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This paper describes the synthesis of a cerium(IV)-based molecular gear composed of a thioether functionalized phthalocyanine anchoring ligand, and a helical naphthalocyanine rotating cogwheel functionalized with four carbazoles. The naphthalocyanine ligand 9 was obtained after eleven steps (overall yield of 0.2%) as a mixture of three geometrical isomers, two of which are chiral and exhibit high levels of steric hindrance, as shown by DFT calculations. Their attributions have been made using 1H-NMR based on their different symmetry groups. The ratio of isomers was also determined and the prochiral C4h naphthalocyanine shown to be the major compound (55%). Its heteroleptic complexation with cerium (IV) and the anchoring phthalocyanine ligand 10 gave the targeted molecular gear in a 16% yield.
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Phthalocyanines and their double-decker complexes are interesting in designing rotative molecular machines, which are crucial for the development of molecular motors and gears. This study explores the design and synthesis of three bulky phthalocyanine ligands functionalized at the α-positions with phenothiazine or carbazole fragments, aiming to investigate dynamic rotational motions in these sterically hindered molecular complexes. Homoleptic and heteroleptic double-decker complexes were synthesized through the complexation of these ligands with Ce(IV). Notably, CeIV(Pc2)2 and CeIV(Pc3)2, both homoleptic complexes, exhibited blocked rotational motions even at high temperatures. The heteroleptic CeIV(Pc)(Pc3) complex, designed to lower symmetry, demonstrated switchable rotation along the pseudo-C4 symmetry axis upon heating the solution. Variable-temperature 1H-NMR studies revealed distinct dynamic behaviors in these complexes. This study provides insights into the rotational dynamics of sterically hindered double-decker complexes, paving the way for their use in the field of rotative molecular machines.
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The "precursor approach" has proved particularly valuable for the preparation of insoluble and unstable π-conjugated polycyclic compounds (π-CPCs), which cannot be synthesized via in-solution organic chemistry, for their improved processing, as well as for their electronic investigation both at the material and single-molecule scales. This method relies on the synthesis and processing of soluble and stable direct precursors of the target π-CPCs, followed by their final conversion in situ, triggered by thermal activation, photoirradiation or redox control. Beside well-established reactions involving the elimination of carbon-based small molecules, i.e., retro-Diels-Alder and decarbonylation processes, the late-stage extrusion of chalcogen fragments has emerged as a highly promising synthetic tool to access a wider variety of π-conjugated polycyclic structures and thus to expand the potentialities of the "precursor approach" for further improvements of molecular materials' performances. This review gives an overview of synthetic strategies towards π-CPCs involving the ultimate elimination of chalcogen fragments upon thermal activation, photoirradiation and electron exchange.
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This paper reports the synthesis of ruthenium-based molecular gear prototypes composed of a brominated or non-brominated pentaphenylcyclopentadienyl ligand as an anchoring unit and a tripodal ligand with aryl-functionalized indazoles as a rotating cogwheel. Single crystal structures of the ruthenium complexes revealed that the appended aryl groups increase the apparent diameter of the cogwheel rendering them larger than the diameter of the anchoring units and consequently making them suitable for intermolecular gearing motions once the complexes will be adsorbed on a surface.
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We report the synthesis of conceptually new prototypes of molecular winches with the ultimate aim to investigate the work performed by a single ruthenium-based molecular motor anchored on a surface by probing its ability to pull a load upon electrically-driven directional rotation. According to a technomimetic design, the motor was embedded in a winch structure, with a long flexible polyethylene glycol chain terminated by an azide hook to connect a variety of molecular loads. The structure of the motor was first derivatized by means of two sequential cross-coupling reactions involving a penta(4-halogenophenyl)cyclopentadienyl hydrotris(indazolyl)borate ruthenium(II) precursor and the resulting benzylamine derivative was next exploited as key intermediate in the divergent synthesis of a family of nanowinch prototypes. A one-pot method involving sequential peptide coupling and Cu-catalyzed azide-alkyne cycloaddition was developed to yield four loaded nanowinches, with load fragments encompassing triptycene, fullerene and porphyrin moieties.
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Azidas , Rutênio , Alcinos , Ciclização , Reação de CicloadiçãoRESUMO
This review highlights the major efforts devoted to the development of molecular gears over the past 40â years, from pioneering covalent bis-triptycyl systems undergoing intramolecular correlated rotation in solution, to the most recent examples of gearing systems anchored on a surface, which allow intermolecular transmission of mechanical power. Emphasis is laid on the different strategies devised progressively to control the architectures of molecular bevel and spur gears, as intramolecular systems in solution or intermolecular systems on surfaces, while aiming at increased efficiency, complexity and functionality.
