Journal of Materials Chemistry C
Paper
N-derivative. Combined DFT calculations and CV analysis show
that the energy gap of ethylene and azomethine based
compound NTE and NTI is lower than that of acetylene based
NTA. This was ascribed to the lower overlap of the C–C sp bond
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M. Gazzano, A. Zanelli, M. Monari, M. G. Lobello, F. De
Angelis, V. Biondo, G. Generali, S. Troisi, W. Koopman,
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2
with the p-conjugated system, with respect to the C–C sp bonds
and is in good accordance to what was observed for N-free
systems. While the HOMO levels decrease in the order NTE >
NTI > NTA, the LUMOs of NTE and NTA have almost the same
energy. However, a slightly lower LUMO energy was found for
NTI likely due to the electron withdrawing effect of the azo-
methine moiety.
Thin deposits obtained by solution casting present high
crystallinity for all compounds showing concomitant poly-
morphs. Indeed, the simultaneous presence of crystals with
different morphology and uorescence was detected by optical
microscopy for NTE and NTA samples. XRD conrms the poly-
morphic nature of the different crystals. Crystallization
attempts are currently under way for dening the single crystal
structure. Nevertheless, successful control of the crystal phase
was achieved by thermal treatments of the lms. Indeed, space
resolved uorescence spectra, DSC and XRD analysis conrm
that thermal heating allows us to irreversibly convert one
polymorph into the other. Exploiting such features, we
produced a TTI device able to monitor thermal changes of the
lm by optical microscopy.
This work introduces a chemical design strategy to tune the
optoelectronic properties and polymorphism attitude of small
molecules usable for TTI devices. Concomitant polymorph
formation combined with the possibility of controlling the
polymorph type and solid state uorescence, may enable the
development of new organic devices and sensors based on
functional polymorph conversion.
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