SUN Ling-Zhi WANG Yu- LIN Sen LIU Jin-Ming LI Zhong-Feng ZHANG Jing-Wei JIN Qiong-Hu-

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Synthesis, Characterization andLuminescent Properties of Two Copper(I) Complexes Based on 2,2?-Biquinoline and PhosphorousLigand①

SUN Ling-ZhiaWANG Yua- LIN SenaLIU Jian-MingbLI Zhong-FengaZHANG Jiang-WeicJIN Qiong-Huaa-②

a(100048)b(100871)c(116023)

copper, crystal structures, 2,2?-biquinoline, luminescence;

1 INTRODUCTION

In recent years, the complexes of copper(I) have attracted considerable attention because they display intensive and complicated excited state behaviors, and show great prospect of application in OLEDs, sensors, solar cells and photochemical reactions[1-3]. Among them, the cheaper copper(I) complexes with phosphine and nitrogen heteracyclic ligands are often used to design photo-luminescent materials[4].

Triphenylphosphine (PPh3) is an organophospho- rous ligand of a strong electron which has great coordination ability, and it has been used by many research groups[5, 6]. Complexes bearing phosphorus ligands including PPh3and [bis(2-diphenylphos- phino)ethyl]ether (DPEphos) show one-dimensional chain structures through C–H···interactions[7, 8]and remarkable photoluminescent behavior due to their strong rigidity[9]. And the nitrogenous ligands such as 2,2?-biquinoline (Biq), which act as the high electron-delocalized ligands, are also used in the construction of luminescent complexes.

In luminescent Cu(I) complexes, there are four key types of electron transitions[10], metal to ligand charge transfer (MLCT), ligand to metal charge transfer (LMCT), ligand to ligand charge transfer (LLCT) and intraligand charge transfer (ILCT). In addition, for most phosphorescent Cu(I) complexes, the two highest occupied molecular orbitals (HOMOs) have predominant metal Cu(d) character, and there are two lowest unoccupied orbitals (LUMOs), which are essentially* orbitals located in the diimine ligands[11, 12]. And the excited states of compounds often play important roles in photoinduced electron and energy transfer process[13]. As for optical functional materials, quantum yield () and lifetimes () are two important factors that have an influence on physical properties of luminescent[14]. In the past work, many research groups found that quantum yields are related to many factors, such as the types of ligands, the structures of complexes and anionic species of complexes. And in this paper, we comparedof the complexes formed by different anions and discussed the effect of different anions on the luminescence properties. The effects of different phosphorous ligands on the photophysical properties of the complexes are also discussed in this paper.

The terahertz spectra are used to probe the vibrational modes in the far-infrared and sub- millimeter regions of the electromagnetic spectrum. It is a useful tool to character the structures of these complexes and to study the functions of polarity complexes[15]. In this work, the three complexes were measured by the ultrashort coherent terahertz radiation (0.2～3 THz) (3～133 cm-1).

In our previous work, our group have synthesized some copper(I) complexes containing mixed nitro- gen and phosphorus ligands[16-18]. In this paper, three copper(I) complexes [Cu(DPEphos)(Biq)]CF3SO3(1),[Cu(PPh3)2(Biq)]CF3SO3(2) and [Cu(PPh3)2(Biq)]ClO4(3) with phosphorus ligands and Biq were synthesized. All the three complexes have been characterized by IR,1H NMR,31P NMR, single- crystal X-ray diffraction and THz absorption spectra, and they have been tested through luminescent performance including the quantum yield (QY) and lifetimes. Also the effects of anions and phosphorous ligands on the photophysical properties of the com- plexes are discussed in this paper.

2 EXPERIMENTAL

2. 1 Materials and measurements

All chemical reagents are commercially available and used without furthermore treatment. FT-IR spectra (KBr pellets) were measured on a Perkin- Elmer Infrared spectrometer. C, H and N elemental analyses were carried out on an Elementar Vario MICRO CUBE (Germany) elemental analyzer. Room-temperature fluorescence spectra were measured on F-4500 FL Spectrophotometer.1H- NMR and31P NMR were recorded at room temperature with a Bruker DPX 600 spectrometer.

