Family of Highly Luminescent Pure Ionic Copper(I) Bromide Based

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Functional Inorganic Materials and Devices

A Family of Highly Luminescent Pure Ionic Copper(I) Bromide-based Hybrid Materials Shuqin Chen, Jianmei Gao, Junyu Chang, Yanqi Li, Changxin Huangfu, Hu Meng, Yu Wang, Guangjie Xia, and Liang Feng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b02418 • Publication Date (Web): 24 Apr 2019 Downloaded from http://pubs.acs.org on April 24, 2019

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ACS Applied Materials & Interfaces

A Family of Highly Luminescent Pure Ionic Copper(I) Bromide-based Hybrid Materials Shuqin Chen,†§ Jianmei Gao,†§ Junyu Chang,†§ Yanqi Li,†§ Changxin Huangfu,†§ Hu Meng,† Yu Wang,† Guangjie Xia,‡ and Liang Feng†* † CAS Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China ‡ Department of Chemistry and Centre for Scientific Modeling and Computation, Chinese University of Hong Kong, Shatin, Hong Kong, P. R. China § University of Chinese Academy of Sciences, Beijing 100049, P. R. China. KEYWORDS: hybrids materials; copper(I) halide clusters; tetra-alkylammonium cation; copper(I) bromide; amines sensing

ABSTRACT: While a number of highly luminescent copper(I) halide-based hybrid materials built on coordinate bonds (Cu-L; L=N, P, S-based ligands) have been achieved, the poor structural stability largely limited their commercialization. In contrast, according to the previous studies, the ionic structures (L-free) are more stable than those built on Cu-L coordinate bonds. However, the extremely weak emission hinders their optical applications. Herein, we report a tetraalkylammonium cation-induced strategy for the synthesis of stable and highly luminescent ionic CuBr-based hybrid materials. It is interesting to find that the tetra-alkylammonium cations with different chains could induce diverse CuBr-based anions. And most of these CuBr-based hybrids are highly luminescent, which make them of promising candidates as alternative phosphors and of potential applications in sensing.

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INTRODUCTION Inorganic−organic hybrid semiconductors are a class of functional materials whose constituents are inorganic and organic modules. Aside from the advantages of both components, these materials can create new features which may be potentially useful for optical, electrical and magnetic applications.1-4 Among many hybrid materials, copper(I) halide-based hybrids [CunXm(L)z; X=Cl, Br, I; L=N, P, S-based ligands] have attracted tremendous attention due to their diverse structures, superior optical properties, and the abundance of copper in the nature.5-12 Given that CunXm(L)z can be used as a substitute for rare-earth element-based phosphors, there are many studies dealing with its luminescence properties.13-15 For example, Li’s group have synthesized a series of CunXm(L)z hybrids including optical tunable one-dimensional (1D)-CuI(L), and highly luminescent different-dimensional (nD, n=0, 1, 2 and 3)-Cu2I2(L)n.16-17 Recently, Yao’s group prepared a series of highly luminescent inks based on copper–iodine hybrids via confining the Cu(I)–I hybrid clusters in microemulsion droplets.18 The obtained inks whose light-emission colors can cover the whole visible spectrum range, can be used as photoluminescent paints and the emitting layer of LEDs. Despite these successes, most of the hybrid materials are molecular clusters built on coordinate bonds (Cu-L; L=N, P, S based ligands) between inorganic and organic modules, and the poor structural stability largely limited their commercialization. The previous studies reveal that the ionic structures (L-free, made of cationic modules and anionic copper(I) halide clusters) typically have much more thermal stability compared to those built on coordinate bonds (Cu-L; L=N, P, Sbased ligands) between inorganic and organic modules (see the Supporting Information (SI), Table S1, S2).19-21 While some ionic copper(I) halide clusters such as one-dimensional (1D)-(Cu2I3)nn−, two-dimensional (2-D)-(Cu3I4)-, (Cu4I2)2+ and (Cu6I2)4+ cationic aggregates have been reported.22-


