Tuning the Semiconducting Behaviors of New Alternating
Dithienyldiketopyrrolopyrrole–Azulene Conjugated Polymers by
Varying the Linking Positions of Azulene
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Abstract
Three
new conjugated polymers <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> with dithienyldiketopyrrolopyrrole (DPP) and azulene
moieties were synthesized and characterized. The five-membered rings
of azulene are connected with DPP in <b>DPPA1</b> and <b>DPPA2</b>, whereas the seven-membered ring of azulene is incorporated
into the backbone of <b>DPPA3</b>. The LUMO energy of <b>DPPA3</b>, which was determined on the basis of the respective
cyclic voltammograms and absorption spectra, is lower than those of <b>DPPA1</b> and <b>DPPA2</b>. OFETs were successfully fabricated
with thin films of <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b>. Thin films of <b>DPPA1</b> and <b>DPPA2</b> exhibit p-type semiconducting properties with hole mobilities up
to 0.97 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, whereas typical ambipolar behavior is found for thin film of <b>DPPA3</b> with hole and electron mobilities reaching 0.062 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and 0.021 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively.
The results reveal that semiconducting properties of <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> can be tuned by varying
the linkage positions of azulene with DPP moieties. Furthermore, <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> were tested
preliminarily as photovoltaic materials. The power conversion efficiency
(PCE) reaches 2.04% for the blending thin film <b>DPPA1</b> with
PC<sub>71</sub>BM