Molecular-length induced inversion of rectification in diblock pyrimidinyl–phenyl molecular junctions

Based on ab initio theory and nonequilibrium Green’s function method, rectification in diblock pyrimidinyl–phenyl molecular diodes with various molecular lengths is investigated theoretically. The results demonstrate two opposite rectifying directions depending on the molecular length. Molecular orbital analysis via molecular projected self-consistent Hamiltonian reveals two competitive rectification mechanisms, asymmetric molecular level shift and asymmetric evolution of electronic wave functions under biases, determining the rectifying direction. A critical molecular length is predicted where the dominant mechanism is exchanged. The ab initio calculations display an intrinsic inversion of rectification caused by molecular length in pyrimidinyl–phenyl diodes, which provides a way to modulate rectifying behaviors.