- Email: [email protected]
Synthesis, structures and photoluminescent properties of Cu+ complexes with extended π-systems
Inorganic Chemistry Communications 21 (2012) 160–162
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structures and photoluminescent properties of Cu + complexes with extended π-systems Gang-Qiang Yin b, Heng-Chi Lian a, Qing-Ling Ni a, Liu-Cheng Gui a, Kun-Guo Yang a, Xiu-Jian Wang a,⁎ a b
School of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, China School of Pharmacy, Guangdong Medical College, Zhanjiang 524023, China
a r t i c l e
i n f o
Article history: Received 4 January 2012 Accepted 1 May 2012 Available online 8 May 2012 Keywords: Cu(I) Luminescent properties Imine Phosphine
a b s t r a c t Three complexes [Cu2(pz)(pda)2(CH3CN)2](BF4)2 (1), [Cu2(tpphz)(pda)2](BF4)2(CH3CN)4 (2) and [Cu2(bfimbz) (pda)2](BF4)2 (3) (pba=N,N′-bis((diphenylphosphino)methyl)benzenamine, pz=pyrazine, tpphz=tetrapyrido [3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine, bfimbz = 1,4-bis([1,10]-phenanthroline[5,6-d]imidazol-2-yl)-benzene) have been synthesized. They are centrosymmetric dinuclear complexes constructed respectively by bridging imine ligands of pz, tpphz and bfimbz linking two [Cu(pda)] moieties. Ligand pda performs as a terminal bidentate ligand. The solid state luminescence of 1, 2 and 3 are 542, 632 and 584 nm, respectively, while their lifetimes are 86.6, 78.5 and 37.8 μs respectively. The rigid π-conjugated system of the imine ligand could play an active role in intramolecular photoinduced energy or electron transfer between two Cu+ moieties. © 2012 Elsevier B.V. All rights reserved.
The heteroleptic Cu(I) compounds containing phosphines and N-donor ligands often exhibit highly emissive metal-to-ligand-chargetransfer (MLCT) state, and are considered as a potential to replace other organometallic phosphors based on the noble metal ions (ruthenium, iridium, platinum) due to the relatively low cost and non-toxicity [1–3]. Recently, a large amount of phosphine and diimine ligands are designed for systematic research on the photophysical properties of Cu(I) complexes, and works mainly focus on the mononuclear Cu complexes [4–7]. Two or more component system connected by the bridging ligand could afford electronic coupling between the linked partners to allow intercomponent photoinduced energy- and/or electron-transfer processes [8–11]. However, these photoinduced transfer are not observed in the ever reported luminescent properties of two or more nuclear Cu+ complexes based on the bridging phosphine and terminal diimine ligands (phenanthroline or 2,9-dimethylphenanthroline). Rigid and linear heteroaromatic entities pyrazine (pz), tetrapyrido [3,2-a:2′,3′-c:3″,2″- h:2‴,3‴-j]phenazine (tpphz) and 1,4-bis([1,10] phenanthroline[5,6-d]imidazol-2-yl)benzene (bfimbz) are the πconjugated systems exhibiting low-lying π*-orbitals. The role of the conjugated π-electron systems is not only structural, however, as it has been shown that their nature has profound effects on the electron and energy transfer rates. As a bridging ligand, they are suitable for the study of intramolecular photoinduced energy or electron transfer between two or more components. In this paper we use pz, tpphz and bfimbz as bridging ligands and N,N′-bis((diphenylphosphino)methyl) benzenamine (pba) as a terminal chelating ligand to develop
⁎ Corresponding author. E-mail address: [email protected] (X-J. Wang). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2012.05.005
[Cu2(pz)(pda)2(CH3CN)2] (1), [Cu2(tpphz)(pda)2] (2) and [Cu2(bfimbz) (pda)2] (3) [12]. Their synthesis, structures and photoluminescent properties are studied. These three complexes are stable in the air. Complexes 2 and 3 are indissoluble in other solvents except for DMF and DMSO, maybe due to the large size and rigidity of tpphz and bfimbz. X-ray diffraction analyses show that the construction of 1, 2 and 3 are similar [13,14]. Ligand pba performs as a chelate ligand to coordinate to one Cu + ion affording a [Cu(pba)]+ moiety. Two [Cu(pba)] + moieties are bridged by one pz, tpphz and bfimbz, respectively, to produce 1, 2 and 3 which are centrosymmetric with the centroid located at the center of the bridging imine ligand. (Fig. 1). The Cu…Cu distances in 1, 2 and 3 are 6.99, 12.78 and 20.16 Å, respectively. In 1, each Cu + is four-coordinated by two P atoms from one pba and two N atoms from one pz and one CH3CN respectively, exhibiting a distorted tetrahedral geometry. But in 2 and 3, each Cu+ adopts a distorted tetrahedral geometry consisting of two P atoms from one pba and two N atoms from one