Linear and Unanticipated Second-Order Nonlinear Optical Properties of Benzylic Amide [2]Catenane Thin Films: Evidence of Partial Rotation of the Interlocked Molecular Rings in the Solid State

Abstract

make the hydrophobic inner micronetwork water soluble. Experiments directed at the synthesis of hollow micronetworks, which exhibit two shells of different polarity, are currently in progress. ExperimentalThe micronetworks were prepared, by the base catalyzed procedure, as described previously [17±19]. For the preparation of the hollow spheres (sample HK70) the surfactant benzethonium chloride (3.0 g, Aldrich, M = 448 g mol ±1 ) was dissolved in water (125.0 g) containing NaOH (300 mg, 10 wt.-%). Dimethoxydimethylsilane (11.0 g) was added, with vigorous stirring, at room temperature over 1 h. After stirring for a further 12 h the silanol end groups of the PDMS chains were endcapped using methoxytrimethylsilane (100 mg).A mixture of methytrimethoxysilane (10.0 g) and dimethoxydimethylsilane (4.0 g) was added over 1 h and the resultant mixture stirred for a further 5 h. In order to prevent the remaining reactive silanol groups from undergoing interparticle condensation, the endcapping procedure was repeated twice more, with methoxytrimethylsilane (2.5 g), before the removal of the surfactant. The dispersion was destabilized by the addition of methanol and centrifuged. The precipitate was washed three times with methanol, to remove the surfactant, and then dissolved in toluene.At this stage the endcapping of the silanol groups is not yet quantitative. Therefore, hexamethyldisilazane (5.0 g, Wacker-Chemie GmbH, M = 164 g mol ±1 ) was added to the toluene solution and the reaction mixture was stirred, at room temperature, for 12 h. The micronetworks were again precipitated with methanol, centrifuged and dried. A colorless, sticky residue was obtained.In order to remove the linear PDMS chains from the core of the micronetworks the residue was dissolved in THF and ultrafiltered (Millipore cellulose 30 000) 4±5 times. The solvent was evaporated, the solid residue dissolved in benzene, and freeze-dried overnight. Yield: 3.5 g of a colorless powder. Sample VK70 was prepared as described previously [19].Static and dynamic light scattering measurements were performed with standard equipment utilizing an ALV SP-86 goniometer, an ALV 3000 correlator, and a Spectra Physics 2060-11s Krypton ion laser light source (647.1 nm wavelength, 500 mW power) or an ALV SP-125 goniometer, an ALV 5000 correlator, and a Spectra Physics 2060-04s Argon ion laser light source (514.0 nm, 250 mW). Correlation functions were analyzed by the method of cumulants.All samples described here exhibited normalized second cumulants of m 2 < 0.05, and no angular dependence of the diffusion coefficients was observed. Before conducting any measurements the toluene solution (0.2 g L ±1 < c < 1.5 g L ±1 ) was filtered through a 0.2 mm Millex FGN Teflon filter.The refractive index increments were measured with a special, homebuilt, interferometer utilizing a small laser (Polytec, wavelength 543 nm or uniphase, 632 nm) [20].Atomic force micrographs were recorded with a Nanoscope III instrument (Digital Instruments, St. Barbara, CA) operating in tapping mode at a ...

Synthetic Molecular Motors and Mechanical Machines

“…The problem of achieving controlled movement within surface‐mounted or solid‐state interlocked molecules is more demanding, however, with both components constrained to the solid support or interface at all times. The first evidence for externally stimulated submolecular motions of a catenane in the solid state was observed when a vacuum‐evaporated thin film of a benzylic amide [2]catenane was subjected to oscillating electric fields and produced an unexpected second‐order nonlinear optical effect 406. 407 In earlier studies, thin films of a metal‐templated polyrotaxane were deposited on a carbon electrode by electropolymerization of pyrrole rings 408.…”

Au10(SG)10: A Chiral Gold Catenane Nanocluster with Zero Confined Electrons. Optical Properties and First-Principles Theoretical Analysis

“…[25]Also catenane structures were found to present large optical nonlinearites. [26][27][28] The asymmetry in the ground and excited states topology plays an essential role in the observed nonlinear optical properties. A high charge transfer character may be observed for catenanes, where charge transfers from one part of the molecule (macrocycle, thread) to the other causes large asymmetries in the molecule and large changes of the dipolar moment in the ground and the excited states.…”

“…Mechanically interlocked molecules such as catenanes present remarkable structural and chiroptical properties. , The chirality of catenanes can originate either from the presence of chiral elements or from directionality in both rings . Also catenane structures were found to present large optical nonlinearites. − The asymmetry in the ground- and excited-state topology plays an essential role in the observed NLO properties. A high charge transfer character may be observed for catenanes, where charge transfers from one part of the molecule (macrocycle, thread) to the other cause large asymmetries in the molecule and large changes of the dipolar moment in the ground and the excited states.…”

Synthetische molekulare Motoren und mechanische Maschinen

“…Die ersten Hinweise auf extern stimulierte submolekulare Bewegungen eines Catenans im Festkörper wurden erhalten, als ein im Vakuum abgeschiedener dünner Film eines Benzylamid‐[2]Catenans oszillierenden elektrischen Feldern ausgesetzt wurde. Dabei trat ein nichtlinearer optischer Effekt zweiter Ordnung auf 406. 407 Dünne Filme eines Polyrotaxans mit Metalltemplat waren zuvor schon durch die Elektropolymerisation von Pyrrol auf Kohleelektroden hergestellt worden 408.…”