Vibrational excitations
provoked by coupling effects during charge
transport through single molecules are intrinsic energy dissipation
phenomena, in close analogy to electron–phonon coupling in
solids. One fundamental challenge in molecular electronics is the
quantitative determination of charge-vibrational (electron–phonon)
coupling for single-molecule junctions. The ability to record electron–phonon
coupling phenomena at the single-molecule level is a key prerequisite
to fully rationalize and optimize charge-transport efficiencies for
specific molecular configurations and currents. Here we exemplarily
determine the pertaining coupling characteristics for a current-carrying
chemically well-defined molecule by synchronous vibrational and current–voltage
spectroscopy. These metal-molecule-metal junction insights are complemented
by time-resolved infrared spectroscopy to assess the intramolecular
vibrational relaxation dynamics. By measuring and analyzing the steady-state
vibrational distribution during transient charge transport in a bis-phenylethynyl-anthracene
derivative using anti-Stokes Raman scattering, we find ∼0.5
vibrational excitations per elementary charge passing through the
metal-molecule-metal junction, by means of a rate model ansatz and
quantum-chemical calculations.
The polymer dynamics in concentrated solutions of poly(N-isopropyl acrylamide) in water/methanol mixtures is investigated using light and neutron scattering.
Infrared-activated vibrations in
the fingerprint region induced
by structural rearrangement of the polymer in the presence of a charge
are used to identify polaronic species in femtosecond spectroscopy.
This is possible without resorting to complex spectral modeling or
excitation density dependence of the different charge carriers. Their
dynamics are investigated in bulk heterojunctions formed of a polythiophene
derivative with TiO2 nanoparticle acceptors, as well as
in the pure polymer. The water-soluble polymer poly[3-(potassium-6-hexanoate)thiophene-2,5-diyl]
(P3P6T) is compared with the intensely studied poly(3-hexylthiophene-2,5-diyl)
(P3HT). Distinct bands are attributed to polarons and polaron pairs.
Pairs with a lifetime of a few picoseconds are generated within the
time resolution. In the presence of the acceptor, polaron yield rises
with respect to the generated polaron pairs. Diffusion of polarons
from 10 ps onward is identified as being either of predominantly intrachain
or interchain character, depending on the degree of order present
in the polymer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.