2. 2 Synthesis of [Cu(POP)(Biq)]CF3SO3 (1)

A mixture of CuCF3SO3(0.0629 g, 0.2 mmol), Biq (0.0513 g, 0.2 mmol) and POP (0.1616 g, 0.3 mmol) was stirred in CH3OH (5.0 mL) and CH2Cl2(5.0 mL) for 6 hours. The insoluble filtrate was evaporated slowly at room temperature for several days, the orange single crystals of [Cu(POP)(Biq)]CF3SO3can be obtained. Elemental analysis for C55H41.17CuF3N2O4.59P2S: calcd.: C, 64.89; H, 4.08; N 2.75%. Found: C, 65.33; H, 3.99; N, 2.83%.1H NMR (600 MHz, DMSO, 298 K): 6.98～7.42 ppm (m, POP-aromatic ring), 7.56～8.92 ppm (m, overlap with the solvent peak signal, Biq-aromatic ring).31P NMR (600 MHz, DMSO, 298 K):= –11.60 ppm(s, POP). IR for 1 (KBr pellets, cm-1): 3051 (m), 1563 (m), 1459 (s), 1433 (s), 1259 (w), 1223 (s), 1180 (w), 1092 (m), 1069 (w), 1026 (m), 878 (w), 747 (s), 696 (s), 503 (m), 469 (w).

2. 3 Synthesis of [Cu(PPh3)2(Biq)]CF3SO3 (2)

A mixture of CuCF3SO3(0.0753g,0.3mmol), Biq(0.0513g,0.2 mmol) and PPh3(0.1050 g,0.4mmol) was stirred in CH3OH(5.0 mL) and CH2Cl2(5.0 mL) for 6 hours. Several days later, the orange single crystals of [Cu(PPh3)2(Biq)]CF3SO3were filtrated. Elemental analysis for C56.47H47.88CuF3N2O4.47P2S: calcd.: C, 64.43; H, 4.64; N, 2.69%. Found: C, 65.02; H, 4.38; N, 2.76%.1H NMR (600 MHz, DMSO, 298 K): 7.11～7.41 ppm (m, PPh3-aromatic ring), 7.56～8.91 ppm (m, overlap with the solvent peak signal, Biq-aromatic ring).31P NMR (600 MHz, DMSO, 298 K):= –1.19 ppm(s, PPh3). IR for 2 (KBr pellets, cm-1): 1594(w), 1507(w), 1480(m), 1222(w), 1145(m), 1030(s), 997(w), 787(w), 747(m), 695(s), 518(m).

2. 4 Synthesis of [Cu(PPh3)2(Biq)]ClO4 (3)

A mixture of CuClO4(0.0654 g, 0.2 mmol), Biq (0.0513 g, 0.2 mmol) and PPh3(0.1050 g, 0.4 mmol) was dissolved in solvent (CH3OH: CH2Cl2= 1:1) and fully agitated at room temperature for 6 h. The filtrate was evaporated slowly at room temperature. Then orange single crystals of [Cu(PPh3)2(Biq)]ClO4can be gotten5 days later. Elemental analysis for C56H45ClCuN3O4P2: calcd.: C, 68.29; H, 4.61; N, 4.27%. Found: C, 68.41; H, 4.35; N, 2.99%.1H- NMR (600 MHz, DMSO, 298 K): 7.11～7.41 ppm (m, PPh3-aromatic ring), 7.55～8.91 ppm (m, overlap with the solvent peak signal, Biq-aromatic ring).31P NMR (600 MHz, DMSO, 298 K):= –1.19 ppm(s, PPh3). IR for 3 (KBr pellets, cm-1): 1593 (m), 1507 (m), 1480 (m), 1434 (s), 1214 (w), 1092 (s), 997 (m), 871 (w), 831 (m), 743 (s), 696 (s), 623 (m).

2. 5 Structure determination

Single crystals of the title complexes were moun- ted on a Bruker Smart 1000 CCD diffractometer equipped with a graphite-monochromated Mo(= 0.71073 ?) radiation at 298 K. Complex 1 is a yellow single crystal with dimensions of 0.34mm × 0.32mm × 0.25mm. In the range of 3.126<<29.335°, a total of 9419 reflections were collected and 7939 were independent (int= 0.0234). The final least-squares cycle gave= 0.0450,= 0.1051 (= 1/[2(F2) + (0.0412)2+ 2.5021], where= (F2+ 2F2)/3) for 7939 observed reflections with> 2();= 1.069, (Δ/)max= 0.001, (Δ)min= –0.746 and (Δ)max= 1.040 e/?3.Complex 2 is a yellow single crystal with dimensions of 0.35mm × 0.34mm × 0.30mm. In the range of 3.264<<29.274°, a total of 4897 reflections were collected and 4169 were independent (int= 0.0248). The final least-squares cycle gave= 0.0430,= 0.1148 (= 1/[2(F2) + (0.0558)2+ 11.0854], where= (F2+ 2F2)/3) for 4169 observed reflections with> 2().= 1.054, (Δ/)max= 0.000, (Δ)min= –0.281 and (Δ)max= 0.833 e/?3. Complex 3 is a yellow single crystal with dimensions of 0.55mm × 0.45mm × 0.40mm. In the range of 3.379<<29.187°, a total of 4670 reflections were collected and 3825 were independent (int= 0.0326). The final least-squares cycle gave= 0.0731,= 0.2036 (= 1/[2(F2) + (0.1191)2+ 21.8000], where= (F2+ 2F2)/3) for 3825 observed reflections with> 2();= 1.066, (Δ/)max= 0.000, (Δ)min= –1.241 and (Δ)max= 1.445 e/?3.

