Supramolecular Polymorphism of an Ir(III) Complex: Kinetic/Thermodynamic Control and Mechano-Responsiveness

Polymorphism is of central importance in pharmaceuticals, crystal engineering, and materials science, where distinct structural forms can yield markedly different properties and functions. However, despite its significance, achieving fine control and reliable prediction of polymorphs, particularly in supramolecular assemblies, remains a formidable challenge. Herein, we report the formation of three different polymorphs (nanoparticles 1A, nanospheres 1B, and nanosheets 1C) of Ir(III) complex 1 at room temperature in the same solvent composition and concentration. Among them, 1A and 1B are kinetic species, whereas 1C corresponds to the thermodynamic product. Denaturation studies elucidate the species evolution and establish the stability regimes of the three polymorphs through concentration-solvent phase diagrams. Complementary thermodynamic studies of 1B and 1C further provide the concentration-temperature phase diagrams. Importantly, the conversion of 1B to 1C is mechano-responsive, and mechanical force is necessary for the formation of 1C while heating is unable to drive the conversion of 1B to 1C. Analysis of the thermodynamic parameters provides insights into the polymorphism of 1 and enables the interconversion of 1B and 1C by coupling heating/cooling and stirring. Finally, we demonstrate the role of 1B as a delayed intermediate in living supramolecular polymerization and in the preparation of 2D block heterostructures, where seed-dependent morphological changes of supramolecular polymers are observed. This work unveils the kinetic, thermodynamic, and stimulus-responsive factors governing supramolecular polymorphism, paving the way for the design of functional materials with tunable properties.