Mutual Restriction-Driven Anomalous Multistage Piezochromic Behavior in Copper(I) Thiocyanate/Isoquinoline Coordination Polymers

Piezochromic materials exhibiting pressure-responsive photoluminescence have emerged as promising candidates for advanced optoelectronic applications. Coordination polymers incorporating copper(I) thiocyanate and π-conjugated ligands present particular interest due to their structural adaptability and tunable emission properties. We herein report the first comprehensive investigation of the anomalous piezochromic behavior in the coordination polymer [Cu(SCN)(iqi)]n (iqi=isoquinoline), employing in situ high-pressure spectroscopy measurements. The emission intensity of [Cu(SCN)(iqi)]n initially increases, then slightly decreases, followed by a stable plateau, and eventually decreases under compression, accompanied by a red-shift in the emission spectra. Through combined spectral analysis and structural considerations, we attribute this unique behavior to the pressure-induced interplay between enhanced charge transfer efficiency and structural deformation. Our findings highlight the potential of copper(I)-based coordination polymers as versatile platforms for developing pressure-sensitive optical devices and smart sensory materials.