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Establishing methods for controlling aspects of large amplitude submolecular movements is a prerequisite for the development of artificial devices that function through rotary motion at the molecular level. Here we demonstrate that the rate of rotation of the interlocked components of fumaramide-derived [2]rotaxanes can be accelerated, by >6 orders of magnitude, by isomerizing them to the corresponding maleamide [2]rotaxanes by using light. molecular machines ͉ dynamics L arge amplitude internal rotations that resemble to some extent processes found in authentic machinery have recently inspired analogic molecular versions of gears (1), turnstiles (2), brakes (3), ratchets (4, 5), rotors (6), and unidirectional spinning motors (7-10) and are an inherent characteristic of many catenanes and rotaxanes (11-13). Establishing methods for controlling aspects of such movements is a prerequisite for the development of artificial devices that function through rotary motion at the molecular level. In this regard, we recently reported the unexpected discovery that the rate of rotation of the interlocked components of benzylic amide macrocyclecontaining nitrone and fumaramide [2]rotaxanes can be slowed (''dampened'') by 2-3 orders of magnitude by applying a modest (Ϸ1 V⅐cm Ϫ1) external oscillating electric field (14). Here we demonstrate that the rate of rotation of the interlocked components of the olefin-based rotaxanes can also be accelerated, by Ͼ6 orders of magnitude, using another broadly useful stimulus, light.Fumaramide threads template the assembly of benzylic amide macrocycles around them to form rotaxanes in high yields (15). This cheap and simple preparative procedure (suitable threads are prepared in a single step from fumaryl chloride and a bulky primary or secondary amine) is particularly efficient because the trans-olefin fixes the two hydrogen bond-accepting groups of the thread in an arrangement that is complementary to the geometry of the hydrogen bonddonating sites of the forming macrocycle. However, the feature of the fumaramide unit that makes it such an effective template also provides an opportunity to enforce a geometrical change in the thread after rotaxane formation, thus altering the nature and strength of the interactions between the interlocked components. Isomerization of the olefin from E-to Z-must necessarily disrupt the near-ideal hydrogen bonding motif between macrocycle and thread and therefore also change any internal dynamics governed by those interactions.To test this idea, the photochemical isomerization of three fumaramide-based threads (E-1-3) and rotaxanes (E-4-6) was investigated. The synthesis of rotaxanes E-4 and E-6 has been described (15), and E-5 was prepared in analogous fashion from the corresponding thread, E-2, isophthaloyl dichloride and p-xylylene diamine (Scheme 1).** Under the same reaction conditions the cis-olefin (maleamide) threads, Z-1-3, did not give detectable quantities of the corresponding Z-rotaxanes. Experimental ProceduresGeneral Method for the Photoisomeri...

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Phase stabilizers identified from a top-down strategy overcome microstructure instability of organic solar cells induced by thermal or photo stress.

Simulation data are presented for a coarse-grained model of polycarbonate (BPA-PC), which allow for a detailed comparison of different ways to study the chain dynamics and predict the entanglement molecular weight. Most of the standard experimental quantities are determined for the very same set of systems and thus provide an opportunity for a detailed comparison of data far beyond typical experiments or simulations. By employing a suitably coarse-grained model, which still contains the essentials of the BPA-PC structure, simulation times compared to atomistic simulations could be extended by several orders of magnitude, reaching well into the characteristic experimental regime. We find that a recently developed topological entanglement analysis compares well with a direct determination of the modulus from simulations as with experiments on well-characterized samples. This confirms the extraordinarily small value of the entanglement molecular weight on Me between 1200 and 1400 corresponding to Ne close to 5.

We extend a previous dual scale modeling approach for the behavior of polymers near a metal surface to a variety of end groups. Our approach combines a coarse-grained polymer model with ab initio DFT calculations. Such a procedure was applied to a melt of phenolic-like terminated Bisphenol A-polycarbonate (BPA-PC) interacting with a (111) nickel surface (Delle Site, L.; Abrams, C. F.; Alavi, A.; Kremer, K. Phys. Rev. Lett. 2002, 89, 156103. Abrams, C. F.; Delle Site, L.; Kremer, K. Phys. Rev. E 2003, 67, 021807). This work extends this study to different chain-end modifications of BPA-PC, p-tert-butylphenolic, p-tetramethylpropylphenolic, and p-cumylphenolic. We show how the interplay between adsorption energies and conformational entropy selects different morphologies for the various melts at the interface. Implications of these results for realistic technical materials are finally discussed.

The first statistical analyses of the X-ray crystal structures of mechanically interlocked molecular architectures, the first molecular mechanics-based solid-state calculations on such structures and atomic force microscopy (AFM) experiments are used in combination to predict and test which types of benzylic amide macrocycle-containing rotaxanes possess mobile components in the crystalline phase and thus could form the basis of solid-state devices that function through mechanical motion at the molecular level. The statistical studies and calculations show that crystals formed by rotaxanes possess similarities and unanticipated differences with respect to the crystal packing of noninterlocked molecules. Trends in the rotaxane series correlate quantities related to crystal packing, molecular size, stoichiometry, and H-bonding. In accordance with the findings of Gavezzotti et al. for conventional molecular architectures, a principal component analysis (PCA) showed that three vectors related to the size, packing parameters, and stoichiometry are sufficient to describe the crystal properties of benzylic amide macrocycle-containing rotaxanes. When hydrogen bond-related quantities are included in a second PCA, they combine with the size and the stoichiometry vectors but not with packing-related parameters, indicating that the intramolecular "saturation" of the H-bonds (between the interlocked components) takes precedence over crystal assembly (i.e., intermolecular packing) in these systems. However, cluster analyses also suggest a major role for the energy of interaction between the macrocycle and its crystal environment. The identification of such a "privileged" interaction is of fundamental importance to the development of rotaxanes with in-crystal mobility of one or more of their interlocked components, a prerequisite for the exploitation of molecular level mechanical motion in the solid state. The set of trends found, together with the calculated energies, was used to propose guidelines for which benzylic amide macrocycle-containing rotaxanes are best suited to become building blocks for systems with mobile submolecular units in the crystalline phase. An experimental test of the predictive power of such guidelines was carried out using AFM on a rotaxane and its thread, identified by the study as a promising candidate for solid-state mobility. Intuitively, the rotaxane should be less mobile in the solid state since it has multiple sets of both hydrogen bond donors and acceptors that can form strong inter- and intramolecular H-bonds. Conversely, the thread has no hydrogen bond donors and cannot form such bonds. The AFM experiments, however, confirm the statistical analysis prediction that the rotaxane is considerably more mobile in the solid than the thread.

Shedding light on a mechanical event: Films of a polymer–rotaxane conjugate were cast on quartz slides, the films were covered with aluminum masks, and the unmasked areas were exposed to vapors of DMSO. The solvent induces a change in position of the macrocycle in the molecular shuttle that leads to “on” states of the rotaxane fluorescence in the unmasked areas (see image).