

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