Photoresponsive Photoacid-Macroion Nano-Assemblies

Abstract

In this study, light-responsive nano-assemblies with light-switchable size based on photoacids are presented. Anionic disulfonated napthol derivates and cationic dendrimer macroions are used as building blocks for electrostatic self-assembly. Nanoparticles are already formed under the exclusion of light as a result of electrostatic interactions. Upon photoexcitation, an excited-state dissociation of the photoacidic hydroxyl group takes place, which leads to a more highly charged linker molecule and, subsequently, to a change in size and structure of the nano-assemblies. The effects of the charge ratio and the concentration on the stability have been examined with absorption spectroscopy and ζ-potential measurements. The influence of the chemical structure of three isomeric photoacids on the size and shape of the nanoscale aggregates has been studied by dynamic light scattering and atomic force microscopy, revealing a direct correlation of the strength of the photoacid with the changes of the assemblies upon irradiation.

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

“…Atomic force microscopy (AFM) was performed using a NanoWizard 4 from JPK instrument (Berlin, Germany) operated in the tapping-mode with a fixed-spring cantilever holder and a USC-F0.3-k0.3-10 ultrashort cantilever with a force constant of 0.3 Nm −1 . The cantilever has been tested and established for organic samples of low height [ 67 , 84 ]. The AFM samples were prepared by drop-casting the solution on cleaved mica substrate.…”

“…While it had been well-established to access oligomer formation and gelation, a light-switchable particle size has remained a challenge until realized through the mentioned electrostatic self-assembly combining a polyelectrolyte and an ionic azo dye [ 4 ]. Moreover, recently we have developed a switchable nano-assembly system based on photoacids [ 66 – 67 ]. Photoacids are molecules for which light irradiation leads to an enhanced proton dissociation and thus to a more highly charged molecule.…”

Functional Nano-Objects by Electrostatic Self-Assembly: Structure, Switching, and Photocatalysis

“…After this study, the Gröhn group extended the systems to develop a deeper understanding. Different photoacids were combined with G4 dendrimer ( Zika et al, 2020 ). In this case, the photoacids have already two negative charges in the ground state.…”

Joining Two Switches in One Nano‐Object: Photoacidity and Photoisomerization in Electrostatic Self‐Assembly

“…Electrostatic self‐assembly allowed to address the size of nano‐objects in solution [50] . In the recent past, we have utilized the special property of photoacids, an excited‐state proton dissociation, to trigger both, nano‐object formation and size [51–53] …”