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However, the extremely weak emission with low luminescence quantum yields hinders their

applications. Very recently, Li’s group reported an all-in-one CumIm+n(L)n hybrid materials by combining ionic and coordinate bonds in molecular crystals, and greatly enhanced structural stability while maintaining the high luminescence.26 Nevertheless, the synthesis of ligands for these all-in-one CumIm+n(L)n hybrid materials is complicate. Moreover, since the optical properties of copper(I) halide-based hybrids typically depend on their structures, nuclear numbers and CuCu interactions, it’s difficult to control the formation of ionic copper(I) halide-based hybrids and achieve multiple emitting pure ionic copper(I) halide-based hybrids.27-30 The hybrid compounds built on pure ionic structures (especially pure ionic CuBr-based hybrids) with both highly emission and robustness to the best of our knowledge, has barely been reported. Herein, we introduced a tetra-alkylammonium cation-induced strategy, and synthesized a family of pure ionic CuBr-based hybrid materials with satisfied stability and high luminescence. The tetra-alkylammonium cations can induce and stabilize the anionic inorganic modules. In addition, considering the effect of tetra-alkylammonium cations to the structures of the anionic inorganic modules and the relationships between structures and optical properties, tetra-alkylammonium bromides with different alkyl chains were employed to synthesize multiple emitting pure ionic CuBr-based hybrids. The density functional theory (DFT) calculations discover that the luminescence of these ionic CuBr-based compounds can be assigned to “metal-centered” emission (MC). The high optical performance and the excellent stability endow these ionic CuBr-based hybrids with the potential for the fabrication of white LEDs and amine vapors sensing. EXPERIMENTAL SECTION


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Materials: CuBr (99.0%), ethanol (99.0%), isopropanol (99.0%), tetramethylammonium bromide (TMAB, 98.0%), tetraethylammonium bromide (TEAB, 98.0%), tetrapropylammonium bromide (TPAB, 98.0%), and tetrabutylammonium bromide (TBAB, 99.0%) were purchased from Shanghai Jingchun Reagent Co. Tributylmethylammonium bromide (TBMAB, >98.0%) was obtained from Adamas Reagent Ltd. All chemicals were used without further purification. Characterization: Single crystal X-ray diffraction (SCXRD) data were collected at 298 K for 1, 3, 3-2, and 293 K for 2, 4, 5 on a Gemini ultra diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Using Olex2, the structures were then solved with the ShelXS structure solution program using Direct Methods and refined with the XL refinement package using Least Squares minimization.31 Notably, the parameter of _diffrn_measured_fraction _theta_full for compound 3-1 is low. This is probably due to the poor quality and poor diffracting power of the crystal. Powder X-ray diffraction (PXRD) patterns of the as-synthesized products were collected with Cu Kα (λ = 1.5406 Å) radiation on an X-ray diffractometer (PANalytical X'Pert PRO), operating at 40 kV and 40 mA. Measurements were carried out at room temperature with a scan speed of 5 ° min-1 and a step size of 0.03° (2θ). The thermal stability of the compounds was measured by thermogravimetric (TG) analysis using a Simultaneous Thermal Analysis Apparatus (Netzsch, STA449F3). Pure powder samples were heated in an aluminium oxide crucible and the profiles were recorded from 40 °C to 800 °C under nitrogen flow at a ramp rate of 10 °C min-1. The fluorescent spectra of samples in powder form were measured at room temperature using a fluorimeter (Edinburgh, FLS980), set-up with a xenon flash lamp and an integrating sphere. Absolute quantum yields (QYs) of the compounds were obtained on the same fluorimeter with a xenon monochromatic light source. BaSO4 was used as the reference sample. Luminescence lifetime was also measured on the same fluorimeter (Edinburgh, FLS980) and a


