Peter Rechsteiner

Bio: Peter Rechsteiner is an academic researcher from University of Bern. The author has contributed to research in topics: Polarity (physics) & Paramagnetism. The author has an hindex of 7, co-authored 11 publications receiving 234 citations. Previous affiliations of Peter Rechsteiner include University of Münster.

Phase-sensitive second harmonic microscopy reveals bipolar twinning of Markov-type molecular crystals

Abstract: Phase-sensitive second harmonic microscopy (PS-SHGM) opens up the possibility of imaging the bipolar state of Markov-type organic supramolecular crystals. During the cocrystallization of dipolar guest and nonpolar host compounds, channel-type inclusion compounds form crystals composed of adjacent macrodomains featuring opposite polarities. Through a comparison with crystals of known absolute polarity, the application of PS-SHGM allows a fast noncontact mapping of the domain structure and a determination of the absolute polarity of thin organic and other nonlinear opical crystals.

Probing magnetic exchange interactions in molecular magnets: an inclusion compound of a dithiadiazolyl radical

Abstract: Co-sublimation of the dithiadiazolyl radical, p-NCC 6 H 4 CNSSN 2 with the inclusion-forming host compound perhydrotriphenylene (PHTP) leads to trichroic crystals of the host-guest complex [PHTP-2]. Molecules of 2 are linked through a CN‥S interaction (ca. 3.03 A) to form polar chains within the channels of the PHTP host lattice. The host-guest ratio is approximately 5:1. Pyroelectric and non-linear optic responses indicate that crystals of [PHTP-2] are macroscopically polar. A combination of variable temperature solid state EPR spectroscopy and magnetic susceptibility measurements are used to probe the electronic properties of [PHTP-2]; whilst [PHTP-2] is paramagnetic, no exchange coupling between neighbouring molecules of 2 within the channels could be established. The implications of these results on the magnetic exchange pathway of the weak ferromagnet, β-p-NCC 6 F 4 CNSSN β-1, are discussed.

Statistically Controlled Self‐Assembly of Polar Molecular Crystals

Abstract: 858. [3] F. S. Spano, S. Mukamel, Phys. Rev. 1989, A 40, 5783. [4] H. Ishihara, K. Cho, Phys. Rev. 1990, B42, 1724. [5] D. Avnir, D. Levy, R. Reisfeld, J. Phys. Chem. 1984, 88, 5957. [6] D. Avnir, V. R. Kaufman, R. Reisfeld, J. Non-Cryst. Solids 1985, 74, 395. [7] C. Sanchez, F. Ribot, New J. Chem. 1994, 18, 1007. [8] Sol-gel Science (Eds: C. J. Brinker, G. W. Scherer) Academic Press, New York 1990. [9] G. S. He, J. Zieba, J. T. Bradshaw, Kazmierczak, P. N. Prasad, Opt. Comm. 1993, 104, 102. [10] V. S. Gorelik, A. D. Kudryavtseva, A. I. Sokolovskaya, N. V. Chernega, Opt. Spectrosc. 1996, 81, 369. [11] J. POcaut, J. P. LOvy, R. Masse, J. Mater. Chem. 1993, 3, 999. [12] M. Bienfait, R. Kern, Bull. Soc. Franc. MinOr. Crist. 1964, 87, 604. [13] F. Lefaucheux, M. C. Robert, in Crystal Growth in Gels. Handbook of Crystal Growth, (Ed: D. T. J. Hurle), North-Holland, Amsterdam 1994, 2b, p. 1271. [14] V. K. LaMer, R. H. Dinegar, J. Am. Chem. Soc. 1950, 17, 4847.

Phase-sensitive second-harmonic microscopy reveals polarity of topologically centrosymmetric molecular crystals

Abstract: Phase-sensitive second-harmonic microscopy is applied to reveal grow-in polarity in topologically centrosymmetric crystals of 4-chloro-4′-nitrostilben. As predicted by the Markow model of layer-by-layer polarity formation, growth along + and −b-direction in P21/c is producing optical nonlinearity in both sectors associated with the b axis. Present experiments show that formation of a pyroelectric symmetry class is a stochastic property of molecular crystals grown from dipolar compounds and near to thermodynamic equilibrium.

