Cyclometallated Pt(II) Complexes Containing a Functionalized Bis‐Urea Alkynyl Ligand: Probing Aggregation Mediated by Hydrogen BondsversusPt⋅⋅⋅Pt and π−π Interactions

Abstract

AbstractNeutral cyclometallated Pt(II) complexes [(C^Nt−Bu^Nt−Bu)Pt−R] (4–5) containing a bis‐urea alkynyl (R) ligand have been prepared and fully characterized. The dichotomous nature of4–5makes it difficult to anticipate which interactions (hydrogen bonds, π−π stacking and Pt⋅⋅⋅Pt) will dominate their assembly process. The aggregation properties of4–5were thus probed by multifarious analytical (UV/Vis, FT‐IR, NMR, MS, CD, emission) and computational (DFT, TD‐DFT) techniques. CD analyses of sergeants‐and‐soldiers type mixtures between4and an enantiopure Pt‐free monomer(S,S)‐3reveal that no amplification of supramolecular helicity occurs in this system. In fact, complex4acts as competitor or chain capper, likely through hydrogen bonding, of the homochiral assemblies formed by(S,S)‐3. In DMSO,1H NMR and DOSY analyses indicate that4and5form aggregates. Likewise, the aggregation is promoted by the addition of H2O as suggested by red shift of the lowest energy emission band, which might originate from a3MMLCT excited state. TD‐DFT calculations confirm that self‐aggregation occurs through Pt⋅⋅⋅Pt and π−π interactions yielding head‐to‐tail aggregates in DMSO and DMSO/H2O mixtures. Our study therefore suggests a (condition dependent) competitive rather than a cooperative mode of action of the different types of interactions present in aggregates of4–5.