Light-Induced Formation/Scission of C–N, C–O, and C–S Bonds Enables Switchable Stability/Degradability in Covalent Systems

Abstract

The manipulation of covalent bonds could be directed toward degradable, recyclable, and sustainable materials. However, there is an intrinsic conflict between properties of stability and degradability. Here we report light-controlled formation/scission of three types of covalent bonds (C–N, C–O, and C–S) through photoswitching between equilibrium and nonequilibrium states of dynamic covalent systems, achieving dual benefits of photoaddressable stability and cleavability. The photocyclization of dithienylethene fused aldehyde ring–chain tautomers turns on the reactivity, incorporating/releasing amines, alcohols, and thiols reversibly with high efficiency, respectively. Upon photocycloreversion the system is shifted to kinetically locked out-of-equilibrium form, enabling remarkable robustness of covalent assemblies. Reaction coupling allows remote and directional control of a diverse range of equilibria and further broadens the scope. Through locking and unlocking covalent linkages with light when needed, the utility is demonstrated with capture/release of bioactive molecules, modification of surfaces, and creation of polymers exhibiting tailored stability and degradability/recyclability. The versatile toolbox for photoswitchable dynamic covalent reactions to toggle matters on and off should be appealing to many endeavors.

Photoinduced generation of carbocations enabled by the promotion of aromaticity

“…60 By manipulating the aromatic/antiaromatic character of intermediates and kinetic barriers with photoswitching, we demonstrated light-induced on/off toggling of dynamic covalent acetal/thioacetal chemistry. 61…”

“…60 By manipulating the aromatic/antiaromatic character of intermediates and kinetic barriers with photoswitching, we demonstrated light-induced on/off toggling of dynamic covalent acetal/thioacetal chemistry. 61 Although the combination of photoswitches and carbocations, including azulene-and tritanol-derived cations, has been reported, [62][63][64][65][66] light-mediated stability enhancement of carbocations is challenging. The on-demand generation of carbocations by light irradiation could potentially solve the instability issue.…”

2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water

“…[17][18][19][20][21] The photoswitching of DAEs nds application in the development of stimuli-responsive materials and light-controllable processes (Scheme 1A(b)). [22][23][24][25][26][27] The photorearrangement with formation of bicyclic aromatics is a recently discovered transformation (Scheme 1A(c)) that is promising for various applications, including organic synthesis, 28-30 photopharmacology 31 and click-chemistry. 32 Water-soluble DAEs bearing solubilizing charged groups are in demand for various photopharmacological and biomedical applications (Scheme 1B).…”

2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water

“…[17][18][19][20][21] The photoswitching of DAEs finds application in the development of stimuli-responsive materials and light-controllable processes (Scheme 1Ab). [22][23][24][25][26][27] The photorearrangement with formation of bicyclic aromatics is a recently discovered transformation (Scheme 1Aс) that is promising for various applications, including organic synthesis, [28][29][30] photopharmacology 31 and click-chemistry. 32 Scheme 1.…”