Semi-empirical absorption corrections were applied using SABABS program. All the structures were solved by direct methods using SHELXS program of the SHELXTL-97 package and refined with SHELXL-97[19, 20]. Metal atom centers were located from the-maps and other non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinements were performed by full-matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on2. The hydrogen atoms were generated geometrically and refined with displacement parameters riding on the concerned atoms. The crystallization solvent was lost from the crystal and could not be resolved unambiguously. The contribution of the missing solvent to the calculated structure factors was taken into account by using a SQUEEZE routine of PLATON[21]. The missing solvent was not taken into account in the unit cell content.

3 RESULTS AND DISCUSSION

3. 1 NMR analysis

All of the complexes were tested by1H NMR and31P NMR at room temperature in the solvent of deuterium of DMSO (600 MHz, DMSO, 298 K). The1H NMR signals are listed as follows: 6.98～7.42 ppm (m, POP-aromatic ring), 7.56～8.92 ppm (m, overlap with the solvent peak signal, Biq- aromatic ring) for complex 1; 7.11～7.41 ppm (m, PPh3-aromatic ring), 7.56～8.91 ppm (m, overlap with the solvent peak signal, Biq-aromatic ring) for complex 2;7.11～7.41 ppm (m, PPh3-aromatic ring), 7.55～8.91 ppm (, overlap with the solvent peak signal, Biq-aromatic ring) for complex 3. In the1H NMR spectra of complexes 1～3 the signals in the range 7.55～8.92 ppm can be attributed to protons from the benzene rings of Biq ligands. The charac- teristic peak at 6.98 ppm in the1H NMR spectra of complex 1 is due to the existence of P ligand (POP) in complex 1. The31P NMR signals are listed as follows:= –11.60 ppm (s, POP) for complex 1,= –1.19 ppm (s, PPh3) for complex 2,= –1.19 ppm (s, PPh3) for complex 3.

3. 2 Crystal structure description

Three functional Cu(I) complexes 1～3 have been synthesized by one-pot reaction of different copper(I) salts with DPEphos, Biq, and PPh3ligands (Scheme 1) The influence of the anions on the coordination modes of the complexes has been discussed in the literatures[22, 23]. We also have reported the structures of some metal complexes which are affected by the coordination modes[24, 25]. The selected bond lengths and bond angles of 1～3 are listed in Table 1.

Table 1. Selected Bond Lengths (?) and Bond Angles (°) for Complexes 1～3

Scheme 1. Syntheses of complexes 1～3

Fig. 1. Molecular structure of complex 1. Thermal ellipsoids are drawn at the 30% probability level. All hydrogen atoms and anions are omitted for clarity

Fig. 2. One-dimensional infinite chain bridged by C–H···interaction of complex 1. Most hydrogen atoms, and all anions and a part of phenyl rings are omitted for clarity

Complexes 2 and 3 crystallize in the monoclinic2/space group. The structure analysis reveals the formation of a mononuclear complex of Cu(I) with ligands PPh3and Biq. The asymmetric units of 2 and 3 contain one crystallographically independent Cu(I) atom, one N-donor Biq ligand, and two PPh3to form a distorted tetrahedral geometry with CuN2P2coordination environment (Fig. 3). In these com- plexes, the anion is used to balance the charge, and the primary bond lengths and bond angles are listed in Table 1. The Cu–P and Cu–N distances in complex 2 (2.281(7) and 2.107(2) ?) are a little longer than those observed in 3 (2.277(11) and 2.104(4) ?), which shows that the effect of anions on the bond length is not significant. Due to the difference of N-donor ligand, the fluctuation range of P–Cu–N (109.24(6)～115.23(6)°) in 2 and 3 is obviously shorter than that in [CuClneoPPh3] (neo = neocuproine, 123.61(6)～124.99(6)°][27]. The crystal packing of 2 and 3reveals 1infinite chain structures formed through C–H···interactions (Figs. 4 and 5). In complex 2, C–H···interactions are formed by the phenyl protons from Biq and the aromatic rings from PPh3, and in 3 C–H···interac- tions are formed by the phenyl protons and aromatic rings from two PPh3ligands.

