Two-stage directed self-assembly of a cyclic [3]catenane.

Interlocked molecules possess properties and functions that depend upon their intricate connectivity. In addition to the topologically trivial rotaxanes, whose structures may be captured by a planar graph, the topologically non-trivial knots and catenanes represent some of chemistry's most challenging synthetic targets because of the three-dimensional assembly necessary for their construction. Here we report the synthesis of a cyclic [3]catenane, which consists of three mutually interpenetrating rings, via an unusual synthetic route. Five distinct building blocks self-assemble into a heteroleptic triangular framework composed of two joined Fe(II)3L3 circular helicates. Subcomponent exchange then enables specific points in the framework to be linked together to generate the cyclic [3]catenane product. Our method represents an advance both in the intricacy of the metal-templated self-assembly procedure and in the use of selective imine exchange to generate a topologically complex product.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) and a Marie Curie fellowship for J.J.H. (ITN-2010–264645). The authors thank the Diamond Light Source (UK) for synchrotron beamtime on I19 (MT7984 and MT8464).This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/nchem.220

Discovering privileged topologies of molecular knots with self-assembling models

Despite the several available strategies to build complex supramolecular constructs, only a handful of different molecular knots have been synthesised so far. Here, in response to the quest for further designable topologies, we use Monte Carlo sampling and molecular dynamics simulations, informed by general principles of supramolecular assembly, as a discovery tool for thermodynamically and kinetically accessible knot types made of helical templates. By combining this approach with the exhaustive enumeration of molecular braiding patterns applicable to more general template geometries, we find that only few selected shapes have the closed, symmetric and quasi-planar character typical of synthetic knots. The corresponding collection of admissible topologies is extremely restricted. It covers all known molecular knots but it especially includes a limited set of novel complex ones that have not yet been obtained experimentally, such as 10124 and 15n41185, making them privileged targets for future self-assembling experiments

An amphiphilic C-60 derivative with a tris(2,2 '-bipyridine)ruthenium(II) polar head group: synthesis and incorporation in Langmuir films

An amphiphilic C60 derivative with a tris(2,2′-bipyridine)ruthenium(II) polar head group has been prepared. The Langmuir film of this compound has been characterized by its surface pressure versus molecular area (Π/A) isotherm and Brewster angle microscopy (BAM) observations

Homoleptic and heteroleptic Ru-II complexes with extended phenanthroline-based ligands

Four Ru-II complexes of general formula [Ru(PT)(3)](2+), [Ru(NT)(3)](2+), [Ru(PT)(bpy)(2)](2+), and [Ru(NT)(bpy)(2)](2+), where PT = 10,13-bis((triisopropylsilyl)ethynyl)dipyrido[3,2-a:2',3'-c]phenazine, NT = 10,15-bis((triisopropylsilyl)ethynyl)benzo[i]dipyrido[3,2-a:2',3'-c]phenazine and bpy = 2,2'-bipyridine have been synthesized. Their electrochemical and photophysical properties have been studied, with the aid of DFF and TD-DFT theoretical methods. The extended phenanthroline ligand PT exhibits two reduction processes at -0.98 and -1.55 (versus SCE) and no clearly detectable oxidation processes; the more extended analogue NT is substantially easier to reduce by about 300 mV. In the four complexes, the two first reduction processes are centered on the extended phenanthroline ligands, and, according to DFT calculations, also oxidations are likely to be located on such moieties. PT and NT exhibit green-yellow fluorescence at 298 and 77K with photoluminescence quantum yields of 3.4% and 62.1%, respectively, at room temperature. At 77 K, a strong and long-lived phosphorescence is detected only for PT (lambda(max) = 658 nm, tau = 29 ms). In oxygen-free solution at 298 K [Ru(PT)(3)](2+) and [Ru(PT)(bpy)(2)](2+) exhibit a very weak emission band with lambda(max) about 700 nm, which extends towards the near infrared region and is unambiguously attributed to emission from the lowest triplet level centered on the PT ligand; its emission intensity is strongly enhanced at 77 K where lifetimes of 724 and 767 ns are measured for [Ru(PT)(3)](2+) and [Ru(PT)(bpy)(2)](2+), respectively. The two complexes with the NT ligand show no triplet emission as observed for the PT analogues, but only a faint fluorescence signal attributable to negligible amounts of free ligand in solution. Photophysical data are fully rationalized with DFF methods, which always predict that the lowest triplet excited state is centered on the extended phenanthroline ligand in all of the investigated R-II complexes. The estimated energy of the lowest triplet level of the PT-based compounds is in good agreement with the experimental value determined from the phosphorescence spectra. Moreover, the theoretical model rationalizes the lack of phosphorescence for the NT series, because the lowest triplet is estimated to be at 0.97 eV above the ground state (approximate to 1280 nm), where non-radiative deactivations prevail. (C) 2014 Elsevier Ltd. All rights reserved