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microsecond μF900 xenon flash lamp was chosen as light source. Optical diffuse reflectance spectra of the powder samples were recorded on a Perkin–Elmer Lambda 950 spectrophotometer within 200–800 nm at room temperature. BaSO4 powder was used as a standard. The band gaps were determined from optical absorption data using the Kubelka−Munk function, (1-R) 2/2R=a/s, where R is reflectance, a is the absorption coefficient and s is the scattering coefficient (treated as a constant). Computational Methodology: Density functional theory (DFT) calculations were performed within the formalism of the projector augmented wave (PAW) method, as implemented in the Vienna ab initio simulation package (VASP).32 In all calculations, the generalized gradient approximation (GGA) expressed by the Perdew, Burke and Ernzerhof (PBE) functional is adopted, and the electronic states were expanded in a plane-wave basis with a cutoff of 400 eV. The DFTD3 approach was used to describe the van der Waals corrections.33 During both geometry optimizations and DOS calculations, typically the Brillouin-zone sampling was performed under a 8 × 8 × 8 k-point grid in combination with the Methfessel-Paxton scheme. As the system is relatively large in case of compounds 3-1, 4, 5 (368, 196, 224, atoms per unit cell respectively), the k-point grid is loose to 4 × 4 × 4 for compounds 3-1, 4 and to 6 × 6 × 6 for compound 5. The convergence criteria for energy was set to be 0.1 × 10-5 eV. A Gaussian broadening of 0.05 eV was implemented in the Brillouin-zone integration. Synthesis of [N(CH3)4]3[Cu2Br5] (1): The procedure is similar to previously described.34 A mixture of CuBr (0.14 g, 1 mmol), TMAB (0.15 g, 1 mmol) and isopropanol (20 mL) were refluxed at 100 ºC for 1 hour. The mixture was then filtered while hot to remove unreacted CuBr and other impurities. The filtrate was allowed to cool slowly to room temperature and stand for 3 hours.


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Pure-phased sample containing colorless rod-like crystals 1 were collected by filtration and dried at room temperature for 24 hours. The yield is 43%. Synthesis of [N(CH3CH2)4]2[Cu2Br4] (2): The synthesis of powder compound 2 is similar to the mentioned procedure of compound 1, except TMAB (0.15 g, 1 mmol) was changed to TEAB (0.21 g, 1 mmol). To obtain crystals 2, CuBr (0.14 g, 1 mmol), TEAB (0.21 g, 1 mmol) and ethanol (30 mL) were refluxed at 100 °C for 2 hours. The solution was filtered while hot and then cooled slowly to room temperature. Colorless rod-like crystals 2 were collected by filtration and the crystals were then naturally dried for 5 hours. The yield of powder compound 2 is 55%. Synthesis of [N(C3H7)4]2[Cu4Br6] (3-1): TPAB (0.53 g, 2 mmol) and ethanol (20 mL) were substituted for TMAB (0.15 g, 1 mmol), isopropanol (20 mL), respectively, in synthetic progress of 1 to obtain colorless plate-like crystals 3-1. The mixtures were refluxed at 100 ºC for 1 hour. A suitable crystal was selected for the single crystal X-ray diffraction analysis. The yield is 40%. Synthesis of [N(C3H7)4][CuBr2] (3-2): CuBr (0.14 g, 1 mmol) and TPAB (0.53 g, 2 mmol) were dissolved in isopropanol (10 mL), which was then heated at 60 °C for 30 mins. The hot solution was filtered and then cooled slowly to room temperature. After 5 hours, colorless platelike crystals crystals 3-2 were collected by filtration and dried at room temperature for 24 hours. The yield is 52%. Synthesis of [N(C4H9)4][CuBr2] (4): The crystals 4 were prepared as the mentioned procedure of 1, except TMAB (0.15 g, 1 mmol) was changed to TBAB (0.32 g, 1 mmol). The mixtures were refluxed at 100 ºC for 1 hour. The yield is 76%.


