Protonation effects on electron transport through diblock molecular junctions: A theoretical study

et al. 2012

J. Phys. Chem. C

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 [

Section: Introductionmentioning

confidence: 92%

Section: Theoretical Model and Computational Detailsmentioning

confidence: 99%

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

et al. 2012

J. Phys. Chem. C

“…9,10 Furthermore, experiment has found that the rectifying is independent of the temperature in the range between 300 and 50 K. 11 Understanding the mechanism of the rectifiers has been the subject of a great deal of theoretical works. 12−16 The factors affecting the rectification properties, such as protonation of the molecule in acid solution 17,18 and the effect of the molecular length 19,20 have been further investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, diblock co-oligomer diodes with donor–acceptor (D–A) structure have captured a lot of attention as promising intrinsic molecular diodes. − It has been reported that a clear and reproducible rectification can be achieved and the rectifying direction can be controlled by adjusting the molecular orientation. , Furthermore, experiment has found that the rectifying is independent of the temperature in the range between 300 and 50 K . Understanding the mechanism of the rectifiers has been the subject of a great deal of theoretical works. − The factors affecting the rectification properties, such as protonation of the molecule in acid solution , and the effect of the molecular length , have been further investigated.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Rectification in Diblock Co-oligomer Diodes by Adjusting Anchoring Groups for Both Symmetric and Asymmetric Electrodes

Song

et al. 2012

J. Phys. Chem. C

The rectifying properties in dipyrimidinyl-diphenyl co-oligomer diodes with asymmetric anchoring groups were investigated using density functional theory combined with the nonequilibrium Green’s function method. Effects of asymmetric interfaces caused by both the anchoring groups and/or contact geometries of electrodes have been investigated. Our results showed that the rectifying behavior of the co-oligomer diode could be reversed or largely enhanced by adjusting asymmetric anchoring groups. Whether the asymmetric contact geometries play a positive or negative role in improving the rectifying behavior is closely related to each molecular diode. The mechanism of modulation was analyzed in terms of molecular projected self-consistent Hamiltonian states and transmission spectra. The theoretical simulations are helpful for understanding recent experimental results [Lee et al. Langmuir 2009, 25, 1495 and Hihath et al. ACS Nano 2011, 5, 8331]. Moreover, the mechanism of the rectification only due to the electrode asymmetry was explained, and a single-molecule diode with significant rectifying behaviors has been theoretically designed.

“…Asymmetric molecule-electrode contacts include asymmetric terminal anchoring groups, molecule-electrode contact configurations, and electrode materials. It has been found that the rectifying properties of devices can be fine-tuned by changing the molecular length 11 12 , terminal anchoring groups 13 14 15 , side groups 12 , molecule-electrode contact configurations 16 17 18 , the acid-base property of the solution 7 19 20 , and the external potential field 21 .…”

mentioning

confidence: 99%

Rectifying Properties of Oligo(Phenylene Ethynylene) Heterometallic Molecular Junctions: Molecular Length and Side Group Effects

et al. 2014

Sci Rep

The rectifying properties of α,ω-dithiol terminated oligo(phenylene ethynylene) molecules sandwiched between heterometallic electrodes, including the molecular length and side group effects, are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. The results show nonlinear variation with changes in molecule length: when the molecule becomes longer, the current decreases at first and then increases while the rectification shifts in the opposite direction. This stems from the change in molecular eigenstates and the coupling between the molecule and electrodes caused by different molecular lengths. The rectifying behavior of heterometallic molecular junctions can be attributed to the asymmetric molecule-electrode contacts, which lead to asymmetric electronic tunneling spectra, molecular eigenvalues, molecular orbitals, and potential drop at reversed equivalent bias voltages. Our results provide a fundamental understanding of the rectification of heterometallic molecular junction, and a prediction of rectifiers with different rectification properties from those in the experiment, using electrodes with reduced sizes.