Unexpectedly Large Couplings Between Orthogonal Units in Anthraquinone Polymers

We investigate the unusual electronic properties of directly linked 1,4‐polyanthraquinones (14PAQ). The dihedral angle between the anthraquinones’ (AQ) molecular planes is found to be close to 90°. Contrary to the prevailing notion that the interaction between orthogonal units is negligible due to the broken π‐electron conjugation, the couplings between neighboring AQ units are found not to have a minimum at 90° and to be much larger than expected.

The unexpectedly large electronic coupling between orthogonal AQ units is explained by the interaction between the lone pairs of the carbonylic oxygen and the π system of the neighboring unit, which allows favorable overlap between frontier molecular orbitals at the orthogonal geometry. We show that this effect, which we describe computationally for the first time, can be strengthened by adding more quinone units.

The effect of thermal fluctuations on the couplings is assessed through ab initio molecular dynamics simulations. The distributions of the couplings reveal that electron transport is resilient to dynamic disorder in all systems considered, while the hole couplings are much more sensitive to disorder.

We describe lone pair‐π interactions as a previously largely overlooked conjugation mechanism to be incorporated in a new class of disorder‐resilient semiconducting redox polymers.