phenanthroline moiety. The average bond distances of Cu\N and Cu\P, as well as the bite angles of P\Cu\P and N\Cu\N are 2.07 Å, 2.24 Å, 103.8° and 80.7°, respectively, which have no significant difference compared with the corresponding values in the previously studied [Cu(NN)(PP)] systems [7]. In 1, the pz ring has a weak intramolecular π–π interaction with one phenyl ring attached to the P atom (Fig. 1a). The dihedral angle and ring-centroid distance are 37.7° and 4.17 Å respectively. There is no apparent intermolecular π–π interaction. In 2, the phenyl ring tethered to the tertiary N in pba has a dihedral angle of 78.9° with tpphz plane and is involved into intermolecular π–π stacking interactions with the phenyl ring of phenanthroline moiety in adjacent molecule (the ring-centered distance: 3.58 Å), resulting in adjacent molecules being T‐shaped
G-Q. Yin et al. / Inorganic Chemistry Communications 21 (2012) 160–162
Fig. 1. The structures of complexes 1 (a), 2 (b), and 3 (c). Selected bond lengths (Å) and angles (°) for 1: Cu1\N3 2.005(2), Cu1\N2 2.112(2), Cu1\P 2.258(1), Cu1\P2 2.266(1), P1\Cu1\P2 101.1(1), N3\Cu1\N2 100.9(1); for 2: Cu1\N2 2.058(3), Cu1\N3 2.095(3), Cu1\P1 2.230(1), Cu1\P2 2.253(1), N2\Cu1\N3 80.7(1), P1\Cu1\P2 103.2(1); and for 3: Cu1\N3 2.054(5), Cu1\N2 2.084(6), Cu1\P1 2.227(2), Cu1\P2 2.257(2), N3\Cu1\N2 80.8(2), P1\Cu1\P2 104.4(1).
161
Fig. 3. The absorption spectra of 1, 2 and 3 in DMF solution.
orientation to each other (Fig. 2). In 3, the central phenyl ring of bfimbz has a tilted angel of 12.5° to the phenanthroline–imidazole plane, resulting in the whole bfimbz molecule not fully π-conjugated. Neighboring molecules in the packing structure of 3 are arranged parallelly through the C\H…π interactions between the arene ring of bfimbz and the phenyl ring attached to one phosphine group. The UV/vis absorption spectra of complexes 1, 2 and 3 in DMF are shown in Fig. 3. The absorption spectra in the short wavelength region below 320 nm are attributed to ligand-centered (LC) transitions of the imine and dpa ligands, while the low-energy bands ranging from 340 to 480 nm exhibit metal-to-ligand charge transfer (MLCT) character. Complexes 1 and 2 show very similar absorption spectra in the short wavelength region due to analog ligands. Upon excitation at ~400 nm at room temperature, 1–3 exhibit the solid state emission bands maximized at 542, 632 and 584 nm respectively (Fig. 4), while their excited state lifetimes are 86.6, 78.5 and 37.8 μs respectively. The large values of the Stock shift together with excited state lifetimes in the microsecond domain indicate that these observed emissions are MLCT triplet origin, similar to the other phosphine–diimine complexes of Cu(I). Analogously to the earlier results, the emissive triplet excited state may be ascribed to CT transitions, which have a considerable contribution of MLCT character. The lifetimes of these three complexes increase with the size decrease, possibly due to strong vibrationally relaxed behavior of the large-sized complex. This tendency is similar to our earlier reported [Cu(NN)(PP)] systems in which organophosphine as bridging ligand and diimine as terminal ligand [7]. Nevertheless the lifetimes
of 1 and 2 are obviously much longer than those of our reported [Cu(NN)(PP)] complexes where the bridging organophosphines have no electron-transfer ability between two Cu+ centers. The fully πconjugated pz and tpphz in 1 and 2 could induce the intramolecular photoinduced energy or electron transfer between two Cu + moieties that could lengthen the excited state. Due to only partially π-conjugation in bfimbz with a more elongated distance that doesn't support the intramolecular photoinduced energy or electron transfer, 3 exhibits similar lifetime as the other phosphine–diimine complexes of Cu(I). The luminescent wavelengths of 1 and 3 are close to that of [Cu(pba)(phen)] + [7]. The largest Stock shift of 2 could be ascribed to non-radiation transition induced by the long-ranged intramolecular electron transfer which is the effect of increased π* delocalization upon binding of the second metal, as well as the strong intermolecular π–π interactions. Due to intramolecular π–π interaction, complex 1 exhibits less vibrational relaxation which decreases the Stock shift relative to 2 and 3. In summary, dinuclear copper complexes 1, 2 and 3 are built based on rigid bridging imine ligands. Their luminescent properties are studied. The longer lifetimes of 1 and 2, compared with the reported [Cu(NN)(PP)] system, show that the rigid π-conjugated system could
Fig. 2. The intermolecular π–π interactions in 2.
