Reversible Mechanochromic Luminescence of Tetranuclear Cuprous Complexes

Abstract

Mechanochromic luminescence materials have attracted rapidly growing interest. Nevertheless, the designed synthesis of such materials remains a challenge, and there have been few examples based on weak intramolecular interactions. Herein, we report a new approach for preparing mechanochromic luminescence materials of Cu­(I) complexes, i.e., constructing a photoluminescence system that bears a large coplanar multinuclear Cu­(I) unit showing weak intramolecular π···π interactions with the planar rings of the coordinated ligands in the molecule. Using it, a series of novel mechanochromic luminescent tetranuclear Cu­(I) complexes have been successfully designed and synthesized. As revealed by single-crystal X-ray crystallography, these Cu­(I) complexes share an identical {Cu4[μ3-η2(N,N),η1(N),η1(N)-pyridyltetrazole]2}2+ planar fragment whose coplanar pyridyl rings exhibit weak intramolecular π···π interactions with the phenyl rings of the coordinated phosphine ligands in the molecule. All of these Cu­(I) complexes exhibit reversible mechanochromic luminescence, which can be attributed to the change in the rigidity of the molecular structure resulting from the disruption and restoration of intramolecular π···π interactions between the pyridyl and phenyl rings triggered by grinding and CH2Cl2 vapor, as supported by powder X-ray diffraction and Fourier transform infrared spectrometry. In addition, the results might provide a new route for developing mechanochromic luminescence materials of Cu­(I) complexes for intelligent responsive luminescent devices.

Recent Advances in Mechanochromism of Metal-Organic Compounds

“…The research results indicated that the weak πacid•••base interactions existed between the Cu unit and the carbazole group and the Cu•••Cu interactions played an important role for their turn-on mechanochromism. For tetranuclear Cu(I) complexes, there were many factors that might affect the mechanochromism, such as the change of the Cu•••Cu distance, π-π interactions and the complex geometry (Benito et al, 2014;Peng et al, 2020;Utrera-Melero et al, 2020;Perruchas, 2021). In 2020, Hu's group discovered a supersalt-type Cu(I)-thiolate cluster with irreversible mechanochromism for the first time, which was not completely caused by the CA phase transition (Hu et al, 2020).…”

A Perspective on Cephalopods Mimicry and Bioinspired Technologies toward Proprioceptive Autonomous Soft Robots

“…[159,162,176,[202][203][204] The list is not exhaustive and for mechanochromic materials we address the reader to the comprehensive reviews of Sagara et al [150] and Chen et al [205] Moreover, several innovative molecular systems which can display different colors upon change of conformation or crystal structures, could expand the scope of mechanochromic materials in the near future, making more colorations available and improving the performances of the materials in terms of sensibility and reliability. [206][207][208][209][210][211][212] Applications such as sensors, displays, memories, optical waveguides for hydrostatic or flex measurements, and light-emitting fabrics, [151,186,204,[213][214][215][216][217] represent a solid foundation for the spreading of mechanoresponsivity in the robotic communities. The self-healing properties found in several of the aforementioned systems are also of particular interest for soft robotics.…”

Ethynyl π-coordinated and non-coordinated mononuclear Cu(i) halide diphosphine complexes: synthesis and photophysical studies

“…)-2.7229(11) Å and Cu-P: 2.2598(10)-2.292(3) Å), and this suggests stronger chelating abilities in three-coordinate Cu(I) halide complexes as a result of the introduction of ethynyl. The introduction of electron-rich CRC will increase the conjugation of the whole molecule and the electron density of the P atoms, and the P atoms are more easily coordinated with Cu(I).…”

“…Cu(I) complexes have received particularly wide attention as a promising alternative to phosphorescent complexes based on noble metals such as iridium or platinum due to their excellent luminescence, high abundance and low price. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] When Ma and his colleagues first reported a highly luminescent tetranuclear complex Cu 4 (CRCph) 4 L 2 (L = 1,8-bis(diphenylphosphino)-3,6-dioxaoctane) as an emitting layer in EL devices, it opened a door to Cu(I) complexbased fabrication of OLEDs. 18 Compared with phosphorescent (triplet harvesting) materials, thermally activated delayed fluorescence (TADF, singlet harvesting) materials are designed to display a very small energy gap DE(S 1 -T 1 ), but under thermal activation, reverse ISC from the lowest excited triplet (T 1 ) to the lowest excited singlet (S 1 ) is possible.…”