Photodynamic covalent bonds regulated by visible light for soft matter materials

Photodynamic covalent bonds (PDCBs) are covalent linkages that can be reversibly cleaved and reformed by light irradiation. PDCBs hold key potential in soft matter materials design for advanced applications, including self-healing, shape-shifting, materials recycling, and topological transformation. Controlling the photodynamic exchange with visible light offers significant benefits in tuning the materials properties, broadening the applications of light-responsive soft matter materials in biological environments. Significant progress has been made in redshifting the photoreactivity of commonly used photodynamic PDCBs, including the reversible [2+2] photocycloadditions and photo-induced radical exchanges. Recently introduced photodynamic interactions can also be influenced by extremely mild conditions, such as cleavage in darkness, enabling formation of light-stabilised dynamic materials. The activation wavelength of PDCBs can be extended further into the red/near-infrared region by combination with redshifted photoswitches. Photodynamic bond forming systems (i.e., systems that respond with defined bond formation at one wavelength and cleavage at a disparate yet defined wavelength) are essential for adaptive soft matter materials design. This emerging field has thus far been dominated by the need to use UV light to induce bond cleavage and to some extent to induce bond formation. The next critical frontier in the field is to substantially redshift both the bond formation and cleavage reaction into biologically benign irradiation regimes that commence beyond 400 nm. Herein, we concisely summarise, on the basis of critically selected examples, the progress that has been made to date both on the fundamental photochemical level as well as in the associated materials realm. In addition, we highlight future avenues and opportunities to progress the field. Photodynamic bond forming systems (i.e., systems that respond with defined bond formation at one wavelength and cleavage at a disparate yet defined wavelength) are essential for adaptive soft matter materials design. This emerging field has thus far been dominated by the need to use UV light to induce bond cleavage and to some extent to induce bond formation. The next critical frontier in the field is to substantially redshift both the bond formation and cleavage reaction into biologically benign irradiation regimes that commence beyond 400 nm. Herein, we concisely summarise, on the basis of critically selected examples, the progress that has been made to date both on the fundamental photochemical level as well as in the associated materials realm. In addition, we highlight future avenues and opportunities to progress the field.