Design of nanoscale molecular wire based on 3, 6-Diphenyl-1, 2, 4, 5-Tetrazine and effect of external electric field on electron transfer in conjugated molecular wire Z. Bayat a,n , S. Danesh nia a , S.J. Mahdizadeh b a Department of Chemistry, Islamic Azad University-Quchan Branch, Iran b Department of Chemistry, Ferdowsi University of Mashhad, Mashhad, Iran article info Article history: Received 9 September 2010 Received in revised form 16 March 2011 Accepted 22 March 2011 Available online 14 April 2011 abstract The electron transport characteristics of a 3, 6-Diphenyl-1, 2, 4, 5-Tetrazine (DPT) single molecular conductor are investigated via the density functional theory (DFT) method. The molecule sandwiched between two gold surfaces. Different linkers such as sulfur, nitrogen, oxygen, CS, CO, CN, NO and NN have been considered to study the role of linkage in the conduction properties of the molecular wire. The charge transfer across the metal–molecule and bonding nature at the interfacial contact were performed by means of the natural bond orbital (NBO) analysis. It is found that Au can covalently bond to DPT through nitrogen or sulfur linkages while its weak interaction through oxygen linkage has non- covalent character in nature. The dependence of the molecular electronic structure of the gold– molecule complexes on the external electric field (EF) has also been studied. It is found that the external EF modifies both the geometry and electronic structure of the molecular wires. The application of EF may increase the molecular conjugation and the induced dipole moment, while decreasing the HOMO–LUMO gap. It may also make the spatial distributions of the frontier molecular orbital’s move from a fully delocalized form to a partially localized one depending on the EF strength. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Comprehension of chemical interaction between electrode metals and molecular wires is very fundamental and important to the basic design of single-electron devices. One of the most important goals in the engineering of electronic devices is the miniaturization. The present technologies of micro-structuring semiconductor material are expected to reach their limits in the next decade. Nanoscale charge transfer is important to both the frontier of fundamental science and to applications in molecular electronics including problems as diverse as sensors, photonics, electro-catalysis, and solar photo conversion. Recently the trans- port behavior of coupled quantum dot systems were studied using the master (rate) equation approach in the Coulomb blockade regime [1]. Progress in the area of nanoscale charge transfer requires interdisciplinary collaboration, combining a wide range of materials synthesis and characterization, a challen- ging range of experimental techniques to probe charge-transfer processes, as well as theory for their interpretation. Current interest ranges from the utilization of single or small groups of (usually organic) molecules as components in electronic devices to the exploitation of semiconductor and metal nanoparticles because of their high surface areas and other size-dependent properties [2]. Over thirty years ago, Aviram and Ratner [3] proposed theoretically that molecular wire should have the ability to rectify electronic current. Construction of a molecular wire requires an elongated molecule consisting of conjugated molecular units, which contain alternating single and double (or triplet) bonds through which electron can flow easily from one end to other. Recently, many experimental [4–6] and theoretical studies [7–10] have elucidated the transport properties through metal/molecule/metal heterostructures. A particular challenge stems from the realization that the properties of molecular wires are strongly influenced by (i) characteristics of the molecule, (ii) the nature of linkage, and thus metal–molecule interaction [11]. In the molecular level, the quantum effects play an important role. A theoretical analysis of the frontier molecular orbitals of these molecules will give a clear picture of the structure–property relationship and ultimately the synthetic strategy and molecular engineering techniques and energy difference between HOMO and LUMO known as HOMO–LUMO gap (HLG) can be utilized to reach the reality [12–14]. Here, HOMO denotes the highest occupied molecular orbital while LUMO shows the lowest unoc- cupied molecular orbital [15,16]. The energy gap has been Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2011.03.018 n Corresponding author. Tel.: þ989151811750; fax: þ985812233239. E-mail address: z.bayat@ymail.com (Z. Bayat). Physica E 43 (2011) 1569–1575