Patterning through Controlled Submolecular Motion: Rotaxane-Based Switches and Logic Gates that Function in Solution and Polymer Films David A. Leigh et al. Angew. Chem. Int. Ed. 2005, 44, Tobe Lab. Keiji Nishihara

Contents ・ Introduction ・ Results and Discussions ・ Summary Rotaxane Structure Molecular Switches Materials Applications

Rotaxane Structure ・ Macrocycle and thread are mechanically interlocked but are not covalently bonded. High mobility ex. Shuttling, Circumrotation ・ Synthesis of rotaxane was very difficult for its peculiar structure. ・ By using host-guest interaction or self-assembly, synthesis of rotaxane becomes more easily and efficiently since the late 1980s. Stopper Macrocycle Thread

Concept of Molecular Switches Response : conductivity, circular dichroism, fluorescence External stimuli : light, redox, protonation, pH, temperature, solvent effect Shuttling Station: the site where the macrocyle exists stable ・ A rotaxane in which the positon of macrocycle can be controlled by changing the stability of station with external stimuli. Molecular Switches “Off state” “On state”

Materials Applications The electrochromic response of the solid-state polymer devices. Green ground-state : after a +1 V oxidizing potential: Red/Purple relaxed back to the ground-state: Green Only simple rotaxanes have been used to create patterned surfaces. ・ There are few examples where shuttling has been demonstrated in polymer-based media. Suitable for materials applications J. R. Heath et al., Angew. Chem. Int. Ed. 2004, 43, D. A. Leigh et al., Science 2003, 299, 531.

Design of Thread 1 Anthracene: fluorophore (also act as “stopper”) Glycylglycine: hydrogen-bonding site, “station” C 11 alkyl chain: “solvophobic” station Second stopper

Design of Rotaxane 2, 3, and 3 ・ 2H + ・ 2CF 3 CO 2 - ・ Quenching the fluorescence of anthracene though distance- dependent electron transfer

Partial 1 H NMR spectra in CDCl 3 (400 MHz, 298 K) ・ The signals for H c and H e of glycylglycine station are shielded by  =1.2 and 0.4 ppm in the rotaxane. The macrocycle resides principally over the peptide residue of the rotaxane. rotaxane 2 thread 1

X-ray crystal structure of 3’ (3’: a close structural analogue of rotaxane 3.) ・ the macrocycle binding to the glycylglycine station though a network of intercomponent hydrogen bonds.

Partial 1 H NMR spectra in [D 6 ]DMSO (400 MHz, 298 K) thread 1 rotaxane 2 ・ the signals of the alkyl chain: strongly shielded ・ the signals of the glycylglycine unit: essentially unchanged The macrocycle encapsulates the alkyl chain. alkyl chain

Functional group interaction in solution ・ Solvent effect In CHCl 3 (chloroform ) In DMSO (dimethylsulfoxide ) amide-amide hydogen bonding : more favorable alkyl chain-phenyl ring solvophobic interaction: favorable : nonpolar solvent : aprotic polar solvent DMSO molecule: solvation CHCl 3 molecule: solvation the macrocycle held firmly on the peptide station the macrocycle to be localized on alkyl-chain station

Fluorescence of rotaxane 2 in CH 2 Cl 2 in DMSO ・ The ratio of fluorescence quantum yields is as high as 15: 1 (l ex =340 nm, 1 x M, 298 K) ・ The variations in intensity observed with the different solvents is caused by the change in the relative separation of the fluorophore and quencher. The switching mechanism in solution:

Polymer analogues of 2 and 3 ・ [2]rotaxane P5 and P6 contained approximately 10% w/w of peptide rotaxane endgroups. The behavior of polymers P5 and P6 in solution exactly mirrored those of the small-molecule analogues, 2 and 3. ・ 1 H NMR studies in CDCl 3 and [D 6 ]DMSO Poly(methyl methacrylate) (PMMA)-based: nonpolar ・ The polymer films were of good optical quality!

