Conductance Switching and Many-Valued Logic in Porphyrin Assemblies

Abstract

We investigate quantum interference in the transport properties of porphyrinbased molecular devices, and are able to develop a minimal but qualitatively accurate model of conductance based on the maximally localized Wannier functions of just the isolated molecule. We find that transmission at or near the Fermi level can be engineered to vary by orders of magnitude in response to hydrogen tautomerization in the inner ring, a recently developed experimental capability. This allows us to suggest that tape porphyrins can act as molecular-size memory units, displaying many-valued logic. SECTION: Energy Conversion and Storage; Energy and Charge TransportO ne of the emerging areas of research in single-molecule electronics is to employ the wave nature of electrons to control current flow in nanoscale devices. In particular, "quantum interference" in ballistic transport through aromatic systems, especially for the prototypical example, benzene, has been studied extensively both experimentally 1,2 and theoretically. 3−6 It has been shown that the transmission function of benzene can vary by orders of magnitude when the relative orientations of the thiol disubstitution linkers is changed between the para, ortho, and meta configurations. The origin of quantum interference is embedded in the underlying molecular symmetry and electronic structure of the orbitals, and, in particular, in the phase and amplitude of the frontier orbitals of the anchoring atoms linking the molecule to the electrodes. 6,7 The discovery of quantum interference effects has raised a lot of interest in designing single-molecule switches as functional electronic elements. 4,8−10 However, most of the strategies proposed remain to date at the conceptual stage, either lacking practical avenues to control transport or involving drastic conformational changes that are incompatible with realistic device setups. An ideal molecular switch, other than being bistable and reversible, should retain a similar molecular structure and binding strengths to the substrate before and after switching. It has been recently demonstrated that these criteria can be fulfilled by inner-ring hydrogen tautomerization reactions in naphthalocyanines, 11 where tautomerization is induced by electron injection through an scanning tunneling microscope (STM) tip under a bias voltage above the lowest unoccupied molecular orbital (LUMO) resonance. Motivated by this work, we investigate here the porphyrin family of molecules, whose small bandgaps and planar structure render them a very promising candidate for nanoscale device fabrication, 12−15 with the goal of identifying quantum interference effects that can be accurately maneuvered by hydrogen tautomerization. In fact, as one of the most tailorable building blocks for supramolecular systems, porphyrins have long been considered as potential candidates in nanoelectronics application. 16,17 To proceed, we first show how a model based on maximally localized Wannier functions (MLWFs) 18 and the wide-band limit (WBL) approximation acts as a...

Optical and morphological properties of ultra-thin H2 TPP, H4 TPP and ZnTPP films

“…Conversely, we believe that perturbing the electronic properties of molecular tautomers (in our case by adding two more H atoms), without any change of their orientation, represents a reasonable alternative in the development of new devices based on molecular tautomers. However, starting from an ordered array of tautomers, it could even be possible to switch the hydrogen atoms alignment of a porphyrin domain by flowing an in‐plane current along the molecular pathways if the current is tuned at a frequency that maximizes energy transfer to that of the N–H vibration .…”

Quantum equilibration of the double-proton transfer in a model system porphine

“…80) on the control of the scaffold structural freedom by means of surface anchoring 81,83 or molecular assembling. 82,84 Finally, let us mention a recent work where the third law of thermodynamics is investigated for a 1D model boron rotor B 13 + . 55 In ref.…”

Tailoring the Polarity of Charge Carriers in Graphene–Porphine–Graphene Molecular Junctions through Linkage Motifs

“…Besides metallic electrodes, molecules with a small HOMO–LUMO gap are also necessary, aiming to reduce the energy separation between the FMOs and the Fermi level of the electrodes. Porphyrin, well-known for its small HOMO–LUMO gap, rigid π-conjugated structure and unique light harvesting properties, is an excellent candidate for nanoelectronic and photovoltaic devices. − Recently, through dehydrogenation reaction, He et al demonstrated that porphines can be steered toward the graphene edges forming C–C covalent bonds, thus providing an avenue to construct graphene-porphine-graphene (GPG) molecular junctions . Motivated by this work, here we theoretically investigate the electronic transport properties of porphine bridged between two semi-infinite graphene electrodes by employing the nonequilibrium Green’s function formalism combined with density functional theory (that is, the so-called NEGF+DFT approach).…”