Binary ionic porphyrin nanosheets: electronic and light-harvesting properties regulated by crystal structure† Yongming Tian, ab Christine M. Beavers, c Tito Busani, de Kathleen E. Martin, ae John L. Jacobsen, f Brandon Q. Mercado, f Brian S. Swartzentruber, a Frank van Swol, ae Craig J. Medforth eg and John A. Shelnutt * ah Received 22nd November 2011, Accepted 10th January 2012 DOI: 10.1039/c2nr11826b Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(II) tetra(4- sulfonatophenyl)porphyrin (ZnTPPS) and tin(IV) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room temperature preparation of the nanosheets has provided the first X-ray crystal structure of a cooperative binary ionic (CBI) solid. The unit cell contains one and one-half molecules of aquo- ZnTPPS 4 (an electron donor) and three half molecules of dihydroxy-SnTNMePyP 4+ (an electron acceptor). Charge balance in the solid is reached without any non-porphyrinic ions, as previously determined for other CBI nanomaterials by non-crystallographic means. The crystal structure reveals a complicated molecular arrangement with slipped p–p stacking only occurring in isolated dimers of one of the symmetrically unique zinc porphyrins. Consistent with the crystal structure, UV-visible J-aggregate bands indicative of exciton delocalization and extended p–p stacking are not observed. XRD measurements show that the structure of the Zn/Sn nanosheets is distinct from that of Zn/Sn four-leaf clover-like CBI solids reported previously. In contrast with the Zn/Sn clovers that do exhibit J-aggregate bands and are photoconductive, the nanosheets are not photoconductive. Even so, the nanosheets act as light-harvesting structures in an artificial photosynthesis system capable of reducing water to hydrogen but not as efficiently as the Zn/Sn clovers. Introduction New highly-absorbing and stable optoelectronic materials are of intense interest especially for the development of renewable and sustainable energy sources. 1–6 Crystalline solids composed of two or more different light-absorbing molecules are of particular interest because they possess myriad advantageous photo- physical and photochemical processes that can be exploited. Recently, we described a novel class of nano- and microscale organic optoelectronic solids synthesized by ionic self-assembly of oppositely charged porphyrin ions. 7–12 Because of the potential for cooperative interactions between the two types of porphyrins (e.g., electron donors and acceptors) these versatile and tunable materials are described as Cooperative Binary Ionic (CBI) solids. The properties of CBI materials are expected to depend on factors such as the functionality of the individual porphyrin a Advanced Materials Laboratory and Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM, 87106, United States. E-mail: jasheln@unm.edu; Fax: +505-272-7077; Tel: +505-306-8472 b Department of Materials Engineering, New Mexico Institute of Mining and Technology, Socorro, NM, 87801, United States c Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA, 94720, United States d Universidade Nova de Lisboa at CENIMAT/I3N, Departamento de Ci^ encia dos Materials, Faculdade de Ci^ encias e Tecnologia, CEMOP- UNINOVA, 2829-516 Caparica, Portugal e Departments of Electrical and Computer Engineering, and Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM, 87106, United States f Department of Chemistry, University of California, Davis, CA, 95616, United States g REQUIMTE/Departamento de Qu ımica e Bioqu ımica, Faculdade de Ci^ encias, Universidade do Porto, 4169-007 Porto, Portugal h Department of Chemistry, University of Georgia, Athens, GA, 30602, United States † Electronic supplementary information (ESI) available: Details of the crystallographic refinement, tables of refinement parameters and bond distances and NSD analysis, and figures showing SEM images of Zn/Sn nanosheets and clovers, the solid grown at different porphyrin concentrations, SEM images of nanosheets at high and low magnification, an ORTEP image showing the five crystallographically distinct porphyrin molecules and the water molecules, and a view of the crystal structure down the b axis are given in the ESI. CCDC reference number 833006. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2nr11826b This journal is ª The Royal Society of Chemistry 2012 Nanoscale, 2012, 4, 1695–1700 | 1695 Dynamic Article Links C < Nanoscale Cite this: Nanoscale, 2012, 4, 1695 www.rsc.org/nanoscale PAPER