3 research outputs found
Light-Directed Patchy Particle Fabrication and Assembly from Isotropic Silver Nanoparticles
We
demonstrate the creation of anisotropic patchy silver nanospheroids
(AgNSs) using linearly polarized UV light and a photo-uncaging <i>o</i>-nitrobenzyl-based ligand, which anchors to the AgNSs by
two gold-sulfur bonds. Exposure to a 1 J/cm<sup>2</sup> dose of UV
light induces a photo-uncaging reaction in the ligand that reveals
a primary amine on the surface. By using linearly polarized UV light,
we meter the exposure dose such that only the poles of the nanoparticle
receive a full dose, limiting the photo-uncaging reaction primarily
to the particle’s plasmonic hot spots. We reveal this anisotropy
by preferentially adhering negatively charged gold nanospheres (AuNSs)
to the AgNSs’ poles by using the electrostatic attraction between
them and the positively charged primary amines generated by photo-uncaging.
When the assembly is performed onto silver particles that are immobilized
on a substrate, it results in nanoscale structures with a strong tendency
to align with the polarization of the exposing light. This manifests
in polarimetric spectroscopy as a linear dichroism aligned with the
polarization direction
Plasmon-Induced Photoreaction of <i>o</i>‑Nitrobenzyl-Based Ligands under 550 nm Light
We
have studied the plasmon-driven photoreaction of a dual thiol-anchored <i>o</i>-nitrobenzyl-based photouncaging ligand on silver nanoparticles.
Previous results have shown that this compound strongly anchors to
gold surfaces, and a 1 J/cm<sup>2</sup> dose of UV light induces the
intended photoreaction, uncaging an amine on the surface. This allows
for photopatterning and the selective adhesion of gold nanospheres
(AuNSs) to a surface via electrostatic attraction between the positively
charged amines and negatively charged AuNSs. Here, we report that
when the ligand is adsorbed on a silver nanospheroid film (AgNS),
an additional photoreaction induced by green light inhibits AuNSs
adhesion in the UV exposed film. Our findings suggest that this is
a result of the neutralization of the amine group’s ability
to become charged, as opposed to the removal of the ligand from the
surface of the silver nanospheroids. We hypothesize that this neutralization
may be due to a form of hot-hole-induced photocatalysis, resulting
in an Nî—»N double bond between two neighboring ligands. This
reaction has been documented in similarly amine-terminated moieties.
This neutralization allows for a more fine-tuned, plasmonically based
control of the ligand’s photoreaction, as the green light exposure
only affects the ligand if it has previously been cleaved by UV light,
and makes it possible to perform reverse photopatterning on the surface
High Photoreactivity of <i>o</i>‑Nitrobenzyl Ligands on Gold
We
have studied the photopatterning of a gold surface functionalized
with a self-assembled monolayer of an <i>o</i>-nitrobenzyl-based
photouncaging ligand bound to the gold surface with a dual thiol anchor.
We find that the dose of UV light required to induce the photoreaction
on gold is very similar to the dose in an alcohol solution, even though
many optical phenomena are strongly suppressed on metal surfaces.
We attribute this finding to a combination of the large skin depth
in gold at UV wavelengths, the high speed of the photoreaction, and
the spatially indirect nature of the lowest excited singlet. Any photoreactive
compounds where the quantum efficiency of fluorescence is sufficiently
low, preferably no larger than about 10<sup>–5</sup> in the
case of gold surfaces, will show a similarly high photoreactivity
in metal-surface monolayers