Controlling the lifetimes of dynamic nanoparticle aggregates by spiropyran functionalization

Abstract

Novel light-responsive nanoparticles were synthesized by decorating the surfaces of gold and silver nanoparticles with a nitrospiropyran molecular photoswitch. Upon exposure to UV light in nonpolar solvents, these nanoparticles self-assembled to afford spherical aggregates, which disassembled rapidly when the UV stimulus was turned off. The sizes of these aggregates depended on the nanoparticle concentration, and their lifetimes could be controlled by adjusting the surface concentration of nitrospiropyran on the nanoparticles. The conformational flexibility of nitrospiropyran, which was altered by modifying the structure of the background ligand, had a profound impact on the self-assembly process. By coating the nanoparticles with a spiropyran lacking the nitro group, a conceptually different self-assembly system, relying on a reversible proton transfer, was realized. The resulting particles spontaneously (in the dark) assembled into aggregates that could be readily disassembled upon exposure to blue light.

Recent Implementations of Molecular Photoswitches into Smart Materials and Biological Systems

“…Non‐photochromic NPs decorated with carboxylic acid groups can change their assembly state upon irradiation of the surrounding SP‐containing photoswitchable medium, in which acidity is reversibly increased upon exposure to blue light (Figure b) . Alternatively, gold and silver NPs with surfaces decorated with SP could be reversibly aggregated in nonpolar solutions with UV light …”

The Many Ways to Assemble Nanoparticles Using Light

“…c) Rapid disassembly of aggregates of spiropyran‐functionalized gold NPs at different fractional coverages of the NPs with spiropyran. b,c) Reproduced with permission . Copyright 2016, The Royal Society of Chemistry.…”

“…The τ 1/2 values of MC in toluene are as much as four orders of magnitude smaller than those of typical cis ‐azobenzenes (τ 1/2 ≈ 1 day in toluene). To verify whether this large difference in the stability of the metastable forms could translate into the lifetimes of NP aggregates induced by cis ‐AB versus MC, Kundu and co‐workers synthesized differently sized nanoparticles and nanoclusters decorated with a thiolated spiropyran. Indeed, aggregates generated by briefly (<1 min) irradiating these NPs to UV light (Figure b) persisted for much shorter periods, with their decomposition in the dark complete within as little as 1 min (Figure c; compare with days for AB‐coated NPs) .…”

Photoresponsive Passive Micromixers Based on Spiropyran Size‐Tunable Hydrogels

“…[28][29][30][31][32][33] This shape change can also be achieved using light by incorporation of a photochromic dye in the poly mer hydrogel. [34][35][36][37][38] Upon switching the illumination on and off, [39] the volume of the hydrogel can be switched between two states. Tuning these switching conditions, i.e., the isomerization rates, [40][41][42] macromolecular machines can be achieved that can be switched on and off.…”