Synthesis, characterization, and air stability study of pyrimido[4,5-g]quinazoline-4,9-dione-based polymers for organic thin film transistors†
We report two novel π-conjugated polymers, PPQ2T-TVT-24 and PPQ2T-TT-24, containing the pyrimido[4,5-g]quinazoline-4,9-dione moiety and thieno[3,2-b]thiophene (TT) and (E)-1,2-bis(thiophen-2-yl)ethene (TVT), respectively, via the Stille cross-coupling reaction. Both polymers displayed good thermal stability and promising field effect transistor performance with hole mobilities of up to 3.08 × 10−3 cm2 V−1 s−1 for PPQ2T-TT-24 and 5.34 × 10−3 cm2 V−1 s−1 for PPQ2T-TVT-24. The ambient air stability of the organic thin film transistors based on these two polymers along with another previously reported PQ polymer containing bithiophene (BT) units, PPQ2T-BT-24, was studied. It was found that the moisture (H2O) in the ambient air is a detrimental component responsible for the degradation of the device performance, while oxygen, in contrast, could enhance the carrier mobility. Our study showed that the electron donor comonomer unit significantly influenced the stability of these polymers towards moisture in the stability order of TT > BT ≫ TVT. It was shown that the interaction between H2O and PPQ2T-TT-24 is physisorption and the device performance could be fully recovered, while the interaction of H2O with two other polymers involved chemical reactions, leading to permanent damages to the polymers and only partially recovered device performance upon removal of moisture.