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Effects of Substitution on Reorganization Energies in Oligo(-phenylene ethynylene) Molecular Wires



Steven W. Robey, Jacob Ciszek, J M. Tour


Observations of non-linear transport characteristics in nanoscale junctions triggered interest in phenylene ethynylene oligomers as potential electronic switching elements. Motivated by suggestions of vibronic origins for this behavior, we have studied intramolecular reorganization effects with a focus on examining the effect of -NO2 group substitution on reorganization energies, ereorg. Optical absorption and gas phase photoelectron data provide experimental estimates for reorganization energies involved in the formation of excitonic and cationic states, respectively. These measurements suggest ereorg is in the range from about 200 to 400 meV for OPE. Measurements also suggest a similar value for the -NO2 substituted molecule. Consideration of data for both OPE and NO2-OPE leads to a value of 350 100 meV for this molecular system. Complementary calculations of ereorg, based on adiabatic potential energy surfaces, were also performed. Depending on the DFT functional and basis set employed, values range between about 100 meV and 230 meV. Calculations indicate that ereorg for both holes and electrons are significantly larger than the comparable fused ring acene, anthracene. Calculations reveal that cation relaxation is nearly independent of -NO2 substitution, but suggest that the anion reorganization energy might be increased by as much as 33 % for the NO2-OPE molecule compared to OPE.
Journal of Physical Chemistry C


electronic structure, molecular electronics, nanotechnology, negative differential resistance, vibronic


Robey, S. , Ciszek, J. and Tour, J. (2008), Effects of Substitution on Reorganization Energies in Oligo(-phenylene ethynylene) Molecular Wires, Journal of Physical Chemistry C (Accessed April 15, 2024)
Created October 16, 2008