Solvent- and Stoichiometry-Controlled Assembly and Mechanoresponsive Behavior of Carbazole–Pyrimidine-Derived Cu(I) Coordination Polymers

The rational design of mechanochromic luminescent copper(I) coordination polymers (CPs) via the strategic incorporation of fluorophore ligands presents a promising approach for developing robust and efficient stimuli-responsive materials. In this work, three distinct CPs were synthesized by reacting CuI with 9-(pyrimidin-5-yl)-9H-carbazole (5-CzPm) under varied solvent systems and stoichiometric conditions. The reaction in acetonitrile, under different CuI and ligand ratios, led to the formation of one-dimensional (1D) [Cu2(μ3-I)2(5-CzPm)2]n CP1 and [Cu4(μ3-I)4(μ2-5-CzPm)(CH3CN)2]n CP2, while the use of an acetonitrile and dichloromethane mixed solvent system yielded the two-dimensional (2D) [Cu4(μ3-I)4(μ2-5-CzPm)]n CP3. The synthesized CPs incorporate structurally diverse secondary building units (SBUs): CP1 features a Cu2I2 chain motif, CP2 contains a Cu4I4 staircase-type cluster, and CP3 adopts a Cu4I4 cubane-type SBU. All three CPs were found to be emissive, with CP1 showing a reversible mechanochromic response. CP3 also displays a mechanochromic response; however, the changes are irreversible. Detailed studies suggest that mechanical stimulation induces a phase transformation: CP1 undergoes a reversible amorphous–crystalline cycle, whereas CP3 irreversibly converts into a mixture of CP1 and CP2 upon acetonitrile exposure.