Fig. 4. The emission spectra of 1, 2 and 3 in the solid state.
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support the intramolecular photoinduced energy or electron transfer between two Cu + luminophore.
[10]
Acknowledgement This work is financially sponsored by the National Natural Foundation of China (no. 20863001), the Natural Foundation of Guangxi Province (2011GXNSFA018041), and the Programme for Excellent Talents in Guangxi Higher Education Institutions.
[11]
[12]
Appendix A. Supplementary material Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.inoche.2012.05.005. References [1] Q. Zhang, Q. Zhou, Y. Cheng, L. Wang, D. Ma, X. Jing, F. Wang, Highly efficient electroluminescence from green-light-emitting electrochemical cells based on CuI complexes, Adv. Funct. Mater. 16 (2006) 1203–1208. [2] Y. Wang, B. Li, Y. Liu, L. Zhang, Q. Zuo, L. Shi, Z. Su, Highly sensitive oxygen sensors based on Cu(I) complex–polystyrene composite nanofibrous membranes prepared by electrospinning, Chem. Commun. (2009) 5868–5870. [3] T. Kern, U. Monkowius, M. Zabel, G. Knör, Mononuclear copper(I) complexes containing redox-active 1,2-bis(aryl-imino)acenaphthene acceptor ligands: synthesis, crystal structures and tuneable electronic properties, Eur. J. Inorg. Chem. 26 (2010) 4148–4156. [4] D.G. Cuttell, S.-M. Kuang, P.E. Fanwick, D.R. McMillin, R.A. Walton, Simple Cu(I) complexes with unprecedented excited-state lifetimes, J. Am. Chem. Soc. 124 (2002) 6–7. [5] K. Saito, T. Arai, N. Takahashi, T. Tsukuda, T. Tsubomura, A series of luminescent Cu(I) mixed-ligand complexes containing 2,9-dimethyl-1,10-phenanthroline and simple diphosphine ligands, Dalton Trans. (2006) 4444–4448. [6] H. Xia, L. He, M. Zhang, M. Zeng, X. Wang, D. Lu, Y. Ma, Efficient electrophosphorescence from low-cost copper(I) complex, Opt. Mater. 29 (2007) 667–671. [7] R. Hou, T.-H. Huang, X.-J. Wang, X.-F. Jiang, Q.-L. Ni, L.-C. Gui, Y.-J. Fan, Y.-L. Tan, Synthesis, structural characterization and luminescent properties of a series of Cu(I) complexes based on polyphosphine ligands, Dalton Trans. 40 (2011) 7551–7558. [8] S. Rau, B. Schäfer, D. Gleich, E. Anders, M. Rudolph, M. Friedrich, H. Görls, W. Henry, J.G. Vos, A supramolecular photocatalyst for the production of hydrogen and the selective hydrogenation of tolane, Angew. Chem. Int. Ed. 45 (2006) 6215–6218. [9] P. Sun, A. Krishnan, A. Yadav, S. Singh, F.M. MacDonnell, D.W. Armstrong, Enantiomeric separations of ruthenium(II) polypyridyl complexes using high-
[13]
[14]
performance liquid chromatography (HPLC) with cyclodextrin chiral stationary phases (CSPs), Inorg. Chem. 46 (2007) 10312–10320. E. Ishow, A. Gourdon, J.-P. Launay, C. Chiorboli, F. Scandola, Synthesis, mass spectrometry, and spectroscopic properties of a dinuclear ruthenium complex comprising a 20 Å long fully aromatic bridging ligand, Inorg. Chem. 38 (1999) 1504–1510. J. Frey, C. Tock, J.-P. Collin, V. Heitz, J.