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1.
Artigo em Inglês | MEDLINE | ID: mdl-32396687

RESUMO

The general principles guiding the design of molecular machines based on interlocked structures are well known. Nonetheless, the identification of suitable molecular components for a precise tuning of the energetic parameters that determine the mechanical link is still challenging. Indeed, what are the reasons of the "all-or-nothing" effect, which turns a molecular "speed-bump" into a stopper in pseudorotaxane-based architectures? Here we investigate the threading and dethreading processes for a representative class of molecular components, based on symmetric dibenzylammonium axles and dibenzo[24]crown-8 ether, with a joint experimental-computational strategy. From the analysis of quantitative data and an atomistic insight, we derive simple rules correlating the kinetic behaviour with the substitution pattern, and provide rational guidelines for the design of modules to be integrated in molecular switches and motors with sophisticated dynamic features.

2.
Adv Mater ; 32(20): e1906064, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31957172

RESUMO

Research on artificial photoactivated molecular machines has moved in recent years from a basic scientific endeavor toward a more applicative effort. Nowadays, the prospect of reproducing the operation of natural nanomachines with artificial counterparts is no longer a dream but a concrete possibility. The progress toward the construction of molecular-machine-based devices and materials in which light irradiation results in the execution of a task as a result of nanoscale movements is illustrated here. After a brief description of a few basic types of photoactivated molecular machines, significant examples of their exploitation to perform predetermined functions are presented. These include switchable catalysts, nanoactuators that interact with cellular membranes, transporters of small molecular cargos, and active joints capable of mechanically coupling molecular-scale movements. Investigations aimed at harnessing the collective operation of a multitude of molecular machines organized in arrays to perform tasks at the microscale and macroscale in hard and soft materials are also reviewed. Surfaces, gels, liquid crystals, polymers, and self-assembled nanostructures are described wherein the nanoscale movement of embedded molecular machines is amplified, allowing the realization of muscle-like actuators, microfluidic devices, and polymeric materials for light energy transduction and storage.

3.
Chem Rev ; 120(1): 200-268, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31415169

RESUMO

Directed motion at the nanoscale is a central attribute of life, and chemically driven motor proteins are nature's choice to accomplish it. Motivated and inspired by such bionanodevices, in the past few decades chemists have developed artificial prototypes of molecular motors, namely, multicomponent synthetic species that exhibit directionally controlled, stimuli-induced movements of their parts. In this context, photonic and redox stimuli represent highly appealing modes of activation, particularly from a technological viewpoint. Here we describe the evolution of the field of photo- and redox-driven artificial molecular motors, and we provide a comprehensive review of the work published in the past 5 years. After an analysis of the general principles that govern controlled and directed movement at the molecular scale, we describe the fundamental photochemical and redox processes that can enable its realization. The main classes of light- and redox-driven molecular motors are illustrated, with a particular focus on recent designs, and a thorough description of the functions performed by these kinds of devices according to literature reports is presented. Limitations, challenges, and future perspectives of the field are critically discussed.

4.
Chem Commun (Camb) ; 55(84): 12595-12602, 2019 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-31580358

RESUMO

Molecular machines powered by light are appropriately designed multicomponent molecular structures that exploit photochemical processes to perform controlled movements. We discuss the advances in the design and investigation of light-driven molecular machines by presenting a selection of examples from the past decade.

5.
Chem Commun (Camb) ; 55(79): 11860-11863, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31528890

RESUMO

An easy to synthesize azobenzene based amphiphile spontaneously self-assembles into monodisperse nanoaggregates in water. The large difference in the critical aggregation concentration between the E and Z stereoisomeric forms enables photocontrol of its aggregation state over a wide concentration range: light-triggered release and uptake of lipophilic molecules is achieved in aqueous solution.


Assuntos
Compostos Azo/química , Nanocápsulas/química , Corantes Fluorescentes/química , Interações Hidrofóbicas e Hidrofílicas , Luz , Tamanho da Partícula , Processos Fotoquímicos , Polietilenoglicóis/química , Estereoisomerismo , Água/química
6.
Chem Sci ; 10(19): 5104-5113, 2019 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31183062

RESUMO

Rigid, Y-shaped imidazole compounds containing the bis(thienyl)ethene moiety were designed and synthesized. The 4,5-bis(benzothienyl)-2-phenylimidazolium cations were then used as axles for [2]pseudorotaxane formation with 24-membered crown ether wheels. It was demonstrated using 1H NMR spectroscopy, UV-Vis absorption and emission spectroscopies that this host-guest interaction results in significant changes in the photochromic properties of the imidazolium axles. This is a rare example of gated photochromism, which exploits the recognition event of an interpenetrated molecular system to tune the photochromic properties in one of the components.

7.
J Am Chem Soc ; 141(23): 9129-9133, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31129959

RESUMO

We 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 coconformations. This result represents an unprecedented example of chiral molecular recognition and can disclose innovative approaches to enantioselective sensing and catalysis.

8.
Photochem Photobiol Sci ; 18(9): 2281-2286, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-30968923

RESUMO

Shape-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.

