Terpyridine-based donor–acceptor metallo-supramolecular polymers with tunable band gaps: Synthesis and characterization

• The strong electron-donating fused-rings moieties leads to increase of the HOMO.
• Coordination with the transition ion causes decrease of the LUMO.
• The wide absorption comes from the ICT transitions in D-A metallo-polymers.

Three new building blocks containing the electron-donor fused-ring motifs carbazole, dithienosilole (DTS) and dithienopyrrole (DTP) and the 2,2′:6′,2″-terpyridine electron-acceptor motif were designed and synthesized. Directed by transition metal ions, the self-assembly of the building blocks triggered polymerization to form the corresponding metallo-supramolecular polymers PCzTPY, PSiTPY and PNTPY, respectively. The UV–vis absorption maxima of the building blocks occur at long wavelengths (351, 368 and 430 nm for CzTPY, SiTPY and NTPY, respectively), which arises from intramolecular charge transfer (ICT) transitions. However, the absorption maxima of their corresponding metallo-supramolecular polymers are clearly red-shifted (to 394, 431 and 509 nm for PCzTPY, PSiTPY and PNTPY, respectively), which is caused by the incorporation of the transition metal ion into the backbones of the target polymers. Based on the above strategies, the resulting metallo-polymers exhibit reduced energy gaps, which are 2.07, 1.97 and 1.56 eV for the PCzTPY, PSiTPY and PNTPY metallo-supramolecular polymers, respectively.