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    Local Electronic Structure of a Single-Layer Porphyrin-Containing Covalent Organic Framework

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    Type
    Article
    Authors
    Chen, Chen
    Joshi, Trinity cc
    Li, Huifang
    Chavez, Anton D.
    Pedramrazi, Zahra
    Liu, Pei-Nian cc
    Li, Hong cc
    Dichtel, William R. cc
    Bredas, Jean-Luc cc
    Crommie, Michael F. cc
    KAUST Department
    KAUST Solar Center (KSC)
    Laboratory for Computational and Theoretical Chemistry of Advanced Materials
    Material Science and Engineering Program
    Physical Science and Engineering (PSE) Division
    Date
    2017-12-26
    Online Publication Date
    2017-12-26
    Print Publication Date
    2018-01-23
    Permanent link to this record
    http://hdl.handle.net/10754/626973
    
    Metadata
    Show full item record
    Abstract
    We have characterized the local electronic structure of a porphyrin-containing single-layer covalent organic framework (COF) exhibiting a square lattice. The COF monolayer was obtained by the deposition of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMA) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) onto a Au(111) surface in ultrahigh vacuum followed by annealing to facilitate Schiff-base condensations between monomers. Scanning tunneling spectroscopy (STS) experiments conducted on isolated TAPP precursor molecules and the covalently linked COF networks yield similar transport (HOMO-LUMO) gaps of 1.85 ± 0.05 eV and 1.98 ± 0.04 eV, respectively. The COF orbital energy alignment, however, undergoes a significant downward shift compared to isolated TAPP molecules due to the electron-withdrawing nature of the imine bond formed during COF synthesis. Direct imaging of the COF local density of states (LDOS) via dI/dV mapping reveals that the COF HOMO and LUMO states are localized mainly on the porphyrin cores and that the HOMO displays reduced symmetry. DFT calculations reproduce the imine-induced negative shift in orbital energies and reveal that the origin of the reduced COF wave function symmetry is a saddle-like structure adopted by the porphyrin macrocycle due to its interactions with the Au(111) substrate.
    Citation
    Chen C, Joshi T, Li H, Chavez AD, Pedramrazi Z, et al. (2017) Local Electronic Structure of a Single-Layer Porphyrin-Containing Covalent Organic Framework. ACS Nano 12: 385–391. Available: http://dx.doi.org/10.1021/acsnano.7b06529.
    Sponsors
    This research was supported by the Army Research Office Multidisciplinary University Research Initiative (MURI) program under Grant No. W911NF-15-1-0447 (STM spectroscopy, precursor synthesis), by the Army Research Office Grant No. W911NF-17-1-0339 to Georgia Tech (DFT calculations), and by the U.S. Department of Energy, Office of Basic Energy Sciences, Nanomachine Program under Contract No. DEAC02-05CH11231 (sample preparation). The KAUST IT Research Computing Team and the KAUST Supercomputing Laboratory are gratefully acknowledged for providing generous computational resources for part of our theoretical work. T.J. acknowledges support from NSF Graduate Research Fellowship Program under Grant No. DGE 1106400. A.D.C. acknowledges support from the NDSEG Fellowship Program.
    Publisher
    American Chemical Society (ACS)
    Journal
    ACS Nano
    DOI
    10.1021/acsnano.7b06529
    PubMed ID
    29261279
    Additional Links
    http://pubs.acs.org/doi/10.1021/acsnano.7b06529
    ae974a485f413a2113503eed53cd6c53
    10.1021/acsnano.7b06529
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program; KAUST Solar Center (KSC)

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