-P. Sauvage, K. Rissanen, Cyclic [2] pseudorotaxane tetramers consisting of two rigid rods threaded through two bis-macrocycles: copper(I)-templated synthesis and X-ray structure studies, J. Am. Chem. Soc. 130 (2008) 11013–11022. [Cu2(pz)(pda)2(CH3CN)2](BF4)2 (1): A mixture of [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol) and pda (0.0490 g, 0.10 mmol) in 6 ml CH3CN/CH2Cl2 (2:4) was stirred at room temperature for 0.5 h and then pz (0.0040 g, 0.05 mmol) was added. This reaction mixture was stirred for an additional 1 h and filtered. The resulted yellow solution was diffused by diethyl ether. Four days later, yellow block crystals were afforded. Yield: 0.0430 g (60%). Anal. calcd for C72H68N6B2F8P4Cu2: C, 59.92; H, 4.72; N, 5.83. Found: C, 60.21; H, 4.50; N, 5.52. IR (cm− 1): 1594(s), 1498(s), 1482(s), 1436(s), 1418(s), 1203(s), 1053(vs), 856(s), 747(s), 696(s), 504(m). ESI-MS: m/z = 552 [Cu(dpa)]+.[Cu2(tpphz)(pda)2] (BF4)2(CH3CN)4 (2): Similar to 1, using [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol), pda (0.0490 g, 0.10 mmol) and tpphz (0.020 g, 0.05 mmol) in 6 ml CH3CN/CH2Cl2/DMF (2:1:3) to yield orange block crystals. Yield: 0.0590 g (65%). Anal. calcd for C96H82N12B2F8P4Cu2: C, 63.12; H, 4.49; N, 9.19. Found: C, 63.41; H, 4.74; N, 9.47. IR (cm− 1): 1594(s), 1502(s), 1481(s), 1435(s), 1394(s), 1372(s), 1124(s), 1083(vs), 1063(vs), 1037(vs), 851(m), 737(vs), 693(vs), 508(m). ESI-MS: m/z = 745 [Cu2(tpphz)(pda)2]2 +.[Cu2(bfimbz)(pda)2](BF4)2 (3): Similar to 1, using [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol), pda (0.0490 g, 0.10 mmol), and bfimbz (0.026 g, 0.05 mmol) in 7 ml CH3CN//DMF (2:5) to yield yellow block crystals. Yield: 0.0450 g (50%). Anal. calcd for C96H76N10B2F8P4Cu2: C, 64.21; H, 4.24; N, 7.80. Found: C, 65.61; H, 4.34; N, 7.62. IR (cm− 1): 1593(m), 1502(m), 1474(m), 1450(m), 1434(m), 1372(m), 1120(m), 1083(vs), 854(m), 737(m), 493(m). ESI-MS: m/z = 552 [Cu(dpa)]+, 809 [Cu2(bfimbz)(pda)2]2 +. Reflection intensity data for 1, 2 and 3 were collected at 293 K on a Oxford ‘Xcalibur, Sapphire3, Gemini ultra’ diffractometer using the ω technique with Enhance Ultra (Mo) X-ray Source (λ = 0.7107 Å) for 1 and 3, and with Enhance Ultra (Cu) X-ray Source (λ = 1.54184 Å) for 2. All the structures were solved by direct methods and refined with the full-matrix least-squares on F2 using SHELXTL. Most of the hydrogen atoms were introduced into the last cycle of the refinement from geometrical calculations and refined by using a riding model. Crystal data for 1: C72H68N6B2F8P4Cu2, Mr= 1441.90, Triclinic, space group P − 1, a = 8.757(3)Å, b = 12.304(6)Å, c = 16.129(6)Å, α = 84.71(4)° β = 80.51(3)° γ = 76.59(4)° V= 1664.79(1)Å3, Z = 1, F(000)= 742, GOF = 0.979, R1= 0.0349, wR2= 0.0797 [I> 2σ(I)]. Crystal data for 2: C96H88N10B2F8O2P4Cu2, Mr= 1838.34, Monoclinic, space group P21/c, a = 14.659(2)Å, b = 18.033(3)Å, c = 17.259(3)Å, β = 105.594(2)° V = 4394.42(1)Å3, Z = 2, F(000)= 1900, GOF = 1.079, R1 = 0.0582, wR2 = 0.1667 [I> 2σ(I)]. Crystal data for 3: C96H76N10B2F8P4Cu2, Mr= 1794.25, Monoclinic, space group P21/c, a = 9.460(3)Å, b = 16.326(7)Å, c = 27.189(1)Å, β = 105.90(4)° V = 4038.4(3)Å3, Z = 2, F(000)= 1844, GOF = 0.821, R1 = 0.0717, wR2= 0.1342 [I> 2σ(I)].
