Dual luminescence in solid CuI(piperazine): hypothesis of an emissive 1-D delocalized excited state

Abstract

Solid [CuI( piperazine) 0.5 ] ∞ , characterized by a structure with an infinite double chain of CuI, presents an unexpected dual luminescence. The short copper-copper distances allow the existence of both cluster-centered and 1-D delocalized electronic transitions, as emerged from theoretical calculations. Beyond the more common cluster-centered emission a higher energy band, which differs in lifetime and in temperature dependence, is observed.One of the most prominent classes of luminescent coordination compounds is that of copper(I) halides, due to their promising features for application in the field of optoelectronics. [1][2][3][4][5] They are easily synthesized 6,7 and tunable in emission color, [8][9][10] with high emission quantum yields in the solid state. 7,10,11 Copper(I) halide compounds can be considered as a valid alternative to luminescent metal complexes of precious (i.e. Ir or Os) and rare earth metals, which are expensive and environmentally problematic. 12 The luminescence properties of the copper halide clusters arise from a remarkable variety of emissive states, which have been extensively investigated in the last 30 years and can be summarized as follows: (a) a low-energy emission, attributed to a triplet cluster-centered ( 3 CC) excited state, is observed in the case of metal center interactions [13][14][15][16][17][18][19] and is independent of the nature of the ligand engaged in the complex; (b) a highenergy emission, attributed to a triplet halide-to-ligand charge transfer ( 3 XLCT) excited state, may show up in the presence of unsaturated ligands with accessible π-orbitals. 20 Moreover, recent studies have shown that several copper compounds present a thermally activated delayed fluorescence (TADF): Cu(I) halide-bridged compounds with P^N ligands are characterized by (metal + halide)-to-ligand charge transfer ((M + X) LCT) excited states where the low singlet-triplet energy gap allows emission from both the singlet and the triplet excited states, depending on the temperature. [21][22][23] The structure of [CuI( piperazine) 0.5 ] ∞ 24 is characterized by a one-dimensional copper iodide polymeric structure. The infinite double chain of CuI is described as castellated, 25 as shown in Fig. 1a, and the tetrahedral coordination of the copper(I) ions is fulfilled by the bridging piperazine to construct a 3D network (Fig. 1b and c). The inorganic chain is generated by the sequence of an inversion center and 2-fold axis symmetry elements, thus two different copper distances are present (2.771(1) Å and 2.729(1) Å). Although the presence of infinite double chain motifs has been observed in 20 struc-

The Assembly of Unique Hexanuclear Copper(I) Complexes with Effective White Luminescence

“…These structural motifs are extensively studied by various physical methods, including X-ray diffraction (XRD) analysis. The diversity of structures of copper­(I) complexes is reflected in a rich set of photophysical properties including dual emission, thermally activated delayed fluorescence (TADF), and “stimuli-responsive” luminescence. − The design and stabilization of copper­(I) complexes with the various structural motifs can be performed on the basis of various N-heteroaryl substituted phosphine ligands such as pyridylphosphines. , During the past decade, the large amount of works devoted to the mono-, di-, or tetranuclear copper­(I) complexes based on the pyridylphosphines appeared. − ,,− Due to the presence of a pyridyl fragment, complexes with the above-mentioned ligands demonstrate rich luminescent properties, e.g., “stimuli-responsive” luminescence or intensive emission in broad spectral ranges. It has been shown that the structure of pyridylphosphine ligands influences not only the types of formed copper clusters but also luminescent characteristics within one type of complexes.…”

Changing the Game of Time Resolved X-Ray Diffraction on the Mechanochemistry Playground by Downsizing

“…Mechanochemistry has emerged as an attractive and sustainable synthetic tool 1,2 with applications for the synthesis of organic, [3][4][5][6][7] inorganic, [8][9][10] and hybrid metal-organic molecules and materials. [11][12][13][14] It is increasingly clear that many traditional solution based chemical reactions can be performed in the presence of very little or no solvent using mechanochemical approaches. 15 Providing "greener" and potentially less expensive strategies than traditional solution methods, 1,[16][17][18] mechanochemistry was dubbed by the International Union for Pure and Applied Chemistry (IUPAC) as one of the 10 chemical innovations that will change our world.…”

Electronic Excitations in Crystalline Solids through the Maximum Overlap Method

“…Among the luminescent copper(I) halides, [CuI(piperazine) 0.5 ] ∞ is a peculiar compound that exhibits dual luminescence, a feature that is of potential relevance in technological applications. In recent years, within the framework of a synergetic theoretical− experimental study, 21 we have characterized its excitations through ab initio post-SCF methods. 41 At that time, we were not able to investigate the actual luminescence properties, as we had no tools for optimizing geometries in the excited state, as we have developed in this work.…”

“…We here apply our MOM geometry optimizer to this structure so as to analyze the structural and electronic changes of the long-lived excited state. As in previous work, 21 we considered two excitations around the Fermi level, namely, HOMO → LUMO and HOMO − 1 → LUMO + 1, in the Γpoint only. A pob-TZVP basis set was used, along with a hybrid PBE functional with 10% of HF exchange.…”