Molecular Excitonic Networks Organized by DNA Scaffolds

Analogous to electronic circuits, molecular excitonic networks transport excitons through dye assemblies. Controlling this transport is critical to realizing artificial photosynthesis and alternative logic circuit platforms. DNA scaffolds are a powerful way to organize dye molecules on the nanoscale. Recently, we have shown that cyanine (Cy) dye aggregates on DNA exhibit strong electronic coupling, delocalized excitons, and long-lived vibronic coherences that could be exploited for quantum information and sensing applications. An unintended consequence is the creation of non-radiative relaxation pathways that can drastically shorten exciton lifetimes. Understanding the effect of aggregate geometry and environment on these pathways is critical to the development of useful molecular excitonic networks.

Here, we examine a series of chemically-modified Cy dye aggregates organized on DNA scaffolds. The observed Davydov splitting and redistribution of oscillator strength among vibronic states is well described by vibronic exciton theory, allowing for extraction of the coupling strength and dye aggregate geometry. We find that the rate of non-radiative relaxation depends on the relative dye orientation and can be suppressed by increasing solvent viscosity to restrict dye motion. This represents a step towards overcoming a hurdle to realizing molecular excitonic networks on DNA that are suitable for photonics applications.