Synthesis and Study of Donor–Acceptor Conjugated Polymers via a Green Indophenine Polymerization Strategy

In this study, we endeavored to synthesize conjugated polymers utilizing the conditions of the indophenine reaction, which is known for its facile and environmentally friendly synthetic approach. The indophenine reaction is extensively used for the synthesis of various of small molecules. The synthesized isatin-based precursor compounds (3–6) were well characterized by IR, NMR (1H and 13C), and HRMS analysis. Four conjugated polymers P1–P4 were synthesized by concentrated sulfuric acid catalyzed indophenine reactions between compounds 3–6 and dialkoxythiophene. The HOMO energy level of the synthesized polymers was found to be below −5.8 eV. Polymers showed a low-lying LUMO energy level close to −4.3 eV. Gel permeation chromatography (GPC) analysis of polymers showed values of the weight-average molecular weight in the range of 24.7 to 30.5 kDa. Thermogravimetric analysis (TGA) showed that all polymers were quite stable up to ∼300 °C. The obtained RMS roughness values measured by atomic force measurement (AFM) analysis were 15.38, 14.33, 10.05, and 5.58 nm for polymers P1, P2, P3, and P4, respectively. The measured space charge current limited (SCLC) hole mobilities of polymers P1, P2, P3, and P4 were 7.66 × 10–2, 9.04 × 10–2, 9.81 × 10–2, and 1.02 × 10–1 cm2 V–1 S–1, respectively. The obtained OFET mobilities for the films of polymers P1, P2, P3, and P4 were 0.095 × 10–3, 0.1766 × 10–3, 0.2417 × 10–3, and 0.2905 × 10–3 cm2 V–1 s–1, respectively.