Research ArticleAPPLIED SCIENCES AND ENGINEERING

Supramolecular architectures of molecularly thin yet robust free-standing layers

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Science Advances  22 Feb 2019:
Vol. 5, no. 2, eaav4489
DOI: 10.1126/sciadv.aav4489
  • Fig. 1 Chemical structure and interfacial self-assembly characterization of 1.

    (A) Molecular structure of para-methyl-cyano-tetra-propoxy-calix[4]arene, 1. (B) Extended structure found in the crystal structure of 1 showing methyl-cyano functionalities pointing away from macrocycle cavities. Color code: C, gray; N, blue; O, red. Hydrogen atoms are omitted for clarity. (C) Surface pressure area compression isotherm of 1 on pure water displayed three distinct phases with phase transitions at surface pressure values of 3.4 (α) and 17.9 mN m−1 (β), corresponding to molecular area values of 97 and 84 Å2 molecule−1, respectively. Letter labels indicate the position on the isotherm where the corresponding BAM micrographs were acquired. (D to I) BAM micrographs of the monolayer of 1 on pure water. Large crystalline monolayer domains grow after the first phase transition (10 mN m−1). Upon further compression, the crystalline network expands and covers the whole available area at the air-water interface. Scale bar, 100 μm.

  • Fig. 2 Surface spectroscopy analysis of 1-based monolayers.

    (A to C) X-ray photoelectron spectra of the monolayer of 1 transferred onto HOPG by the LS method for C1s, N1s, and O1s peaks. arb. u., arbitrary units. (C) The O1s spectrum can be fitted with two peaks, 532.5 and 533.2 eV, representing O–C of 1 and an insignificant amount of H2O (~6% of the O1s spectrum) (14). A precise interpretation of the C1s spectrum is challenging because of multiple peaks overlapping for different C entities of 1. (D to F) Room temperature N-K edge x-ray absorption spectra (Ev + Eh) and LD of the monolayer of 1 on HOPG. (D) The transition into the unoccupied π* MO of the CN groups is visible as a distinct peak at 400.6 eV. (E) Integrated intensity of the LD of the π* signal as a function of the x-ray incidence angle with respect to the surface normal. (F) The data are consistent with an average orientation of <γ> = 57° of the CN groups. The dashed line corresponds to <γ> = 57° ± 1°.

  • Fig. 3 Molecular resolution AFM imaging of the monolayer of 1.

    (A) AFM images of the monolayer of 1 transferred onto HOPG via the LS method. (B) The high-resolution image of the crystalline network of the monolayer shows a highly ordered network formed from the single molecules of 1. [C (top view) and D (side view)] Molecular model of the building blocks of 1 interacting via the proposed dipole-dipole interaction in the well-ordered monolayer.

  • Fig. 4 Cryo-TEM investigation of the free-standing monolayer of 1.

    (A) TEM analysis of the monolayer of 1 transferred via the LS method on a lacey carbon TEM grid [dark areas in the picture are areas of thick carbon from the “lacey carbon” substrate as it is widely used as a TEM substrate for its nonuniform and wide openings (black arrow)]. The layer has fractured and lost contact in some areas with the lacey carbon. In these areas, the free-standing monolayer can be visualized, as shown with white arrows. (B) The electron diffraction pattern of the free-standing monolayer of 1 confirms the squarely symmetric packing structure of the crystalline layer. The profile lines across the diffraction pattern (fig. S7) reveal a unit cell size of 15 Å, consistent with the AFM acquired and the molecular model of the self-assembled monolayer of 1.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/2/eaav4489/DC1

    Section S1. Materials and methods

    Section S2. Contact angle measurement

    Section S3. Spectroscopic ellipsometry

    Section S4. X-ray photoelectron spectroscopy

    Section S5. Atomic force microscopy

    Section S6. Transmission electron microscopy

    Fig. S1. Synthetic route to 5,11,17,23-tetramethylcyano-25,26,27,28-tetrapropoxy calix[4]arene (1) and spectroscopic details of 1.

    Fig. S2. X-ray crystal structure determination details of 1.

    Fig. S3. Interfacial properties of the monolayer of 1 in the presence of transition metal ions in the subphase.

    Fig. S4. Interfacial properties of the monolayer of 1 in the presence of ACN molecules as competitors with the CN functional groups of 1 for dipole-dipole interactions.

    Fig. S5. Surface analysis of the monolayer of 1 in the presence of transition metal ions in the subphase.

    Fig. S6. AFM height analysis of the transferred monolayer of 1 from pure water subphase onto HOPG by the LS method.

    Fig. S7. Diffraction analysis of the free-standing monolayer of 1 by means of high-resolution cryo-TEM analysis.

    Table S1. X-ray crystal structure determination detail of 1.

    Table S2. X-ray crystal structure determination detail of 1.

    Table S3. X-ray crystal structure determination detail of 1.

    Table S4. X-ray crystal structure determination detail of 1.

    Table S5. X-ray crystal structure determination detail of 1.

    Table S6. X-ray crystal structure determination detail of 1.

    Table S7. X-ray crystal structure determination detail of 1.

    Table S8. X-ray crystal structure determination detail of 1.

    Table S9. Characteristic values of the surface pressure-area compression isotherm of 1.

    Table S10. Contact angle measurements on the monolayer of 1 transferred from the air-water interface onto HOPG.

    References (2632)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Materials and methods
    • Section S2. Contact angle measurement
    • Section S3. Spectroscopic ellipsometry
    • Section S4. X-ray photoelectron spectroscopy
    • Section S5. Atomic force microscopy
    • Section S6. Transmission electron microscopy
    • Fig. S1. Synthetic route to 5,11,17,23-tetramethylcyano-25,26,27,28-tetrapropoxy calix4arene (1) and spectroscopic details of 1.
    • Fig. S2. X-ray crystal structure determination details of 1.
    • Fig. S3. Interfacial properties of the monolayer of 1 in the presence of transition metal ions in the subphase.
    • Fig. S4. Interfacial properties of the monolayer of 1 in the presence of ACN molecules as competitors with the CN functional groups of 1 for dipole-dipole interactions.
    • Fig. S5. Surface analysis of the monolayer of 1 in the presence of transition metal ions in the subphase.
    • Fig. S6. AFM height analysis of the transferred monolayer of 1 from pure water subphase onto HOPG by the LS method.
    • Fig. S7. Diffraction analysis of the free-standing monolayer of 1 by means of high-resolution cryo-TEM analysis.
    • Table S1. X-ray crystal structure determination detail of 1.
    • Table S2. X-ray crystal structure determination detail of 1.
    • Table S3. X-ray crystal structure determination detail of 1.
    • Table S4. X-ray crystal structure determination detail of 1.
    • Table S5. X-ray crystal structure determination detail of 1.
    • Table S6. X-ray crystal structure determination detail of 1.
    • Table S7. X-ray crystal structure determination detail of 1.
    • Table S8. X-ray crystal structure determination detail of 1.
    • Table S9. Characteristic values of the surface pressure-area compression isotherm of 1.
    • Table S10. Contact angle measurements on the monolayer of 1 transferred from the air-water interface onto HOPG.
    • References (2632)

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