Polymorphic Copper Iodide Clusters: Insights into the Mechanochromic Luminescence Properties

Abstract

An in-depth study of mechanochromic and thermochromic luminescent copper iodide clusters exhibiting structural polymorphism is reported and gives new insights into the origin of the mechanochromic luminescence properties. The two different crystalline polymorphs exhibit distinct luminescence properties with one being green emissive and the other one being yellow emissive. Upon mechanical grinding, only one of the polymorphs exhibits great modification of its emission from green to yellow. Interestingly, the photophysical properties of the resulting partially amorphous crushed compound are closed to those of the other yellow polymorph. Comparative structural and optical analyses of the different phases including a solution of clusters permit us to establish a correlation between the Cu-Cu bond distances and the luminescence properties. In addition, the local structure of the [Cu4I4P4] cluster cores has been probed by (31)P and (65)Cu solid-state NMR analysis, which readily indicates that the grinding process modifies the phosphorus and copper atoms environments. The mechanochromic phenomenon is thus explained by the disruption of the crystal packing within intermolecular interactions inducing shortening of the Cu-Cu bond distances in the [Cu4I4] cluster core and eventually modification of the emissive state. These results definitely establish the role of cuprophilic interactions in the mechanochromism of copper iodide clusters. More generally, this study constitutes a step further into the understanding of the mechanism involved in the mechanochromic luminescent properties of metal-based compounds.

Cu(I) hybrid inorganic–organic materials with intriguing stimuli responsive and optoelectronic properties

“…X ray diffraction studies revealed that the guest solvents, despite not having interaction with the host framework, do modulate the molecular packing and stacking in different ways that translates into the varied influences on Cu···Cu interactions through the outer organic ligand shell. Perruchas et al reported a cubane Cu(I) cluster showing mechano, thermo and vapochromic luminescent behavior [89]. [Cu 4 I 4 (PPh 2 (CH 2 ) 2 (CH 3 ) 2 SiOSi(CH 3 ) 2 (CH 2 ) 2 PPh 2 ) 2 ], 100, presents two A c c e p t e d M a n u s c r i p t Edited Mar 5 39 different crystalline polymorphs which exhibit distinct luminescence properties with one being green emissive 100a (λ em = 522 nm) and the other one being yellow emissive 100b (λ em = 571 nm) at room temperature ( Figure 19).…”

Hydrothermal synthesis of nitrogen and boron doped carbon quantum dots with yellow-green emission for sensing Cr(vi), anti-counterfeiting and cell imaging

“…Surprisingly, the maximum uorescence emission wavelength exhibited a large blue shi when compared with NB-CQDs in aqueous solution, which may be attributed to the alteration of average NB-CQDs/ NB-CQDs distance. 27,28 The compactness of the NB-CQDs/PVA lm induced the interaction between these NB-CQDs, thus increasing the average NB-CQDs/NB-CQDs distance, resulting into the blue shi in the uorescence emission. 28 …”

Reversible Mechanochromic Delayed Fluorescence in 2D Metal–Organic Micro/Nanosheets: Switching Singlet–Triplet States through Transformation between Exciplex and Excimer

“…During last few years, metal–organic hybrid materials (such as coordination polymers, metal–organic frameworks and complexes) with mechanochromism have also been increasingly investigated. According to the mechanisms, metal–organic mechanochromic materials can be divided into two types: (1) most of as‐reported systems are metal‐centered phosphorescence emission based on altering the arrangement of metals or clusters under the mechanical stimulus, such as Au I ,4 Pt II ,5 Cu I ,6 and Ir III ,7 etc. ; (2) the others involve fluorescence emission based on the change of the stacking mode and interaction of ligands, such as ligand‐based Zn II 8 and Cd II 9…”