Interference effects in phtalocyanine controlled by H-H tautomerization: a potential two-terminal unimolecular electronic switch

TL;DR

This study explores how hydrogen tautomerization in phthalocyanine influences electronic transport, demonstrating potential for molecular switching and NDR effects in two-terminal junctions with cumulene and gold leads.

Contribution

It reveals how H-H tautomerization modulates interference effects and conductance in phthalocyanine, proposing a new mechanism for molecular electronic switches.

Findings

Large conductance change between tautomer states in low bias

Pronounced NDR observed at high bias with gold leads

Interference effects cause significant current modulation

Abstract

We investigate the electrical transport properties of two hydrogen tautomer configurations of phthalocyanine (H2Pc) connected to cumulene and gold leads. Hydrogen tautomerization affects the electronic state of H2Pc by switching the character of molecular orbitals with the same symmetry close to the Fermi level. The near degeneracy between the HOMO and HOMO-1 leads to pronounced interference effects, causing a large change in current for the two tautomer configuratons, especially in the low-bias regime. Two types of planar junctions are considered: cumulene-H2Pc-cumulene and gold-H2Pc-gold. Both demonstrate prominent difference in molecular conductance between ON and OFF states. In addition, junctions with gold leads show pronounced negative differential resistance (NDR) at high bias voltage, as well as weak NDR at intermediate bias.