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

preprint
revised on 08.03.2020 and posted on 09.03.2020 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.

Funding

This project was funded by intramural funds at TIFR Hyderabad from the Department of Atomic Energy (DAE).

History

Email Address of Submitting Author

ramakrishnan@tifrh.res.in

Institution

Tata Institute of Fundamental Research, Centre for Interdisciplinary Sciences

Country

India

ORCID For Submitting Author

0000-0002-7288-9238

Declaration of Conflict of Interest

The author declares no conflict of interest

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