Application of Structural Principles to the Design of Triptycene-Based Molecular Gears with Parallel Axes

This perspective discusses the important aspects of the design of molecular gear systems based on triptycene. Molecular systems are categorized into three classes according to the orientation of the gear axes: i) bent (bevel gears), ii) linear, and ii) parallel (spur gears). To date, no examples of molecular gears in which the axes of rotation lie in parallel have been reported; correspondingly, the bulk of this report focuses on the factors one must evaluate to construct such systems

Conformations of large macrocycles and ring-in-ring complexes

This work was supported by the Swiss National Science Foundation.A kinetically directed, stepwise approach towards molecular Borromean links enabled the isolation and structural characterization of synthetic intermediates along the way. Here we report the synthesis and crystal structures of three flexible macrocyclic intermediates and a new ring-in-ring complex, anchored together through ruthenium(ii) centers, which contains open terpyridine caps in the inner Ring II. Terpyridines circumvent the conformational cis/trans limitations of bipyridines and the new ring-in-ring complex forms tetrametallic complexes with Zn(ii), Pt(ii) and Ru(iii) metal ions. Analysis of the four macrocyclic structures provides a good foundation for the conformational flexibility in these complexes and demonstrates the robust applicability of the terpyridine design elements towards the engineered synthesis of ring-in-ring topologies.Publisher PDFPeer reviewe

Topical Developments in High-Field Dynamic Nuclear Polarization

We report our recent efforts directed at improving high-field dynamic nuclear polarization (DNP) experiments. We investigated a series of thiourea nitroxide radicals and the associated DNP enhancements ranging from ε=25 to 82, which demonstrate the impact of molecular structure on performance. We directly polarized low-gamma nuclei, including [superscript 13]C, [superscript 2]H, and [superscript 17]O, by the cross effect mechanism using trityl radicals as a polarization agent. We discuss a variety of sample preparation techniques for DNP with emphasis on the benefits of methods that do not use a glass-forming cryoprotecting matrix. Lastly, we describe a corrugated waveguide for use in a 700 MHz/460 GHz DNP system that improves microwave delivery and increases enhancements up to 50%.National Institutes of Health (U.S.) (Grant EB002804)National Institutes of Health (U.S.) (Grant EB003151)National Institutes of Health (U.S.) (Grant EB002026)National Institutes of Health (U.S.) (Grant EB001960)National Institutes of Health (U.S.) (Grant EB001035)National Institutes of Health (U.S.) (Grant EB001965)National Institutes of Health (U.S.) (Grant EB004866)National Institute of General Medical Sciences (U.S.) (Grant GM095843)Natural Sciences and Engineering Research Council of Canada (Postdoctoral Fellowship

Towards the molecular Borromean link with three unequal rings: double-threaded ruthenium(ii) ring-in-ring complexes

This study describes synthetic efforts towards the molecular Borromean link consisting of three unequal rings. The design and strategy involve step by step construction of a ruthenium(II) templated ring-in-ring complex doubly threaded with endocyclic ligands ready for the macrocyclization. The control over the topology is achieved by using specially designed directional building blocks based on 2,2’:6’,2’’-terpyridine. Preliminary macrocyclization attempts utilizing the copper-mediated Eglington reaction provide the mass spectrometric evidence consistent with the ruthenium(II) complex of the molecular Borromean link

Synthesis and Properties of the 5,10,15-Trimesityltruxen-5-yl Radical

The synthesis of a long-lived, truxene-based radical that is highly delocalized and exhibits a narrow EPR absorption is reported. The radical is stable for multiple hours in a solution exposed to air and remains for months in the solid state under inert gas. Characterization and properties are discussed

Molecular Spur Gears Comprising Triptycene Rotators and Bibenzimidazole-Based Stators

Dynamic gearing of molecular spur gears, the most common type of mechanical gear, is elucidated. Molecular design and conformational analysis show that derivatives of 4,4-bis­(triptycen-9-ylethynyl)­bibenzimidazole represent suitable constructs to investigate gearing behavior of collateral triptycene (Tp) groups. To test this design, DFT calculations (B97-D/Def2-TZVP) were employed and the results suggest that these molecules undergo geared rotation preferentially to gear slippage. Synthesis of derivatives was carried out, providing a series of molecular spur gears, including the first desymmetrized spur gear molecules, which were subsequently subjected to stereochemical analysis

Synthesis and Electronic Properties of Fluoreno[2,1‑<i>a</i>]fluorenedione and Fluoreno[1,2‑<i>a</i>]fluorenedione

The [2,1-<i>a</i>]- and [1,2-<i>a</i>]-isomers of fluorenofluorenedione have been synthesized via intramolecular Friedel–Crafts acylations. DFT calculations indicate that the [1,2-<i>a</i>]-isomer adopts a twisted, helical <i>C</i>₂-symmetric structure and that its protonated form is the thermodynamic product of the Friedel–Crafts acylation in hot sulfuric acid. Absorption spectroscopy and cyclic voltammetry measurements provide experimental estimations of frontier molecular orbital energy levels, which are reported and discussed

Synthesis, X-ray crystal structures, and computational studies of 1,1’-bridged 4,4’-diaryl-2,2’-bibenzimidazoles: novel building blocks for supramolecular structures

A series of C-shaped, 1,1'-alkyl-bridged 4,4'-diaryl-2,2'-bibenzimidazoles has been synthesized. The crystal structures of these compounds have been determined and packing diagrams demonstrate that these molecules either form linear intercalated molecular chains or include solvent molecules in the solid state. Crystal structures are compared to computational structures determined using density functional theory, with the BMK/DZV(2d,p) method. The C-shaped or tweezer-like geometry enables them to act as building blocks for supramolecular architectures