10.1021/acs.jpcc.8b03635.s004 T. Salzillo T. Salzillo S. d’Agostino S. d’Agostino A. Rivalta A. Rivalta A. Giunchi A. Giunchi A. Brillante A. Brillante R. G. Della Valle R. G. Della Valle N. Bedoya-Martínez N. Bedoya-Martínez E. Zojer E. Zojer F. Grepioni F. Grepioni E. Venuti E. Venuti Structural, Spectroscopic, and Computational Characterization of the Concomitant Polymorphs of the Natural Semiconductor Indigo American Chemical Society 2018 characterization calculation Raman Structural spectroscopy polymorph XRD bulk device Indigo drop-cast films 2018-07-11 00:00:00 Media https://acs.figshare.com/articles/media/Structural_Spectroscopic_and_Computational_Characterization_of_the_Concomitant_Polymorphs_of_the_Natural_Semiconductor_Indigo/6935963 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.