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Projeto de investigação
Engineering of Nanostructures with Giant Magneto-Piezoelectric and Multicaloric Functionalities
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Gate-tunable electroluminescence in Aviram-Ratner-type molecules: Kinetic description
Publication . Petrov, Elmar G.; Gorbach, Victor V.; Ragulya, Andrey V.; Lyubchik, Andrey; Lyubchik, Svetlana; DQ - Departamento de Química; LAQV@REQUIMTE; AIP - American Institute of Physics
A theoretical study of the mechanisms of electroluminescence (EL) generation in photoactive molecules with donor and acceptor centers linked by saturated σ-bonds (molecules of the Aviram-Ratner-type) is presented. The approach is based on the kinetics of single-electron transitions between many-body molecular states. This study shows that the EL polarity arises due to asymmetric coupling of molecular orbitals of the photochromic part of the molecule to the electrodes. The gate voltage controls the power of the EL through the occupancy of the excited singlet state. The shifting of the orbital energies forms a resonant or a non-resonant path for the transmission of electrons through the molecule. The action of the gate voltage is reflected in specific critical voltages. An analytical dependence of the critical voltages on the energies of molecular states involved in the formation of EL, as well as on the gate voltage, was derived for both positive and negative polarities. Conditions under which the gate voltage lowers the absolute value of the bias voltage that is responsible for the activation of the resonance mechanism of EL formation were also established. This is an important factor in control of EL in molecular junctions.
Features of superexchange nonresonant tunneling conductance in anchored molecular wires
Publication . Petrov, Elmar G.; Shevchenko, Yevgen V.; Snitsarev, Vladislav; Gorbach, Victor V.; Ragulya, Andrey V.; Lyubchik, Svetlana; DQ - Departamento de Química; LAQV@REQUIMTE; AIP - American Institute of Physics
A modified superexchange model is used to clarify the physical mechanisms for the formation of nonresonant tunneling conductance in terminated molecular wires. Due to the specific relationship between its key parameters, this model has wider areas of applicability compared to the flat-barrier model and the standard superexchange model, which are widely involved for the physical interpretation of experimental results. Moreover, the results obtained in the two latest models appear in the modified model as characteristic limiting cases. Our estimates show that the exponential decay of conductance, characterized by an attenuation factor β (per repeating unit), is limited by the conditions β ≤ 1.2 and β ≥ 3.7 for the flat-barrier and standard models, respectively. At the same time, the modified superexchange model yields β > 0, which, thus, allows us to analyze the tunneling conductance in molecular wires containing both saturated and conjugated bonds. We also show that for a small number of N repeating wire units (about 3-6 depending on the value of β), the exponential dependence of conductance on N is violated and, accordingly, contact conductance is not identical to conductance at N = 0. Formulas are found which, on the basis of experimental data, make it possible to establish the values of superexchange parameters as well as indicate the conditions of possible hybridization between the orbitals of the anchor groups and the adjacent end units belonging to the interior wire region. One example is the establishment of features in the tunneling conductance of terminated alkane chains caused by the nature of their anchor groups.
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Entidade financiadora
European Commission
Programa de financiamento
H2020
Número da atribuição
778072