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structures and photoluminescent properties of Cu + complexes with extended π-systems Gang-Qiang Yin b, Heng-Chi Lian a, Qing-Ling Ni a, Liu-Cheng Gui a, Kun-Guo Yang a, Xiu-Jian Wang a,⁎ a b
School of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, China School of Pharmacy, Guangdong Medical College, Zhanjiang 524023, China
a r t i c l e
i n f o
Article history: Received 4 January 2012 Accepted 1 May 2012 Available online 8 May 2012 Keywords: Cu(I) Luminescent properties Imine Phosphine
a b s t r a c t Three complexes [Cu2(pz)(pda)2(CH3CN)2](BF4)2 (1), [Cu2(tpphz)(pda)2](BF4)2(CH3CN)4 (2) and [Cu2(bfimbz) (pda)2](BF4)2 (3) (pba=N,N′-bis((diphenylphosphino)methyl)benzenamine, pz=pyrazine, tpphz=tetrapyrido [3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine, bfimbz = 1,4-bis([1,10]-phenanthroline[5,6-d]imidazol-2-yl)-benzene) have been synthesized. They are centrosymmetric dinuclear complexes constructed respectively by bridging imine ligands of pz, tpphz and bfimbz linking two [Cu(pda)] moieties. Ligand pda performs as a terminal bidentate ligand. The solid state luminescence of 1, 2 and 3 are 542, 632 and 584 nm, respectively, while their lifetimes are 86.6, 78.5 and 37.8 μs respectively. The rigid π-conjugated system of the imine ligand could play an active role in intramolecular photoinduced energy or electron transfer between two Cu+ moieties. © 2012 Elsevier B.V. All rights reserved.
The heteroleptic Cu(I) compounds containing phosphines and N-donor ligands often exhibit highly emissive metal-to-ligand-chargetransfer (MLCT) state, and are considered as a potential to replace other organometallic phosphors based on the noble metal ions (ruthenium, iridium, platinum) due to the relatively low cost and non-toxicity [1–3]. Recently, a large amount of phosphine and diimine ligands are designed for systematic research on the photophysical properties of Cu(I) complexes, and works mainly focus on the mononuclear Cu complexes [4–7]. Two or more component system connected by the bridging ligand could afford electronic coupling between the linked partners to allow intercomponent photoinduced energy- and/or electron-transfer processes [8–11]. However, these photoinduced transfer are not observed in the ever reported luminescent properties of two or more nuclear Cu+ complexes based on the bridging phosphine and terminal diimine ligands (phenanthroline or 2,9-dimethylphenanthroline). Rigid and linear heteroaromatic entities pyrazine (pz), tetrapyrido [3,2-a:2′,3′-c:3″,2″- h:2‴,3‴-j]phenazine (tpphz) and 1,4-bis([1,10] phenanthroline[5,6-d]imidazol-2-yl)benzene (bfimbz) are the πconjugated systems exhibiting low-lying π*-orbitals. The role of the conjugated π-electron systems is not only structural, however, as it has been shown that their nature has profound effects on the electron and energy transfer rates. As a bridging ligand, they are suitable for the study of intramolecular photoinduced energy or electron transfer between two or more components. In this paper we use pz, tpphz and bfimbz as bridging ligands and N,N′-bis((diphenylphosphino)methyl) benzenamine (pba) as a terminal chelating ligand to develop
