New Donor–Acceptor–Donor
Molecules with
Pechmann Dye as the Core Moiety for Solution-Processed Good-Performance
Organic Field-Effect Transistors
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Abstract
In this paper, we report the synthesis and characterization
of
two new D-A-D molecules (<i>E</i>)-5,5′-bis(5-(benzo[<i>b</i>]thiophen-2-yl)thiophen-2-yl)-1,1′-bis(2-ethyl-
hexyl)-[3,3′-bipyrrolylidene]-2,2′(1<i>H</i>,1′<i>H</i>)-dione (<b>BTBPD</b>) and (<i>E</i>)-5,5′-bis- (5-(benzo[<i>b</i>]furan-2-yl)thiophen-2-yl)-1,1′-bis(2-ethylhexyl)-[3,3′-bipyrrolylidene]-2,2′(1<i>H</i>,1′<i>H</i>)-dione (<b>BFBPD</b>). They entail bipyrrolylidene-2,2′(1<i>H</i>,1′<i>H</i>)-dione (<b>BPD</b>, known as Pechmann dye) as the
electron-accepting core that is flanked by two benzo[<i>b</i>]thiophene moieties and two benzo[<i>b</i>]furan moieties,
respectively. Crystal structures of <b>BTBPD</b> and <b>BFBPD</b> provide solid evidence for the intermolecular donor–acceptor
(D-A) interactions, which are favorable for improving charge transport
performance. Organic field-effect transistors (OFETs) were prepared
based on thin films of <b>BTBPD</b> and <b>BFBPD</b> through
solution-processed technique. OFETs of <b>BTBPD</b> exhibit
relatively high hole mobility up to 1.4 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> with high on/off ratio up to 10<sup>6</sup>. In comparison, the hole mobility of OFETs with <b>BFBPD</b> (0.14 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) is relatively low, because of the poor thin-film morphology and
low molecular ordering, even after annealing. Thin-film morphological
and XRD studies were carried out to understand the variation of hole
mobilities after annealing at different temperatures. The present
studies clearly demonstrate the potentials of <b>BPD</b> that
is planar and polar as the electron-acceptor moiety to build D-A molecules
for organic semiconductors with good performance