A hierarchical, compact and efficient phenanthrene supramolecular polymer light harvesting antenna.

Reaching extremely high levels of sophistication of naturally occurring supramolecular polymers (SPs) with artificial structures represents a paradigm with important underlying application potential in various fields such as biomaterials and optoelectronics. A key challenge in synthetic SP research is mimicking the complex hierarchical and multiple level folding of natural SPs, such as DNA for instance. In previous works, we have developed an artificial mimic of the chlorosome pigment antenna, consisting of micrometer-long phenanthrene-based SP nanofibers, with exceptional light-harvesting properties. In the present work, we have advanced this system one step further, by assembling the Trimer A nanofibers into sophisticated hierarchical nanostructures. To our knowledge, this work is the first report of hierarchical nanostructures of a functional synthetic SP. The polymerization was monitored by means of UV/visible and fluorescence spectroscopy. Cryo-EM and AFM revealed high aspect-ratio nanoribbons as well as large annular nanostructures. Our thorough study with acridine orange as the energy acceptor shows that the excellent light-harvesting antenna effect is preserved. The annular nanostructures observed are unprecedented in the field of synthetic hierarchical SPs, and this constitutes a notable chemical achievement. We also report the first calculation of a dimensionality compression factor, and we found a remarkable two-orders-of-magnitude reduction for an annular structure. Overall, the present work shows that dimensional compression does not impede light-harvesting performance. It paves the way, in SP science, for potential applications such as advanced energy materials.