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. 2019 Apr 12;12(8):1211.
doi: 10.3390/ma12081211.

Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks

Aaron D Nicholas  1 , Rebeka M Bullard  2 , Amelia M Wheaton  3 , Michaela Streep  4 , Victoria A Nicholas  5 , Robert D Pike  6 , Howard H Patterson  7
Affiliations

Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks

Aaron D Nicholas et al. Materials (Basel). .

Abstract

The structures of three tetramethylammonium cyanocuprate(I) 3D networks [NMe4]2[Cu(CN)2]2•0.25H2O (1), [NMe4][Cu3(CN)4] (2), and [NMe4][Cu2(CN)3] (3), (Me4N = tetramethylammonium), and the photophysics of 1 and 2 are reported. These complexes are prepared by combining aqueous solutions of the simple salts tetramethylammonium chloride and potassium dicyanocuprate. Single-crystal X-ray diffraction analysis of complex 1 reveals {Cu2(CN)2(μ2-CN)4} rhomboids crosslinked by cyano ligands and D3h {Cu(CN)3} metal clusters into a 3D coordination polymer, while 2 features independent 2D layers of fused hexagonal {Cu8(CN)8} rings where two Cu(I) centers reside in a linear C∞v coordination sphere. Metallophilic interactions are observed in 1 as close Cu⋯Cu distances, but are noticeably absent in 2. Complex 3 is a simple honeycomb sheet composed of trigonal planar Cu(I) centers with no Cu…Cu interactions. Temperature and time-dependent luminescence of 1 and 2 have been performed between 298 K and 78 K and demonstrate that 1 is a dual singlet/triplet emitter at low temperatures while 2 is a triplet-only emitter. DFT and TD-DFT calculations were used to help interpret the experimental findings. Optical memory experiments show that 1 and 2 are both optical memory active. These complexes undergo a reduction of emission intensity upon laser irradiation at 255 nm although this loss is much faster in 2. The loss of emission intensity is reversible in both cases by applying heat to the sample. We propose a light-induced electron transfer mechanism for the optical memory behavior observed.

