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.
Highlights
Inorganic nanoparticles (NPs) exhibit a host of fascinating physicochemical properties, many of which can be controlled by modulating the NP–NP coupling.[1,2] For example, optical,[3,4] magnetic,[5] electronic,[6,7] and SERS8,9 properties have been manipulated by adjusting the interparticle distance
Our initial experiments with model compounds confirmed this reasoning: we found that whereas the cis form of a simple azobenzene decayed with a first-order rate constant of k ≈ 0.41 day−1, the open-ring isomer of the parent spiropyran isomerized with k ≈ 0.13 s−1 – i.e., over four orders of magnitude faster
Encouraged by these results, we hypothesized that the dark lifetimes of the aggregates of MC-decorated NPs would be markedly shorter than those assembled from the same NPs functionalized with monolayers of azobenzene, and that it should be possible to control the aggregate lifetimes by adjusting the surface concentration of spiropyran
Summary
Inorganic nanoparticles (NPs) exhibit a host of fascinating physicochemical properties, many of which can be controlled by modulating the NP–NP coupling.[1,2] For example, optical,[3,4] magnetic,[5] electronic,[6,7] and SERS8,9 properties have been manipulated by adjusting the interparticle distance. All of the above systems and applications suffer from the drawback that in order to induce a fast backisomerization reaction (and the disassembly of NP aggregates) within short time scales, applying a second stimulus (namely, visible light) is required In light of this limitation, it would be desired to fabricate NP aggregates that disassemble as soon as the stimulus inducing self-assembly is removed. Working with significantly larger (∼300–900 nm) silica colloids coated with a spiropyran-rich polymer shell, Bell and Piech found that the disassembly in the dark was complete in >3 hours Encouraged by these results, we hypothesized that the dark lifetimes of the aggregates of MC-decorated NPs would be markedly shorter than those assembled from the same NPs functionalized with monolayers of azobenzene, and that it should be possible to control the aggregate lifetimes by adjusting the surface concentration of spiropyran
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
