Donor–Acceptor Stenhouse Adduct‐Polydimethylsiloxane‐Conjugates for Enhanced Photoswitching in Bulk Polymers

Abstract

Donor-acceptor Stenhouse adducts (DASAs) are a rapidly emerging class of visible light-activated photochromes and DASA-functionalized polymers hold great promise as biocompatible photoresponsive materials. However, the photoswitching performance of DASAs in solid polymer matrices is often low, particularly in materials below their glass transition temperature. To overcome this limitation, DASAs are conjugated to polydimethylsiloxanes which have a glass transition temperature far below room temperature and which can create a mobile molecular environment around the DASAs for achieving more solution-like photoswitching kinetics in bulk polymers. The dispersion of DASAs conjugated to such flexible oligomers into solid polymer matrices allows for more effective and tunable DASA photoswitching in stiff polymers, such as poly(methyl methacrylate), without requiring modifications of the matrix. The photoswitching of conjugates with varying polymer molecular weight, linker type, and architecture is characterized via time-dependent UV-vis spectroscopy in organic solvents and blended into polymethacrylate films. In addition, DASA-functionalized polydimethylsiloxane networks, accessible via the same synthetic route, provide an alternative solution for achieving fast and efficient DASA photoswitching in the bulk owing to their intrinsic softness and flexibility. These findings may contribute to the development of DASA-functionalized materials with better tunable, more effective, and more reversible modulation of their optical properties.

Mechanically Gated Formation of Donor–Acceptor Stenhouse Adducts Enabling Mechanochemical Multicolor Soft Lithography

“…7). 32 Analogous experiments performed using indoline and diethylamine produced similar results (Supplementary Figs. 8 and 9).…”

Donor–acceptor Stenhouse adduct functionalised polymer microspheres

“…41,47 When held at or above the host polymer's T g , DASA switching kinetics markedly improve. 38,41,46 Studies by Sroda et al . have also shown that the level of DASA functionalisation itself affects T g and elastic modulus of the host polymer, 38 while Yap et al .…”

“…In the solid state, effective and reversible switching of polymer-bound DASAs is dependent on the polymer's glass transition temperature (T g ) 41,47 . When held at or above the host polymer's T g , DASA switching kinetics markedly improve 38,41,46 . Studies by Sroda et al have also shown that the level of DASA functionalisation itself affects T g and elastic modulus of the host polymer 38 , while Yap et al demonstrated polymer chain-length dependence on DASA switching performance, with shorter chains of (~20 monomer units) showing faster switching compared to longer chain-lengths of (~100 monomer units) 43 .…”

“…[37][38][39] Several groups rapidly realised the potential of DASAs to yield light-responsive materials and nanostructures, achieved through the covalent attachment of DASAs to polymers. 34,[40][41][42][43][44][45][46] However, the reversible switching process of DASAs is complicated when polymer-bound, as it is additionally dependent on the host polymer's properties. When solvated, DASA-polymers exhibit significantly improved switching behaviour compared to dry, solid-state conditions.…”

“…41,47 When held at or above the host polymer's T g , DASA switching kinetics markedly improve. 38,41,46 Studies by Sroda et al have also shown that the level of DASA functionalisation itself affects T g and elastic modulus of the host polymer, 38 while Yap et al demonstrated polymer chain-length dependence on DASA switching performance, with shorter chains (of ∼20 monomer units) showing faster switching compared to longer chainlengths (of ∼100 monomer units). 43 Despite DASA-polymer interactions being underexplored, the property changes associated with DASA photoswitching has led to the development of new light-responsive materials in the fields of targeted drug delivery, 35,48 wavelength-selective polymersome biocatalysis, 42,49 photolithography, 50 3D printing, 50,51 encryption, 52 surface wettability, 36,53 detection of toxic chemical warfare agents 54 and photothermal actuation.…”