Promoting the Furan Ring‐Opening Reaction to Access New Donor–Acceptor Stenhouse Adducts with Hexafluoroisopropanol

Abstract

Donor-acceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with avariety of emerging applications in photoresponsive materials.T heir two-step modular synthesis,centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible.However, the use of less reactive donors or acceptors renders the process slow and low yielding,which has limited their development. We demonstrate here that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) promotes the ring-opening reaction and stabilizes the open isomer,a llowing greatly reduced reaction times and increased yields for knownderivatives.Inaddition, it provides access to previously unattainable DASA-based photoswitches and DASA-polymer conjugates.T he role of HFIP and the photochromic properties of as et of new DASAs is probed using ac ombination of 1 HNMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer halflives for the first time.

Donor–Acceptor Stenhouse Adduct Displaying Reversible Photoswitching in Water and Neuronal Activity

“…19 DASA compounds absorb visible-to-NIR light because of their highly conjugated push− pull structure and planar backbone, which shifts their absorption to wavelengths up to 750 nm. 20 Their accessible synthetic route has enabled the development of a library of DASA derivatives with variable donors, 20,21 acceptors, 22 and different triene backbone designs 17,23−25 results in a zwitterionic cyclic colorless photoproduct. In the second 20 and third 22 generations, the use of an aniline donor moiety yields mainly nonzwitterionic photoproducts.…”

“…DASA compounds absorb visible-to-NIR light because of their highly conjugated push–pull structure and planar backbone, which shifts their absorption to wavelengths up to 750 nm . Their accessible synthetic route has enabled the development of a library of DASA derivatives with variable donors, , acceptors, and different triene backbone designs ,− to customize physicochemical and photochromic properties. The cyclic compound obtained by photoconversion sets apart the first and subsequent generations of DASAs.…”

Photochromic Performance of Donor‐Acceptor Stenhouse Adducts in Polymer Binders and Solution

“…To date there have only been a few investigations of the photochromic performance of DASAs both dispersed into [10,26] and conjugated to a polymer matrix. [10,13,15,[27][28][29][30] Ulrich et al aimed to tailor DASA photoswitching performance and eliminate phase separation via polymer conjugation, finding that when the dyes are conjugated to rigid glassy polymers, near irreversible photoswitching can be drastically accelerated when the temperature is raised above the glass transition temperature of the polymer. [27] DASA-polymer conjugates formed into a solid load bearing polymer support demonstrated a mechanical response stimulated by photo-thermal actuation.…”

“…Most practical applications of photo switching systems require rapid, reversible photo‐switching within a polymer matrix, however, because of the strong solvent dependence on the switching rates on the solvent, properties of DASAs dispersed within polymer matrices are expected to be a highly complicated combination of contributions from matrix solubility and matrix rigidity. To date there have only been a few investigations of the photochromic performance of DASAs both dispersed into [10,26] and conjugated to a polymer matrix [10,13,15,27–30] . Ulrich et al .…”

Light-Responsive Solid–Solid Phase Change Materials for Photon and Thermal Energy Storage

“…Molecular solar thermal (MOST) energy storage compounds that store photon energy in strained chemical bonds upon photoisomerization have emerged as a novel material that harnesses solar energy and releases the stored energy as heat on demand. − MOST compounds are generally photoswitches that undergo structural isomerization between the ground-state and metastable-state isomeric forms, and the energy difference between the two isomers, i.e., isomerization energy (Δ H iso ), is stored in the system. Among various photoswitch designs known to date, including norbornadienes, − dihydroazulenes, − hydrazones, − spiropyrans, , donor–acceptor Stenhouse adducts, , and fulvalene diruthenium complexes, , azobenzene and its derivatives have been extensively explored for MOST energy storage, due to the ease of synthesis and derivatization, , tunable optical properties and thermal half-lives ( t 1/2 ), − and reversible isomerization over many cycles with little degradation . Azobenzene derivatives also undergo large structural and polarity changes upon E–Z isomerization, which often results in the phase transition between the crystalline E and liquid Z isomers.…”