Photo‐Controlled [4+4] Cycloaddition of Anthryl‐Polymer Systems: A Versatile Approach to Fabricate Functional Materials

Abstract

The reversible photo‐induced [4+4] cycloaddition reaction of anthracene enables multiple cycles of dimerization and scission, allowing phototunable linkage of molecular fragments for the synthesis of polymer scaffolds. New functional materials ranging from hydrogels to shape‐memory polymers were designed from anthryl‐polymer systems because of their diverse photochemical reactivity and responsiveness. Light as an external stimulus allows for the remote and precise spatiotemporal control of materials without the need for additional reagents. Depending on how the photoreactive anthracene moieties were introduced, the interaction of anthryl‐polymer systems with light results in various processes such as polymerization, cyclization, and cross‐linking. Structural modifications of anthracene derivatives could shift their absorption from the ultraviolet to the visible light region, widening their range of applications including biologically relevant studies. These applications are further diversified and enhanced by the reversibility of the dimerization reaction using light and heat as stimuli. In this review, current developments in the synthesis and photodimerization of anthracene‐containing polymers and their emerging applications in the fabrication of new materials are discussed.

Cascade synthesis of architecture-transformable thermo-labile multisite multiblock copolymers

“…Polymer Chemistry cene dimerization (Scheme S1 †), and the combination of thiolactone chemistry, [67][68][69][70][71] ring-opening polymerization (ROP), and UV-induced radical polymerization 72 and anthracene dimerization [19][20][21][22][23][24][25] is adopted to achieve (BAB) n -g-C/D-type multiblock graft copolymers, in which C is poly(ethylene glycol) (PEG), and D is poly(ε-caprolactone) (PCL) or poly(N-isopropylacrylamide) (PNIPAM). Meanwhile, thermolysis of (BAB) n -type copolymers is performed to obtain mixtures of P(St-co-MTL) l -b-PSt m (A′B) and P(St-co-MTL) l -b-PSt 2m -b-P(St-co-MTL) l (A′B 2 A′), and the thermolysis of PEG/PNIPAM-heterografted copolymer affords mixtures of comblike-linear and comblike-linear-comblike block copolymers.…”

“…Among them, architecture-transformable multisite polymers (ATMPs) are promising precursors to achieve a wide range of derivatives with distinct chain architectures. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] With the incorporation of stimu-lus-labile linkages into the backbone or end groups, ATMPs are subjected to reversible or irreversible topological transformations upon external stimuli. For instance, distinct functional linkers involving pH-cleavable ester group 18 and photo-/ thermo-labile anthracene dimer (AntD) group [19][20][21][22][23][24][25] have been incorporated into ATMPs to achieve stimulus-triggered cleavage and reconstruction of chain architectures.…”

“…[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] With the incorporation of stimu-lus-labile linkages into the backbone or end groups, ATMPs are subjected to reversible or irreversible topological transformations upon external stimuli. For instance, distinct functional linkers involving pH-cleavable ester group 18 and photo-/ thermo-labile anthracene dimer (AntD) group [19][20][21][22][23][24][25] have been incorporated into ATMPs to achieve stimulus-triggered cleavage and reconstruction of chain architectures. The emergence of stimuli-responsive ATMPs allows to reconstruct novel architectural polymers via reaction driven topological transformation, during which the physical properties can be continuously regulated.…”

“…In this context, styrene (St) and 2-maleimidyl-4-thiobutyrolactone (MTL) are subjected to one-shot copolymerization to generate (BAB) n -type (A = P(St- co -MTL) 2 l , B = PSt m ) MMBPs via tandem ATRP and ATRC, followed by organobase-catalyzed cleavage of ester groups (OCE) to degrade into (A′B- co -BA′) r ′ -type copolymers with reduced block number and distinct connection mode of P(St- co -MTL) l (A′) and PSt m (B) blocks, in which l and m denote the degree of polymerization (Scheme 1). On this basis, representative MMBPs are chosen to synthesize intrachain folding MMBPs via UV-induced anthracene dimerization (Scheme S1†), and the combination of thiolactone chemistry, 67–71 ring-opening polymerization (ROP), and UV-induced radical polymerization 72 and anthracene dimerization 19–25 is adopted to achieve (BAB) n - g -C/D-type multiblock graft copolymers, in which C is poly(ethylene glycol) (PEG), and D is poly( ε -caprolactone) (PCL) or poly( N -isopropylacrylamide) (PNIPAM). Meanwhile, thermolysis of (BAB) n -type copolymers is performed to obtain mixtures of P(St- co -MTL) l - b -PSt m (A′B) and P(St- co -MTL) l - b -PSt 2 m - b -P(St- co -MTL) l (A′B 2 A′), and the thermolysis of PEG/PNIPAM-heterografted copolymer affords mixtures of comblike-linear and comblike-linear-comblike block copolymers.…”

Template-Controlled Supramolecular Photodimerization of 2-Substituted Anthracenes Mediated by Metal–NHC Complexes

“…Photochemical reaction, as one of the most attractive research areas in green chemistry, has become a powerful tool for the design and synthesis of novel products that are inaccessible via conventional thermal reactions . Particularly, the [4 + 4] photodimerization of anthracene is one of the most extensively investigated photochemical reactions and has enormous potential in chemical synthesis. − However, such photochemical transformation always suffers from nonspecific regio- and stereoselectivity during the photoreactions in homogeneous solutions and thus results in product mixtures of diverse configurations . Therefore, developing a controllable strategy that can efficiently generate photochemical products with a definite configuration in solution is of interest. − …”