3 research outputs found
An Ultimate Stereocontrol in Asymmetric Synthesis of Optically Pure Fully Aromatic Helicenes
The
role of the helicity of small molecules in enantioselective
catalysis, molecular recognition, self-assembly, material science,
biology, and nanoscience is much less understood than that of point-,
axial-, or planar-chiral molecules. To uncover the envisaged potential
of helically chiral polyaromatics represented by iconic helicenes,
their availability in an optically pure form through asymmetric synthesis
is urgently needed. We provide a solution to this problem present
since the birth of helicene chemistry in 1956 by developing a general
synthetic methodology for the preparation of uniformly enantiopure
fully aromatic [5]-, [6]-, and [7]helicenes and their functionalized
derivatives. [2 + 2 + 2] Cycloisomerization of chiral triynes combined
with asymmetric transformation of the first kind (ultimately controlled
by the 1,3-allylic-type strain) is central to this endeavor. The point-to-helical
chirality transfer utilizing a traceless chiral auxiliary features
a remarkable resistance to diverse structural perturbations
Large Converse Piezoelectric Effect Measured on a Single Molecule on a Metallic Surface
The converse piezoelectric effect
is a phenomenon in which mechanical
strain is generated in a material due to an applied electrical field.
In this work, we demonstrate the converse piezoelectric effect in
single heptahelicene-derived molecules on the Ag(111) surface using
atomic force microscopy (AFM) and total energy density functional
theory (DFT) calculations. The force–distance spectroscopy
acquired over a wide range of bias voltages reveals a linear shift
of the tip–sample distance at which the contact between the
molecule and tip apex is established. We demonstrate that this effect
is caused by the bias-induced deformation of the spring-like scaffold
of the helical polyaromatic molecules. We attribute this effect to
coupling of a soft vibrational mode of the molecular helix with a
vertical electric dipole induced by molecule–substrate charge
transfer. In addition, we also performed the same spectroscopic measurements
on a more rigid <i>o</i>-carborane dithiol molecule on the
Ag(111) surface. In this case, we identify a weaker linear electromechanical
response, which underpins the importance of the helical scaffold on
the observed piezoelectric response
Large Converse Piezoelectric Effect Measured on a Single Molecule on a Metallic Surface
The converse piezoelectric effect
is a phenomenon in which mechanical
strain is generated in a material due to an applied electrical field.
In this work, we demonstrate the converse piezoelectric effect in
single heptahelicene-derived molecules on the Ag(111) surface using
atomic force microscopy (AFM) and total energy density functional
theory (DFT) calculations. The force–distance spectroscopy
acquired over a wide range of bias voltages reveals a linear shift
of the tip–sample distance at which the contact between the
molecule and tip apex is established. We demonstrate that this effect
is caused by the bias-induced deformation of the spring-like scaffold
of the helical polyaromatic molecules. We attribute this effect to
coupling of a soft vibrational mode of the molecular helix with a
vertical electric dipole induced by molecule–substrate charge
transfer. In addition, we also performed the same spectroscopic measurements
on a more rigid <i>o</i>-carborane dithiol molecule on the
Ag(111) surface. In this case, we identify a weaker linear electromechanical
response, which underpins the importance of the helical scaffold on
the observed piezoelectric response