Multi-stimulus semiconductor Cu(I)-I-pyrimidine coordination polymer with thermo and mechanocromic sensing

This work shows a detailed study of the synthesis, structural characterization, electrical, thermal, and mechanical luminescent behavior of one-dimensional coordination polymer formed by a Cu(I)-I double chain, using 2-amino-4 chloropyrimidine as ligand. The asymmetric structure of double chain type [Cu(L)I]n, (L= 2-amino-4-chloropyrimidine (aCLpym)) with Cu-Cu distances shorter than the sum of the van der Waals radii of two copper atoms, and the substantial flexibility of this structure are crucial to understanding its optoelectronic behavior. The electrical conductivity values at 295 K are in agreement with a possible semiconductor behavior. Additionally, the luminescence properties of this coordination polymer (CP) are characterized at ambient conditions (ambient pressure (AP) and 295 K) by a non-symmetric High Energy (HE) band centered at 465 nm, tentatively assigned to a mixed 3(I+M)LCT. The intensity of the emission increase lowering the temperature. A structural contraction can explain this behaviour, clearly observed when solving the structures employing single-crystal X-ray diffraction of the compound at 296 K and 110 K. A strong mechanochromic behavior was observed when hydrostatic pressure is applied, with the appearance of an additional Low Energy (LE) band around 650 nm, which for this kind of CuI CPs is typically associated with transitions in the CuI cluster-core, involving 3IMCT and clustered centered 3d10→3d94s1 (3MCC) states. This latter because of the shortening with the pressure of the Cu-Cu distances below the Van der Waals limit. Moreover, the study of the mechanochromic behavior versus pressure exerted by grinding shows a decrease in the intensity of the emission due to the increase in the number of defects and decrease in the particle size