Charge-Transfer Selectivity and Quantum Interference in Real-Time Electron Dynamics: Gaining Insights from Time-Dependent Configuration Interaction Simulations

2020-03-09T13:18:17Z (GMT) by Raghunathan Ramakrishnan
Many-electron wavepacket dynamics based on time-dependent configuration interaction (TDCI) is a numerically rigorous approach to quantitatively model electron-transfer across molecular junctions. TDCI simulations of cyanobenzene thiolates---para- and meta-linked to an acceptor gold atom---show donor states conjugating with the benzene $\pi$-network to allow better through-molecule electron migration in the para isomer compared to the meta counterpart. For dynamics involving non-conjugating states, we find electron-injection to stem exclusively from distance-dependent non-resonant quantum mechanical tunneling, in which case the meta isomer exhibits better dynamics. Computed trend in donor-to-acceptor net-electron transfer through differently linked azulene bridges agrees with the trend seen in low-bias conductivity measurements. Disruption of $\pi$-conjugation has been shown to be the cause of diminished electron-injection through the 1,3-azulene, a pathological case for graph-based diagnosis of destructive quantum interference. Furthermore, we demonstrate quantum interference of many-electron wavefunctions to drive para- vs. meta- selectivity in the coherent evolution of superposed $\pi$(CN)- and $\sigma$(NC-C)-type wavepackets. Analyses reveal that in the para-linked benzene, $\sigma$ and $\pi$ MOs localized at the donor terminal are in-phase leading to constructive interference of electron density distribution while phase-flip of one of the MOs in the meta isomer results in destructive interference. These findings suggest that a priori detection of orbital phase-flip and quantum coherence conditions can aid in molecular device design strategies.