DNA Encoded Self-Assembly of Molecular Semiconductors for Light-Harvesting

Plants transport and convert solar energy into radical-pairs at the ‘reaction center’ to generate fuel. Nature achieves this with a homogeneous set of pigments, where the host protein environment facilitates tailored couplings between many pigments each with their own function. In contrast, exquisite control over artificial semiconductors for exciton circuits and solar cells remains lacking. Our ability to synthetically generate molecular networks with prescribed nanoscale structure is lacking. To address this gap towards well-designed molecular optoelectronics, we report the development of DNA scaffolds hosting chromophores,¹ to enhance excited state evolution for solar light harvesting.<br/><br/>Here we study the exciton evolution between strongly coupled perylene diimide (PDI) dye pairs scaffolded in DNA. PDIs are exemplar molecular aggregates as they produce a range of photoinduced excited states, depending on their spatial organization.² To study how we can map a specific excited-state pathway to a PDI-DNA structure, we exploited the molecular precision of DNA base-pairing and nanoscale rigidity of DNA origami to generate a library of optoelectronic constructs. We make hundreds of nucleic acid-chromophore conjugates and self-assemble them intro prescribed shapes. Using ultrafast spectroscopy, we identified designs that gave rise to different photoinduced species, including excimers and charge-transfer states. Next, we use computational modelling to pinpoint geometrical features that can be linked to a specific excited-state pathway. Our synthetic DNA platform offers the ability to rapidly survey the structure-property of molecular aggregates and identify optimized structures that can be useful for applications in excitonic devices, including solar conversion and quantum information.<br/><br/>1. <i>Chem. Sci.</i>, 2022, <b>13</b>, 13020-13031<br/>2. <i>J. Am. Chem. Soc.</i> 2022, 144, <b>1</b>, 368–376