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

Neutral 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 of 4–5 makes it difficult to anticipate which interactions (hydrogen bonds, π−π stacking and Pt⋅⋅⋅Pt) will dominate their assembly process. The aggregation properties of 4–5 were 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 between 4 and an enantiopure Pt‐free monomer (S,S)‐3 reveal that no amplification of supramolecular helicity occurs in this system. In fact, complex 4 acts 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 that 4 and 5 form 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 a 3MMLCT 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 of 4–5. Bis‐urea functionalized cyclometalated Pt(II) complex acts as a competitor or chain capper of the helical assemblies form by a complementary enantiopure bisurea (in blue) likely through hydrogen bonding. In more polar media, these complexes exhibit aggregation by means of π−π stacking and Pt⋅⋅⋅Pt interactions.