Structural Isomerism Effect in Platinum(II) Acetylide-Based Supramolecular Polymers

The self-assembly of π-aromatic organic and organometallic molecules into long-range-ordered supramolecular polymers is dictated by a variety of molecular parameters and external conditions. In this work, structural isomerism, representing one of the potent molecular parameters, has been investigated to modulate the self-assembly behaviors. Two platinum(II) acetylide-based structural isomers, with different N-hexyl substitution positions on the inner benzotriazole core, have been designed. Thanks to the synergistic participation of hydrogen-bonding and π-π-stacking interactions, both platinum(II) acetylide-based compounds are prone to forming supramolecular polymers via a nucleation-elongation cooperative mechanism in apolar media. Thermal hysteresis phenomena are observed for both compounds, suggesting the different supramolecular polymerization pathways upon cooling and heating. Remarkably, in addition to the spectroscopic difference, these two supramolecular polymers display distinct thermostability and rheological moduli, ascribing to different binding enthalpies of the neighboring monomers. Overall, it is evident that a minor variation at the molecular level brings huge differences to the properties of long-range-ordered supramolecular polymers. The current study illustrates the importance of the structural isomerism effect for the rational design of π-functional supramolecular materials.