⁎ Corresponding author. E-mail address: [email protected] (X-J. Wang). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2012.05.005
[Cu2(pz)(pda)2(CH3CN)2] (1), [Cu2(tpphz)(pda)2] (2) and [Cu2(bfimbz) (pda)2] (3) [12]. Their synthesis, structures and photoluminescent properties are studied. These three complexes are stable in the air. Complexes 2 and 3 are indissoluble in other solvents except for DMF and DMSO, maybe due to the large size and rigidity of tpphz and bfimbz. X-ray diffraction analyses show that the construction of 1, 2 and 3 are similar [13,14]. Ligand pba performs as a chelate ligand to coordinate to one Cu + ion affording a [Cu(pba)]+ moiety. Two [Cu(pba)] + moieties are bridged by one pz, tpphz and bfimbz, respectively, to produce 1, 2 and 3 which are centrosymmetric with the centroid located at the center of the bridging imine ligand. (Fig. 1). The Cu…Cu distances in 1, 2 and 3 are 6.99, 12.78 and 20.16 Å, respectively. In 1, each Cu + is four-coordinated by two P atoms from one pba and two N atoms from one pz and one CH3CN respectively, exhibiting a distorted tetrahedral geometry. But in 2 and 3, each Cu+ adopts a distorted tetrahedral geometry consisting of two P atoms from one pba and two N atoms from one phenanthroline moiety. The average bond distances of Cu\N and Cu\P, as well as the bite angles of P\Cu\P and N\Cu\N are 2.07 Å, 2.24 Å, 103.8° and 80.7°, respectively, which have no significant difference compared with the corresponding values in the previously studied [Cu(NN)(PP)] systems [7]. In 1, the pz ring has a weak intramolecular π–π interaction with one phenyl ring attached to the P atom (Fig. 1a). The dihedral angle and ring-centroid distance are 37.7° and 4.17 Å respectively. There is no apparent intermolecular π–π interaction. In 2, the phenyl ring tethered to the tertiary N in pba has a dihedral angle of 78.9° with tpphz plane and is involved into intermolecular π–π stacking interactions with the phenyl ring of phenanthroline moiety in adjacent molecule (the ring-centered distance: 3.58 Å), resulting in adjacent molecules being T‐shaped
G-Q. Yin et al. / Inorganic Chemistry Communications 21 (2012) 160–162
Fig. 1. The structures of complexes 1 (a), 2 (b), and 3 (c). Selected bond lengths (Å) and angles (°) for 1: Cu1\N3 2.005(2), Cu1\N2 2.112(2), Cu1\P 2.258(1), Cu1\P2 2.266(1), P1\Cu1\P2 101.1(1), N3\Cu1\N2 100.9(1); for 2: Cu1\N2 2.058(3), Cu1\N3 2.095(3), Cu1\P1 2.230(1), Cu1\P2 2.253(1), N2\Cu1\N3 80.7(1), P1\Cu1\P2 103.2(1); and for 3: Cu1\N3 2.054(5), Cu1\N2 2.084(6), Cu1\P1 2.227(2), Cu1\P2 2.257(2), N3\Cu1\N2 80.8(2), P1\Cu1\P2 104.4(1).
161
Fig. 3. The absorption spectra of 1, 2 and 3 in DMF solution.