3. 3 Luminescent properties

The luminescent excitation and emission spectra of complexes 1～3 are measured in the solid state at room temperature (seen in Fig. 6). And the fluore- scence spectra were compared with the spectra of the corresponding ligands. Because of the10electronic configuration of the copper(I), these complexes of copper(I) exhibit interesting lumine- scence properties. The emission peaks of PPh3and POP are at 402 nm (ex= 372 nm)[28]and 453 nm (ex= 317 nm)[29],respectively. In the fluorescence emission spectra of complexes 1～3, the emission peaks are found at 598 nm (ex= 375 nm for 1), 592 nm (ex= 385 nm for 2) and 591 nm (ex= 376 nm for 3) respectively, which are shown to be luminescent on excitation at the MLCT band.Compared with complex 1, the maximum peaks of luminescence emission for 2 have a little blue shift, which can be explained in terms of the conjugated structure of phosphorous ligand. The POP ligand has stronger rigidity structure and strongersystem, leading to longer luminescence emission wavelength for complex 1. Complexes 2 and 3 have similar structures except for anions (CF3SO3-for 2, ClO4-for 3), so their luminescence emission performance is basically the same. The emission spectra of complexes 1～3 indicate that the origins of these emissions all involve the emissive state, resulting from the ligand-centered (-*) transition.

Fig. 3. Molecular structure of complexes 2 and 3. Thermal ellipsoids are drawn at the 30% probability level. All hydrogen atoms and anions are omitted for clarity

Fig. 4. One-dimensional infinite chain bridged by C–H···interaction of complex 2. Most hydrogen atoms, and all anions and a part of phenyl rings are omitted for clarity

Fig. 5. One-dimensional infinite chain bridged by C–H···interaction of complex 3.Most hydrogen atoms, and all anions and a part of phenyl rings are omitted for clarity

Fig. 6. Luminescent spectra of complexes 1, 2 and 3 in the solid state at room temperature

The quantum yield (QY)and lifetimesof complexes 1～3 are also measured in the solid state at room temperature, and the photophysical data of complexes 1～3 are shown in Table 2. The QYof complexes 1～3 are 8.7%, 13.4% and 13.7%, respectively. The lifetimes of the emission com- plexes are 6.7, 7.3 and 7.4s, respectively, which are in the typical range of triplet state phosphore- scence in Cu(I) complexes. Moreover, the quantum yield of complex 2 (= 13.4%) is higher than that of complex 1 (= 8.7%). The luminescence enhancement of complex 2 is mainly caused by the existence oftwo PPh3ligands in 2[30]. Because the compositions of complexes 2 and 3 are the same except for the anions, the quantum yields (13.4% for 2, 13.7% for 3) and lifetimes (7.3s for 2, 7.4s for 3) are basically the same. Therefore, we can con- clude that the photophysical properties of the complexes are mainly affected by the phosphorus ligands in the complexes, and are almost indepen- dent of the anions contained.

Table 2. Photophysical Data for Complexes 1～3

3. 4 THz analysis

The room temperature terahertz (THz) absorption spectra of complexes 1～3were measured in the range of 0.2～3.0 THz. All the three complexes have characteristic resonance peaks. The peaks found for each compound are listed as follows: complex 1 0.35, 0.47, 0.59, 0.88, 1.00, 1.28, 1.41, 1.58, 1.77, 2.11, 2.22, 2.40, 2.69, 2.81 THz; complex 2 0.69, 1.35, 1.58, 1.93, 2.05, 2.29, 2.40, 2.52, 2.69 THz; complex 3 0.47,1.13, 1.70, 1.87, 1.99, 2.10, 2.22, 2.34, 2.46, 2.64, 2.81 THz (Fig. 7). Compared with complex 2, the location of the peaks of complex 3 is signi- ficantly different, which is due to their different anions. The THz-TDS shows a more sensitive nature than other technologies. Hence, THz-TDS may be a burgeoning spectroscopy in the isostructural com- plexes.

Fig. 7. Terahertz spectra of complexes 1～3 in the range of 0.2～3.0 THz

4 CONCLUSION

Three novel copper(I) complexes, namely [Cu(DPEphos)(Biq)]CF3SO3(1) and [Cu(PPh3)2(Biq)]CF3SO3(2) and [Cu(PPh3)2(Biq)]ClO4(3), have been synthesized and characterized by X-ray diffraction, IR,1H and31P NMR and fluorescence spectra. Single-crystal X-ray diffraction reveals that these three complexes show a four-coordination mode. There are C–H···interactions between aromatic rings and methyl protons in these complexes. These complexes show a fascinating 1infinite chain via C–H···. In the emission spectra, shifts of emission peak are derived from ligand-centered (-*) transition. We hope our results could offer a new strategy for the design of supramolecular complexes.

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2 January 2018;

27March 2018 (CCDC 1813677 for 1, CCDC 1558490 for 2 and CCDC 1558491 for 3)

① This work has been supported by the National Natural Science Foundation of China (Nos. 21171119 and 81573822) and the Beijing Municipal Natural Science Foundation (No. 2172017)

. E-mail: jinqh@cnu.edu.cn

10.14102/j.cnki.0254-5861.2011-1942