Synthesis and optoelectronic properties of novel alternate copolymers based on diketopyrrolopyrrole and triarylamine units spaced by flexible chain

A series of alternate copolymers D‑co‑Ts named P(DPP‑TA) P(DPP‑Cz) and P(DPP‑DB) consisting of both diketopyrrolopyrrole (DPP) and different triarylamine (TAA) units, were synthesized by Stille cross-coupling reaction in which DPP acts as an acceptor and TAA acts as a donor. These D‑co‑Ts show good thermal stability in nitrogen (N₂) atmosphere. The solutions of D‑co‑Ts have strong UV–vis absorption bands in the range of 313 nm to 344 nm and have fluorescence (PL) peaks at from 415 nm to 496 nm with high quantum efficiency. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and E_g were combined with via cyclic voltammograms (CV) as −5.19 eV to −5.41 eV, −3.77 eV to −3.80 eV, and 1.42 eV to 1.62 eV, respectively. The P(DPP‑TA) film shows the evident color changes from original yellow to brownish to blue. New absorption peaks of P(DPP‑TA) appear at 412 nm and 938 nm with increasing voltage in the UV–vis spectrophotometer, indicating D‑co‑Ts can be promising electrochromic materials. The highest coloration efficiency reaches up to be 270 cm² C⁻¹ for the P(DPP‑Cz). The memory performances of the ITO/polymer/Al sandwich devices were also studied, in which D‑co‑Ts exhibit the typical nonvolatile rewritable flash memory characteristics. The device of P(DPP‑DB) shows an ON/OFF current ratio of 5.80 × 10⁴ under a threshold voltage of −1.80 V. Furthermore, in the explosive detection tests, the copolymer shows new emission band at 570 nm with addition of TNT, and the PL quenching efficiency goes up to be 82%.