Control of Electron Transport by Manipulating the Conjugated Framework

Abstract

We present a systematic analysis of molecular level alignments and electron transport characteristics based on the nonequilibrium Green's function (NEGF) approach combined with density functional theory (DFT) for six conjugated molecules (PTP, CPTP, NiPTP, CoPTP4, CoPTP5, and FePTP) containing different types of conjugated frameworks. The conjugated molecules are classified into three groups according to the incorporated component into the conjugated framework where group I, group II, and group III contain antiaromatic, nonaromatic, and aromatic units, respectively. The results show that the combining of non- and antiaromatic components increases the conductance due to the close alignment of the HOMO level relative to the Fermi level. Consequently, the order of current follows the manner of group I > group II > group III ([NiPTP > CoPTP4 > CPTP] > [CoPTP5 > FePTP] > [PTP]). The important feature emerging from this work is that the distinct response of each group to molecule-contact coupling and applied bias voltage causes distinguishable features of electron transport characteristics and these factors may give an insight into the design of new nanoscale molecular electronic devices.

A single molecule rectifier with strong push-pull coupling

“…13 We have used HF instead of density functional theory because hybrid exchange-correlation functionals, local density approximation, and generalized gradient approximation, are well known to overestimate the polarizabilities of quasilinear systems and do not reproduce the localization of the molecular orbitals and inversion behavior observed with HF-based methods. Electronic addresses: agsf@fisica.ufc.br and jordan@ufpa.br.…”

The Role of Aromaticity and the π‐Conjugated Framework in Multiporphyrinic Systems as Single‐Molecule Switches

“…The contacts and the devices are described using the LanL2DZ basis set19 incorporating relativistic core pseudopotentials, because this basis set provides a good description of the contact surface density of states around the Fermi level 20. The details of our approach and theoretical formula for computing the physical observations are described in our previous work 5…”

“…Herein, we define the device part as an “extended molecule” including the molecule itself and six nearest‐neighbor gold atoms on each metal surface, to account for the charge and potential perturbations of the metal surface caused by molecular adsorption 5. The geometry of the adsorbed molecule is taken to be the same as the singlet geometry of the free molecule optimized at the B3PW91/6‐31G(d) level of theory.…”

“…Since the advent of molecular electronics,1 an abundance of organic functional molecules have been designed and investigated as components in electronic devices, such as molecular wires, rectifiers, and switches 2. Accompanied by the synthesis of functional organic molecules, the advancement of techniques for characterizing and manipulating individual molecules3 and the availability of first‐principles methods to describe electron tunneling through atomic chains or single molecules4, 5 make it possible to realize molecular electronic devices. Among functional molecules, porphyrin is one of the most extensively studied macrocyclic systems because it offers a variety of desirable features, such as a rigid planar geometry, high stability, intense electronic absorption and emission, a small highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, and an 18 π ‐conjugated electronic network in a square‐planar circuit.…”

“…Therefore, each isomer has a different arrangement of porphyrin units and aromatic character accompanying the different contact structures (see Figure 1). It is of interest to investigate the electron‐transport characteristics of multiporphyrinic systems according to the contact structures, by taking into consideration the concept of aromaticity and the π ‐conjugated framework 5. We propose multiporphyrinic systems as prospective building blocks for molecular devices through the understanding of the structural dependence of electron transport.…”