Self-assembled supramolecular materials based on ruthenium(ii) complexes with exceptional optical and photothermal properties

Abstract

Ruthenium complexes have been extensively studied due to their prominent photochemical, photophysical, and electrochemical properties. However, research on the construction and properties of supramolecular materials self-assembled by ruthenium complexes remains limited. Here, by designing the connecting ligands and the self-assembly process, we constructed two new supramolecular materials (Ru-bipb-n and Ru-bdppz-n) connected by ruthenium(II) complexes. These two materials exhibit unique properties compared to their parent binuclear complexes. Ru-bipb-n displays remarkable dual-emission properties with impressive blue light emission in organic solvents. Its notable pH sensitivity makes it an ideal candidate as a ratiometric fluorescent probe for pH measurements, with a wide pH application range and an exceptionally long excited-state lifetime. By altering the connecting ligands, we obtained the second supramolecular material Ru-bdppz-n, which has a more extended π-conjugation plane. Ru-bdppz-n features unique full-band absorption properties from UV-visible to near-infrared (NIR) regions (200–2000 nm). Under 808 nm laser irradiation, Ru-bdppz-n exhibits outstanding photothermal conversion ability, with temperatures as high as 220 °C and 76 °C for solid powder and water dispersion, respectively, and shows excellent thermal stability, holding promise for solar energy harvesting and conversion applications. Mechanism investigations indicate that the extended π-conjugate plane of the ligand bdppz and the formation of the polymer chain promote NIR absorption and photothermal conversion. We believe that this will provide inspiration for the rational design of ruthenium-connected supramolecular materials with specified functionality.