Incorporation of V(V) clusters into polymer hydrogels has been used to impart photo-responsive behavior and this results in tuning of the properties of the hydrogel during light irradiation. To define the photochemistry in these systems, V(V) coordinated to simple hydroxy acids (tartrates) was used to represent polyoxovanadates. The photochemistry was studied using Ultraviolet visible spectrometry, X–ray crystallography, gas chromatography, FTIR and electron paramagnetic resonance (EPR) spectroscopy. Irradiation at 365 nm caused the V(V) tartrate to change from yellow through green to brownish purple, developing a characteristic three–band absorption spectrum with maxima corresponding to a V(IV) photoproduct. EPR spectroscopy confirmed a reduction from diamagnetic V(V) to paramagnetic V(IV) taking place with the growth of an 8-line V(IV) hyperfine pattern over time. Inspired by these findings we have now developed interesting macroscopic effects in cellulose-agarose hydrogels with the light responsive properties of vanadium. A concomitant oxidative decarboxylation of the polysaccharide was noticeable upon the reduction of V(V) to V(IV). This reduction of the metal ion and possible breakdown of polysaccharide chain induce irreversible changes in the microstructure of the hydrogel which enables the controlled delivery of V(IV) and possibly an encapsulated cargo. A significant drop in hydrogel properties like storage and loss modulus, viscosity drop in polymer solution and increase in pore sizes were observed through irradiation. Interestingly, a photomask can be used to create discrete patterns on these materials upon irradiation. We now expect to develop exciting macroscopic effects with the light responsive properties of vanadium in polysaccharide-based materials.

Photochemistry of vanadium clusters and applications for responsive materials

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.