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RotaçãoRESUMO
A molecular motor that has been previously shown to rotate when fueled by electrons through a scanning tunneling microscope tip has been functionalized with a terarylene photochrome fragment on its rotating subunit. Photoisomerization has been performed under UV irradiation. Variable-temperature 1H NMR and UV-vis studies demonstrate the rotational motion and its braking action after photoisomerization. The braking action can be reversed by thermal heating. Once the rigid and planar closed form is obtained, the rotation is effectively slowed at lower temperature, making this new rotor a potential motor with an independent response to electrons and light.
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The photophysical properties of heteroleptic rotor-like Ru(ii) complexes containing both a cyclopentadienyl-type ligand and a hydrotris(indazolyl)borate chelating unit with a piano stool structure (Ar5L1-Ru-S1 and L3-Ru-S1) and their corresponding subunits have been investigated. The complexes show peculiar absorption features when compared with their related ligands or fragments. L3-Ru-S1 was found to be non-emissive, while Ar5L1-Ru-S1 showed a weak emission with a quantum yield of 0.27%. With the help of DFT calculations, we demonstrate that the new absorption features can be attributed to ruthenium-based charge transfer transitions which involve the π* orbitals of the phenyl substituents of the cyclopentadienyl ligand.
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Invited for the cover of this issue is Gwénaël Rapenne and co-workers from CEMES-CNRS at University Paul Sabatier, Toulouse, France and from NAIST, Nara, Japan. The image depicts an artistic representation of a nanocar race. Read the full text of the article at 10.1002/chem.202001999.
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The design and synthesis of a new family of nanocars is reported. To control their motion, we integrated a dipole which can be tuned thanks to strategic donor and acceptor substituents at the 5- and 15-positions of the porphyrin backbone. The two other meso positions are substituted with ethynyltriptycene moieties which are known to act as wheels. Full characterization of nine nanocars is presented as well as the electrochemistry of these push-pull molecules. DFT calculations allowed us to evaluate the magnitude of the dipoles and to understand the electrochemical behavior and how it is affected by the electron donating and accepting groups present. An X-ray crystal structure of one nanocar has also been obtained.
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The design and synthesis of two families of molecular-gear prototypes is reported, with the aim of assembling them into trains of gears on a surface and ultimately achieving controlled intermolecular gearing motion. These piano-stool ruthenium complexes incorporate a hydrotris(indazolyl)borate moiety as tripodal rotation axle and a pentaarylcyclopentadienyl ligand as star-shaped cogwheel, equipped with five teeth ranging from pseudo-1D aryl groups to large planar 2D paddles. A divergent synthetic approach was followed, starting from a pentakis(p-bromophenyl)cyclopentadienyl ruthenium(II) complex as key precursor or from its iodinated counterpart, obtained by copper-catalyzed aromatic Br/I exchange. Subsequent fivefold cross-coupling reactions with various partners allowed high structural diversity to be reached and yielded molecular-gear prototypes with aryl-, carbazole-, BODIPY- and porphyrin-derived teeth of increasing size and length.
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Terarylene frameworks containing benzothiazole as a photoprecursor of hydride donors are presented. We here report on two new scaffolds along with their photoreactivity in solution. Through use of selected external oxidants, the photogeneration of hydride donors is monitored using UV-visible, NMR, and TEM methods. As a proof-of-concept, photogeneration of hydride in the presence of Ag+ gave rise to the formation of Ag nanoparticles.
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This review article presents our accomplished work on the synthesis of molecular triptycene wheels and their introduction into nanovehicles such as wheelbarrows and nanocars, equipped with two and four wheels, respectively. The architecture of nanovehicles is based on polycyclic aromatic hydrocarbons, which provide a potential cargo zone. Our strategy allowed us to obtain planar or curved nanocars, exhibiting different mobilities on metallic surfaces. Our curved nanocar participated in the first nanocar race organized in Toulouse (France) on 28 and 29 April 2017.
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Técnicas de Química Sintética , Nanoestruturas/química , França , Modelos Químicos , Modelos Moleculares , Estrutura Molecular , Nanoestruturas/ultraestruturaRESUMO
In the last decade, many nanomachines with controlled molecular motions have been studied, mainly on metallic surfaces, which are easy to obtain very clean, and are stable over months. However, the studies of mechanical properties of nanomachines are mainly performed at very low temperatures, usually between 5 and 80â K, which prevents any kind of applications. In this Minireview, we will present our strategy to operate at higher temperatures, in particular through the use of semiconducting silicon surfaces. We also review our best achievements in the field through some examples of rotating molecular machines that have been designed, synthesized, and studied in our groups. On metallic surfaces, the nanovehicles are molecules with two or four triptycenes as wheels and the molecular motor is built around a ruthenium organometallic center with a piano-stool geometry and peripheric ferrocenyl groups. On semiconducting silicon surfaces, vehicles are also made from triptycene fragments and the rotor is a pentaphenylbenzene molecule.
