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.