Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 137, Issue 48, Pages 15241-15246Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.5b10027
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Funding
- Argonne-Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0001059]
- U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-AC02-06CH11357]
- E.I. DuPont de Nemours Co.
- Dow Chemical Company
- Northwestern University
- National Center for Research Resources [5P41RR007707]
- National Institute of General Medical Sciences from the National Institutes of Health [8P41GM103543]
- MRSEC program at the Materials Research Center [NSF DMR-1121262]
- Nanoscale Science and Engineering Center at the International Institute for Nanotechnology [NSF EEC-0647560]
- National Science Foundation [CHE-9871268]
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Light harvesting supramolecular assemblies are potentially useful structures as components of solar-to-fuel conversion materials. The development of these functional constructs requires an understanding of optimal packing modes for chromophores. We investigated here assembly in water and the photocatalytic function of perylene monoimide chromophore amphiphiles with different alkyl linker lengths separating their hydrophobic core and the hydrophilic carboxylate headgroup. We found that these chromophore amphiphiles (CAs) self-assemble into charged nanostructures of increasing aspect ratio as the linker length is increased. The addition of salt to screen the charged nanostructures induced the formation of hydrogels and led to internal crystallization within some of the nanostructures. For linker lengths up to seven methylenes, the CAs were found to pack into 2D crystalline unit cells within ribbon-shaped nanostructures, whereas the nine methylene CAs assembled into long nanofibers without crystalline molecular packing. At the same time, the different molecular packing arrangements after charge screening led to different absorbance spectra, despite the identical electronic properties of all PMI amphiphiles. While the crystalline CAs formed electronically coupled H-aggregates, only CAs with intermediate linker lengths showed evidence of high intermolecular orbital overlap. Photocatalytic hydrogen production using a nickel-based catalyst was observed in all hydrogels, with the highest turnovers observed for CA gels having intermediate linker lengths. We conclude that the improved photocatalytic performance of the hydrogels formed by supramolecular assemblies of the intermediate linker CA molecules likely arises from improved exciton splitting efficiencies due to their higher orbital overlap.
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