High-Resolution Near-Edge X-ray Absorption Fine Structure Study of Condensed Polyacenes

Rocco, Maria Luiza M.; Häming, M.; Moura, Carlos E. V. de; Barbatti, Mario; Rocha, Alexandre B.; Schöll, A.; Umbach, E.

doi:10.1021/acs.jpcc.8b08945

Cited by 9 publications

(14 citation statements)

References 51 publications

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“…Figure c) shows nicely that the lowest energy excitations of the different perfluorinated acenes (indicated by dashed lines), which correspond to excitations into the LUMO, decrease with the acene length, as indicated by the calculated orbital energies (cf. Figure ) and parallels the situation observed for the nonsubstituted acenes . A precise assignment of the other π* resonances is not so simple, as initial state effects (i.e., slight differences in the C 1s binding energy for the different carbon atoms within the molecule), as well as final state effects, such as electron relaxation also affect the NEXAFS spectra.…”

Section: Resultssupporting

confidence: 60%

Perfluorinated Acenes: Crystalline Phases, Polymorph-Selective Growth, and Optoelectronic Properties

et al. 2021

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The emerging field of organic electronics triggers the search for new molecular semiconductors and fluorophores. Since optoelectronic properties of molecular solids also depend crucially on molecular packing motifs, it is not sufficient to only consider single-molecule properties, but also to gain precise knowledge of the crystalline phases to understand structure−property relationships. Here, we analyze and compare structural and optoelectronic properties of perfluorinated acenes ranging from perfluoronaphthalene (PFN) via perfluoroanthracene (PFA) and perfluorotetracene (PFT) to perfluoropentacene (PFP), while previous studies, due to the lack of availability of PFA and PFT, were limited to PFN and PFP, which exhibit rather different crystal structures. Applying various crystallization techniques such as gradient sublimation, solution growth, and liquid-assisted organic molecular beam deposition, we identified different crystalline phases that allow closing this structural gap. A comparison of all known phases reveals clear trends in the molecular packing motifs, which are rationalized by corresponding Hirshfeld analyses. Using UV/vis and X-ray absorption spectroscopy, also optoelectronic solid state properties of the various compounds were analyzed, and from a comparison with the corresponding solution spectra, the exciton binding energies are estimated. In addition, we demonstrate that like PFP PFT also exhibits a π-stacked polymorph in films grown on graphene, where molecules are flat lying and adopt a slip-stacked packing. This interface-mediated phase is found to be stable only for PFP and PFT, while it is unstable for the smaller PFA. Finally, we demonstrate for the case of PFT that the different packing motifs occurring in the various phases have a strong influence on the photoluminescence spectra.

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Section: Resultssupporting

confidence: 60%

Perfluorinated Acenes: Crystalline Phases, Polymorph-Selective Growth, and Optoelectronic Properties

et al. 2021

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“…The split resonances located at 284.6 and 285.3 eV can be assigned to CC (C 1s→π*) from chemically different carbons. [ 64 ] The similar peak located at 285.5 eV in the spectrum of SA‐Fe/CN shows only one peak because the N‐doped graphite substrate possesses inequivalent carbons with a continuous chemical state, indicating the carbonization of Fe(phen) 3 . The peak located at 288.5 eV is attributed to C 1s→π* of CN in the spectra of both samples.…”

Section: Resultsmentioning

confidence: 99%

“…The split resonances located at 284.6 and 285.3 eV can be assigned to CC (C 1s→π*) from chemically different carbons. [64] The similar peak located at 285.5 eV in the spectrum of SA-Fe/CN shows only one peak because the N-doped graphite substrate possesses inequivalent Adv. Mater.…”

