Correlation of Substituent Parameter Values to Electronic Properties of Molecules
- PDF / 89,806 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 48 Downloads / 159 Views
B9.63.1
Correlation of Substituent Parameter Values to Electronic Properties of Molecules Natalie Carroll1, Nikita Matsunaga2 and Karl Sohlberg1 Chemistry Department, Drexel University Philadelphia, PA, 19104, U.S.A. 2 Department of Chemistry and Biochemistry, Long Island University Brooklyn, N.Y., 11201, U.S.A. 1
ABSTRACT There are a vast number of organic compounds that could be considered for use in molecular electronics. Because of this, the need for efficient and economical screening tools has emerged. We have demonstrated that the substituent parameter values (σ), commonly found in advanced organic chemistry textbooks, correlate very strongly with features of the charge migration process. This result supports the use of the σ values as a low cost time saving tool in the selection of compounds for use in molecular electronic devices. INTRODUCTION The development of single molecule electronic devices is a challenging goal, that if realized could revolutionize computation, remote sensing, medicine etc. Recently there has been considerable effort to both measure the electrical properties of single molecules [1-4] and to describe these properties theoretically [5,6]. The development of molecular electronics technology could be greatly accelerated with a technique for selecting appropriate molecular species from the vast catalog of potential compounds. For various applications, a property termed negative differential resistance (NDR) is particularly desirable. In devices exhibiting NDR, the current as a function of applied voltage is not linear as is the case with classical conductors. Within some range, increasing the applied potential leads to a drop in current. This is known as negative differential resistance (NDR) and can lead to peaks in the I/V characteristic [2,5,7]. It has been experimentally observed that self-assembled monolayers (SAMs) of certain conjugated organic molecules exhibit NDR upon application of a potential difference perpendicular to the SAM [1-2]. As reported, key to NDR is the presence of a nitro substituent (~NO2), such as in the molecule 2’-amino-4-ethynylphenyl-4’-ethynylphenyl-5’-nitro-1benzenethiolate and similar ~NO2 containing molecules. The advantages of using organic compounds as possible molecular wires and nanoelectronic components are a low resistance to electron transfer due to delocalized pi-molecular orbitals [4,8,9], and biocompatibility for bioelectronic devices [10]. The obvious dependence of NDR on the chemical nature of a substituent group present in a molecule, suggested we investigate substituent parameter (σ) values as a possible marker of molecular electronic properties. Historically, it has been observed that substituents influence the chemical behavior of a compound and the σ values were developed to quantify the substituent effect. In the 1930s, Hammet [11] noted that substituents systematically change the free energy of proton dissociation of benzoic acid derivatives and the free energy of hydrolysis of ethyl benzoate derivatives [12]. By plotting the substitue
Data Loading...
