Designing molecular materials with tunable excitonic properties is key for enhancing excitonic transport efficiency in light harvesting and molecular information applications. In strongly-coupled chromophore aggregates exciton flow is controlled by electrostatic interactions between neighboring dyes. However, in aggregates consisting of multiple interacting chromophores an exciton will often delocalize across the molecular network, reducing the output of population in a specific direction. Here we introduce the concept of imaginary coupling as a novel method for controlling excitonic populations, which can be induced in molecular aggregates consisting of coupled dyes simultaneously excited through circularly and linearly polarized light. In highly symmetric molecules such as porphyrins, circular polarization induces an electronic current across the ring that selects one of two delocalized excitations according to the direction of the light (e.g., right or left). We demonstrate that imaginary coupling can be generated from the interaction of these excitons with linearly-polarized excitations in molecules with reduced symmetry, like cyanine dyes. We applied this model to investigate multiple constructs of coupled Cy3 and porphyrin molecules, demonstrating that the real and imaginary components of the interaction can be controlled through changes in the geometrical arrangement and the direction of the light. We found that activating specific components of the electronic coupling led to a directional flow of the excitons within the network of dyes. Paired with nanoscale technologies to specify chromophore geometries (e.g., DNA scaffolding techniques), our results show a promising strategy for improving exciton transport in optoelectronic materials.

Imaginary excitonic coupling in porphyrin-cyanine aggregates via optically induced electronic ring currents

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.