Effect of exposing to DMSO vapor: shuttling ・ No fluorescence of the P5 film when illuminated with UV light In the nonpolar environment of PMMA-like film the macrocycle resides over the peptide portion of the thread Efficient quenching of the anthracene fluorescence Exposing the P5-coated slides to DMSO vapor: shuttling the characteristic blue anthracene fluorescene Masked with aluminium grids ・ The system is reversible. before after

Effect of exposing to CF 3 CO 2 H vapor: protonation ・ P6 films were fluorescent when illuminated with UV light. The pyridine units of the macrocycle need to be protonated to quench the excited state of anthracene. Exposing P6-coated slides to CF 3 CO 2 H vapors (P6→P6 ・ (2H + ・ 2CF 3 CO 2 - ) n : protonation) Fluorescence was no longer observed. A distinct pattern of dark (nonfluorescent) bands resulting from P6 films upon exposure to CF 3 CO 2 H vapor through a striped aluminum mask (a). before after

The response of P6 to the different combination of two stimuli 1. rotation of the aluminum grid by 90º 2. exposure of the film shown in (b) to DMSO vapor Criss-cross pattern was obtained. ・ The response of P6 to the different combinations of two stimuli (DMSO and protons) corresponds to an “INHIBIT” logic gate. ・ The effect of the acid stimulus involves some deterioration in the optical quality of the film.

Molecular logic gates: “INHIBIT” logic gate INHIBITOR: Input 2 ・ A NOT circuit preceding one terminal of an AND gate acts as an INHIBITOR. Output = Input 1 ・ Input 2 ・ In the case of rotaxane P6, exposing to DMSO vapor acts as INHIBITOR. MOLECULAR-SCALE LOGIC GATES For a recent review: A. P. de Silva, N. D. McClenaghan, Chem.Eur. J. 2004, 10,

Summary ・ The authors have described a class of molecular shuttles in which translational isomerism of the components can be controlled to either permit or preclude fluorescence quenching by intercomponent electron transfer in both solution and polymer films. ・ The optical response can be unambiguously ascribed to changes in the relative positions of macrocycle and thread. ・ The present work demonstrates that some of the switching mechanisms, properties, and logic operations established for molecular shuttles in solution can be transferred to media that are more suitable for materials which function through controlled submolecular motion.

Molecular Switches 1: conductivity External stimuli: Redox A molecular switch tunnel junction in its Off and On states. (left) Structural formula of a bistable [2]rotaxane ・ at a specific voltage, this rotaxane switches from a stable Off state to metastable On state with a different conductivity. A. H. Flood et al., Science 2004, 306,

Molecular Switches 2: circular dichroism External stimuli: light (E)-isomer Only (Z)-isomer gives a CD response. glycyl- L -leucine (Gly-Leu) unit: well-exprssed chiral environment ・ Upon photoisomerism of the olefin station (E→Z), the macrocycle moves to the glycyl- L -leucine (Gly-Leu) unit. (Z)-isomer D. A. Leigh et al., J. Am.Chem. Soc. 2003, 125,

Molecular Switches 3: fluorescence External stumuli: light ・ (E)-isomer converted into (Z)-isomer by photoisomerism. (E)-isomer anthracene unit (Z)-isomer electron transfer pyridinium unit A remarkable 200:1 intensity ratio between (E)-and (Z)-isomer. Because of distance-dependent electron transfer from anthracene unit to pyridinium units. (Z)(Z)(E)(E) PSS D. A. Leigh et al., J. Am. Chem. Soc. 2004, 126,

Functional group interaction profiles (FGIP)  : hydrogen-bond donor constant  : hydrogen-bond acceptor constant Blue  G H-bond < 0 favorable interaction Red  G H-bond > 0 unfavorable interaction contour lines ( 等高線 ) ・ FGIP provide a benchmark for estimating the magnitudes of intermolecular interactions. In chloroform: nonpolarIn DMSO: polar C. A. Hunter Angew. Chem. Int. Ed. 2004, 43,

Functional group interaction profiles (FGIP) in chloroform amide-amide interaction: favorable alkyl chain-phenyl ring interaction: unfavorable ・ The authors expect the tertiary structure to feature the macrocycle held firmly on the peptide station by well-defined hydrogen-bonding network. Strong quenching of the anthracene fluorescence

Functional group interaction profiles (FGIP) in DMSO amide-amide interaction: unfavorable alkyl chain-phenyl ring interaction: favorable ・ The authors expect the macrocycle to be localized on alkyl- chain station but in a variety of positions owing to the general solvophobic interactions.

Electron-transfer process in solution The very efficient quenching observed in nonpolar solvents (ex. chloroform, dichloromethane) The electron-transfer process in rotaxanes 2 and 3 ・ 2H + is close to the Marcus optimal region. ・ The variations in intensity observed with the different solvents is caused by the change in the relative separation of the fluorophore and quencher.  ・ The electron transfer process in the rotaxanes: barrierless and insensitive to the polarity of the solvent. The switching mechanism in solution: