Identifying and explaining vibrational modes of quinacridones: Via temperature-resolved terahertz spectroscopy: Absorption experiments and solid-state density functional theory simulations

A. D. Squires, Adam J. Zaczek, R. A. Lewis, Timothy M. Korter

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Quinacridone and its substituted analogs are pigments widely used in art and industry. The temperature dependence of the crystal structures of two quinacridone polymorphs (β and γ), along with the common variant 2,9-dimethylquinacridone, were investigated using powder X-ray diffraction and terahertz spectroscopy. These were then compared with solid-state density functional theory simulations of both structures and vibrations. X-ray patterns were collected at eight temperatures in the range 13-298 K and terahertz spectra at fifteen temperatures in the range 20-300 K. Simulations were at absolute zero and at appropriate expansions to model room temperature. It was found that some of the powder X-ray diffraction features in only β-quinacridone (15.7°, 19.7° and 31.2° at 13 K) underwent anomalous shifting with temperature change. We attribute this to the unique coplanar hydrogen bonding pattern of β-quinacridone compared to the other solids, with the unusual diffraction peaks originating from crystallographic planes perpendicular to the a axis intermolecular hydrogen bonds. This observation coincides with a contraction of the a axis with heating and results from its relatively weak N-H⋯O hydrogen bonds and significant C-H⋯H-C repulsions. Associated with this anomalous contraction, for β-quinacridone only spectral peaks are seen to increase in energy with temperature

Original languageEnglish (US)
Pages (from-to)19672-19679
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume22
Issue number35
DOIs
StatePublished - Sep 21 2020

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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