Supramolecular Chirality Synchronization in Thin Films of Plasmonic Nanocomposites

Mirror
symmetry breaking in materials is a fascinating phenomenon
that has practical implications for various optoelectronic technologies.
Chiral plasmonic materials are particularly appealing due to their
strong and specific interactions with light. In this work we broaden
the portfolio of available strategies toward the preparation of chiral
plasmonic assemblies, by applying the principles of chirality synchronizationa
phenomenon known for small molecules, which results in the formation
of chiral domains from transiently chiral molecules. We report the
controlled cocrystallization of 23 nm gold nanoparticles and liquid
crystal molecules yielding domains made of highly ordered, helical
nanofibers, preferentially twisted to the right or to the left within
each domain. We confirmed that such micrometer sized domains exhibit
strong, far-field circular dichroism (CD) signals, even though the
bulk material is racemic. We further highlight the potential of the
proposed approach to realize chiral plasmonic thin films by using
a mechanical chirality discrimination method. Toward this end, we
developed a rapid CD imaging technique based on the use of polarized
light optical microscopy (POM), which enabled probing the CD signal
with micrometer-scale resolution, despite of linear dichroism and
birefringence in the sample. The developed methodology allows us to
extend intrinsically local effects of chiral synchronization to the
macroscopic scale, thereby broadening the available tools for chirality
manipulation in chiral plasmonic systems.