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The research lead by the PI has made progress in the area of the proposed studies of molecular and nano-scale conductance. In particular, schemes based on both chemical and physical means to control molecular conductances have been investigated by the PI's research group.  We have also made much progress in studying dynamical aspects of the electron transport process.

As reported last year, a high-profile experiment was simulated by our research group.  In the experiment led by Prof. Nuckolls, Co(II)  ions, by combined means of lithography and chemical self-assembly  molecular devices that bridge conjugated organic systems were  assembled (Tang, Jin Yao, et al Angew. Chem. Int. Ed., 46, (2007),  3892) Structure-function relationships, which had not been considered  before, were indicated by the PI's calculations to explain the measurements.[1] More recently we have considered  several chemical modifications that can be applied to the fabrication  scheme for achieving even stronger conductances and abilities for controlling the current.[2] We have considered  changes of the organic ligand to directly increase the spatial overlap due to the stacking interactions. We have also considered changing the bridging  ligand identity.

We have also made progress in other studies that aim to control the  electron transport based on molecular scale properties of the  junction. In one recent study, we elaborate on the symmetry rules  that determine the gating response of the  junction.[3]

Next, we have made substantial progress on the study of dynamical  aspects of the dynamics of electron transport. In our first  publication addressing the time dependent transport, we resolve the transient current through model electronic channels.[4] We then implement the
 derived time-dependent approach to analyze the effect of an existing  bias on the spectra of a molecular system.[4]  Drastic effects of the non-equilibrium conditions are reflected on  the spectra of the biased systems as shown by the modeling.  The bias is shown to both inhibit allowed excitations and to enable  excitations that are otherwise not accessible for the equilibrated system.  These spectral changes are a result of the flux flowing  through the molecular system that must be addressed by a dynamical  perspective. These results are still pending publication.

Finally, most  recently we have modeled a three states system, where current is driven oppositely to an applied constant bias. This negative response is to a photo excitation that leads to  population inversion. The population inversion can be  harvested to yield negative current as reflected by the simulations.  This is a scheme of great importance for the research aiming to  improve energy conversion of solar radiation.

Reference
[1] Perrine, Trilisa M., Berto, Timothy and Dunietz, Barry D. ‘Enhanced Conductance via
Induced pi-Stacking Interactions in Cobalt( II) Terpyridine Bridged Complexes.’ J. Phys.
Chem. B, 112(50), (2008), 16070–16075.
[2] Perrine, T. and Dunietz, B. D. ‘Contact geometry symmetry dependence of field effect
gating in single molecule transistors.’ J. Am. Chem. Soc., Submitted.
[3] Prociuk, A. and Dunietz, B. D. ‘Time-dependent current through electronic channel models
using a mixed time-frequency solution of the equations of motion.’ Phys. Rev. B, 78, (2008),
165112.
[4] Prociuk, A. and Dunietz, B. D. Atomic and Molecular Systems, Dynamics, Spectroscopy,
Clusters, and Nanostructures, chapter On the electronic spectra of a molecular bridge under
non-equilibrium electric potential conditions. Springer (2009).