9.
ACS Appl Mater Interfaces ; 11(18): 16864-16871, 2019 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-30993968

RESUMO

The control over aggregation pathways is a key requirement for present and future technologies, as it can provide access to a variety of sophisticated structures with unique functional properties. In this work, we demonstrate an unprecedented control over the supramolecular self-assembly of a semiconductive material, based on a naphthalenediimide core functionalized with phenyl-thiophene moieties at the imide termini, by trapping the molecules into different arrangements depending on the crystallization conditions. The control of the solvent evaporation rate enables the growth of highly elaborated hierarchical self-assembled structures: either in an energy-minimum thermodynamic state when the solvent is slowly evaporated forming needle-shaped crystals (polymorph α) or in a local energy-minimum state when the solvent is rapidly evaporated leading to the formation of nanofibers (polymorph ß). The exceptional persistence of the kinetically trapped ß form allowed the study and comparison of its characteristics with that of the stable α form, revealing the importance of molecular aggregation geometry in functional properties. Intriguingly, we found that compared to the thermodynamically stable α phase, characterized by a J-type aggregation, the ß phase exhibits (i) an unusual strong blue shift of the emission from the charge-transfer state responsible for the solid-state luminescent enhancement, (ii) a higher work function with a "rigid shift" of the electronic levels, as shown by Kelvin probe force microscopy and cyclic voltammetry measurements, and (iii) a superior field-effect transistor mobility in agreement with an H-type aggregation as indicated by X-ray analysis and theoretical calculations.

10.
J Am Chem Soc ; 140(39): 12323-12327, 2018 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-30251843

RESUMO

The proliferation of light-activated switches in recent years has enabled their use in a broad range of applications encompassing an array of research fields and disciplines. All current systems, however, have limitations (e.g., from complicated synthesis to incompatibility in biologically relevant media and lack of switching in the solid-state) that can stifle their real-life application. Here we report on a system that packs most, if not all, the desired, targeted and sought-after traits from photochromic compounds (bistability, switching in various media ranging from serum to solid-state, while exhibiting ON/OFF fluorescence emission switching, and two-photon assisted near-infrared light toggling) in an easily accessible structure.

11.
Angew Chem Int Ed Engl ; 57(46): 15034-15039, 2018 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-30187995

RESUMO

Azobenzene is a prototypical molecular switch that can be reversibly photoisomerized between the nearly planar and apolar trans form, and the distorted, polar cis form. Most studies related to azobenzene derivatives have focused on planar adsorbed molecules. We present herein the study of a three-dimensional shape-persistent molecular architecture consisting of four tetrahedrally arranged azobenzene units that is adsorbed on a Ag(111) surface. While the azobenzenes of the tripod in contact with the surface lost their switching ability, different isomers of the upright standing arm of the tetramer were obtained reversibly and efficiently by illumination at different wavelengths, revealing time constants of only a few minutes. Diffusion on the surface was dependent on the isomeric state-trans or cis-of the upright oriented azobenzene group. Hence, molecular mobility can be modulated by its isomeric state, which suggests that molecular growth processes could be controlled by external stimuli.

12.
Photochem Photobiol Sci ; 17(6): 734-740, 2018 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-29722402

RESUMO

Among the plethora of photochromes reported so far, azobenzene has been proven to be the most suitable photoswitch for molecular systems and materials, due to its highly efficient and clean E-Z photoisomerization. Here we report two ammonium-based molecular axles bearing one or two p-cyanoazobenzene units at the extremities, able to form pseudorotaxanes with a crown ether macrocycle. The photochemistry of these compounds was studied in the isolated forms and in the pseudorotaxanes, showing that the functionalization speeds up the threading process without affecting the photochemical properties of the system. These results suggest that the investigated pseudorotaxanes can form the basis of new prototypes of artificial molecular-level pumps.

13.
ChemistryOpen ; 7(2): 169-179, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29435402

RESUMO

Movement is one of the central attributes of life, and a key feature in many technological processes. While artificial motion is typically provided by macroscopic engines powered by internal combustion or electrical energy, movement in living organisms is produced by machines and motors of molecular size that typically exploit the energy of chemical fuels at ambient temperature to generate forces and ultimately execute functions. The progress in several areas of chemistry, together with an improved understanding of biomolecular machines, has led to the development of a large variety of wholly synthetic molecular machines. These systems have the potential to bring about radical innovations in several areas of technology and medicine. In this Minireview, we discuss, with the help of a few examples, the multidisciplinary aspects of research on artificial molecular machines and highlight its translational character.

14.
Eur J Inorg Chem ; 2018(42): 4589-4603, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31007574

RESUMO

Molecular and supramolecular-based systems and materials that can perform predetermined functions in response to light stimulation have been extensively studied in the past three decades. Their investigation continues to be a highly stimulating topic of chemical research, not only because of the inherent scientific value related to a bottom-up approach to functional nanostructures, but also for the prospective applications in diverse fields of technology and medicine. Light is an important tool in this context, as it can be conveniently used both for supplying energy to the system and for probing its states and transformations. In this microreview we recall some basic aspects of light-induced processes in (supra)molecular assemblies, and discuss their exploitation to implement novel functionalities with nanostructured devices, machines and materials. To this aim we illustrate a few examples from our own recent work, which are meant to illustrate the trends of current research in the field.

