Dynamic Supramolecular Ruthenium‐Based Gels Responsive to Visible/NIR Light and Heat

Abstract

A simple supramolecular crosslinked gel is reported with a photosensitive ruthenium bipyridine complex functioning as a crosslinker and poly(4‐vinylpyridine) (P4VP) as a macromolecular ligand. Irradiation of the organogels in H2O/MeOH with visible and NIR light (in a multiphoton process) leads to cleavage of pyridine moieties from the ruthenium complex breaking the cross‐links and causing degelation and hence solubilization of the P4VP chains. Real‐time (RT) photorheology experiments of thin films showed a rapid degelation in several seconds, whereas larger bulk samples could also be photocleaved. Furthermore, the gels could be reformed or healed by simple heating of the system and restoration of the metal–ligand crosslinks. The relatively simple dynamic system with a high sensitivity towards light in the visible and NIR region make them interesting positive photoresists for nano/micropatterning applications, as was demonstrated by writing, erasing, and rewriting of the gels by single‐ and multiphoton lithography.

Visible Light Photocleavable Ruthenium-Based Molecular Gates to Reversibly Control Release from Mesoporous Silica Nanoparticles

“…Significantly, an increased signal detected under darkness after 300 min demonstrated the maximum stability of the system in the suspension (data not shown). In acetonitrile, the photocleavage follows a two-step process, as already reported [24], where the cleavage of the first ligand is significantly faster than the second one. In contrary, in water only one ligand is expected to cleave.…”

“…Indeed, while originally investigated for the release of biologically active molecules [22], such complexes have recently been used in materials science to prepare photocleavable hydrogels [23]. The reaction has also been demonstrated to be reversible according to the solvents and ligand combinations, leading to the development of dynamic self-healable photoresponsive polymers, reported by our group [24], and for reconfigurable surfaces developed by Wu and co-workers that can be photochemically manipulated in rapidly changing environments [25].…”

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“… 1029 Similarly, supramolecular crosslinked gels with a photosensitive ruthenium bipyridine complex functioning as a crosslinker and poly(4-vinylpyridine) as a macromolecular ligand were developed by Teasdale and Monkowius. 1030 Photolysis of these organogels with visible (>395 nm) and NIR light (1028 nm; a multiphoton process) resulted in the liberation of the pyridine moieties and degelation.…”

Green-light photocleavable meso-methyl BODIPY building blocks for macromolecular chemistry

“…A significant class of photoclip compounds include those classically termed "photocages", defined as materials that release a molecule upon irradiation due to cleavage of a specific bond 13,14 . Examples of commonly investigated photocages include o-nitrobenzyl 15,16 or coumarinyl [17][18][19] groups and metal-complexes such as ruthenium 8,20 among others 4,13,14,21 . The vast majority of reported chromophores are predominantly receptive to light-absorption in the ultra-violet (UV) or near UV range and consequently suffer from a low material penetration depth, as well as photodamage when used in biological tissue 4 .…”