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Synthesis of [N(C4H9)3CH3]2[Cu4Br6] (5): CuBr (0.07 g, 1 mmol) and TBMAB (0.14 g, 1 mmol) were dissolved in isopropanol (12.5 mL), which was then refluxed for 30 mins at 100 °C. The solution was filtered while hot and then cooled slowly to room temperature. After 3 hours, colorless plate-like crystals 5 were collected by filtration and dried at room temperature for 24 hours. The yield is 32%. Fabrication of White LEDs: White LEDs were fabricated by combining UV chips (365 nm, 1 W, 300 mA, Epileds), compound 3-1 powder, commercial green phosphor (Ba, Sr)2SiO4: Eu2+ and blue phosphor BAM:Eu2+ (BP). The three-component phosphors were mixed with silicone thoroughly. After that process, the mixtures were then deposited on a LED chip. The electroluminescent property test of WLEDs driven at different current (ranging from 20 to 300 mA) were performed using an HAAS2000 integrated sphere which equipped with an EVERFINE analyzer system. Amines Sensing: The fabrication of five dyes-contained colorimetric sensor array was similar to our previous work.35-37 Briefly, the wax-based patterns consisted of five circles were printed onto the Whatman Grade no. 41 quantitative filter paper (GE healthcare, UK) using a Xerox Phaser 8560DN (Fuji, Japan). The printed paper was then heated to 120 °C for 15 mins. After that, five ionic CuBr-based compounds, compounds 1 (10 mg), 2 (6 mg), 3-1 (2 mg), 4 (10 mg), and 5 (2 mg) were individually dispersed in ethylene glycol (0.5 mL), acetonitrile (125 μL), acetonitrile (1 mL), dichloromethane (0.5 mL) and acetonitrile(1 mL). 1 μL of each solution was then separately printed onto the wax-based paper. The five dyes-contained colorimetric sensor array was stored in N2-filled container for further experiments. The amines sensing experiments were carried out in an airtight and lightproof container (18 L) with a gas generator. In detail, the amine solution was injected into gas generator (operating at 17 W and 1.15 A) and was then heated for 3 mins. Then,


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the fabricated paper-based sensor array fixed in the container reacted with amines vapor for 20 mins. Under the irradiation of 254 nm UV source light, a Nikon D7000 digital camera (equipped with an AF-S 60 mm f/2.8 G macro lens) was employed for the imaging of the five dyes-contained array “before” and “after” the reaction. Adobe Photoshop software was used to digitize the difference of red, green and blue (ΔRGB) values between the “before-reaction” and “after-reaction ” . A hierarchical cluster analysis (HCA) result was achieved via statistical exploration of the ΔRGB values using the multivariate statistical package (MVSP). Ultrasonication and Grinding Method: For ultrasonication, the stoichiometric tetraalkylammonium salts and CuBr were dispersed in cyclohexane (10 mL) and sonicated for 30 min. The mixture was then purified by centrifugation and washed three times with hot isopropanol. The powder products were obtained after dried at room temperature for 24 hours. For grinding method, the stoichiometric tetra-alkylammonium salts and CuBr were added into in a mortar. After mechanical grinding for 30 min, the powder products were washed three times with hot isopropanol and then dried at room temperature for 24 hours. Table 1. List of Ionic CuBr-based Compounds with their Unit Cell Parameters and Space Groups.

Compound

[N(CH3)4]3[Cu2Br5] (1)

Unit cell parameter (Å, deg) a=14.2576(13) b=11.3297(10) c=15.2584(14) α=103.630(6) β=94.826(9) γ= 90(6)

Space group

C2/c


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[N(C2H5)4]2[Cu2Br4] (2)

a=8.3505(8) b=13.7641(13) c=11.0507(11) α=90 β=97.076(9) γ= 90

P21/c

[N(C3H7)4]2[Cu4Br6] (3-1)

a=15.5454(11) b=15.5454(11) c=15.5737(18) α=90 β=90 γ=90

P42/n

[N(C3H7)4][CuBr2] (3-2)

a=8.9036(11) b=7.5883(14) c=13.0176(13) α=90 β=91.001(10) γ= 90

P2/n

[N(C4H9)4][CuBr2] (4)

a=13.049(2) b=10.2073(12) c=15.993(2) α=90 β=92.305(15) γ= 90

C2/c

[N(C4H9)3CH3]2[Cu4Br6] (5)

a=10.0193(11) b=11.1991(12) c=19.364(2) α=73.838(10) β=84.077(9) γ=88.098(9)

P-1

RESULTS AND DISCUSSION Structure Description. The synthesis procedure was similar with previously described.34 Briefly, CuBr and tetra-alkylammonium bromides were heated to react in alcohol solvent to obtain ionic CuBr-based hybrid materials. The single crystal X-ray diffraction (SCXRD) analyses revealed that the inorganic modules of these compounds are all 0D anions and organic modules are tetra-alkyl ammonium cations (Figure 1 and Figure S1-S6, Table 1 and S3). There are no


