A class of tunable visible and near-infrared donor−acceptor Stenhouse adduct (DASA) photoswitches were efficiently synthesized in two to four steps from commercially available starting materials with minimal purification. Using either Meldrum's or barbituric acid "acceptors" in combination with aniline-based "donors", an absorption range spanning from 450 to 750 nm is obtained. Additionally, photoisomerization results in complete decoloration for all adducts, yielding fully transparent, colorless solutions and films. Detailed investigations using density functional theory, nuclear magnetic resonance, and visible absorption spectroscopies provide valuable insight into the unique structure−property relationships for this novel class of photoswitches. As a final demonstration, selective photochromism is accomplished in a variety of solvents and polymer matrices, a significant advantage for applications of this new generation of DASAs.

A novel library of tunable negative photochromic compounds, donor-acceptor Stenhouse adducts (DASAs), is reported. Tailoring the electron deficient "acceptor" moiety yielded DASAs that can be activated with mild visible and far red light. The effect of acceptor composition on reactivity, absorption, equilibrium, and cyclability is exploited for the design of high performance photoswitches. The structural changes to the carbon acid acceptor also provide access to new, more structurally diverse DASA derivatives by facilitating the ring-opening reaction with electron deficient amine donors.

The effect of catalyst strength on polyester−alcohol dynamic covalent exchange was systematically studied using Brønsted acids and a low-T g poly(4-methylcaprolactone) vitrimer formulation. Relaxation times, activation energies, and Arrhenius prefactors are correlated with pK a . Strong protic acids induce facile network relaxation at 25°C on the order of 10 4 −10 5 s, significantly faster than Lewis acid alternatives that function only above 100°C. Activation energies span 49−67 kJ/mol and increase as pK a decreases. The opposite trend is observed with the Arrhenius prefactor. We anticipate that the quantitative understanding of Brønsted acid effects disclosed herein will be of utility in future studies that exploit acid-catalyzed dynamic covalent bond exchange.

A novel methodology for printing 3D objects with spatially resolved mechanical and chemical properties is reported. Photochromic molecules are used to control polymerization through coherent bleaching fronts, providing large depths of cure and rapid build rates without the need for moving parts. The coupling of these photoswitches with resin mixtures containing orthogonal photo-crosslinking systems allows simultaneous and selective curing of multiple networks, providing access to 3D objects with chemically and mechanically distinct domains. The power of this approach is showcased through the one-step fabrication of bioinspired soft joints and mechanically reinforced "brick-and-mortar" structures.

A modular synthesis of Donor−Acceptor Stenhouse Adduct (DASA) polymer conjugates is described. Pentafluorophenyl-ester chemistry is employed to incorporate aromatic amines into acrylate and methacrylate copolymers, which are subsequently coupled with activated furans to generate polymers bearing a range of DASA units in a modular manner. The effect of polymer glass transition temperature on switching kinetics is studied, showing dramatic rate enhancements in going from a glassy to a rubbery matrix. Moreover, tuning the DASA absorption profile allows for selective switching, as demonstrated by ternary photopatterning, with potential applications in rewriteable data storage.