The Effect of Different Anchor Groups on Spectral and Electronic Properties of Single Molecule Junctions

Abstract

Understanding charge transport of single molecules sandwiched between electrodes is of fundamental importance for molecular electronics. The structural properties of oligo (phenylene-ethynylene) (OPE) with five different anchor groups (thiol (SH), pyridine (PY), methyl sulfide (SMe), tetramethylsilane (TMS) and dibenzothiophene (DBT)). The optimized molecular junction geometries conform well to a description of the SH, SMe and BDT contacted compounds forming an angle of 52º contact between anchor groups and the under coordinated gold atoms of the gold electrodes. In addition, it shows that PY and TMS contact groups create an angle of 160°.Undoubtedly, these structural aspects will affect the junction formation probability and all other properties (electronic and spectral) of these molecules. On the other hand, The transmission coefficient value of all molecules was high. This can understand in terms of the quantum interference is a constructive interference and there is not a destructive interference signature and that (OPE-1) introduces a high value of transmission coefficient (5.8×10^-4), while the lowest value of the transmission (3.12×10^-6) is presented by molecule (OPE-4). The molecule OPE-4 with TMS anchor groups produces the highest f_em (2.4), while the molecule (OPE-2) with PY contact groups shows the lowest f_em (1.8).