Mechanochromic Switching between Delayed Fluorescence and Phosphorescence of Luminescent Coordination Polymers Composed of Dinuclear Copper(I) Iodide Rhombic Cores

The synthesis and photophysical properties of two luminescent CuI coordination polymers, [Cu2 I2 (PPh3 )2 (3-tpyb)]n and [Cu2 I2 (PPh3 )2 (4-tpyb)]n (Cu-3-tpyb and Cu-4-tpyb; PPh3 =triphenylphosphine, m-tpyb=1,3,5-tris(m-pyridyl)benzene (m=3, 4)), are described. X-ray structural analysis indicated that one-dimensional coordination chains comprising rhombic {Cu2 I2 (PPh3 )2 } cores and m-tpyb bridging ligands were formed. Both Cu-3-tpyb and Cu-4-tpyb exhibited blue-to-yellow thermally activated delayed fluorescence (TADF) that originated from mixing of the metal-to-ligand and halide-to-ligand charge-transfer excited states and moderate emission quantum yields of 0.29 and 0.27, respectively, at 298 K. Further, mechanochromic luminescence was observed for both complexes. The emission lifetimes indicated that the origin of emission switched from TADF to phosphorescence, which was derived from the triplet cluster-centered (3 CC) emissive state generated by grinding-induced amorphization.