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coordinate bonds (Cu-L, L=N, P, S-based ligands) between inorganic and organic modules in the crystal. Each copper(I) atom of [Cu2Br5]3- (1), [Cu2Br4]2- (2) and [Cu4Br6]2- (3-1, 5) anions is coordinated to three bromide atoms in an approximately trigonal-planar arrangement. In contrast, the [CuBr2]- anions in the compounds 3-2 and 4 are linear monomers containing a copper(I) atom coordinated to two bromide atoms. It is noteworthy that the tetra-nuclear [Cu4Br6]2- anion in the compound 3-1 displays crystallographic disorder (see the SI, Figure S3b), which could be attributed to the two possible orientations of the copper(I) tetrahedron. This phenomenon is similar to the earlier case.38,39 Phase purities of these compounds were checked by powder X-ray diffraction determination (see the SI, Figure S7-S8). The experimental and the simulated PXRD for most compounds match well. While there is a few extra peaks for compound 1, which might indicate phase impurities and may be explained by the poor solubility of tetramethylammonium bromide (TMAB).

Figure 1. Powder samples under 254 nm UV light, anionic inorganic motifs and cationic motifs obtained for the six compounds.


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Table 2. Maximum PL Wavelength and QY, CIE Coordinates, Luminescence Lifetime (Ʈ) and Decomposition Tem-peratures of CuBr-based Compounds.

Compound

λmax (nm)

Emission color

CIE

QY (%) (λex/nm)

[N(CH3)4]3[Cu2Br5] (1)

542

yellow

0.35, 0.51

91 (315)

80.70

291

[N(C2H5)4]2[Cu2Br4](2)

476

blue

0.18, 0.25

91 (317)

53.53

265

[N(C3H7)4]2[Cu4Br6](3-1)

664

orangered

0.53, 0.43

97 (386)

39.04

274

[N(C3H7)4][CuBr2](3-2)

507

green

0.20, 0.40

83 (254)

248.98

254

[N(C4H9)4][CuBr2](4)

504

green

0.22, 0.40

97 (254)

11.99

262

[N(C4H9)3CH3]2[Cu4Br6](5)

623

yelloworange

0.50, 0.45

2 (365)

41.73

287

Ʈ(μs)

Decomposition temperature (ºC)

Previous reports presented that anionic configurations in the halocuprate(I) anions are strongly dependent on the size of the cations.40-42 According to these reports, the coordination numbers of Cu(I) in the halocuprate(I) anions appear to diminish with the increase of the size of tetra-alkyl ammonium cations. It could be explained by the steric hindrance of cations increases with the increase of chain lengths and the dilution imposed on the halogen ligands by the tetra-alkyl ammonium cations.

43-44

Therefore, the relationship between the coordination numbers of Cu(I)

and the chain lengths of tetra-alkyl ammonium cations was studied in this work. As shown in the SI (Table S4), the coordination numbers of Cu(I) in the compounds (1), (2), (3-1), (3-2), (4) and (5) are 3, 3, 3, 2, 2 and 3, respectively. The coordination numbers of Cu(I) in the ionic CuBr-based hybrid clusters diminish from 3 to 2 with the increase of the chain lengths of tetra-alkyl ammonium cations, which is partly similar to previous reports.45


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Figure 2. (a) PL spectra of six compounds. Inset: powder sample of corresponding compounds under 254 nm UV light, from left to right: 2, 4, 3-2, 1, 5, 3-1. (b) Density of states plots for compound 3-1. Optical Properties. The as-synthesized ionic CuBr-based hybrid compounds exhibit strong luminescence emission under excitation at 254 nm. The emission spectra and excitation spectra for these six compounds are shown in Figure 2a and S9. The photoluminescence spectra of these


