| Abstract
| - The shuttling process of α-CyD in three rotaxanes (1−3) containing α-cyclodextrin (α-CyD) asa ring, azobenzene as a photoactive group, viologen as an energy barrier for slipping of the ring, and2,4-dinitrobenzene as a stopper was investigated. The trans−cis photoisomerization of 1 by UV lightirradiation occurred in both DMSO and water due to the movement of α-CyD toward the ethylene group,while the photoisomerization of 2 occurred in DMSO, but not in water. No photoisomerization was observedfor 3 in both water and DMSO. The activation parameters of 1 and 1-ref in DMSO are subject to acompensation relation between ΔS⧧ and ΔH⧧; however, in water, the ΔS⧧ terms are not compensated bythe ΔH⧧ terms. Alternating irradiation of the UV and visible lights resulted in a reversible change in theinduced circular dichroism (ICD) bands of trans-1 and cis-1. In contrast, after the UV light irradiation, theICD band of trans-2 decreased without the appearance of any bands of cis-2. The NMR spectra of 2 inDMSO showed coalescence of the split signals for the methylene and for the viologen protons due to theshuttling of α-CyD. Both the NOE differential spectra for cis-1 in water after UV light irradiation and 2 inDMSO after heating to 120 °C showed the negative NOE peaks assigned to interior protons of α-CyD,suggesting that α-CyD in cis-1 exists at the one ethylene moiety, and α-CyDs in cis-2 and 2 heated inDMSO exist at the propylene moieties.
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