Illusory Connection between Cross-Conjugation and Quantum Interference

Abstract

Quantum interference, be it destructive or constructive, has a substantial influence on the magnitude of molecular conductance and consequently there is significant interest in predicting these effects. It is commonly thought that cross-conjugated paths result in suppressed conductance due to destructive quantum interference. Using Hückel theory and DFT calculations we investigate systems that break this cross-conjugation rule of thumb. We predict and rationalize how a class of conjugated molecules containing closed loops can exhibit destructive interference despite being linearly conjugated and exhibit constructive interference despite being cross-conjugated. The arguments build on the graphical rules derived by Markussen et al. 1 and the hitherto neglected effects of closed loops in the molecular structure. Finally, we identify the 1,3 connected Azulene molecule as belonging to the closed-loop class and argue that this explains recent measurements of its electrical conductance.

Close relation between quantum interference in molecular conductance and diradical existence

“…S12 and ref. 69), yet its augmented structure 2 seems to be described by an all-bonded Lewis or Kekulé resonance structure. However, things are not quite as they seem.…”

Driven Liouville von Neumann Approach for Time-Dependent Electronic Transport Calculations in a Nonorthogonal Basis-Set Representation

“…[1][2][3][4] Over the past four decades this field has matured to a point where measurements and calculations of steady-state transport characteristics of individual molecules are routinely performed in many laboratories. [5][6][7] Different aspects, such as conductance switching, [8][9][10][11][12] rectification, [13][14][15][16][17][18] thermopower effects, 19-24 interference effects, [25][26][27][28] chemical composition, 29 and lead-molecule coupling schemes, 18,[30][31][32][33] have been explored aiming to realize a molecular device exhibiting the desired functionality and efficiency.…”

Characterizing destructive quantum interference in electron transport

“…Having developed and described our characterization scheme for DQI, we now apply it to two physical setups that are not well understood. First is DQI at complex energies [11,38,46], and then nontrivial moleculeelectrode couplings [25,33] in the next subsection.…”

“…In general, DQI at a complex energy occurs when two instances of DQI with real energies 'collide' and the locations travel off into the complex plane [38]. In this way, if a molecule exhibits DQI at two nearby energies, slight perturbations may cause the DQI to move off into the complex plane, thus increasing transmission [46].…”