Halocuprate(i) zigzag chain structures with N-methylated DABCO cations – bright metal-centered luminescence and thermally activated color shifts

Abstract

Two compounds 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane catena-tetra-μ-halo-dicuprate(I) with DABCOMe2 Cu2X4 (1: X = Br, 2: X = I) were synthesized by hydrothermal reaction of copper(I) halides with the corresponding 1,4-diazoniabicyclo[2.2.2]octane (DABCO) dihydrohalides in an acetonitrile/methanol mixture. Both compounds crystallize monoclinically, 1 with a = 9.169(4) Å, b = 10.916(6) Å, c = 15.349(6) Å, β = 93.93(2)°, V = 1533(1) Å(3), Z = 4, space group P2(1)/n (no. 14) and 2 with a = 15.826(9) Å, b = 9.476(5) Å, c = 22.90(2) Å, β = 90.56(5)°, V = 3434(5) Å(3), Z = 8, space group P2(1) (no. 4), respectively (lattice constants refined from powder diffraction data measured at 293 K). The cations in both compounds are formed by in situ N-methylation of DABCOH2(2+) cations by methanol in a S(N)2 reaction. Both compounds contain an anionic copper(I) halide chain structure consisting of trans edge-sharing CuX4 tetrahedra. The chains are strongly kinked at every 2(nd) junction thus forming a zigzag structure. The shortest halide-halide distances are observed between the halide ions of adjacent tetrahedra which are approaching each other due to the kinking. This structure type shows a specific luminescence behavior. Under optical excitation, the compounds exhibit yellow (1) and green (2) emission with photoluminescence quantum yields of Φ(PL) = 52 and 4%, respectively, at ambient temperature. According to DFT and TDDFT calculations, the emission is assigned to be a phosphorescence essentially involving a metal centered transition between the HOMO consisting mainly of copper 3d and halide p orbitals and the LUMO consisting mainly of copper 4s and 4p orbitals. The temperature dependence of the emission spectra, decay times, and quantum yields has been investigated in detail, especially for 1. From the resulting trends it can be concluded that the emission for T≤ 100 K stems from energetically lower lying copper halide segments. Such segments represent the structural motif of the halocuprate(I) chains. With increasing temperature energetically higher lying segments are populated which also emit, but open the pathway for thermally activated energy transfer to quenching defects.

Bulk Assembly of Zero-Dimensional Organic Copper Bromide Hybrid with Bright Self-Trapped Exciton Emission and High Antiwater Stability

“…Among the various alternatives, low-dimensional cuprous-based metal halides have attracted much attention owing to their high PLQY, earth abundance, and low cost, and low toxicity. − For example, Jun et al reported a kind of zero-dimensional (0D) Cs 3 Cu 2 I 5 single crystals (SCs) with coexisting tetrahedral and trigonal Cu + sites and a highly efficient blue emission (PLQY ∼ 90%) . Li et al successfully prepared high-quality CsCu 2 I 3 SCs by an antisolvent vapor-assisted method and developed a high-speed UV-to-vis photodetector .…”

Supramolecular Interactions Modulating Electrical Conductivity and Nanoprocessing of Copper–Iodine Double-Chain Coordination Polymers

“…Coordination polymers (CPs) are a large group of compounds which depending on the selected building blocks (metal ions and organic ligands) have a great structural variety and an immense diversity of physical and chemical properties. − Thanks to their infinite structure and function tailorability that originates from the abundant building blocks, these materials can present, among other properties, interesting electrical conductivity. − For instance, the paradigmatic case of MMX chains with platinum, iodine, and dithiocarboxylato ligands is particularly outstanding due to its high electrical conductivity even at room temperature, as well as the metallic to semiconducting phase transitions showed by them with the temperature. ,− Their intriguing features have also been analyzed at the nanoscale to demonstrate their potential as a source of novel molecular wires. , Indeed, several CPs show significant electrical conductivity. In this context, copper­(I) halides have been subjected to a number of studies, particularly for those with ligands with π* or σ* orbitals suitable for efficient d π metal orbitals overlapping. − ,, As a result of their structural diversity, originating from the polymerization of copper–halogen-based subunits, − double Cu–X chains are a subclass of CPs that can generate multifunctional materials showing combination of electrical conductivity and photoluminescence. ,, Moreover, the electrical conductivity found in some of the Cu–X double chains suggests their potential use as electronic materials . The features reported on copper­(I) double chains with iodide as bridging ligands are also noticeable, since they show interesting luminescent properties. ,,,,− More recently, we have found that although this family of compounds shows rather similar structures the double Cu–I chain presents a high degree of structural flexibility, suggesting an elastic spring like behavior when these CPs are exposed to external physical and/or chemical stimuli.…”

Observation of Contrary Thermo-responsive Trend for Single Crystal and Powder Samples in Mechano-, Thermo- and Solvato-responsive Luminescent Cubane [Ag4I4L4] Cluster

“…The emission lifetimes significantly increased with decreasing the temperature. This finding could be due to the relation of decreased non-radiative rate to the high spin-orbit coupling of Ag(I) ions and fast intersystem crossing 38 . This behavior is also observed in the emissive copper(I) and silver(I) complexes with the thermally activated delayed fluorescence 39,40 .

Figure 3Temperature-dependent emission spectra of single crystal 1 from 5 to 300 K. Inset: Images for single crystals under ambient light at room temperature (left), under 365 nm UV lamp irradiation at room temperature (middle) and in liquid nitrogen (77k) (right).

Figure 4Temperature-dependent emission spectra of 1 in ground powder state from 5 to 300 K. Inset: Images for powder sample under 365 nm UV lamp irradiation in liquid nitrogen (left) and at room temperature (right).

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