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

Abstract

The shuttling process of alpha-CyD in three rotaxanes (1-3) containing alpha-cyclodextrin (alpha-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 alpha-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 deltaS(double dagger) and deltaH(double dagger); however, in water, the deltaS(double dagger) terms are not compensated by the deltaH(double dagger) 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 alpha-CyD. Both the NOE differential spectra for cis-1 in water after UV light irradiation and 2 in DMSO after heating to 120 degrees C showed the negative NOE peaks assigned to interior protons of alpha-CyD, suggesting that alpha-CyD in cis-1 exists at the one ethylene moiety, and alpha-CyDs in cis-2 and 2 heated in DMSO exist at the propylene moieties.

Pentiptycene‐Derived Light‐Driven Molecular Brakes: Substituent Effects of the Brake Component

“…The mixture was concentrated under reduced pressure, and the residue was dissolved in CH 2 Cl 2 and washed wish brine. The organic layer was dried over anhydrous MgSO 4 14.5, 23.3, 24.5, 27.0, 30.0, 30.2, 31.1, 32.6, 35.0, 48.7, 51.6, 76.7, 123.1, 123.7, 124.0, 124.1, 125.1, 125.6, 125.7, 127.1, 134.7, 137.6, 137.7, 143.1, 145.9, 146.2, 149.2, 150.3 22.1, 25.6, 28.7, 28.9, 29.7, 31.4, 34.6, 47.3, 50.0, 75.5, 121.0, 123.4, 123.7, 125.0, 126.3, 134.9, 136.0, 137.1, 141.6, 142.1, 145.1, 145.3, 148.1, 150.8 22.1, 23.0, 25.7, 28.8, 28.9, 29.7, 31.4, 32.8, 47.4, 50.6, 75.5, 122.7, 123.2, 123.3, 123.6, 123.7, 124.4, 124.4, 124.6, 124.8, 125.7, 134.4, 134.8, 135.8, 141.3, 144.7, 145.1, 145.2, 145.4, 147.7, 147.9 22.1, 25.6, 28.7, 28.9, 29.7, 30.5, 31.4, 33.6, 75.4, 120.7, 122.8, 122.9, 123.1, 123.3, 123.6, 124.4, 124.4, 124.4, 124.8, 124.8, 125.7, 134.8, 135.1, 141.3, 144.7, 145.1, 145.2, 145.5, 147.9, 149.5 …”

“…The concept of the "bottom-up approach toward miniature devices" has led to the development of many prototypes of molecule-and supramolecule-based machinery systems [1] that mimic the macroscopic counterparts such as brakes, [2] gears, [3] shuttles, [4] and motors. [5] One of the most important issues in operating a molecular machine is the input of energy (fuel).…”

Orthogonal switching of a single supramolecular complex

“…In particular, azobenzene derivatives have been extensively used as guests to form inclusion complexes with asymmetric macrocyclic hosts achieving binary photochemical devices [12][13][14][15][16][17] , based on its well-documented photoisomerism 18 . Although symmetric macrocyclic hosts such as cucurbit[n]urils, (n ¼ 7 and 8) have been used to form either binary inclusion complexes with CB [7] 19,20 , or ternary complexes with CB [8] and methylviologen (MV 2 þ ) 21 , no photoresponsive CB systems have been demonstrated.…”

Molecular machines operated by light

“…The photoisomerization about a -C=C-bond is at the basis of a very interesting class of molecular rotary motors based on sterically hindered alkenes [19,65,66]. Molecular shuttles relying on the photoisomerization of azobenzene or stilbene units have also been reported [67][68][69][70].…”