Ternalization Approach for Tuning Light Absorption and Crystalline Structure of Diketopyrrolopyrrole-Based Polymer Using Bisthiadiazole Unit

Abstract

Diketopyrrolopyrrole (DPP) and bisthiadiazole (BTDz)-based terpolymers were developed to obtain tunable optical properties and crystalline structures. Using dibromo-compounds of DPP and BTDz with distannylated thienylene vinylene (TV) moieties, high molecular weight polymers (44,100-99,200) with varied BTDz compositions (25, 50, or 75 mol%) were obtained. The introduction of BTDz generated a complementary light absorption band in the short-wavelength region (∼550 nm), while the DPP units created an intramolecular charge transfer band at ∼730 nm. As a result, terpolymers with a deep highest occupied molecular orbital energy of −5.50 eV and narrow bandgap of <1.5 eV were obtained. In addition, the crystal orientation of the DPP-based polymer was changed from edge-on to face-on by copolymerizing with only 25 mol% BTDz units.