Influence of Structural
Variation on the Solid-State
Properties of Diketopyrrolopyrrole-Based Oligophenylenethiophenes:
Single-Crystal Structures, Thermal Properties, Optical Bandgaps, Energy
Levels, Film Morphology, and Hole Mobility
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Abstract
Five new compounds, based on diketopyrrolopyrrole (DPP)
and phenylene
thiophene (PT) moieties, were synthesized to investigate the effect
of structural variations on solid state properties, such as single-crystal
structures, optical absorption, energy levels, thermal phase transitions,
film morphology, and hole mobility. The molecular structures were
modified by means of (i) backbone length by changing the number of
thiophenes on both sides of DPP, (ii) alkyl substitution (<i>n</i>-hexyl or ethylhexyl) on DPP, and (iii) the presence of
an <i>n</i>-hexyl group at the end of the molecular backbone.
These DPP-based oligophenylenethiophenes were systematically characterized
by UV–visible spectroscopy, differential scanning calorimetry
(DSC), thermogravimetric analysis (TGA), cyclic voltammetry (CV),
ultraviolet photoelectron spectroscopy (UPS), atomic force microscopy
(AFM), and hole-only diodes. Single-crystal structures were provided
to probe insight into structure–property relationships at a
molecule level resolution. This work demonstrates the significance
of alkyl substitution as well as backbone length in tuning material’s
solid-state properties