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How Symmetry Governs the Dihedral Angle Dependence of Intermolecular Spin-Orbit Coupling

Antonio J. Garzon-Ramirez, Connor K. Terry Weatherly, Kyle T. Kairys, Michael R. Wasielewski, Roel Tempelaar

Abstract

Spin-orbit, charge-transfer intersystem crossing (SOCT-ISC) allows for the efficient production of triplet excited states in donor-acceptor (DA) dyads without the involvement of heavy atoms, for use in a myriad of technologies. This process is commonly believed to proceed optimally when the dihedral angle between donor and acceptor moieties is orthogonal. Here, we challenge this idea through a theoretical study unveiling a scenario where spin-orbit couplings (SOCs) are minimized under orthogonal conditions. This scenario is rationalized based on an analysis of the structure-imposed symmetry properties of the involved singlet and triplet states. Notably, in this scenario, finite SOCs demand oblique orientation angles, which in turn requires molecular chirality, suggesting chirality to be a prerequisite for activating the involved SOC pathways.

How Symmetry Governs the Dihedral Angle Dependence of Intermolecular Spin-Orbit Coupling

Abstract

Spin-orbit, charge-transfer intersystem crossing (SOCT-ISC) allows for the efficient production of triplet excited states in donor-acceptor (DA) dyads without the involvement of heavy atoms, for use in a myriad of technologies. This process is commonly believed to proceed optimally when the dihedral angle between donor and acceptor moieties is orthogonal. Here, we challenge this idea through a theoretical study unveiling a scenario where spin-orbit couplings (SOCs) are minimized under orthogonal conditions. This scenario is rationalized based on an analysis of the structure-imposed symmetry properties of the involved singlet and triplet states. Notably, in this scenario, finite SOCs demand oblique orientation angles, which in turn requires molecular chirality, suggesting chirality to be a prerequisite for activating the involved SOC pathways.

Paper Structure

This paper contains 1 section, 2 equations, 4 figures, 2 tables.

Table of Contents

  1. Acknowledgements

Figures (4)

  • Figure 1: Molecular structure of the dyads studied in this work, BD-anthracene (a) and the idealized system C$_2$H$_2$--C$_2$F$_2$ (b).
  • Figure 2: Total SOCs between the two lowest-lying singlet excited states and triplet states as a function of dihedral angle for the BD-anthracene dyad. Shown are results obtained through a constrained geometry optimization of the dyad (markers) and through fusing moieties that were separately geometry-optimized (curves).
  • Figure 3: Polarization-resolved SOCs for the two lowest-lying singlet excited states and triplet states as a function of dihedral angle for the idealized dyad C$_2$H$_2$--C$_2$F$_2$.
  • Figure 4: As in Fig. \ref{['fig:total_SOC']}, but for polarization-resolved SOCs.