Photoluminescence of 1-D Copper(I) Cyanide Chains: A Theoretical Description

Abstract

Solid copper(I) cyanide occurs as extended one-dimensional chains with interesting photophysical properties. To explain the observed luminescence spectroscopy of CuCN, we report a series of computational studies using short bare and potassium-capped [Cu(n)(CN)(n+1)] (-) (n = 1, 2, 3, 4, 5, and 7) chains as CuCN models. On the basis of TD-DFT calculations of these model chains, the excitation transitions in the UV spectrum are assigned as Laporte-allowed pi-pi transitions from MOs with Cu 3d(pi) and CN pi character to empty MOs with Cu 4p and CN pi* character. Transitions between the HOMO (3d(z)) and LUMO (Cu 4p and CN pi*) are symmetry forbidden and are not assigned to the bands in the excitation spectrum. The emission spectrum is assumed to arise from transitions between the lowest triplet excited state and the ground-state singlet. The lowest energy triplet for the model networks has a bent structure due to distortions to remove the degeneracies in the partially occupied MOs of the linear triplet. The S(0)-T gap for the bent triplet chains is consistent with the emission wavelength for bulk CuCN.

Vibrational–Structural Combined Study into Luminescent Mixed Copper(I)/Copper(II) Cyanide Coordination Polymers

“…[32,34] This luminescence results from electronic excitation between π character orbitals, in particular from the dCu/πCN highest occupied molecular orbital (HOMO) to the pCu/π*CN lowest unoccupied molecular orbital (LUMO). [31] After the coordination of ligands with N or S atoms as the binding site, the luminescence moves towards the visible region, as the presence of two different transitions leads to two possible emissive paths: metal to CN ligand and metal to S/Nligand; the CC transitions can be discounted if the Cu···Cu distance is longer than 2.8 Å. [33,74] The emission and excitation spectra of the studied compounds are reported in Figure 2, and the corresponding data are listed in Table 2 together with the emission quantum yields.…”

“…Its 1D chain structure, which is based on twocoordinate metal centers and bridging cyanido ligands, means that CuCN differs from many other inorganic salts characterized by 2D or 3D arrays. [31] The compound exhibits weak luminescence, [32] which generally shifts from the near-UV (392 nm) into the visible region and becomes more intense upon the coordination of nucleophiles, such as thioamide ligands. [33] In general, small ligand differences can cause significant differences to the emission colors of coordination polymers, and this enables luminescence tuning.…”

In situ construction of four copper(I) cyanide coordination polymers: crystal structures, fluorescence and catalytic properties

“…A blue shift of 59 nm in compound 1 was observed compared to free L1, which is probably due to the increase in conjugation upon metal coordination. The red shifts in the emission bands of complexes 2 and 3 may be due to the threecoordinate copper centers and the bent structure of theCuCN-chains, which would allow for distortions that produce multiple triplet states [28].…”

3D-Interpenetrating Frameworks of 3∞[Cu2(CN)4(Me3Pb)2(bpy)] Containing the Rhombic [Cu2(µ3-CN)2] Motifs

“…The emission spectrum of CuCN is assumed to arise from transition between the lowest triplet excited state and the ground state. It is also, supposed that a bent triplet state is responsible for the relatively high energy CuCN emission [33] in addition to the presence of the [Cu 2 (l 3 -CN) 2 ] motifs. The remaining two peaks at 430 and 490 nm can be argued to the MC transition and MLCT, respectively.…”