1,720,973 research outputs found
Toward the control of the creation of mixed monolayers on glassy carbon surfaces by amine oxidation
No full textA versatile and simple methodology for the creation of mixed monolayers on glassy carbon (GC) surfaces was developed, using an osmium–bipyridyl complex and anthraquinone as model redox probes. The work consisted in the electrochemical grafting on GC of a mixture of mono-protected diamine linkers in varying ratios which, after attachment to the surface, allowed orthogonal deprotection. After optimisation of the deprotection conditions, it was possible to remove one of the protecting groups selectively, couple a suitable osmium complex and cap the residual free amines. The removal of the second protecting group allowed the coupling of anthraquinone. The characterisation of the resulting surfaces by cyclic voltammetry showed the variation of the surface coverage of the two redox centres in relation to the initial ratio of the linking amine in solution
An Azobenzene-Bipyridinium Derivative as a Component in the Construction of Photoresponsive Pseudorotaxanes
No full textWe describe the synthesis and characterization of a bipyridinium derivative conjugated with two azobenzene groups (Azo 2 Bpy 2+). The design maintains the ability of the photoswitches to undergo E to Z isomerization upon irradiation to generate a mixture of EE, EZ and ZZ isomers. Moreover, Azo 2 Bpy 2+ is able to undergo self-Assembly with dibenzo[24]crown-8 ether to generate [3]-pseudorotaxanes, driven by the strong cooperative effects, for all its geometric isomers
Defying chemical equilibrium with light
Full text linkChemical systems capable of exploiting an energy source to function away from thermodynamic equilibrium are a hallmark of the biological world. The design and operation of artificial versions of such systems constitute a stimulating and highly challenging scientific goal with considerable expectations for application in synthetic chemistry, catalysis, materials science, energy conversion, and medical therapy. In this context, supplying energy in the form of photons has several elements of conceptual interest and practical advantage. Here we present the progress of research over the past 5 years on artificial molecular-based systems that can use light energy to operate away from equilibrium – an emerging field that has just begun to express its innovative potential
Direct synthetic routes to functionalised crown ethers
Full text linkCrown ethers are macrocyclic hosts that can complex a wide range of inorganic and organic cations as well as neutral guest species. Their widespread utilization in several areas of fundamental and applied chemistry strongly relies on strategies for their functionalisation, in order to obtain compounds that could carry out multiple functions and could be incorporated in sophisticated systems. Although functionalised crown ethers are normally synthesised by templated macrocyclisation using appropriately substituted starting materials, the direct addition of functional groups onto a pre-formed macrocyclic framework is a valuable yet underexplored alternative. Here we review the methodologies for the direct functionalisation of aliphatic and aromatic crown ethers sporadically reported in the literature over a period of four decades. The general approach for the introduction of moieties on aliphatic crown ethers involves a radical mediated cross dehydrogenative coupling initiated either by photochemical or thermal/chemical activation, while aromatic crown ethers are commonly derivatised via electrophilic aromatic substitution. Direct functionalization routes can reduce synthetic effort, allow the later modification of crown ether-based architectures, and disclose new ways to exploit these versatile macrocycles in contemporary supramolecular science and technology
Light‐Responsive (Supra)Molecular Architectures: Recent Advances
Full text linkThe development and investigation of (supra)molecular-based architectures characterized by light-activated functionalities is a highly relevant topic of chemical research. The interest on photo-controlled systems arises not only from their potential applications in different fields of technology but also from their scientific significance related to the understanding of light–matter interactions at the nanoscale. Indeed, light is a peculiar and unique tool as it can be conveniently applied to supply the energy required to affect and operate a system and, at the same time, to probe its state and investigate its transformations. Some basic aspects of light-induced processes in (supra) molecular architectures are discussed here in the frame of their use to implement novel functionalities in nanostructured systems and materials. In this perspective, a few recent examples from our own work will be illustrated which are meant to provide an overview of the current directions in this highly cross-disciplinary field of research
Directional Ring Translocation in a pH‐ and Redox‐Driven Tristable [2]Rotaxane
Full text linkWe describe the synthesis and characterization of a [2]rotaxane comprising a dibenzo-24-crown-8 (DB24C8) macrocyclic component and a thread containing three recognition sites: ammonium (AmH+), bipyridinium (Bpy2+) and triazolium (Trz+). AmH+ and Bpy2+ are responsive to fully orthogonal stimuli, pH and electrochemical, which allows to precisely control the directional translation of the macrocycle along the axle. A better understanding of the processes driving the operation of the system was obtained thanks to an in-depth thermodynamic characterization. Orthogonal stimuli responsive tristable rotaxanes represent the starting point for the creation of linear motors and the development of molecular logic gates
Chemical On/Off Switching of Mechanically Planar Chirality and Chiral Anion Recognition in a [2]Rotaxane Molecular Shuttle
Full text linkWe exploit a reversible acid-base triggered molecular shuttling process to switch an appropriately designed rotaxane between prochiral and mechanically planar chiral forms. The mechanically planar enantiomers and their interconversion, arising from ring shuttling, have been characterized by NMR spectroscopy. We also show that the supramolecular interaction of the positively charged rotaxane with optically active anions causes an imbalance in the population of the two enantiomeric co-conformations. This result represents an unprecedented example of chiral molecular recognition and can disclose innovative approaches to enantioselective sensing and catalysis
Solution and solid state photochromism in a family of shape persistent azobenzene tetramers functionalized with alkyloxy substituents
No full textShape-persistent azobenzene tetramers functionalized at the periphery with alkyloxy substituents of different lengths have been synthesized and their photochemical behaviour has been investigated. Efficient E → Z photoisomerization of the azobenzene units takes place both in solution and in the solid state, a highly desirable yet uncommon property for azobenzene-type photochromic compounds. The solid state E → Z photoisomerization is accompanied by an isothermal crystal-amorphous phase transformation; successively, anisotropic crystals can be grown upon promoting the Z → E isomerization by thermal annealing of the irradiated samples. These results validate the strategy of engineering multiphotochromic architectures with a rigid star-shaped geometry to preserve the solution-based photoreactivity also in the solid state. The observed unexpected photoinduced alignment makes these materials potentially attractive for the development of photo-patternable and photo-responsive surfaces
Second-Generation Light-Fueled Supramolecular Pump
Full text linkWe describe the modular design of a pseudorotaxane-based supramolecular pump and its photochemically driven autonomous nonequilibrium operation in a dissipative regime. These properties derive from careful engineering of the energy maxima and minima along the threading coordinate and their light-triggered modulation. Unlike its precursor, this second-generation system is amenable to functionalization for integration into more complex devices
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