Reversible Photoswitching in Poly(2‐oxazoline) Nanoreactors

Abstract

This contribution reports light responsive catalytic nanoreactors based on poly(2‐oxazoline) diblock copolymers. The hydrophobic block of the copolymer is a random copolymer consisting of a spiropyran functionalized 2‐oxazoline (SPOx) and 2‐(but‐3‐yn‐1‐yl)‐4,5‐dihydrooxazole (ButynOx), while the hydrophilic block is based on 2‐methyl‐2‐oxazoline (MeOx). The block copolymer is terminated with tris(2‐aminoethyl) amine (TREN) that serves as catalyst in a Knoevenagel condensation. Four block copolymers with different ButynOx/SPOx and hydrophilic/hydrophobic ratios are synthesized and self‐assembled through solvent exchange. Micelles and vesicles of various sizes are observed by TEM, which undergo morphological and size changes in response to irradiation with UV light. We hypothesize that these transformations in the nanostructures are caused by increases in the hydrophilicity of the hydrophobic block when spiropyran (SP) isomerizes to merocyanine (MC) in the presence of UV light. The reversible transition from micellar to vesicular nanoreactors resulted in increased reaction kinetics through improved substrate accessibility to the catalytic site, or termination of the catalytic reaction due to polymer precipitation. These nanoreactors present a promising platform towards photoregulating reaction outcomes based on changes in nanostructure morphology.

Cross‐Linked Polymeric Micelles as Catalytic Nanoreactors

“…Cross-linked polymeric micelles should also be able to create "smart" nanoreactors that enable spatio-temporal control over chemical transformations. [52] We recently reported on a photoresponsive SCM nanoreactor to compartmentalize and photoregulate two incompatible enantioselective transforma-tions. The micellar structure was covalently cross-linked by a bifunctional photochromic spiropyran to create a functional shell, which was key to discriminate among substrates/reagents during tandem catalysis.…”

Cascade Processes with Micellar Reaction Media: Recent Advances and Future Directions

“…This effect was attributed to enhanced transport of the substrate after the switch from micelles to vesicles. Polymers could also be designed to precipitate out of solution upon exposure to UV light, stopping the reaction [ 89 ].…”

Compartmentalization and Photoregulating Pathways for Incompatible Tandem Catalysis

“…Scientists have developed multicompartmental catalytic systems based on various strategies including the use of sol–gels, Pickering emulsion droplets, supramolecular metal complex architectures, , and polymers. , Catalytic frameworks fabricated from these materials have realized compartmentalization for multiple active catalytic sites, as epitomized by the cell, and enabled multistep nonorthogonal transformations. − ,− Incorporating responsive elements into the support structures has rendered them “smart”, i.e., allowing for reversible alterations of the physical and chemical properties in response to external stimuli such as temperature, , pH, light, , or enzymes. , The properties of the resulting smart materials impart an additional bioinspired control over single-step catalytic transformations. ,− Manipulation of multicatalytic tandem sequences, however, remains challenging and restricted to the regulation of reactivities via temperature actuation. , This limitation significantly affects the choice of catalysts and limits the feasibility of performing one-pot tandem catalysis at arbitrary temperature ranges. To date, no “smart” catalytic system can use or control different switchable states to tune and activate a desired synthetic pathway among many possible ones during a multistep synthesis.…”