For example, the electrode materials can influence the electronic coupling between electrodes and molecules, such as the interaction of electrode-anchoring group and the alignment of the energy level of electrode-molecule [8, 9]. Typically, most of the conductance measurements of single-molecule junctions were performed by using Au as electrode for its chemically inert property [10]. However, it is also important to study the non-Au electrodes to fully understand the charge transport through single-molecule junctions. We pay attention to the Ag electrodes for the following reasons: Ag has strong optical enhancement property and high catalytic activity [10–12]. It

has a similar electronic structure with Au and Cu and is easy for comparison among them. Single-molecule conductance can be measured by scanning tunneling microscopy (STM) break junction (STM-BJ), mechanically controllable break junction DihydrotestosteroneDHT research buy (MCBJ), STM trapping and conducting atomic force microscopy, and so on [13–21].

Though lots of works have been done on the electron transport of single-molecule junctions by using the above methods, there is limited investigation on single-molecule junctions with non-Au electrodes [10, 22]. We have developed an electrochemical jump-to-contact scanning tunneling microscopy break junction approach (ECSTM-BJ) [23]. By using this approach, single-molecule junctions with carboxylic acid binding to different metallic electrodes were systematically investigated [9, 24]. Since the pyridyl group also ��-Nicotinamide mw has received much attention [15, 17, 25–27], we recently extended this approach to the conductance measurement of pyridyl-based molecules binding to Cu electrode, which shows that the single-molecule conductance with pyridyl-Cu contacts

is smaller than that with pyridyl-Au contacts [28]. In this work, we focus on the single-molecule junctions with pyridyl group (Figure 1a) binding to Ag contacts by ECSTM-BJ. Especially, the influence of the electrochemical potential on the Fermi level of electrode is discussed. Figure 1 Molecular structure and schematic diagram of ECSTM-BJ. (a) Molecular structures of 4,4′-bipyridine (BPY), 1,2-di-(pyridin-4-yl)ethene Smoothened (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA), and (b) schematic diagram of Ag-molecule-Ag junctions formed by the ECSTM-BJ. Methods Au(111) was used as substrate, and mechanically cut Pt-Ir (Φ = 0.25 mm) wires were used as the tips. The latter was insulated by the thermosetting polyethylene glue to reduce the leakage current of the electrochemical reaction. Ag and Pt wire were used as the reference and counter electrodes, respectively. 1,2-Di(pyridin-4-yl)ethene (BPY-EE) and 1,2-di(pyridin-4-yl)ethane (BPY-EA) were purchased from Sigma-Aldrich Corp. (St. Louis, MO, USA), while 4,4′-bipyridine (BPY) and Ag2SO4 (99.999%) were purchased from Alfa Aesar (Ward Hill, MA, USA). H2SO4 was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).