Modulating carrier transfer ability—linker effect on thieno[3,4-c]pyrrole-4,6-dione based conjugated polymers

Abstract

Three conjugated copolymers Q1, Q2 and Q3 were developed based on thieno[3,4-c]pyrrole-4,6-dione (TPD) and two thiophene units. While Q1 was synthesized through direct linkage, Q2 and Q3 were constructed via introduction of a vinylene and ethynylene π-spacer between two thiophene groups. Electrochemical and UV-vis absorption studies as well as theoretical calculations show that the LUMO energy of Q3 is lower than Q1, Q2 while Q2 possesses the narrowest bandgap. OFET devices based on thin-films of Q1 and Q2 can be easily fabricated through a solution-process with conventional techniques, while OFET devices based on thin-films of Q3 are fabricated by drop-casting. Q1 and Q2 showed maximum hole mobilities of 2.2 × 10⁻³ cm² V⁻¹ s⁻¹ and 0.01 cm² V⁻¹ s⁻¹, respectively. Owing to the electron-withdrawing effect of the ethynylene group, Q3 based OFET devices exhibit a clear ambipolar semiconducting property in air conditions, with a maximum hole and electron mobility of 1.2 × 10⁻⁶ cm² V⁻¹ s⁻¹ and 0.6 × 10⁻⁶ cm² V⁻¹ s⁻¹, respectively.