9 research outputs found
Merging Constitutional and Motional Covalent Dynamics in Reversible Imine Formation and Exchange Processes
The formation and exchange processes of imines of salicylaldehyde,
pyridine-2-carboxaldehyde, and benzaldehyde have been studied, showing
that the former has features of particular interest for dynamic covalent
chemistry, displaying high efficiency and fast rates. The monoimines
formed with aliphatic α,ω-diamines display an internal
exchange process of self-transimination type, inducing a local motion
of either “stepping-in-place” or “single-step”
type by bond interchange, whose rate decreases rapidly with the distance
of the terminal amino groups. Control of the speed of the process
over a wide range may be achieved by substituents, solvent composition,
and temperature. These monoimines also undergo intermolecular exchange,
thus merging motional and constitutional covalent behavior within
the same molecule. With polyamines, the monoimines formed execute
internal motions that have been characterized by extensive one-dimensional,
two-dimensional, and EXSY proton NMR studies. In particular, with
linear polyamines, nondirectional displacement occurs by shifting
of the aldehyde residue along the polyamine chain serving as molecular
track. Imines thus behave as simple prototypes of systems displaying
relative motions of molecular moieties, a subject of high current
interest in the investigation of synthetic and biological molecular
motors. The motional processes described are of dynamic covalent nature
and take place without change in molecular constitution. They thus
represent a category of dynamic covalent motions, resulting from reversible
covalent bond formation and dissociation. They extend dynamic covalent
chemistry into the area of molecular motions. A major further step
will be to achieve control of directionality. The results reported
here for imines open wide perspectives, together with other chemical
groups, for the implementation of such features in multifunctional
molecules toward the design of molecular devices presenting a complex
combination of motional and constitutional dynamic behaviors
Acylhydrazones as Widely Tunable Photoswitches
Molecular photoswitches
have attracted much attention in biological
and materials contexts. Despite the fact that existing classes of
these highly interesting functional molecules have been heavily investigated
and optimized, distinct obstacles and inherent limitations remain.
Considerable synthetic efforts and complex structure–property
relationships render the development and exploitation of new photoswitch
families difficult. Here, we focus our attention on acylhydrazones:
a novel, yet underexploited class of photochromic molecules based
on the imine structural motif. We optimized the synthesis of these
potent photoswitches and prepared a library of over 40 compounds,
bearing different substituents in all four crucial positions of the
backbone fragment, and conducted a systematic study of their photochromic
properties as a function of structural variation. This modular family
of organic photoswitches offers a unique combination of properties
and the compounds are easily prepared on large scales within hours,
through an atom-economic synthesis, from commercially available starting
materials. During our thorough spectroscopic investigations, we identified
photoswitches covering a wide range of thermal half-lives of their
(<i>Z</i>)-isomers, from short-lived T-type to thermally
stable P-type derivatives. By proper substitution, excellent band
separation between the absorbance maxima of (<i>E</i>)-
and (<i>Z</i>)-isomers in the UV or visible region could
be achieved. Our library furthermore includes notable examples of
rare negative photochromic systems, and we show that acylhydrazones
are highly fatigue resistant and exhibit good quantum yields
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale
Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds
Manipulating
nanoscopic objects by external stimuli is the cornerstone
of nanoscience. Here, we report the implementation of dynamic covalent
chemistry in the reversible binding and directional motion of fluorescent
nanodiamond particles at a functionalized graphene surface <i>via</i> imine linkages. The dynamic connections allow for controlling
the formation and rupture of these linkages by external stimuli. By
introduction of pH gradients, the nanoparticles are driven to move
along the gradient due to the different rates of the imine condensation
and hydrolysis in the two environments. The multivalent nature of
the particle-to-surface connection ensures that particles remain attached
to the surface, whereas its dynamic character allows for exchange
reaction, thus leading to displacement yet bound behavior in two-dimensional
space. These results open a pathway for thermodynamically controlled
manipulation of objects on the nanoscale