15.
Science ; 356(6341): 906-907, 2017 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-28572350
16.
Chemistry ; 23(26): 6380-6390, 2017 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-28263437

RESUMO

A shape-persistent molecule, featuring four bipyridinium units, has been synthesized that upon reduction undergoes intermolecular pimerization because of the rigid architecture of the molecule. The pimerization process has been investigated by a variety of techniques, such as absorption measurements, EPR spectroscopy, as well as gamma and pulse radiolysis, and compared with the behavior of a model compound. Computational studies have also been performed to support the experimental data. The most interesting feature of the tetramer is that pimerization occurs only above a threshold concentration of monoreduced species, on the contrary to the model compound. Furthermore, there is an increase of the apparent pimerization constant by increasing the concentration of reduced bipyridinium units. These results have been interpreted by the fact that pimerization is favored in the tetrahedrally shaped molecule because of a cooperative mechanism. Each multiply reduced molecule can indeed undergo multiple intermolecular interactions that enhance the stabilization of the system, also leading to hierarchical supramolecular growth. The resulting supramolecular system formed by such intermolecular pimerization should exhibit a diamond-like structure, as suggested by a simplified modeling approach. The intermolecular nature of the pimerization process occurring in the tetramer has been demonstrated by measuring the corresponding bimolecular rate constant by pulsed radiolysis experiments.

17.
ChemistryOpen ; 6(1): 64-72, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28168152

RESUMO

Tris-(N-phenylureido)-calix[6]arene derivatives are heteroditopic non-symmetric molecular hosts that can form pseudorotaxane complexes with 4,4'-bipyridinium-type guests. Owing to the unique structural features and recognition properties of the calix[6]arene wheel, these systems are of interest for the design and synthesis of novel molecular devices and machines. We envisaged that the incorporation of photoactive units in the calixarene skeleton could lead to the development of systems the working modes of which can be governed and monitored by means of light-activated processes. Here, we report on the synthesis, structural characterization, and spectroscopic, photophysical, and electrochemical investigation of two calix[6]arene wheels decorated with three naphthyl groups anchored to either the upper or lower rim of the phenylureido calixarene platform. We found that the naphthyl units interact mutually and with the calixarene skeleton in a different fashion in the two compounds, which thus exhibit a markedly distinct photophysical behavior. For both hosts, the inclusion of a 4,4'-bipyridinium guest activates energy- and/or electron-transfer processes that lead to non-trivial luminescence changes.

18.
Chem Commun (Camb) ; 53(13): 2081-2093, 2017 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-28111647

RESUMO

Phosphorescent materials are mostly based on metal complexes. Metal-free organic molecules usually display phosphorescence only in a rigid matrix at 77 K. In the last few years, there has been increasing interest in the design of organic molecules displaying long-lived and highly intense room-temperature phosphorescence, an extremely difficult task since these two properties are generally conflicting. This review reports the most recent and tutorial examples of molecules that are weakly or non-phosphorescent in deaerated fluid solution and whose room temperature phosphorescence is switched on upon aggregation. The examples are divided into two classes according to the mechanism responsible for switching on phosphorescence: (i) rigidification by crystallization or by encapsulation in a polymeric matrix and (ii) interaction with other molecules of the same type (self-aggregation) or a different type by taking advantage of heavy-atom effects.

19.
Chemphyschem ; 18(13): 1755-1759, 2017 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-28135020

RESUMO

Nonlinear input-output relations are at the basis of the regulation of biochemical processes in living organisms and are important for the development of digital logic circuits based on molecules. In this article we show that a linear change of a chemical input can be translated into an exponential change of a luminescence output in a simple fluorescent acid-base switch based on 8-methoxyquinoline. Such unconventional behavior arises from the fact that part of the light emitted by the switch in its basic form is reabsorbed by the acid form, and is made possible by the particular spectroscopic properties of the two forms. Systems of this kind could act as noise filters in analog-to-digital conversion, and as control elements to increase the functional complexity of artificial molecular devices.


Assuntos
Lógica , Luminescência , Quinolinas/química , Conversão Análogo-Digital , Concentração de Íons de Hidrogênio , Estrutura Molecular
20.
Chem Rec ; 17(7): 700-712, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28054435

RESUMO

The development of nanoscale systems capable to perform specific functions under external control is a challenging task and a fascinating objective in Chemistry. Photochromic compounds undergo radical changes in their physico-chemical properties upon light excitation, for this reason they are valuable building blocks for the construction of photo-controllable molecular devices, machines and materials. The E-Z photoisomerization of azobenzene has been known for almost 80 years and - owing to its high efficiency and excellent reversibility - has been widely employed to introduce an element of photo-control in a large variety of compounds, biomolecules, nanosystems and materials. Here we present some of our research results highlighting how this outstanding photochrome can be utilized to develop systems with light-induced functionalities.

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