<br/>Photosynthetic organisms make use of closely packed pigments embedded in a tuned protein scaffold to absorb solar energy and direct it to the reaction center.These antenna proteins can transport excitation energy (excitons) with remarkable speed and efficiency. However, disentangling principles of design from biological materials can be challenging. In particular, elucidating the role of energetic disorder in tuning the nature of energy transport remains a fundamental question. Here, we study exciton transport in supramolecular light-harvesting nanotubes (LHNs), self-assembled in solution from cyanine dye molecules. A new sample preparation technique greatly reduces light and cryogenic damage, common problems for organic nanomaterials and enables simultaneous quantification of disorder and exciton diffusion lengths as a function of temperature. We observe signatures of exciton-exciton annihilation at extremely low photon fluxes, indicating micron scale excitonic diffusion. Furthermore, our results show that increasing temperature (dynamic disorder) inhibits exciton transport, demonstrating band-like coherent diffusion in LHNs. These findings suggest that quantum coherence plays a role in enhancing energy transfer in analogous highly-ordered photosynthetic molecular aggregates, and illustrates principles of design for materials with long-range exciton diffusion. We have now developed several new molecular aggregates and hybrids which exploit these principles for as effective excitonic antenna.

Understanding and designing self-assembled molecular J-aggregates for long-range coherent energy transport

251st National Meeting (2016)

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