Polymorphic Copper Iodide Anions: Luminescence Thermochromism and Mechanochromism of (PPh₄)₂[Cu₂I₄]

Abstract

The photoluminescent stimuli-responsive properties of two crystalline polymorphs of (PPh4)2[Cu2I4] formula, are reported. Distinct luminescence properties are exhibited by these ionic copper iodide compounds with blue or yellow emission and original luminescence thermochromism and mechanochromism are demonstrated. While one polymorph displays contrasted temperature-dependent emission properties, the other shows great modification of its emission upon mechanical solicitation. Establishment of structure-properties relationships supported by theoretical approach, permit to get insights into the origin of the photoluminescence properties and the mechanisms at play. According to DFT calculations, the different emission bands originate either from the (PPh4) + organic cation or from the [Cu2I4] 2anion. Activation of these two emissive centers appears to be dependent on the crystalline packing of the polymorph. The thermochromism displayed by one polymorph can be attributed to variation in temperature of the relative intensities of two emission bands of two different excited states. The origin is different for the other polymorph with emission bands coming from two independent emissive centers namely, (PPh4) + and [Cu2I4] 2-. The luminescence mechanochromism is attributed to a polymorphic transition. The mechanical solicitation induces a partial transformation of one polymorph into the other within a disordered phase. The mechanochromic mechanism can be related to mechanical modifications of inter-molecular interactions between the (PPh4) + cations. By displaying luminescence properties that dependent on crystalline structure, excitation wavelength, temperature and mechanical solicitation, the studied copper iodides offer a great possibility of emissive color control and switch, a clear demonstration of great potentialities of this family of compounds for developing photoactive materials.

Aggregation-Enhanced Room-Temperature Phosphorescence from Au(I) Complexes Bearing Mesogenic Biphenylethynyl Ligands

“…Au-Au (aurophilic) interactions play an important role in inducing efficient luminescence from aggregates. This interaction is expressed when the distance between neighboring gold atoms falls in the range of 2.8-3.6 Å [3][4][5][6][7][8][9][10][11][12][13]. Since the emission from gold(I) complexes originate mostly from aggregates, their photophysical properties, such as emission color and intensity, are highly sensitive to changes in the aggregated structure.…”

“…Since the emission from gold(I) complexes originate mostly from aggregates, their photophysical properties, such as emission color and intensity, are highly sensitive to changes in the aggregated structure. Significant efforts have been made to study the unique properties of aurophilic systems and to control their photophysical properties using external stimuli, such as heat, pH, and mechanical force [10][11][12]. In particular, liquid-crystalline (LC) gold(I) complexes have attracted much attention in controlling the aggregated structure due to the nature of LC to both self-organize and be responsive to external fields (e.g., electric and magnetic fields).…”

Luminescent Thermochromism and White-Light Emission of a 3D [Ag4Br6] Cluster-Based Coordination Framework with Both Adamantane-like Node and Linker

“…Solid-state luminescent materials are actively pursued because of their potential applications in light-emitting diodes, optical display devices, sensing, and bioimaging. − Among them, metal halide derivatives especially for copper­(I)- and silver­(I)-based compounds − have attracted considerable interest in spite of the tremendous achievements of efficient illuminants in lead halide perovskites with the existence of a biological toxic metal. Because the structure and luminescent thermochromism of [Cu 4 X 4 L 4 ] (L = pyridine) was reported by Hardt and Pierre in the 1970s, a great number of thermoresponsive luminescent metal halide clusters have been designed and constructed.…”

Molecular copper iodide clusters: a distinguishing family of mechanochromic luminescent compounds

“…This is different for the dinuclear [Cu 2 I 2 L 4 ] and [Cu 2 I 4 ] 2complexes whose mechanochromic properties were attributed to modifications of intermolecular interactions, an expected result from their unique Cu-Cu interaction. 98,100 Potential applicability. For practical applications of mechanical sensing, the design of thin films is more suitable compared with powdered luminescent mechanochromic compound with no mechanical strength.…”