Keywords: charge transfer; copper cyanide; crystallography; luminescence; optical memory.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Thermal ellipsoid (50% probability) packing diagram of 1, projected along the b-axis, showing network formation. Me4N+ cations omitted for clarity. Cu orange, N blue, C grey. Selected bond lengths and angles (X = disordered C/N): Cu1-X1 1.960(4), Cu1-X3 2.236(4), Cu1-X4 2.089(4), Cu1-X8 1.963(4), Cu1-Cu3 2.5146(8), Cu2A-X1 2.005(6), Cu2A-C2 2.037(6), Cu2A-C2 2.298(9), Cu2A-X6 1.981(6), Cu2A-Cu2A 2.435(12), Cu3-N2 2.023(4), Cu3-C3 2.007(4), Cu3-C4 2.077(4), Cu4-X5 1.904(5), Cu3-X7 1.988(4), Cu4-N3 1.923(4), Cu4-N4 1.913(4), X1-X1 1.161(6)N2-C2 1.145(6), N3-C3 1.151(6), N4-C4 1.152(5), X5-X5 1.138(10), X6-X6 1.180(8), X7-X7 1.167(8), X8-X8 1.151(8), X1-Cu1-N8 114.60(15), X1-Cu1-X8 114.60(15), X1-Cu1-C4 111.26(15), X8-Cu1-C4 113.10(15), X1-Cu1-C3 111.54(15), X8-Cu1-C3 103.14(15), C4-Cu1-C3 102.20(16), X6-Cu2A-X1 111.0(3), X6-Cu2A-C2 110.1(3), X1-Cu2A-C2 110.4(3), X6-Cu2A-C2 104.6(3), X1-Cu2A-C2 108.7(3), C2-Cu2A-C2 112.0(3), X7-Cu3-C3 110.74(16), X7-Cu3-N2 105.74(14), C3-Cu3-N2 113.45(16), X7-Cu3-C4 106.79(15), C3-Cu3-C4 111.08(17), N2-Cu3-C4 108.69(15), X7-Cu3-Cu1 123.84(11), X5-Cu4-N4 120.58(18), X5-Cu4-N3 119.12(18), and N4-Cu4-N3 120.28(15).
Figure 2
Figure 2
Thermal ellipsoid (40% probability) packing diagram of 2 at 295 K along the c-axis, showing stacked elongated {CuCN}8 hexagons. Me4N+ cations omitted for clarity. Cu orange, N blue, C grey.
Figure 3
Figure 3
Thermal ellipsoid (50% probability) packing diagram of 2 at 100 K along the c-axis, showing staggered {CuCN}8 hexagons. Me4N+ cations and minor occupancy Cu atoms omitted for clarity. Cu orange, N blue, C grey. Selected bond lengths and angles (X = disordered C/N): Cu1-X1 1.857(4), Cu1-X2 1.847(4), Cu1-Cu5 2.9370(9), Cu2-X2 1.931(4), Cu2-X3 1.924(4), Cu2-X4 1.946(4), Cu2-CuA 3.0512(9), Cu3-X4 1.912(4), Cu3-X5 1.931(4), Cu3-X8 1.944(4), Cu4-X5 1.850(4), Cu4-X6 1.844(4), Cu4-Cu6 2.9971(9), X1-X1 1.154(6), Cu5-X3 1.947(4), Cu5-X6 1.927(4), Cu5-X7 1.915(4), Cu6-X1 1.944(4), Cu6-X7 1.933(4), Cu6-X8 1.922(4), X1-X1 1.157(5), X2-X2 1.155(6), X3-X3 1.158(6), X4-X4 1.166(6), X5-X5 1.160(6), X6-X6 1.167(6), X7-X7 1.175(6), X8-X8 1.156(6), X1-Cu1-X2 177.68(18), X1-Cu6-X8 123.78(17), X2-Cu2-X3 125.06(17), X2-Cu2-X4 118.29(17), X3-Cu2-X4 116.27(17), X3-Cu5-X6 116.85(16), X3-Cu5-X7 116.54(16), X4-Cu3-X5 122.42(17), X4-Cu3-X8 119.31(16), X5-Cu3-X8 117.93(16), X5-Cu4-X6 178.72(18), X6-Cu5-X7 126.24(16), X7-Cu6-X1 116.31(16), and X7-Cu6-X8 119.55(16).
Figure 4
Figure 4
Thermal ellipsoid (50% probability) packing diagram of 3, projected along the c-axis, showing network formation. Me4N+ cations omitted for clarity. Cu orange, N blue, C grey. Selected bond lengths and angles (X = disordered C/N): Cu1-X1 1.9311(17), Cu1-X2 1.9485(16), Cu1-X3 1.9421(16), Cu2-X1 1.9398(17), Cu2-X2 1.9656(16), Cu2-X3 1.9645(16), X1-X1 1.170(2), X2-X2 1.169(2), X3-X3 1.168(2), X1-Cu1-X2 120.90(6), X1-Cu1-X3 121.44(6), X2-Cu1-X3 117.17(6), X1-Cu2-X2 119.63(6), X1-Cu2-X3 120.28(6), and X2-Cu2-X3 114.38(6).
Figure 5
Figure 5
Diffuse reflectance spectra of solid samples of 1 and 2 at 298 K.
Figure 6
Figure 6
Luminescence spectra of 1 (top) and 2 (bottom) between 78 K and 298 K. The emission was measured at λex= 315 nm and λex = 330 nm for 1 and 2, respectively.
Figure 7
Figure 7
M06/CEP-31G(d) TD-DFT calculated isodensity representations of molecular orbital transitions (≥10% contribution) of (left) 1 and (right) 2. Calculated at excited state energies for 1 = 300 nm and 2 = 330 nm. A complete list of negligible (<10% contribution) MO transitions can be found in the Supplementary Materials.
Figure 8
Figure 8
Relative emission loss over time for 1 (left) and 2 (right) at 78 K under 255 nm laser irradiation. Note that the emission signal of 1 is deconstructed to show the independent intensities of the dominant emission peak at 430 nm and the less intense emission peak at 526 nm.
Figure 9
Figure 9
Natural log of emission intensity of 2 versus time after 255 nm laser irradiation at variable temperatures.
See this image and copyright information in PMC

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