Effect of Bridging Manner on the Transport Behaviors of Dimethyldihydropyrene/Cyclophanediene Molecular Devices

Abstract

A molecule-electrode interface with different coupling strengths is one of the greatest challenges in fabricating reliable molecular switches. In this paper, the effects of bridging manner on the transport behaviors of a dimethyldihydropyrene/cyclophanediene (DHP/CPD) molecule connected to two graphene nanoribbon (GNR) electrodes have been investigated by using the non-equilibrium Green's function combined with density functional theory. The results show that both current values and ON/OFF ratios can be modulated to more than three orders of magnitude by changing bridging manner. Bias-dependent transmission spectra and molecule-projected self-consistent Hamiltonians are used to illustrate the conductance and switching feature. Furthermore, we demonstrate that the bridging manner modulates the electron transport by changing the energy level alignment between the molecule and the GNR electrodes. This work highlights the ability to achieve distinct conductance and switching performance in single-molecular junctions by varying bridging manners between DHP/CPD molecules and GNR electrodes, thus offering practical insights for designing molecular switches.

Keywords: bridging manner; density functional theory; dimethyldihydropyrene/cyclophanediene; molecular switches.

Figure 1

(a) Molecular geometries of DHP/CPD in front and side view. (b) Schematic diagram of DHP/CPD molecular junctions with GNR electrodes.

Figure 2

Geometric structures of the molecular junctions J1~J4. The gray and white balls represent C and H atoms, respectively. J1 and J2 are constructed by connecting a DHP/CPD to GNRs by CH₂ groups, except there is a vacancy at an edge C atom (circled by the blue dashed line) at the electrode in J2 and the C atoms connected to it are all saturated by H atoms. J3 and J4 have the same electrode edge structure as J2, except the groups between molecule and electrodes are different (circled by the red dashed lines).

Figure 3

Calculated current–voltage (I–V) characteristics and ON/OFF ratios of the molecular junction J1 (a), J2 (b), J3 (c) and J4 (d).

Figure 4

Transmission spectra of the closed form and open form for J1~J4 junctions at zero bias. The E_F is set at zero on the energy scale.

Figure 5

Bias-dependent transmission spectra of J1~J4 junctions. The white dashed lines in each subgraph represent the bias window.

Figure 6

Projected density of states (PDOS) spectra for the central region of J1c~J4c junctions when the bias voltage is set to 0 V (a) and 1.0 V (b). The projection subspace of the scattering region can be divided into three parts, i.e., the left GNR (including the left bridging group), the molecule and the right GNR (including the right bridging group). Local density of states (LDOS) for the central region at E_F under 0 V bias (c). An isovalue of 0.005 is chosen for all plots.

Figure 7

Spatial distribution of the frontier molecular orbitals on the central regions of J1~J4 junctions at zero bias. The isovalue is set to 0.01 for all plots.