Charge-transfer selectivity and quantum interference in real-time electron dynamics: Gaining insights from...

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 π-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. The 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 π-conjugation has been shown to be the cause of diminished electron injection through 1,3-azulene, a pathological case for a graph-based diagnosis of the destructive quantum interference. Furthermore, we demonstrate the quantum interference of many-electron wavefunctions to drive para-vs-meta selectivity in the coherent evolution of superposed π(CN)- and σ(NC-C)-type wavepackets. Analyses reveal that in the para-linked benzene, σ and π MOs localized at the donor terminal are in-phase, leading to the constructive interference of electron density distribution, while the phase-flip of one of the MOs in the meta isomer results in the destructive interference. These findings suggest that a priori detection of orbital phase-flip and quantum coherence conditions can aid in molecular device design strategies.