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In this paper, we present a novel concept for "smarter" photolabile organic compounds combining not one but two caged functions. As proof of principle, this diarylethene-based compound possesses two inhibited chemical groups (OMe and OAc) and its efficient release in different solvents is reported. In low- to medium-polarity media, both MeOH and AcOH are released, with a slight preferential uncaging of AcOH except in 1,4-dioxane, where MeOH is preferentially released. In contrast, DMSO or DMF render AcOH release strongly dominating. DFT calculations of the corresponding photoreactive conformations not only afford strong support to the observed release of MeOH and AcOH but also qualitatively explain the preferential release of acid in terms of dispersive noncovalent interactions. Finally, mechanistic aspects are discussed on the bases of the spectroscopic observations and of the TD-DFT calculations.
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This paper describes the synthesis of triptycene-based building blocks that are able to interact through hydrogen bonds to form one-dimensional self-assembled motifs on surfaces. We designed 9,10-diethynyltriptycene derivatives functionalized at the ethynyl end groups by a variety of hydrogen-bonding groups for homomolecular recognition and complementary building blocks for heteromolecular recognition. We also present the synthesis of bis- and trisethynyltriptycenes with terminal alkyne functional groups available for on-surface azide-alkyne cycloaddition reaction to expand the potential of the triptycene building block.
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In the last decade many molecular machines with controlled molecular motions have been synthesized. In the present review chapter we will present and discuss our contribution to the field, in particular through some examples of rotating molecular machines that have been designed, synthesized, and studied in our group. After starting by explaining why it is so important to study such machines as single molecules, we will focus on two families of molecular machines, nanovehicles and molecular motors. The first members of the nanovehicle family are molecules with two triptycenes as wheels: the axle and the wheelbarrow. Then come the four-wheel nanocars. Since triptycene wheels are not very mobile on metallic surfaces, alternative wheels with a bowl-shape structure have also been synthesized and studied on surfaces. The molecular motors are built around ruthenium organometallic centers and have a piano-stool geometry with peripheric ferrocenyl groups.
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There is a great demand for the technology of molecular delivery into living cells using nanocarriers to realise molecular therapies such as gene delivery and drug delivery systems. Lipid-based nanocarriers offer several advantages for molecular delivery in biological systems, such as easy preparation, high encapsulation efficiency of water-insoluble drug molecules, and excellent biocompatibility. In this paper, we first report the interaction of lipid nanodiscs spontaneously formed by the complexation of an amphiphilic polymethacrylate derivative and phospholipid with intact cells. We evaluated the internalisation of polymethacrylate-based lipid nanodiscs by intact HeLa cells and applied them to the delivery of paclitaxel (PTX), an anticancer drug. The lipid nanodisc showed excellent uptake efficiency compared to conventional liposomes at a concentration where nanodiscs do not show cytotoxicity. In addition, the nanodisc encapsulating PTX showed significantly higher anticancer activity than PTX-loaded liposomes against HeLa cells, reflecting their excellent activity in delivering payloads to intact cells. This study demonstrated the potential of a polymethacrylate-based lipid nanodisc as a novel nanocarrier for molecular delivery to intact cells.
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The interplay between the molecular shape and the intermolecular interaction plays a decisive role in self-assembled structures. Recently, inherent randomness of low ordered assemblies, resulting from lack of short- and long-range periodicities, has attracted significant attention due to the unique structural, electronic, and mechanical properties. Here, we present procrystalline self-assemblies of pentaphenyl cyclopentadienyl derivatives on Ag(111) and Au(111) with scanning tunneling microscopy, operating at 4.3 K under ultrahigh vacuum conditions. Two examples, using 5-fold symmetric molecules substituted with methyl or fluorine groups, show that weak interactions, such as π-π stacking, CH-π interactions, and CH···F hydrogen bonding, play a pivotal role in formation of the procrystalline assembly. Our results may give insights into the intricate relationship between the molecular shape and the intermolecular interaction in the formation of non-crystalline assemblies.
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While hexaphenylsilacyclopentadiene (hexaphenylsilole) is viewed as an archetypal Aggregation-Induced Emission (AIE) luminogen, its isostructural hydrocarbon surrogate hexaphenylcyclopentadiene has strikingly never been investigated in this context, most probably due to a lack of synthetic availability. Herein, we report a straightforward synthesis of hexaphenylcyclopentadiene, via the direct perarylation of cyclopentadiene upon copper(i) catalysis under microwave activation, with the formation of six new C-C bonds in a single synthetic operation. Using zirconocene dichloride as a convenient source of cyclopentadiene and a variety of aryl iodides as coupling partners, this copper-catalysed cross-coupling reaction gave rise to a series of unprecedented hexaarylcyclopentadienes. The latter are direct precursors of extended π-conjugated polycyclic compounds, and their cyclodehydrogenation under Scholl reaction conditions yielded helicenic 17,17-diarylcyclopenta[l,l']diphenanthrenes. These structurally complex polyannelated fluorene derivatives can now be prepared in only two synthetic steps from cyclopentadiene.