Multi-Edge Resonant Tender X-ray Diffraction for Probing the Crystalline Packing of Conjugated Polymers

Abstract

Resonant X-ray diffraction exploits energy-dependent changes in X-ray scattering across an elemental absorption edge to provide additional information about the organization of atoms within the unit cell. Here, we demonstrate the utility of performing resonant X-ray diffraction at multiple absorption edges to provide complementary information about atomic positions and bond orientation. These experiments are achieved through the chlorination of a well-studied naphthalene diimide bithiophene copolymer, P­(NDI2OD-T2), to produce P­(NDI2OD-T2Cl2), enabling measurements at sulfur and chlorine K-edges. Strong modulation of the diffraction intensity is observed at both edges but with significant differences in the observed diffraction anisotropy. These differences in diffraction anisotropy arise due to differences in the orientation of sulfur and chlorine bonds within the unit cell. Simulations of the supramolecular organization of P­(NDI2OD-T2Cl2) have also been performed, with P­(NDI2OD-T2Cl2) showing a similar lowest energy packing geometry to unchlorinated P­(NDI2OD-T2). Comparing the simulated unit cells with the experimental results, we find that the experimental results are best explained by a mixture of anti and syn conformers in thin film samples of P­(NDI2OD-T2Cl2). This observation is in line with the smaller energy barrier computed at the quantum chemical level between the two conformers providing a higher flexibility of the conjugated backbones.

Resonant X-ray Diffraction Reveals the Location of Counterions in Doped Organic Mixed Ionic Conductors

“…Quantitative modeling of the Cl GIRXRD requires the development of f for Cl in ClO 4 . Due to the formal +7 oxidation state of the Cl, the primary resonance is blue-shifted relative to covalently bound Cl . Given the simplicity of the observed spectrum, f was derived by fitting the NEXAFS to a sum of Kramers–Kronig consistent functions: Lorentzian peaks and a B-spline step edge, and then splicing the real part of the analytic function onto the off-resonant, bare-atom values .…”

Resonant Tender X-ray Scattering of Organic Semiconductors

“…Thus, for a given material, all available absorption edges should be studied to provide the most information. In the case of the chlorinated derivative of P­(NDI2OD-T2) studied, chlorination was deduced to produce a mixture of syn and anti conformers, resulting in a less ordered material compared to P­(NDI2OD-T2) …”

“…Multiedge resonant tender X-ray diffraction data of a chlorinated derivative of P­(NDI2OD-T2) taken at (a) the sulfur K-edge and (b) the chlorine K-edge. Reprinted (adapted) with permission from ref . Copyright 2022 American Chemical Society.…”

“…The ability to utilize other edges in the tender X-ray regime has also been shown by studying a chlorinated derivative of P(NDI2OD-T2), see Figure 9. 41 Strong resonant diffraction effects were seen at the chlorine K-edge as well as the sulfur Kedge with interesting differences in the observed diffraction anisotropy: at the sulfur K-edge the intensity of the (100) peak shows the greatest modulation when observed along q z (perpendicular to the X-ray polarization) while for the chlorine K-edge the intensity of the (100) peak shows the greatest modulation when observed along q x (parallel to the X-ray polarization). This observation was interpreted in terms of the different orientations of the bond vectors of the associated C−S and C−Cl bonds, providing the opportunity for the use of different edges to provide additional information for constraining molecular models of crystalline packing.…”

“…In the case of the chlorinated derivative of P(NDI2OD-T2) studied, chlorination was deduced to produce a mixture of syn and anti conformers, resulting in a less ordered material compared to P(NDI2OD-T2). 41 While the study of the diffraction peaks of organic semiconductors is a feature that distinguishes resonant tender X-ray scattering from R-SoXS, tender X-rays can also be used for resonant scattering experiments in the small angle scattering regime 24,42−44 which has been the domain of R-SoXS. A good demonstration of the ability of tender X-rays to study nanoscale features is the observation of the long period of P3HT in thin films, Figure 10.…”