Directed Gradients in the Excited-State Energy Landscape of Poly(3-hexylthiophene) Nanofibers

Funneling excitation energy toward lower energy excitedstatesis a key concept in photosynthesis, which is often realized with atmost two chemically different types of pigment molecules. However,current synthetic approaches to establish energy funnels, or gradients,typically rely on Fo''rster-type energy-transfer cascades alongmany chemically different molecules. Here, we demonstrate an elegantconcept for a gradient in the excited-state energy landscape alongmicrometer-long supramolecular nanofibers based on the conjugatedpolymer poly(3-hexylthiophene), P3HT, as the single component. Preciselyaligned P3HT nanofibers within a supramolecular superstructure areprepared by solution processing involving an efficient supramolecularnucleating agent. Employing hyperspectral imaging, we find that thelowest-energy exciton band edge continuously shifts to lower energiesalong the nanofibers' growth direction. We attribute this directedexcited-state energy gradient to defect fractionation during nanofibergrowth. Our concept provides guidelines for the design of supramolecularstructures with an intrinsic energy gradient for nanophotonic applications.

Automated summary

Funneling excitation energy toward lower energy excited states is a key concept in photosynthesis, often realized with at most two types of pigment molecules. However, current synthetic approaches rely on Fo''rster-type energy-transfer cascades along chemically different molecules. Here, we demonstrate a novel concept where an excited-state energy gradient is achieved along micrometer-long supramolecular nanofibers based on a single component, the conjugated polymer poly(3-hexylthiophene), P3HT. This gradient is attributed to defect fractionation during nanofiber growth and provides guidelines for designing supramolecular structures with intrinsic energy gradients for nanophotonic applications.