Center for Nanoscale Materials, Argonne National Laboratory , Lemont, Illinois 60439, United States.
Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
ACS Nano. 2017 Sep 26;11(9):9112-9118. doi: 10.1021/acsnano.7b03867. Epub 2017 Aug 29.
Light-harvesting biomaterials are an attractive target in photovoltaics, photocatalysis, and artificial photosynthesis. Through peptide self-assembly, complex nanostructures can be engineered to study the role of chromophore organization during light absorption and energy transport. To this end, we demonstrate the one-dimensional transport of excitons along naturally occurring, light-harvesting, Zn-protoporphyrin IX chromophores within self-assembled peptide-amphiphile nanofibers. The internal structure of the nanofibers induces packing of the porphyrins into linear chains. We find that this peptide assembly can enable long-range exciton diffusion, yet it also induces the formation of excimers between adjacent molecules, which serve as exciton traps. Electronic coupling between neighboring porphyrin molecules is confirmed by various spectroscopic methods. The exciton diffusion process is then probed through transient photoluminescence and absorption measurements and fit to a model for one-dimensional hopping. Because excimer formation impedes exciton hopping, increasing the interchromophore spacing allows for improved diffusivity, which we control through porphyrin doping levels. We show that diffusion lengths of over 60 nm are possible at low porphyrin doping, representing an order of magnitude improvement over the highest doping fractions.
在光电、光催化和人工光合作用中，光捕获生物材料是一个很有吸引力的目标。通过肽自组装，可以设计出复杂的纳米结构，以研究在光吸收和能量传递过程中发色团组织的作用。为此，我们在自组装的肽两亲纳米纤维中展示了激子沿着天然存在的光捕获 Zn-原卟啉 IX 发色团的一维输运。纳米纤维的内部结构将卟啉诱导成线性链排列。我们发现这种肽组装可以实现长程激子扩散，但也会诱导相邻分子之间形成激子复合物，作为激子陷阱。通过各种光谱方法证实了相邻卟啉分子之间的电子耦合。然后通过瞬态光致发光和吸收测量来探测激子扩散过程，并拟合到一维跳跃模型中。由于激子复合物的形成阻碍了激子跳跃，增加发色团之间的间距可以提高扩散率，我们通过卟啉掺杂水平来控制。我们表明，在低卟啉掺杂下可以实现超过 60nm 的扩散长度，比最高掺杂分数提高了一个数量级。
