B₃N₃-Substituted Nanographene Molecules: Influence of Planarity on the Electronic Structure and Molecular Orientation in Thin Films

Abstract

BN-substituted nanographene molecules are currently the focus of interest because the substitution of C–C units by isoelectronic and isosteric BN units is a straightforward way of changing the electronic properties of nanographenes. Another parameter influencing the electronic structure, orientation, and growth mode of nanographene molecules is the planarity of the molecules. The electronic structure, orientation, and film growth of the related molecules B3N3-hexa-peri-hexabenzocoronene (BN-HBC), B3N3-hexabenzotriphenylen (BN-HBP), and B3N3-hexabenzotriphenylen-2H (BN-HBP-2H) on Au(111) have been studied by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). XA spectra were simulated using time-dependent density functional theory (TDDFT). The calculation of C 1s excitation spectra allows the assignment of individual transitions and the examination of the degree of cross-linking between biphenyl units. It is shown that the planarity of the molecules distinctly affects the electronic structure, interface properties, as well as growth in thin films.

Planar BN-Doped Nanographenes on Reactive Metal Surfaces: A Promising Pathway for the Preparation of BN-Doped Graphene Layers

“…Analogous to ref , we observes a very similar C 1s spectrum for bulk-like films and the coverage of 1–2 monolayers (Figure S2). The low-intensity interface component (IF) at about 285 eV in Figure a is attributed to the weak but not fully negligible interaction between BN-HBC and the gold substrate (e.g., by electronic coupling) . In such a case, the introduction of an asymmetric peak shape may describe the spectra.…”

“…multilayer films in Figures S3 and S4), the description of C 1s core-level spectra of HBC is more complex due to the number of chemically inequivalent carbon atoms in BN-HBC. Following a recently described model, five different carbon species can be distinguished in C 1s core-level spectra: carbon bonded to hydrogen (CH), boron (CB), and nitrogen (CN); carbon bonded to carbon in proximity to nitrogen (CCN) and to boron (CCB) . Interface properties between BN-HBC and Au(111) were recently studied; for a more detailed discussion, the readers are referred to the literature .…”

“…The low-intensity interface component (IF) at about 285 eV in Figure 3a is attributed to the weak but not fully negligible interaction between BN-HBC and the gold substrate (e.g., by electronic coupling). 31 In such a case, the introduction of an asymmetric peak shape may describe the spectra. Alternatively, the interface component may arise from molecules adsorbed at more reactive sites, like vacancies or step edges, as observed for other organic−metal systems.…”

“…The additional intensity in the C 1s spectra of the monolayers may be described by additional interface peaks (IF) at the high binding energy side, as shown in Figure 5a. For the interpretation of the C 1s core-level spectra, one should remember that BN-HBP is not planar and slightly tilted [as reported for BN-HBP on Au(111)], 31 i.e., in particular, CH atoms have a different distance from the substrate surface and thus the screening effect is different. Moreover, the geometry may change at the interface.…”

Hexacene on Cu(110) and Ag(110): Influence of the Substrate on Molecular Orientation and Interfacial Charge Transfer

“… 55 The K-edge XAS spectra were simulated by applying time-dependent density functional theory as implemented in ORCA: 56 Symmetry-equivalent C 1s orbitals were localized using the Pipek–Mezey procedure, 57 and the TDDFT calculations were carried out by allowing only excitations from the localized 1s orbitals. For a better comparison with the experimental spectra, the discrete excitations were broadened with Gaussian functions of increasing width as described in ref ( 58 ).…”