2 research outputs found
Mode Robustness in Raman Optical Activity
By
reformulating Raman and ROA invariants we provide ground for the definition
of robust modes in ROA spectroscopy. Introduction of two parameters
defining robustness helps characterization and assignment of ROA bands.
Application and use of robustness parameters to [<i>n</i>]Āhelicenes and oxirane/thiirane derivatives are presented
(Semi)ladder-Type Bithiophene Imide-Based All-Acceptor Semiconductors: Synthesis, StructureāProperty Correlations, and Unipolar nāType Transistor Performance
Development of high-performance
unipolar n-type organic semiconductors
still remains as a great challenge. In this work, all-acceptor bithiophene
imide-based ladder-type small molecules BTI<i>n</i> and
semiladder-type homopolymers PBTI<i>n</i> (<i>n</i> = 1ā5) were synthesized, and their structureāproperty
correlations were studied in depth. It was found that Pd-catalyzed
Stille coupling is superior to Ni-mediated Yamamoto coupling to produce
polymers with higher molecular weight and improved polymer quality,
thus leading to greatly increased electron mobility (Ī¼<sub>e</sub>). Due to their all-acceptor backbone, these polymers all exhibit
unipolar n-type transport in organic thin-film transistors, accompanied
by low off-currents (10<sup>ā10</sup>ā10<sup>ā9</sup> A), large on/off current ratios (10<sup>6</sup>), and small threshold
voltages (ā¼15ā25 V). The highest Ī¼<sub>e</sub>, up to 3.71 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>, is attained from PBTI1 with the shortest monomer unit. As the monomer
size is extended, the Ī¼<sub>e</sub> drops by 2 orders to 0.014
cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup> for PBTI5.
This monotonic decrease of Ī¼<sub>e</sub> was also observed in
their homologous BTI<i>n</i> small molecules. This trend
of mobility decrease is in good agreement with the evolvement of disordered
phases within the film, as revealed by Raman spectroscopy and X-ray
diffraction measurements. The extension of the ladder-type building
blocks appears to have a large impact on the motion freedom of the
building blocks and the polymer chains during film formation, thus
negatively affecting film morphology and charge carrier mobility.
The result indicates that synthesizing building blocks with more extended
ladder-type backbone does not necessarily lead to improved mobilities.
This study marks a significant advance in the performance of all-acceptor-type
polymers as unipolar electron transporting materials and provides
useful guidelines for further development of (semi)Āladder-type molecular
and polymeric semiconductors for applications in organic electronics