Thiadiazoloquinoxaline-Fused Acenaphthenequinone imide: A Highly Electron-Withdrawing Acceptor for Ambipolar Semiconducting Polymers with Strong Near-Infrared Absorption

A hitherto unreported heterocyclic imide, thiadiazolo[3,4-g]-quinoxaline-fused acenaphthenequinone imide acceptor (TQAI), is designed and synthesized by incorporating an auxiliary electron-deficient thiadiazolo[3,4-g]-quinoxaline (TQ) annulated in the lateral direction of the acenaphthenequinone imide skeleton. This molecular design makes it possible to generate strong electron affinity by integrating the highly electron-deficient TQ unit with the dicarboxylic acid imide groups. In addition, a largely pi-extended and S/N-enriched pi-conjugated structure can be produced, which facilitates both intermolecular and intramolecular interactions. As a result, the alternating arrangement of TQAI acceptor and thiophene-derivative donor segments, such as 2,5-bis(3-(2-decyltetradecyl)thiophen-2-yl)thieno[3,2-b]thiophene or 3,3 '''-bis(2-decyltetradecyl)-2,2 ':5 ',2 '':5 '', 2 '''-quaterthiophene, in the polymer main chain, endows the target D-A conjugated polymers with desirable photophysical and electrochemical properties. These properties include deep lowest unoccupied molecular orbital levels (LUMO < -3.80 eV), narrow optical band gaps (as low as 0.84 eV), strong light-capturing ability in the second near-infrared window, and strong solid-state organization with a preferred face-on orientation. The organic field-effect transistors, which were made with our synthesized polymers, exhibit typical ambipolar charge transport in an inert atmosphere. PTQAIT-2T shows maximum hole and electron mobilities of 8.1 x 10(-3) and 3.6 x 10(-2) cm(2) V-1 s(-1), respectively. In particular, with a C-60 layer, which is added to facilitate efficient electron trapping and exciton dissociation, the bilayer C-60/PTQAIT-2T phototransistors show a pronounced photosensitivity of 1780, which is 50 times higher than that of pristine PTQAIT-2T devices.

Automated summary

The newly reported heterocyclic imide, thiadiazolo[3,4-g]-quinoxaline-fused acenaphthenequinone imide acceptor (TQAI), designed in this study exhibits strong electron affinity, largely pi-extended pi-conjugated structure, and preferred solid-state organization, leading to desirable photophysical and electrochemical properties in conjugated polymers. The use of TQAI acceptor and thiophene-derivative donor segments in polymer main chain results in deep LUMO levels, narrow optical band gaps, and ambipolar charge transport in organic field-effect transistors, showcasing potential for optoelectronic applications.