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  • 1
    Language: English
    In: Chemical Physics, 01 July 2016, Vol.473, pp.32-39
    Description: Tunneling of electrons through rotor–stator anthracene aldehyde molecular interfaces is studied with a combined and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons’ formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green’s Function Formalism.
    Keywords: Rotor–Stator Molecule ; Anthracene Aldehyde ; Ab Initio ; Tunneling Current ; Quasiclassical Approximation ; Chemistry ; Physics
    ISSN: 0301-0104
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  • 2
    Language: English
    In: Chemical Physics, 2007, Vol.340(1), pp.1-11
    Description: The dynamics of intramolecular torsional motion of central phenylene ring in a series of phenylene ethynylene oligomer derivatives was investigated. On the basis of calculated hindered rotational potentials corresponding to this motion, the torsional energy levels were obtained by solving the torsional Schrödinger equation. Subsequently, the torsional correlation time and transition probability was computed within the Bloembergen–Purcell–Pound (BPP) formalism, considering both the classical and quantum mechanical tunneling contributions to the intramolecular rotation. The results were interpreted in the context of molecular conductivity switching behavior of the considered series of compounds. Also some other parameters relevant to molecular admittance were calculated, such as the HOMO–LUMO energy difference and the spatial extent of the frontier molecular orbitals. Classical electrostatic arguments were applied to understand the physical basis of the conformational stability differences in the studied compounds. It was found that halogenation of the central phenylene ring may be used for fine-tuning of molecular conduction behavior, in the sense of modulating the HOMO–LUMO energy difference, the spatial extent of frontier MOs, as well as the barrier height to torsional motion of the central phenylene ring. The time scale of the temperature induced stochastic conformational switching between the “on” and “off” states, along with the corresponding transition probability could be varied by an order of magnitude upon halogenation of the central phenylene ring. The tunneling contributions to the torsional correlation time were found to be of minor importance in this context, and this quantity may be quite correctly estimated with the classical BPP approach.
    Keywords: Molecular Switching Phenomena ; Phenylene Ethynylene Oligomers ; Molecular Conductance ; Intramolecular Torsions ; Correlation Time ; Frontier Molecular Orbitals ; Density-Functional Theory ; Chemistry ; Physics
    ISSN: 0301-0104
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