2 research outputs found
Kondo Effect in a Neutral and Stable All Organic Radical Single Molecule Break Junction
Organic radicals are neutral, purely
organic molecules exhibiting an intrinsic magnetic moment due to the
presence of an unpaired electron in the molecule in its ground state.
This property, added to the low spināorbit coupling and weak
hyperfine interactions, make neutral organic radicals good candidates
for molecular spintronics insofar as the radical character is stable
in solid state electronic devices. Here we show that the paramagnetism
of the polychlorotriphenylmethyl radical molecule in the form of a
Kondo anomaly is preserved in two- and three-terminal solid-state
devices, regardless of mechanical and electrostatic changes. Indeed,
our results demonstrate that the Kondo anomaly is robust under electrodes
displacement and changes of the electrostatic environment, pointing
to a localized orbital in the radical as the source of magnetism.
Strong support to this picture is provided by density functional calculations
and measurements of the corresponding nonradical species. These results
pave the way toward the use of all-organic neutral radical molecules
in spintronics devices and open the door to further investigations
into Kondo physics
Operative Mechanism of Hole-Assisted Negative Charge Motion in Ground States of Radical-Anion Molecular Wires
Charge
transfer/transport in molecular wires over varying distances
is a subject of great interest. The feasible transport mechanisms
have been generally accounted for on the basis of tunneling or superexchange
charge transfer operating over small distances which progressively
gives way to hopping transport over larger distances. The underlying
molecular sequential steps that likely take place during hopping and
the operative mechanism occurring at intermediate distances have received
much less attention given the difficulty in assessing detailed molecular-level
information. We describe here the operating mechanisms for unimolecular
electron transfer/transport in the ground state of radical-anion mixed-valence
derivatives occurring between their terminal perchlorotriphenylmethyl/ide
groups through thiopheneāvinylene oligomers that act as conjugated
wires of increasing length up to 53 Ć
. The unique finding here
is that the net transport of the electron in the larger molecular
wires is initiated by an electronāhole dissociation intermediated
by hole delocalization (conformationally assisted and thermally dependent)
forming transient mobile polaronic states in the bridge that terminate
by an electronāhole recombination at the other wire extreme.
On the contrary, for the shorter radical-anions our results suggest
that a flickering resonance mechanism which is intermediate between
hopping and superexchange is the operative one. We support these mechanistic
interpretations by applying the pertinent biased kinetic models of
the charge/spin exchange rates determined by electron paramagnetic
resonance and by molecular structural level information obtained from
UVāvis and Raman spectroscopies and by quantum chemical modeling