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A [3]Rotaxane with Three Stable States That Responds to Multiple‐Inputs and Displays Dual Fluorescence Addresses
Author(s) -
Qu DaHui,
Wang QiaoChun,
Ma Xiang,
Tian He
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200401313
Subject(s) - photoisomerization , rotaxane , azobenzene , fluorescence , photochemistry , moiety , chemistry , molecular switch , absorption spectroscopy , isomerization , molecule , supramolecular chemistry , stereochemistry , organic chemistry , optics , physics , catalysis
A [3]rotaxane molecular shuttle containing two α‐cyclodextrin (α‐CD) macrocycles, an azobenzene unit, a stilbene unit, and two different fluorescent naphthalimide units has been investigated. The azobenzene unit and the stilbene unit can be E / Z ‐photoisomerized separately by light excited at different wavelengths. Irradiation at 380 nm resulted in the photoisomerization of the azobenzene unit, leading to the formation of one stable state of the [3]rotaxane ( Z1‐ NNAS‐2CD ); irradiation at 313 nm resulted in the photoisomerization of the stilbene unit, leading to the formation of another stable state of the [3]rotaxane ( Z2‐ NNAS‐2CD ). The reversible conversion of the Z1 and Z2 isomers back to the E isomer by irradiation at 450 nm and 280 nm, respectively, is accompanied by recovery of the absorption and fluorescence spectra of the [3]rotaxane. The E isomer and the two Z isomers have been characterized by 1 H NMR spectroscopy and by two‐dimensional NMR spectroscopy. The light stimuli can induce shuttling motions of the two α‐CD macrocycles on the molecular thread; concomitantly, the absorption and fluorescence spectra of the [3]rotaxane change in a regular way. When the α‐CD macrocycle stays close to the fluorescent moiety, the fluorescence of the moiety become stronger due to the rigidity of the α‐CD ring. As the photoisomerization processes are fully reversible, the photo‐induced shuttling motions of the α‐CD rings can be repeated, accompanied by dual reversible fluorescence signal outputs. The potential application of such light‐induced mechanical motions at the molecular level could provide some insight into the workings of a molecular machine with entirely optical signals, and could provide a cheap, convenient interface for communication between micro‐ and macroworlds.