Ligand-controlled optoelectronic structure and charge transport in oligo(phenylene ethynylene) molecular junctions

Abstract

Abstract

Abstract We present a comprehensive investigation into the effects of ligand substitution on the optoelectronic and electron transport properties of oligo(phenylene ethynylene) (OPE) molecular wires, employing density functional theory in conjunction with the nonequilibrium Green's function formalism. Our results demonstrate that chemical functionalization provides an efficient route to modulate the electronic structure of OPE without disrupting its π-conjugated backbone. Electron-withdrawing substituents, particularly -NO2 and -CN, induce a significant downward shift of the LUMO level, leading to pronounced narrowing of the HOMO-LUMO gap and a redshift of the optical absorption toward lower energies. Analysis of molecular orbitals and excited states reveals liganddependent charge redistribution and orbital localization, which directly govern optical transitions and transport channels. Transport calculations further show that -NO2-and -CN functionalized OPE junctions exhibit enhanced low-bias conductance due to the emergence of energetically accessible transmission resonances near the Fermi level, whereas -NH2 substitution yields more balanced, ambipolar transport behavior. These findings establish a clear structure-property-transport relationship in ligand-functionalized OPE systems and provide molecular-level design guidelines for optimizing π-conjugated molecular wires in nanoelectronic and optoelectronic devices.