Synthesis, physicochemical properties and infrared bioimaging of donor-acceptor (D-A) benzothiadiazole and diketopyrrolopyrrole macromolecules: A combined experimental and theoretical study

Herein the synthesis of the polymer (PHB) and the oligomer (OHDPP) using the Fagnou-type direct arylation reaction with goods yields nearly to 63% is described. These macromolecules were envisioned comprising an electronic donor–acceptor (D-A) structure with 3,4-dihexylthiophene (H) as donor and benzothiadiazole (B) or diketopyrrolopyrrole (DPP) as acceptor moieties. Based on the implemented strategy of synthesis, the combination of H with B, or H with DPP, favored obtaining polymeric and oligomer structures, respectively. Taking advantage of the easy preparation and low cost provided by the arylation reaction compared with other polymerization methods, the strength of the D-A effect induced by B or DPP acceptor fragments was investigated experimentally and theoretically. As a polymer, PHB exhibited a higher thermal stability, but the oligomer OHDPP demonstrated higher intramolecular charge transfer (ICT) effects. Light emissive electronic states were generated in both materials by nonlinear absorption at infrared wavelengths with maximum two-photon absorption (TPA) cross sections of ∼900 GM. The light emission from the macromolecules in organic solutions was observed at the red and infrared wavelength range of the spectrum; when processed in the form of nanoparticles, these macromolecules were exploited as fluorescent labels for the bioimaging of the neuroblastoma cell line SH-SY5Y. Theoretical calculations provided insight into the molecular conformation in solution and generated data on intramolecular interactions. They show more intramolecular interactions in OHDPP due to its molecular planarity, which explains the more effective ICT compared with PHB.