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

Abstract

We investigate the electrical transport properties of two hydrogen tautomer configurations of phthalocyanine (H 2 Pc) connected to cumulene and gold leads. Hydrogen tautomerization affects the electronic state of H 2 Pc 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 configurations, especially in the low-bias regime. Two types of planar junctions are considered: cumulene-H 2 Pc-cumulene and gold-H 2 Pc-gold. Both demonstrate a 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.

A Dramatic Odd–Even Oscillating Behavior for the Current Rectification and Negative Differential Resistance in Carbon‐Chain‐Modified Donor–Acceptor Molecular Devices

“…NDR has been found in a variety of molecular devices, such as phenylethynylene oligomer (OPE) molecular junctions, [ 5 , 6 ] a single benzene ring with a nitro side group [ 23 ] or by an external gate fi eld, [ 24 ] mirror-symmetrical straight carbon nanotube heterojunctions, [ 25 ] carbon nanowires contacted directly to two asymmetric electrodes, [ 26 ] a squashed C 60 molecular device, [ 27 ] and a squeezed carbon monatomic ring, [ 28 ] etc. More recently, Prasongkit et al [ 29 ] studied interference effects in phthalocyanine controlled by H-H tautomerization and found that gold-H 2 Pc-gold junctions show pronounced NDR at high bias voltage, as well as weak NDR at intermediate bias. However, signifi cant NDR has not yet been observed in a single donor-acceptor molecule.…”

“…[ 35 ] All results hitherto showed that carbon chains have exceptional electronics characteristics. [29][30][31][32][33][34][35][36][37][38][39][40] For example, Lang and Avouris [ 37 , 38 ] reported that when carbon chains were connected directly to two Au electrodes, the zero-bias conductance would oscillate as a function of the number of carbon atoms in the chains. Recently, Prasongkit et al [ 40 ] showed that the transmission spectrum and the conductance for carbon chains with a cumulene confi guration depend only weakly on applied bias and the I -V characteristic is nearly linear over a bias region of ± 1 V.…”

Single-Molecule Phenyl-Acetylene-Macrocycle-Based Optoelectronic Switch Functioning as a Quantum-Interference-Effect Transistor

“…Quantum interference is the key feature of coherent quantum transport, and DQI plays an essential role in the H-H tautomerization molecular switch [17] as well as the quantum interference effect transistor (QuIET) [18]. Recently, DQI has been experimentally observed in electron transport through a cross-conjugated molecular junction at room temperature [12].…”

High On/Off Conductance Switching Ratio via H-Tautomerization in Quinone

“…The monotonously high conductance of the ON state can be understood from Figure 3, where it can be seen that more of the high-transmission region is included within the bias window as the bias voltage is increased. In the OFF state at V bias = 0 V, the transmission function shows a transmission dip, or antiresonance, due to destructive zero-bias conductance ratio [the ratio between T(E) in the ON and OFF states] of ∼10 4 , which is much higher than the value of 431 reported in ref 12). The the ON state also has a transmission dip at −0.461 eV.…”

“…12 However, NEGF-DFT calculations with GGA as well as the local density approximation (LDA) have been widely employed. 14,15 More importantly, the QIE that occurs between the HOMO and LUMO derives from the characteristics and symmetry of the molecular orbitals rather than from their precise energetic positions.…”