Tunable Photothermal Actuation Enabled by Photoswitching of Donor–Acceptor Stenhouse Adducts

Abstract

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.

Molecular photoswitches in aqueous environments

“…495 Furthermore, DASAs bearing a dialkylamine donor moiety switch reversibly mainly in aromatic apolar solvents, 478,497 the secondary aniline, present in generation 2 and 3 DASAs, allows for switching in a wider range of solvents, including THF, 492,493 dioxane, 497 halogenated solvents 489,492,493,497 and, MeCN, 492,493,497 and in polymer matrices. [500][501][502] In strong contrast, in polar protic solvents such as methanol and water, the cyclic, hydrophilic form is energetically more stable than the linear isomer and does not isomerize to the linear state. 491 Also, on magnetic nanoparticles, the formation of the cyclic form is irreversible.…”

“…507 The pronounced changes in their geometry and polarity make DASAs interesting candidates for a wide range of applications. 490,491 For instance, they have already been used in responsive polymers, 501,502,508 on surfaces, 509,510 to photocontrol wettability, 500,511 in sensing and, 512,513 for dynamic, selfregulating flows. 514 Furthermore, DASAs are responsive to multiple stimuli 505,512,513 which allows to further tailor their switching behavior.…”

Donor–Acceptor Stenhouse Adducts: Exploring the Effects of Ionic Character

“…[5] Since their discovery in 2014, these molecules have been exploited in an umber of applications,i ncluding targeted drug release, [2,6,7] orthogonal photoswitching, [8] chemical andt hermal sensing, [9][10][11][12] and, most recently,f luid velocity control [13] and photothermal actuation. [14] Synthetic efforts have resulted in three generations of DASAs that vary in their photoswitching properties, such as the thermodynamice quilibrium between the open and closed forms in the absence of light irradiation, wavelength tunability (500-700 nm), switching rates, and solventd ependence. [1][2][3][4] The first generation of DASAs, published in 2014, consist of strongly electron-donatingd ialkylamino donors and Meldrum's or barbituric acid acceptors ( Figure 1).…”

Отрицательный Фотохромизм: Последние Достижения

“…Для создания роботизированных систем предлагается использовать полимерные бислои, состоящие из полиимидной пленки, на которую нанесено полимерное Стенхаус соединение [39]. Такие пленки способны изменять свою конформацию при облучении видимым светом.…”