Molecular Rectangles Featuring Two Parallel NCN-Coordinated Platinum Units: Enhancing Near-Infrared Emission Through Excimer Formation.

New macrocyclic molecules are described that incorporate Pt(NCN) units on opposite edges of a rectangular structure, with xanthene units constituting the other two sides. Here, NCN represents a cyclometallating tridentate ligand based on 2,6-di(2-pyridyl)benzene or its pyrimidine analog. The complexes display strong photoluminescence peaking in the near-infrared region of the spectrum in solution (λmax up to 761 nm). Photophysical data and DFT calculations indicate that the emission arises from "intramolecular excimers"-triplet excited states that form when the two Pt(NCN) units within the molecule are brought into close proximity to interact interfacially. In doped polymers, the necessary molecular distortion is inhibited, but related excited states that emit in a similar region can still form through intermolecular interactions.