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Title: Supramolecular Packing Controls H2 Photocatalysis in Chromophore Amphiphile Hydrogels

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. Here, we investigated 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 turnoversmore » observed for CA gels having intermediate linker lengths. Lastly, 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.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [3] ;  [4]
  1. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry. Argonne-Northwestern Solar Energy Research (ANSER) Center
  2. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry. Simpson Querrey Inst. for BioNanotechnology
  3. Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering
  4. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry. Argonne-Northwestern Solar Energy Research (ANSER) Center. Simpson Querrey Inst. for BioNanotechnology. Dept. of Materials Science and Engineering. Dept. of Medicine. Dept. of Biomedical Engineering
Publication Date:
OSTI Identifier:
1226681
Grant/Contract Number:
SC0001059; AC02-06CH11357; 5P41RR007707; 8P41GM103543; DMR-1121262; EEC-0647560; CHE-9871268
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 137; Journal Issue: 48; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Northwestern Univ., Evanston, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Inst. of Health (NIH) (United States); National Science Foundation (NSF)
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE