title: Supramolecular Packing Controls H₂ Photocatalysis in Chromophore Amphiphile Hydrogels.
abstract: 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.
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Weingarten
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Roman V
authors.initials: RV
authors.lastname: Kazantsev
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Simpson Querrey Institute for BioNanotechnology, Northwestern University , Chicago, Illinois 60611, United States.
authors.forename: Liam C
authors.initials: LC
authors.lastname: Palmer
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Fairfield
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Koltonow
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.|Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.|Simpson Querrey Institute for BioNanotechnology, Northwestern University , Chicago, Illinois 60611, United States.|Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.|Department of Medicine, Northwestern University , Chicago, Illinois 60611, United States.|Department of Biomedical Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Samuel I
authors.initials: SI
authors.lastname: Stupp
mesh_terms: D002384:Catalysis; D020100:Hydrogels; D013056:Spectrophotometry, Ultraviolet
chemical_list: D020100:Hydrogels