β‑Alkyl substituted
Dithieno[2,3‑<i>d</i>;2′,3′<i>-d</i>′]benzo[1,2‑<i>b</i>;4,5‑<i>b</i>′]dithiophene Semiconducting
Materials and Their Application to Solution-Processed Organic Transistors
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Abstract
A novel highly π-extended heteroacene with four
symmetrically
fused thiophene-ring units and solubilizing substituents at the terminal
β-positions on the central ring, dithieno[2,3-<i>d</i>;2′,3′<i>-d</i>′]benzo[1,2-<i>b</i>;4,5-<i>b</i>′]dithiophene (DTBDT) was
synthesized via intramolecular electrophilic coupling reaction. The
α-positions availability in the DTBDT motif enables the preparation
of solution-processable DTBDT-based polymers such as <b>PDTBDT</b>, <b>PDTBDT-BT</b>, <b>PDTBDT-DTBT</b>, and <b>PDTBDT-DTDPP</b>. Even with its highly extended acene-like π-framework, all
polymers show fairly good environmental stability of their highest
occupied molecular orbitals (HOMOs) from −5.21 to −5.59
eV. In the course of our study to assess a profile of semiconductor
properties, field-effect transistor performance of the four DTBDT-containing
copolymers via solution-process is characterized, and <b>PDTBDT-DTDPP</b> exhibits the best electrical performance with a hole mobility of
1.70 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. <b>PDTBDT-DTDPP</b> has a relatively
smaller charge injection barrier for a hole from the gold electrodes
and maintains good coplanarity of the polymer backbone, indicating
the enhanced π–π stacking characteristic and charge
carrier transport. The experimental results demonstrate that our molecular
design strategy for air-stable, high-performance organic semiconductors
is highly promising