Rotaxane 2010/06/02 Tobe Lab. Furutani Hajime 1

Contents What is Rotaxane? History -First Synthesis -Host-Guest Chemistry -Improved Synthetic Method Applications of Rotaxane -Rotaxane Specific Mobility -Molecular Switch -Molecular Machine My Project -Chirality -Rotaxane Specific Chirality -My Project 2

What is Rotaxane ? A rotaxane is a supramolecule consisting of a “dumbbell shaped axle” molecule and a “ring” molecule. ringdumbbell Rotaxane The dumbbell threads into cavity of the ring molecule. The ring molecule is impossible to slip out. There are no strong chemical bond between the two components 3

History -First Synthesis- Harrison, S. et al. J. Am. Chem. Soc., 1967, 89, probabilistic method rotaxane Repetition of above thread-end-cap processes 70 times afforded resulted rotaxanes in only 6% yield. thread end-cap Holes of molecular rings is too small to be threaded. The quite low probability makes rotaxane synthesis difficult. How about using “temporary covalent bonding” ?

History -First Synthesis- Progresses of “Host-Guest Chemistry” improved the situation dramatically. In general, rotaxanes were … 1. difficult to be synthesized. 2. interested only in their structure. 5 Schill, G. et al. 1967; Jus. Liebigs Ann. Chem. 1969, 53, 721 This synthesis needed many steps, and resulted in not good yield.

History -Host-Guest Chemistry- + HostGuestHost-Guest Host-Ring Guest-Axle Host-Guest “Pseudo” rotaxane Rotaxane + A molecule binds another molecule using weak interaction. capping If a ring can bind an axle, a subsequent capping reaction gives a rotaxane. Weak and Attractive Interaction 6

History -Improved Synthetic Method- Crown ethers are well-known as ring-shaped “host” molecules. Crown ethers capture cations in their cavities. If axles have cationic moieties, crownethers capture the axles very efficiently. 22% yield D. H. Busch et al. J. Chem. Soc., Chem. Commun, 1995, 89, Lone pair on oxgen 7 Crown ether Electron negativity

Applications of Rotaxane -Rotaxane Specific Mobility- shuttling One of the most important properties is “mobility”. In above scheme, the ring moves along the axle freely. Improvements of rotaxane syntheses make advanced researches on rotaxane specific properties easily. Because of this property, rotaxanes are expected to be prime candidate of molecular switches, molecular memories and more advanced machines. 8

If a rotaxane consists of a ring and an axle having two cationic moieties, the ring locates on one of the cationic units. J. F. Stoddart et al. J. Am. Chem. Soc., 1998, 120, A position of a ring can be controlled by external stimuli. Applications of Rotaxane -Molecular Switch- 9 This positional control is elementary operation for “molecular switch” and ”molecular memory”

D. A. Leigh et al. Nat. Mater, 2005, 4, Shuttling motion induced by UV light emittion lifted a drop up. The rotaxane worked as a transport machine. Applications of Rotaxane -Molecular Machine- 10

My Project -Chirality- Molecules sometimes have right-handed or left-handed properties. Central chirality Planar chirality Axial chirality Helicity If a molecule in a mirror is not superimposable to an original molecule, the molecule is ”chiral”. 11 **

A rotaxane consisting of an achiral ring and an achiral axle sometimes has chirality. Achiral ring Achiral axle Chiral rotaxane My Project -Rotaxane Specific Chirality- 12

My Project Right-HandedLeft-Handed I’ve been investigating in a rotaxane which can interconvert between right and left handed-properties. And the rotaxane can change the interconversion frequency by photo or thermal stimuli. I’ll talk in detail on presentation next semester. 13

Summary ・ A rotaxane is a supramolecule consisting of a “dumbbell shaped axle” molecule and a “ring” molecule. ・ Synthetic methods of supramolecules having threaded structure were well improved accompanying with Host-Guest chemistry ・ Rotaxanes have high flexibility of mobility. ・ Rotaxanes are expected to be prime candidate for molecular machines. ・ Rotaxanes sometimes have rotaxane-specific chirality. ・ I’ve been investigating in a rotaxane which interconverts between enantiomers. 14