Knotted or unknotted? A theoretical quantum protocol for luminescence simulation of metallo-supramolecular knots

Entangled structures are topological architectures often observed not only in the macroscopic world, but also at the molecular level with many examples in biological systems (DNA, RNA). In recent decades, these fascinating entities have aroused considerable interest among chemists with the advent of metallo-supramolecular knots. Notwithstanding the burgeoning of such metal complexes in literature, their use as luminescent emitters as well as systematic studies on their luminescence properties are still extremely limited. In view of this, a theoretical DFT protocol dedicated to luminescence profile simulations of these peculiar “entwined” species is highly desirable. In this work, we propose a robust and affordable DFT computational workflow able to recreate meticulously the emission band-shape of different metallo-supramolecular knots. As a result of a preparatory DFT benchmark, we decided to use HSEH1PBE/LanL2DZ level via Born-Oppenheimer molecular dynamics to explore the change in the coordination environment around the metal centers in the excited state (S1). Thereupon, a detailed recruiting of TD-DFT functionals recommended the mPW3PBE/LanL2DZ level as the most precise and transferable method to model accurately metallo-supramolecular knots emission spectra as metal ions, internal spacers and interlocking modes vary.