Pathway-dependent Metallosupramolecular Polymerization Regulated by Ligand Geometry

Understanding structure/property correlations in self-assembly is a key but challenging requirement for developing functional materials. Herein, we explore the importance of ligand geometry to fine-tune photophysical properties (MMLCT vs. MLCT excited states) and self-assembly pathways in metallosupramolecular polymerization. To this end, we have designed two hydrophobic Pt(II) complexes, 1 and 2, containing a π-extended bidentate bipyridine ligand with different substitution pattern, resulting in different molecular geometries (linear vs. V-shaped). Detailed comparative studies revealed significant differences for both complexes in terms of their photophysical properties and self-assembly pathways in non-polar media. The V-shaped topology of 1 enables facile face-to-face molecular stacking with a certain curvature leading to luminescent spherical assemblies exhibiting MMLCT states and short Pt⋅⋅⋅Pt contacts via a single-step cooperative pathway. On the other hand, the higher preorganized linear topology of complex 2 induces a two-step competitive self-assembly process leading to the formation of one-dimensional supramolecular polymers with slipped packing and MLCT-originated emission. Our findings broaden the monomer scope for supramolecular polymerization and provide design guidelines for the realization of luminescent supramolecular assemblies.