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ionic CuBr-based compounds can almost cover the whole visible region, with the emission maxima ranging from 476 nm to 664 nm. As shown in Table 2, except for compound 5, each of these hybrid materials displays extremely high luminescence quantum yield with the value up to 91% (1), 91% (2), 97% (3-1), 83% (3-2) and 97% (4) under excitation wavelengths at 315, 317, 386, 254 and 254 nm, respectively. In addition, all of the compounds show a broad and unstructured emission band with large Stokes shift in the solid state at ambient temperature and all their lifetimes are few dozen microseconds order (Table 2). To inspect the emission mechanism of as-synthesized ionic CuBr-based hybrid compounds, density functional theory (DFT) calculations were performed. Previous reports have demonstrated that the halide-to-ligand charge transfer (XLCT), metal-to-ligand charge transfer (MLCT) and “metal-centered” emission (MC) charge transfer mechanism might occur in copper(I) halide-based hybrids.46-50 The results of density functional theory (DFT) calculations (Figure 2b and Figure S10-S14) show that both the valence bands (VBs) and the lowest conduction bands (CBs) of these six compounds are formed mainly from inorganic modules (including Cu 3d, Cu 4s, and Br 4p orbitals). The valence band maximum of these six compounds share common features-the main contributions are the Cu 3d orbitals. While, their conduction band minimum are formed mainly from Cu 4s and Br 4p orbitals, among them, the percentage of Cu 4s orbitals are higher than that of Br 4p orbitals. Therefore, the emissions of as-synthesized ionic CuBr-based hybrid compounds can be assigned to “metal-centered” emission (MC). As shown in Figure S15, the band gaps of these six compounds were also determined from optical absorption data using the Kubelka−Munk function. The experimentally estimated band gaps for compounds 1, 2, 3-1, 3-2, 4, and 5 are 3.08 eV, 3.09 eV, 3.01 eV, 3.13 eV, 3.52 eV and 2.97 eV, separately.


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Stability. The thermal stability and photostability of the ionic CuBr-based compounds were determined. At first, the thermogravimetric (TG) analysis was performed to evaluate the thermal stability of these compounds. As shown in Figure S16 and Table 2, the decomposition temperature of the as-synthesized compounds are ranging from 254 ºC to 291 ºC. It suggests that these ionic hybrids have high thermal stability, which is more excellent than that of many molecular clusters built on coordinate bonds, such as 0D-Cu2I2(3-pc)4 (60 ºC), 1D-Cu2I2(5-me-pm)2 (130 ºC), etc.21, 51

It is noteworthy that the decomposition temperature (TD) of the as-synthesized compounds is

not much different from that of the subgroup I AIO type compounds reported by Li’ group (TD=270 ºC-310 ºC ).26 Whereas the thermal stability of these ionic CuBr-based compounds is more excellent than that of subgroup II AIO type compounds (TD=180 ºC-210 ºC ).26

Figure 3. Photostability tests of four CuBr-based compounds. (a) PL intensities of four compounds after heating at 60 ºC and 80 ºC for 1 h, (b) after exposing to air for months at room temperature (c) after ball milling for 1 h, (d) and after exposing to UV light (254 nm) for hours.


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To evaluate the photostability, four selected compounds were then either heated for one hour in air at 40 ºC and 80 ºC or exposed to air at room temperature for months. As shown in Figure 3a and 3b, the luminescent intensities of selected compounds were maintained > 90% after heating for 1 hour at 80 ºC and were maintained > 80% even after exposed to air for three months. It is noteworthy that the photostability of compound 5 is much poorer than others (see the SI, Figure S17), which could be tentatively ascribed to its hygroscopicity.52-54 In addition, the luminescent intensity of selected compounds were detected after either grinding for 1 hour without protection or exposing to 254 nm UV irradiation (6 w) for hours. Obviously, the decreases in their luminescent intensity are less than 10% compared to their initial values (Figure 3c and 3d). The solvent resistance test was also carried out for the representative compound 1. PL intensities of compound 1 show less than 20% change compared to the initial values after soaking in various solvents for 12 hours (see the SI, Figure S18). All above results indicate that our ionic CuBr-based hybrid compounds have excellent thermal stability and photostability.


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Figure 4. Optical applications. (a) Illuminating WLED lamps (3 V, 1 W). (b) CIE ‐ 1931 chromaticity diagram of the WLED. Inset: powder samples of corresponding phosphors under 365 nm UV light, from left to right: 3-1, BAM:Eu2+(BP), (Ba,Sr)2SiO4:Eu2+, three components-based white phosphors. (c) Amines separation at 500 ppm. The five dyes in color change profiles: top (compound 4); left (compound 2); middle (compound 1); right (compound 3-1); bottom


