A conceptual framework for designing and analyzing complex molecular circuits

Abstract

Assembling and prototyping circuits on a common breadboard scaffold is critical for developing functional single molecule electronic devices. To this end, we recently demonstrated a bis-terpyridine-based molecular breadboard (TPm) junction with conductance readouts which were linear superpositions of five single terminal embedded circuits. Here, we present a full computational framework to create molecular breadboards with the ability to replace/alter individual circuit components. By applying the framework to the bis-terpyridine-based breadboard, we show that the relative conductance of the five constituent single terminal circuits can be varied by more than an order of magnitude by repositioning electrode anchoring nitrogen atoms. Specifically, by placing nitrogen atoms at meta (TPm), ortho (TPo), and para (TPp) positions on the pyridyl rings, individual circuits are tuned by altering destructive multi-orbital quantum interference effects (QIE) and the relative electrode accessibility (REA) of anchoring nitrogen atoms. We introduce a phase-plot analysis to highlight the interdependence of QIE- and REA-induced changes in the conductance of each single terminal circuit in the breadboard. Our studies predict a QIE-induced boost in circuit conductance for TPp relative to TPm which is insensitive to REA. In contrast, REA suppresses the QIE boost for circuit conductance in TPo relative to that in TPm. Our computational framework for designing breadboard junctions includes new quantitative tools to estimate thermal weights of molecular conformations, the relative electrode accessibility of anchoring atoms, and the extent of constructive/destructive quantum interference in charge transport mediated by multiple orbitals. These advances should be also useful for the analysis of other molecular junctions.