Structural, Spectroscopic, and Computational Characterization of the Concomitant Polymorphs of the Natural Semiconductor Indigo

T. Salzillo*, S. D'Agostino, A. Rivalta, A. Giunchi, A. Brillante, R. G. Della Valle, N. Bedoya-Martínez, E. Zojer, F. Grepioni, E. Venuti

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

Indigo [2,2′-bis(2,3-dihydro-3-oxoindolyliden)], a commonly used natural dye, has been shown to exhibit a highly promising semiconducting behavior, allowing for the realization of ambipolar devices. Nevertheless, up to date, it is still unclear which crystal structure is present in the thin films, a piece of information relevant for device applications. In this work, we address this issue by an in-depth characterization of the polymorphs of Indigo in the bulk and in drop-cast films. To do this, X-ray diffraction (XRD) and micro-Raman spectroscopy have been employed jointly, with the support of state-of-the-art density functional theory calculations in the solid state. Structural and spectroscopic characterizations have established that the two known A and B polymorphs grow as concomitant in the bulk under most of the experimental conditions adopted in this work. In the drop-cast films, XRD cannot unambiguously identify the structure, but Raman spectroscopy is effective in establishing that only the B form is present. The calculations augment the experiments, providing valuable insights into the relative thermodynamic stability of the two forms as a function of temperature. They also allow for a more comprehensive characterization of the Raman modes.

Original languageEnglish
Pages (from-to)18422-18431
Number of pages10
JournalThe Journal of Physical Chemistry / C
Volume122
Issue number32
DOIs
Publication statusPublished - 16 Aug 2018

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Fields of Expertise

  • Advanced Materials Science

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