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(compound 5). (d) Hierarchical cluster analysis of digitalized color of five dyes for the five parallel trials. Optical Applications. Among six compounds, compound 3-1 can emit brilliant orange-red emission light under excitation at 365 nm. The high QYs (96.62%) and excellent photostability endow compound 3-1 with the ability to be a candidate as lighting phosphors. Herein, we have prepared a three components-based white phosphor by mixing up compound 3-1 powder with commercial green phosphor (Ba,Sr)2SiO4:Eu2+ and blue phosphor BAM:Eu2+ (BP). The corresponding WLED was fabricated by combining with this three components-based white phosphor and a 365 nm near-UV LED chip (Figure 4a). Figure S19 illustrates the electroluminescence (EL) spectra driven at different current (ranging from 20 to 300 mA). As shown in Figure 4b, the CIE xy coordinates and correlated colour temperature (CCT) of the WLED which are marked in CIE 1931 colour space, are (0.3688, 0.3666) and 4263 K, respectively. Clearly, the colour point of our WLED sits right on the black body Planckian locus. In addition, the colour rendering index (CRI) of our white phosphor is up to 94.9, which is higher than that of the commercial YAG:Ce3+ white LEDs.50 This suggests that compound 3-1 can be used as red phosphor for application of LEDs. Other than superior optical application, the as-synthesized hybrid compounds may also be capable of sensing due to their metal coordination ability. Amines, as regular ligands, were investigated in this work. As expected, the luminescence behavior of the as-synthesized ionic CuBr-based hybrid compounds is sensitive to amines. Different amines can quench the luminescence of ionic CuBr-based compounds in varying degrees owing to the diverse coordinate abilities of different amines with copper(I). Herein, we developed a colorimetric sensor array based on the ionic CuBr-based hybrid compounds for the rapid sensing of five amines vapor, i.e.,


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ethylenediamine, ethylamine, ammonia, triethylamine, and diethylamine. The sensor array was imaged before and after exposure to different amines vapor by a camera under irradiation of 254 nm. After subtracting the “before” image from the “after” image, we could get colour change profiles for the different amines. As shown in Figure 4c, the different colour change profile of each amine vapor provides specific fingerprint for corresponding amine. The digitalized RGB values of colour change profiles (see the SI, Table S5-S10) were statistically explored using the MVSP software. After the hierarchical cluster analysis (HCA), the RGB variation values of 5 amines vapor at 500 ppm and a control could be classified precisely into six clusters (Figure 4d). It indicates that this colorimetric sensor array, which is based on the ionic CuBr-based compounds, can be used for the recognition of amines vapor. CONCLUSIONS In summary, a family of highly luminescent and stable pure ionic CuBr-based hybrids were prepared by a tetra-alkyl ammonium cation-induced strategy in this study. The tetra-alkyl ammonium bromides with different chains were employed to achieve multiple emitting CuBrbased anions. The DFT calculations reveal that the luminescence of these pure ionic CuBr-based compounds can be assigned to “metal-centered” emission (MC). Besides, it’s interesting to find that these highly luminescent ionic CuBr-based hybrids can also be prepared by ultrasonication and grinding method (Figure S20-S21), which can be used for large-scale preparation. The maximum absolute quantum yield (QYs) of as-obtained ionic CuBr-based hybrids are > 95 % in the solid state. This high optical performance and the excellent stability endow these ionic CuBrbased hybrids with the potential for the fabrication of white LEDs and sensing detection. ASSOCIATED CONTENT


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Supporting Information. The following files are available free of charge. Further characterization results and DFT calculations (PDF) Crystallographic data for compound 1, 2, 3-1, 3-2, 4, and 5 (CCDC 1862335, 1862345-1862348, and 1862366) (CIF) CheckCIF/PLATON report (PDF) (PDF) (PDF) (PDF) (PDF) (PDF) AUTHOR INFORMATION Corresponding Author * [email protected]. Present Addresses † Liang Feng: 0000-0002-7586-8424. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We are grateful for financial support from the National Natural Science Foundation of China (Grant 21605141, 21804132) and from Dalian Institute of Chemical Physics (Grant DICP ZZBS201802). ABBREVIATIONS Tetramethylammonium tetrapropylammonium

bromide, bromide,

TMAB; TPAB;

tetraethylammonium tetrabutylammonium

bromide,

TEAB;

bromide,

TBAB;

Tributylmethylammonium bromide, TBMAB.


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Family of Highly Luminescent Pure Ionic Copper(I) Bromide Based

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