Side-Group Effect on Electron Transport of Single Molecular Junctions.

Miao-Ling Huang,Chen Wang,Yong Shao,Ju-Fang Zheng,Xiao-Shun Zhou,Fan Zhang,Hui-Ling Mao,Jin-Xuan Liu,Hu-Jun Xie,Jin-Liang Zhuang

doi:10.3390/mi9050234

Abstract

In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4′-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au electrodes. For the BPY molecular junction, two sets of conductance were found with values around 10−3.1 G0 (high G) and 10−3.7 G0 (low G). The addition of nitro side-group(s) onto the pyridine ring resulted in lower conductance of 10−3.8 G0 for BPY-N and 10−3.9 G0 for BPY-2N, respectively, which can be attributed to the twist angle of two pyridine rings. Moreover, the steric hindrance of nitro group(s) also affects the contacting configuration of electrode-molecule-electrode. As a consequence, only one set of conductance value was observed for BPY-N and BPY-2N. Our work clearly shows the important role of side-groups on the electron transport of single-molecule junctions.

Highlights

Single-molecular junctions have received much attention in recent decades, as they can allow for learning the properties of single molecules, especially the electron transport through single molecules [1,2,3,4]
This effect has been well demonstrated by Xiao et al [15]. They found that the addition of nitro groups to the oligo(phenylene ethynylene)s (OPE)-based single molecular junctions significantly decreases the single molecular conductance due to the HOMO-dominated electron transport in the electrochemical surrounding
Upon varying the number of nitro side-groups, the values of single molecular conductance follow the order of GBPY-2N < GBPY-N < GBPY

Summary

Introduction

Single-molecular junctions have received much attention in recent decades, as they can allow for learning the properties of single molecules, especially the electron transport through single molecules [1,2,3,4]. In electrode-molecule-electrode junctions, molecular structures, electrode materials, anchoring groups, contacting configurations, and environments play important roles in electron transport of single molecular junctions [2,10,11,12,13]. Rance of nitro group(s) contribute to the electron transport of single-molecule junctions. MMaatteerriiaallss aanndd MMeetthhooddss 44,,44′--BBiippyyrriiddiinnee ((BBPPYY)) wwaass bboouugghhtt ffrroomm AAllffaa AAeessaarr ((WWaarrdd HHiillll,, MMAA,, UUSSAA)),, wwhhiillee 33--nniittrroo--44--. ((ppyyrriiddiinn--44--yyll))ppyyrriiddiinnee ((BBPPYY--NN)) aanndd 33--nniittrroo--44--((33--nniittrrooppyyrriiddiinn--44--yyll))ppyyrriiddiinnee ((BBPPYY--22NN)) wweerree ssyynntthheessiizzeedd aaccccoorrddiinnggttooaarreeppoorrtteeddpprroocceedduurerewwitihthslsilgihght tmmodoidfiicfiactaiotinon[2[02]0(]d(edtaeitlaoilfotfhtehseysnythnethsiesscisancabnebfoeufonudnidn tihnethSeupSupplepmleemnteanrtyarMyaMteartiaelrsia).ls). CCoonndduuccttaannccee mmeeaassuurreemmeenntt wwaass ppeerrffoorrmmeeddoonnaaNNaannoossccooppeeIIIIIIaaSSTTMM((VVeeeeccoo,,PPllaaiinnvviieeww,,NNYY,, UUSSAA)),, wwhhiicchh wwaass mmooddiififieedd ttoo ppeerrffoorrmm tthhee ssccaannnniinngg ttuunnnneelliinngg mmiiccrroossccooppee bbrreeaakk jjuunnccttiioonn ((SSTTMM--BBJJ)) [[1111,,2211]]. .TThheeccoonndduuccttaannccee mmeeaassuurreemmeenntt wwaass ccaarrrriieedd oouutt aatt aa bbiiaass vvoollttaaggee ooff 110000 mmVV aanndd nnoorrmmaalliizzeedd bbyy tthhee nnuummbbeerr ooff uusseedd ccuurrvveess. This value is comparable with previously reported results [7,28]. Rupture ddiissttaannccee oobbttaaiinneeddffrroommcoconndduuctcatanncecevavlauleueofo1f01−05−−.550..00GG000ttoo1100−−−000..3.33GG000(0(0.5.5GG000))inineevveerryy ccoonndduuccttaanncceeccuurrvvee((aa)) BBPPYY, (b) BPPYY--NN,, aanndd ((cc)) BBPPYY--22NN

Discussion

Conclusions