The effects of solution-state dielectric and intermolecular interactions on the degree of charges eparation provide ar oute to understanding the switchingp roperties and concentration dependence of donor-acceptorS tenhouse adducts (DASAs). Through solvatochromic analysis of the open-form DASA in conjunction with X-ray diffraction and computational theory,w eh ave analyzed the ionic character of as eries of DASAs. First-and third-generation architectures lead to ah igher zwitterionic resonance contribution of the open form and az witterionic closed form, whereas the second-generation architecture possesses al ess charge-separatedo penf orm and neutral closed form. This can be correlated with equilibrium controla nd photoswitching solvent compatibility. As ar esult of the high contribution of the zwitterionic resonance forms of first-and third-generation DASAs, we were ablet oc ontrol their switching kinetics by meanso fi on concentration,w hereas second-generation DASAs were less affected. Importantly,t hese results show how the previously reported concentration dependenceo f DASAs is not universal,a nd that DASAs with am ore hybrid structure in the open form can achievep hotoswitching at high concentrations.
The isomerization rates of a photochromic donor–acceptor Stenhouse adduct depend on concentration. The net photoisomerization rate decreases with increasing concentration in liquids and polymers.
We
report a visible light-responsive bilayer actuator driven by
the photothermal properties of a unique molecular photoswitch: donor–acceptor
Stenhouse adduct (DASA). We demonstrate a synthetic platform to chemically
conjugate DASA to a load-bearing poly(hexyl methacrylate) (PHMA) matrix
via Diels–Alder click chemistry that enables access to stimuli-responsive
materials on scale. By taking advantage of the negative photochromism
and switching kinetics of DASA, we can tune the thermal expansion
and actuation performance of DASA–PHMA under constant light
intensity. This extends the capabilities of currently available responsive
soft actuators for which mechanical response is determined exclusively
by light intensity and enables the use of abundant broadband light
sources to trigger tunable responses. We demonstrate actuation performance
using a visible light-powered cantilever capable of lifting weight
against gravity as well as a simple crawler. These results add a new
strategy to the toolbox of tunable photothermal actuation by using
the
molecular photoswitch DASA.
We
investigate the influence of the host matrix on the photothermally
driven actuation performance of negatively photochromic, donor–acceptor
Stenhouse adduct (DASA)-based polymers. Using a modular Diels–Alder
“click” platform, we designed polymeric materials with
varying DASA incorporation and investigated the relationships between
the material composition and the resulting physical, mechanical, and
photoswitching properties. We demonstrate that increasing the DASA
concentration in polymer conjugates has a dramatic effect on the material’s
physical and mechanical properties, such as the glass transition temperature
(T
g) and elastic modulus, as well as the
photoswitching properties, which are found to be highly dependent
on T
g. We establish using a simple photoresponsive
bilayer that actuation performance is controlled by the bilayer stiffness
rather than the photochrome incorporation of DASA. Finally, we report
and compare the light-induced property changes in T
g and the elastic modulus between the materials comprising
the open or closed forms of DASAs. Our results demonstrate the importance
of designing a material that is stiff enough to provide the mechanical
strength required for actuation under load, but soft enough to reversibly
switch at the operational temperature and provide key considerations
for the development of application-geared photoswitchable materials.
We identify unique features of a highly-absorbing negatively photochromic molecular switch, donor acceptor Stenhouse adduct (DASA), that enable its use for self-regulating light-activated control of fluid flow. Leveraging features of DASA's chemical properties and solvent-dependent reaction kinetics, we demonstrate its use for photo-controlled Rayleigh-Bénard convection to generate dynamic, self-regulating flows with unparalleled fluid velocities (~mm s −1) simply by illuminating the fluid with visible light. The exceptional absorbance of DASAs in solution, uniquely controllable reaction kinetics and resulting spatially-confined photothermal flows demonstrate the ways in which photoswitches present exciting opportunities for their use in optofluidics applications requiring tunable flow behavior.
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