The dark side of energy transport along excitonic wires: On-site energy barriers facilitate efficient, vibrationally-mediated transport through optically dark subspaces

TL;DR

This paper introduces a counter-intuitive method using on-site energy barriers to enhance exciton transport efficiency in molecular chains by suppressing radiative losses through dark state protection, applicable across various environments.

Contribution

It demonstrates that regular energy barriers can significantly improve exciton transport by exploiting dark states, a novel approach in nanoscale energy transport.

Findings

Transport efficiency can be increased by orders of magnitude.

Dark state protection suppresses radiative recombination.

The method is robust across different thermal and optical conditions.

Abstract

We present a novel, counter-intuitive method, based on dark state protection, for significantly improving exciton transport efficiency through `wires' comprising a chain of molecular sites with an intrinsic energy gradient. Specifically, by introducing `barriers' to the energy landscape at regular intervals along the transport path, we find that undesirable radiative recombination processes are suppressed due to a clear separation of sub-radiant and super-radiant eigenstates in the system. This, in turn, can lead to an improvement in transmitted power by many orders of magnitude, even for very long chains. From there, we analyse the robustness of this phenomenon to changes in both system and environment properties to show that this effect can be beneficial over a range of different thermal and optical environment regimes. Finally, we show that the novel energy landscape presented here may provide a useful foundation for overcoming the short length scales over which exciton diffusion typically occurs in organic photo-voltaics and other nanoscale transport scenarios, thus leading to considerable potential improvements in the efficiency of such devices.