Theoretical Studies on Protonation-Induced Inversion of the Rectifying Direction in Dipyrimidinyl–Diphenyl Diblock Molecular Junctions

Abstract

The protonation effects on electron transport through a conjugated dipyrimidinyl−diphenyl diblock oligomer sandwiched between two gold electrodes were theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. All configurations of protonation on the dipyrimidinyl group of the molecule were considered. The numerical results show that the protonation prefers to improve electron transport ability through the molecular junction. The transmission spectra around the Fermi energy are tuned by the number and locations of protons residing in the molecular junction. It is found that the protonation in the outer pyrimidinyl is favorable for enhancing the rectification ratio, while the protonation in the inner pyrimidinyl plays a dominative role for inverting the rectifying direction. This theoretical work for the first time presents a mechanism for the experimental findings of inversion of the rectifying effect in diblock molecular diodes caused by protonation [

Proportion effect in diblock co-oligomer molecular diodes

“…The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) [23] is adopted for the exchange-correlation function. The well agreement of previous theoretical simulations with experimental measurements [18,19] suggests that PBE exchangecorrelation functional works well in determining the energy alignment between the molecular frontier orbitals and the metal Fermi level. To focus on the valence electron properties and save the computational effects, the improved Troullier-Martins type norm-conserving pseudopotentials [24] are used to describe the core electrons.…”

“…Here, due to the huge calculation cost we only carried out the structural optimization at zero bias. Our previous works [18,19] indicate that a good agreement with experiments can be still obtained even within this treatment.…”

“…For the dipyrimidinyl-diphenyl diodes, some ab-initio calculations demonstrated that the asymmetric shift of the perturbed molecular energy levels is mainly responsible for the rectification [17][18][19]. In our previous study [20], the mechanisms of rectification in cooligomer diodes is well analyzed by investigating the asymmetric bias effect on the co-oligomer, which revealed the coexistence of two mechanisms in the diblock co-oligomer diode: asymmetric wave functions and asymmetric shift of the molecular levels under biases.…”

Spin Polarization at Organic-Ferromagnetic Interface: Effect of Contact Configuration

“…However, the contact angle between the bonds of the Ni and the S atoms as well as the interacting strength will differ with the change of microscopic contact configurations, which may lead to a different interfacial spin polarization. At last, we further construct a special contact configuration which has been adopted to simulate the adsorption in MCB junctions [26,27]. Here three extra Ni atoms are added on the Ni electrode surface to form an equilateral triangle structure.…”

Spin Logic Gates Operated by Protonation and Magnetism in Molecular Combinational Circuits

“…The four states are named as S1 (magnetic field is up, neutral M1), S2 (magnetic field is down, neutral M1), S3 (magnetic field is up, protonation M1) and S4 (magnetic field is down, protonation M1). In effect, the hydrogen atom can be considered as a simple proton which is coupled with the nitrogen atom [26,27] (The Mulliken population shows that the hydrogen atom is almost charged with +|e|). Prior to commencing the study of transport properties of molecular system in molecular combinational circuits, we first optimize the geometrical configurations of M1, M2, and the two molecules in series using density functional theory (DFT) at the B3LYP level, [22,23] as implemented in the Gaussian package, with a 6-311G (d,p) basis set.…”