Synthesis, Photophysical properties and OFET application of thienothiophene and benzothiadiazole based Donor-?-Acceptor-? (D-? -A-?) type conjugated polymers

Novel conjugated donor-pi -acceptor-pi (D-pi -A-pi) type polymers (P1 -P3), possessing thieno[3,2-b]thiophene (TT) with different aromatic substituents as donors, benzo[1-3]thiadiazole (BT) as an acceptor and thiophene as a pi-linker, were designed and synthesized via palladium-catalyzed Stille coupling reaction. Their electronic, optical and thermal properties were investigated using UV-vis and fluorescence spectroscopies, cylic voltam-metry, and thermal gravimetric analysis. Photophysical characterizations of these novel polymers showed a remarkable mega Stokes shift, reaching up to 130 nm and optic/electronic band gaps between 1.70 and 2.00 eV, as well as good thermal stability of degradation temperature at around 260 degrees C. To study the effect of electron donating and withdrawing groups on the electronic properties of the pi-extended polymers, their organic field-effect transistors (OFETs) were fabricated and charge transport characteristics were investigated. While all three polymers showed a p-type field-effect behaviour, dimethylamine substituted P3 exhibited the highest average saturated hole mobility, Ilsat, 0.04 cm2 V-1 s- 1, on/off current ratio, Ion/Ioff = 3.0 x 103, and the smallest subthreshold swing, SS, 250 mV dec-1, outperforming similar p-type D-pi -A-pi semiconducting polymers reported in the literature. The results presented in this work corroborate that the three novel TT-BT polymers have promising potential for electronic and optoelectronic applications, in particular where the tunability of field-effect behaviour is essential for performance.

Automated summary

Novel conjugated donor-pi-acceptor-pi (D-pi-A-pi) type polymers (P1-P3) with thieno[3,2-b]thiophene (TT) as donors, benzo[1-3]thiadiazole (BT) as an acceptor, and thiophene as a pi-linker, were synthesized via palladium-catalyzed Stille coupling reaction. These polymers exhibited a remarkable mega Stokes shift, optic/electronic band gaps between 1.70 and 2.00 eV, and good thermal stability. The dimethylamine substituted P3 showed the highest average saturated hole mobility, on/off current ratio, and the smallest subthreshold swing among similar p-type D-pi-A-pi semiconducting polymers reported in the literature. These novel TT-BT polymers have promising potential for electronic and optoelectronic applications.