A Multi-Mode-Driven Molecular Shuttle:  Photochemically and Thermally Reactive Azobenzene Rotaxanes

• Published in: Journal of the American Chemical Society Vol. 127; no. 45; pp. 15891 - 15899
• Main Authors: Murakami, Hiroto, Kawabuchi, Atsushi, Matsumoto, Rika, Ido, Takeshi, Nakashima, Naotoshi
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 16.11.2005; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Physical Sciences; Science & Technology; PHOTORESPONSIVE CROWN-ETHERS; MACHINES; ISOMERIZATION; COMPLEXES; BETA-CYCLODEXTRIN; TRANSLATIONAL ISOMERISM; SWITCH; CHIRALITY; DUMBBELL; THREAD; Overhauser effect; Oligoholoside; Activation parameter; NMR spectrometry; Cis trans isomerization; Photochemical reaction; Thermal reaction; Experimental study; α-Cyclodextrin; Organic solvent; Methyl sulfoxide; Near ultraviolet radiation; Visible radiation; Reaction mechanism; Kinetic parameter; Aqueous solution; Rate constant; Rotaxane; Ultraviolet visible spectrometry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja053690l

The shuttling process of α-CyD in three rotaxanes (1−3) containing α-cyclodextrin (α-CyD) as a ring, azobenzene as a photoactive group, viologen as an energy barrier for slipping of the ring, and 2,4-dinitrobenzene as a stopper was investigated. The trans − cis photoisomerization of 1 by UV light irradiation 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 observed for 3 in both water and DMSO. The activation parameters of 1 and 1-ref in DMSO are subject to a compensation relation between ΔS ⧧ and ΔH ⧧; however, in water, the ΔS ⧧ terms are not compensated by the ΔH ⧧ terms. Alternating irradiation of the UV and visible lights resulted in a reversible change in the induced circular dichroism (ICD) bands of trans-1 and cis-1. In contrast, after the UV light irradiation, the ICD band of trans-2 decreased without the appearance of any bands of cis-2. The NMR spectra of 2 in DMSO showed coalescence of the split signals for the methylene and for the viologen protons due to the shuttling of α-CyD. Both the NOE differential spectra for cis-1 in water after UV light irradiation and 2 in DMSO 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 in DMSO exist at the propylene moieties.