New Donor–Acceptor–Donor Molecules with Pechmann Dye as the Core Moiety for Solution-Processed Good-Performance Organic Field-Effect Transistors

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 cm² V^–1 s^–1 with high on/off ratio up to 10⁶. In comparison, the hole mobility of OFETs with <b>BFBPD</b> (0.14 cm² V^–1 s^–1) 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