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Title: First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers

Authors:
; ; ORCiD logo [1];  [1]; ORCiD logo
  1. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS) (SC-27)
OSTI Identifier:
1415262
Grant/Contract Number:
AC05-06OR23100
Resource Type:
Journal Article: Published Article
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 17; Related Information: CHORUS Timestamp: 2018-04-21 09:25:10; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English

Citation Formats

Su, Gregory M., Patel, Shrayesh N., Pemmaraju, C. D., Prendergast, David, and Chabinyc, Michael L. First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers. United States: N. p., 2017. Web. doi:10.1021/acs.jpcc.7b01353.
Su, Gregory M., Patel, Shrayesh N., Pemmaraju, C. D., Prendergast, David, & Chabinyc, Michael L. First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers. United States. doi:10.1021/acs.jpcc.7b01353.
Su, Gregory M., Patel, Shrayesh N., Pemmaraju, C. D., Prendergast, David, and Chabinyc, Michael L. Fri . "First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers". United States. doi:10.1021/acs.jpcc.7b01353.
@article{osti_1415262,
title = {First-Principles Predictions of Near-Edge X-ray Absorption Fine Structure Spectra of Semiconducting Polymers},
author = {Su, Gregory M. and Patel, Shrayesh N. and Pemmaraju, C. D. and Prendergast, David and Chabinyc, Michael L.},
abstractNote = {},
doi = {10.1021/acs.jpcc.7b01353},
journal = {Journal of Physical Chemistry. C},
number = 17,
volume = 121,
place = {United States},
year = {Fri Apr 21 00:00:00 EDT 2017},
month = {Fri Apr 21 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1021/acs.jpcc.7b01353

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  • The electronic structure and molecular orientation of semiconducting polymers in thin films determine their ability to transport charge. Methods based on near-edge X-ray absorption fine structure (NEXAFS) spectroscopy can be used to probe both the electronic structure and microstructure of semiconducting polymers in both crystalline and amorphous films. However, it can be challenging to interpret NEXAFS spectra on the basis of experimental data alone, and accurate, predictive calculations are needed to complement experiments. Here, we show that first-principles density functional theory (DFT) can be used to model NEXAFS spectra of semiconducting polymers and to identify the nature of transitions inmore » complicated NEXAFS spectra. Core-level X-ray absorption spectra of a set of semiconducting polymers were calculated using the excited electron and core-hole (XCH) approach based on constrained-occupancy DFT. A comparison of calculations on model oligomers and periodic structures with experimental data revealed the requirements for accurate prediction of NEXAFS spectra of both conjugated homopolymers and donor–acceptor polymers. The NEXAFS spectra predicted by the XCH approach were applied to study molecular orientation in donor–acceptor polymers using experimental spectra and revealed the complexity of using carbon edge spectra in systems with large monomeric units. The XCH approach has sufficient accuracy in predicting experimental NEXAFS spectra of polymers that it should be considered for design and analysis of measurements using soft X-ray techniques, such as resonant soft X-ray scattering and scanning transmission X-ray microscopy.« less
  • The temperature-dependent alignment of semiconducting liquid crystalline fluorene-thiophene copolymer (F8T2) thin film surfaces was investigated using the near-edge X-ray absorption fine structure (NEXAFS) technique. Partial electron yield spectra were recorded over a range of temperatures in order to observe directly the surface orientation as the polymer is heated and cooled through glass, crystal, and liquid crystal phases. In addition, samples annealed under varying processing conditions and quenched to room temperature were analyzed. The NEXAFS data show that (a) in thin F8T2 films at all temperatures the polymer backbone lies in the plane of the substrate, (b) the fluorene and thiophenemore » rings are rotated randomly about the molecular axis, (c) orientation of the polymer backbone can be controlled using a rubbed polyimide alignment layer as a template for liquid crystal orientation, and (d) under proper annealing conditions there is strong temperature-dependent alignment of the copolymer main-chain axis to the rubbing direction which extends from the polyimide/F8T2 interface all the way to the F8T2 surface. The surface alignment does not disappear after annealing at temperatures {approx}30 K above the bulk nematic to isotropic transition.« less
  • The sensitivity of near-edge X-ray absorption fine structure (NEXAFS) to differences in key chemical components of polyurethane polymers is presented. Carbon is NEXAFS spectra of polyurethane polymers made from 4,4{prime}-methylene di-p-phenylene isocyanate (MDI) and toluene diisocyanate (TDI) isocyanate monomers illustrate that there is an unambiguous spectroscopic fingerprint for distinguishing between MDI-based and TDI-based polyurethane polymers. NEXAFS spectra of MDI and TDI polyurea and polyurethane models show that the urea and carbamate (urethane) linkages in these polymers can be distinguished. The NEXAFS spectroscopy of the polyether component of these polymers is discussed, and the differences between the spectra of MDI andmore » TDI polyurethanes synthesized with polyether polyols of different molecular composition and different molecular weight are presented. These polymer spectra reported herein provide appropriate model spectra to represent the pure components for quantitative microanalysis.« less
  • No abstract prepared.
  • Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy is an important tool for probing the structure of conjugated polymer films used in organic electronic devices. High-performance conjugated polymers are often donor-acceptor co-polymers which feature a repeat unit with multiple functional groups. To facilitate better application of NEXAFS spectroscopy to the study of such materials, improved understanding of the observed NEXAFS spectral features is required. In order to examine how the NEXAFS spectrum of a donor-acceptor co-polymer relates to the properties of the sub-units, a series of naphthalene diimide-thiophene-based co-polymers have been studied where the nature and length of the donor co-monomer hasmore » been systematically varied. The spectra of these materials are compared with that of a thiophene homopolymer and naphthalene diimide monomer enabling peak assignment and the influence of inter-unit electronic coupling to be assessed. We find that while it is possible to attribute peaks within the π* manifold as arising primarily due to the naphthalene diimide or thiophene sub-units, very similar dichroism of these peaks is observed indicating that it may not be possible to separately probe the molecular orientation of the separate sub-units with carbon K-edge NEXAFS spectroscopy.« less