Metric Engineering of Soft Molecular Host Frameworks

Abstract: The self-assembly and solid-state structures of host-guest inclusion compounds with lamellar architectures based on a common building block, a resilient hydrogen-bonded sheet consisting of guanidinium ions and sulfonate moieties of organodisulfonate "pillars", are described. The pillars connect adjacent sheets to generate galleries with molecular-scale cavities occupied by guest molecules. The size, shape, and physicochemical character of the inclusion cavities can be systematically adjusted by interchanging framework components while maintaining the lamellar architecture, enabling prediction and control of crystal lattice metrics with a precision that is unusual for "crystal engineering". The reliability of the lamellar architecture is a direct consequence of conformational flexibility exhibited by these hosts that, unlike rigid systems, enables them to achieve optimal packing with guest molecules. The adaptability of these hosts is further reflected by an architectural isomerism that is driven by guest templating during assembly of the inclusion compounds. Host frameworks constructed with various pillars display metric interdependences among specific structural features that reveal a common mechanism by which these soft frameworks adapt to different guests. This unique feature facilitates structure prediction and provides guidance for the design of inclusion compounds based on these hosts.

Supramolecular Synthons and Pattern Recognition

Abstract: The aims of crystal engineering are the understanding of intermolecular interactions and their application in the design of crystal structures with specific architectures and properties. In general, all types of crystal structures may be considered but this article is limited to organic molecular solids. Because of the molecular basis of organic chemistry, the obvious question arises as to whether there are simple connections between the structures of molecules and the crystals that they form. Answers to such questions may be found through a better and more comprehensive understanding of the interactions that control crystal packing. These interactions include strong and weak hydrogen bonds. Patterns of interactions, such as would be useful in a predictive sense, can be obtained by manual inspection or more rigorously with the use of crystallographic databases. Such patterns are termed supramolecular synthons and they depict the various ways in which complementary portions of molecules approach one another. The identification of synthons is then a key step in the design and analysis of crystal structures. Such ideas are also important in the understanding of phenomena such as biological recognition and drug-enzyme binding. Pattern identification also leads to the possibility of comparison of crystal structures. The use of the supramolecular synthon concept facilitates such efforts and in this regard it may be mentioned that synthons combine topological characteristics with chemical information, thereby offering a simplification that is optimal to drawing such comparisons.

Three-dimensional harmonic holographic microcopy using nanoparticles as probes for cell imaging

Abstract: Luminescent markers play a key role in imaging techniques for life science since they provide a contrast mechanism between signal and background. We describe a new type of marker using second harmonic generation (SHG) from noncentrosymmetric BaTiO_3 nanocrystals. These nanoparticles are attractive due to their stable, non-saturating and coherent signal with a femtosecond-scale response time and broad flexibility in the choice of excitation wavelength. We obtained monodispersed BaTiO_3 nanoparticles in colloidal suspensions by coating the particle surface with amine groups. We characterized the SHG efficiency of 90-nm BaTiO_3 particles experimentally and theoretically. Moreover, we use the coherent SHG signal from BaTiO_3 nanoparticles for three-dimensional (3D) imaging without scanning. We built a harmonic holographic (H^2) microscope which records digital holograms at the second harmonic frequency. For the first time, high-resolution 3D distributions of these SHG markers in mammalian cells are successfully captured and interpreted by the H^2 microscope.

Current Opinion in Solid State and Materials Science

Abstract: The complexity of materials aging may be seen as a result of the interplay between several activation processes operating on multiple spatial and temporal scales. Though the disciplines involved may seem disparate at first, material aging fundamentally could be linked by the same set of underlying activations and responses of the system. We examine how recent studies of shear-induced deformation and rheological flow initiated in the soft-matter community can be leveraged to probe the mechanisms of radiation damage in nuclear materials. Bridging these two traditionally separate areas of research demonstrates the emerging notions of mesoscale science as a research frontier concerned with linking macroscale behavior to microscale processes in driven systems. We suggest the combining of microstructuresensitive measurements with fundamental theories and mechanism-specific simulations is essential to addressing metastable materials responses of strongly activated states.