Transport Regulation and Quantum Interference Switching in Pyrrole-Graphene Junctions

A comprehensive first-principles investigation of tunable quantum transport in pyrrole-based molecular junctions is performed by using density functional theory combined with the nonequilibrium Green's function approach. When coupled to zigzag graphene nanoribbon electrodes, the pyrrole monomer/oligomer-based devices exhibit three essential transport characteristics, namely a pronounced negative differential resistance (NDR) effect, nonlinear gate-controlled modulation, and destructive quantum interference (DQI)-induced switching. The current amplitude decreases systematically with increasing oligomer length, while the peak-to-valley ratio increases, reaching a maximum of 17.36. Gate modulation effectively preserves and enhances the NDR effect, where a negative gate voltage shifts the HOMO toward the Fermi level, broadening the HOMO-dominated transmission peak and improving the stability of NDR. Furthermore, conformational rotations disrupt the π-conjugated pathway, inducing strong DQI that drastically suppresses conductance. This mechanism enables a robust molecular switching behavior, achieving an on/off ratio reaching as high as 6.48 × 10³. These results establish clear structure-transport correlations and demonstrate the potential of pyrrole-based molecular junctions for highly tunable functional components in future molecular electronic devices.