Section: Synthesis and Characterization Of Sa-fe/cnmentioning

confidence: 99%

Single‐Atom Fe Catalysts for Fenton‐Like Reactions: Roles of Different N Species

et al. 2022

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atoms in SACs are chemically bonded to elements on the supports. This unique structural characteristic endows SACs with strong metal support interactions (SMSIs) [6][7][8][9][10] and tailorable homogenized active metal sites. [11][12][13][14] SACs have been found to be very favorable in many fields, including electrocatalysis, [15][16][17][18] organocatalysis, [19][20][21] industrial catalysis, [22][23][24] and others. [25][26][27][28][29][30] Consequently, revealing the atomic structure of the central metal atoms and the SMSI in SACs has become an important subject of research because it provides possibilities for rational design of novel SACs for specific reactions. The recent development of advanced characterization techniques, including aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), scanning tunneling microscopy images, extended X-ray absorption fine structure (EXAFS) curve fitting, and DFT modeling, provide crucial tools for identifying the atomic structure. [31][32][33][34][35][36][37] Meanwhile, tremendous efforts have been devoted to exploring SMSIs in SACs and their relationship with catalytic properties. [38][39][40][41] However, a systematic understanding of SMSIs Recognizing and controlling the structure-activity relationships of singleatom catalysts (SACs) is vital for manipulating their catalytic properties for various practical applications. Herein, Fe SACs supported on nitrogen-doped carbon (SA-Fe/CN) are reported, which show high catalytic reactivity (97% degradation of bisphenol A in only 5 min), high stability (80% of reactivity maintained after five runs), and wide pH suitability (working pH range 3-11) toward Fenton-like reactions. The roles of different N species in these reactions are further explored, both experimentally and theoretically. It is discovered that graphitic N is an adsorptive site for the target molecule, pyrrolic N coordinates with Fe(III) and plays a dominant role in the reaction, and pyridinic N, coordinated with Fe(II), is only a minor contributor to the reactivity of SA-Fe/CN. Density functional theory (DFT) calculations reveal that a lower d-band center location of pyrrolic-type Fe sites leads to the easy generation of Fe-oxo intermediates, and thus, excellent catalytic properties.

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“…Following earlier reports on 6A (and also 5A ), the lowest lying main features in C 1s XAS spectra (photon energies <288 eV, denoted A–D in Figure 5 ), can be attributed to transitions into π* orbitals. 12 , 74 , 77 , 78 …”

Section: Resultsmentioning

confidence: 99%

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

et al. 2022

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Hexacene, composed of six linearly fused benzene rings, is an organic semiconductor material with superior electronic properties. The fundamental understanding of the electronic and chemical properties is prerequisite to any possible application in devices. We investigate the orientation and interface properties of highly ordered hexacene monolayers on Ag(110) and Cu(110) with X-ray photoemission spectroscopy (XPS), photoemission orbital tomography (POT), X-ray absorption spectroscopy (XAS), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT). We find pronounced differences in the structural arrangement of the molecules and the electronic properties at the metal/organic interfaces for the two substrates. While on Cu(110) the molecules adsorb with their long molecular axis parallel to the high symmetry substrate direction, on Ag(110), hexacene adsorbs in an azimuthally slightly rotated geometry with respect to the metal rows of the substrate. In both cases, molecular planes are oriented parallel to the substrate. A pronounced charge transfer from both substrates to different molecular states affects the effective charge of different C atoms of the molecule. Through analysis of experimental and theoretical data, we found out that on Ag(110) the LUMO of the molecule is occupied through charge transfer from the metal, whereas on Cu(110) even the LUMO+1 receives a charge. Interface dipoles are determined to a large extent by the push-back effect, which are also found to differ significantly between 6A /Ag(110) and 6A /Cu(110).

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High-Resolution Near-Edge X-ray Absorption Fine Structure Study of Condensed Polyacenes

Cited by 9 publications

References 51 publications

Perfluorinated Acenes: Crystalline Phases, Polymorph-Selective Growth, and Optoelectronic Properties

Perfluorinated Acenes: Crystalline Phases, Polymorph-Selective Growth, and Optoelectronic Properties

Single‐Atom Fe Catalysts for Fenton‐Like Reactions: Roles of Different N Species

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

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