orientation to each other (Fig. 2). In 3, the central phenyl ring of bfimbz has a tilted angel of 12.5° to the phenanthroline–imidazole plane, resulting in the whole bfimbz molecule not fully π-conjugated. Neighboring molecules in the packing structure of 3 are arranged parallelly through the C\H…π interactions between the arene ring of bfimbz and the phenyl ring attached to one phosphine group. The UV/vis absorption spectra of complexes 1, 2 and 3 in DMF are shown in Fig. 3. The absorption spectra in the short wavelength region below 320 nm are attributed to ligand-centered (LC) transitions of the imine and dpa ligands, while the low-energy bands ranging from 340 to 480 nm exhibit metal-to-ligand charge transfer (MLCT) character. Complexes 1 and 2 show very similar absorption spectra in the short wavelength region due to analog ligands. Upon excitation at ~400 nm at room temperature, 1–3 exhibit the solid state emission bands maximized at 542, 632 and 584 nm respectively (Fig. 4), while their excited state lifetimes are 86.6, 78.5 and 37.8 μs respectively. The large values of the Stock shift together with excited state lifetimes in the microsecond domain indicate that these observed emissions are MLCT triplet origin, similar to the other phosphine–diimine complexes of Cu(I). Analogously to the earlier results, the emissive triplet excited state may be ascribed to CT transitions, which have a considerable contribution of MLCT character. The lifetimes of these three complexes increase with the size decrease, possibly due to strong vibrationally relaxed behavior of the large-sized complex. This tendency is similar to our earlier reported [Cu(NN)(PP)] systems in which organophosphine as bridging ligand and diimine as terminal ligand [7]. Nevertheless the lifetimes
of 1 and 2 are obviously much longer than those of our reported [Cu(NN)(PP)] complexes where the bridging organophosphines have no electron-transfer ability between two Cu+ centers. The fully πconjugated pz and tpphz in 1 and 2 could induce the intramolecular photoinduced energy or electron transfer between two Cu + moieties that could lengthen the excited state. Due to only partially π-conjugation in bfimbz with a more elongated distance that doesn't support the intramolecular photoinduced energy or electron transfer, 3 exhibits similar lifetime as the other phosphine–diimine complexes of Cu(I). The luminescent wavelengths of 1 and 3 are close to that of [Cu(pba)(phen)] + [7]. The largest Stock shift of 2 could be ascribed to non-radiation transition induced by the long-ranged intramolecular electron transfer which is the effect of increased π* delocalization upon binding of the second metal, as well as the strong intermolecular π–π interactions. Due to intramolecular π–π interaction, complex 1 exhibits less vibrational relaxation which decreases the Stock shift relative to 2 and 3. In summary, dinuclear copper complexes 1, 2 and 3 are built based on rigid bridging imine ligands. Their luminescent properties are studied. The longer lifetimes of 1 and 2, compared with the reported [Cu(NN)(PP)] system, show that the rigid π-conjugated system could
Fig. 2. The intermolecular π–π interactions in 2.
Fig. 4. The emission spectra of 1, 2 and 3 in the solid state.
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support the intramolecular photoinduced energy or electron transfer between two Cu + luminophore.
[10]
Acknowledgement This work is financially sponsored by the National Natural Foundation of China (no. 20863001), the Natural Foundation of Guangxi Province (2011GXNSFA018041), and the Programme for Excellent Talents in Guangxi Higher Education Institutions.
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[12]
Appendix A. Supplementary material Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.inoche.2012.05.005. References [1] Q. Zhang, Q. Zhou, Y. Cheng, L. Wang, D. Ma, X. Jing, F. Wang, Highly efficient electroluminescence from green-light-emitting electrochemical cells based on CuI complexes, Adv. Funct. Mater. 16 (2006) 1203–1208. [2] Y. Wang, B. Li, Y. Liu, L. Zhang, Q. Zuo, L. Shi, Z. Su, Highly sensitive oxygen sensors based on Cu(I) complex–polystyrene composite nanofibrous membranes prepared by electrospinning, Chem. Commun. (2009) 5868–5870. [3] T. Kern, U. Monkowius, M. Zabel, G. Knör, Mononuclear copper(I) complexes containing redox-active 1,2-bis(aryl-imino)acenaphthene acceptor ligands: synthesis, crystal structures and tuneable electronic properties, Eur. J. Inorg. Chem. 26 (2010) 4148–4156. [4] D.G. Cuttell, S.-M. Kuang, P.E. Fanwick, D.R. McMillin, R.A. Walton, Simple Cu(I) complexes with unprecedented excited-state lifetimes, J. Am. Chem. Soc. 124 (2002) 6–7. [5] K. Saito, T. Arai, N. Takahashi, T. Tsukuda, T. Tsubomura, A series of luminescent Cu(I) mixed-ligand complexes containing 2,9-dimethyl-1,10-phenanthroline and simple diphosphine ligands, Dalton Trans. (2006) 4444–4448. [6] H. Xia, L. He, M. Zhang, M. Zeng, X. Wang, D. Lu, Y. Ma, Efficient electrophosphorescence from low-cost copper(I) complex, Opt. Mater. 29 (2007) 667–671. [7] R. Hou, T.-H. Huang, X.-J. Wang, X.-F. Jiang, Q.-L. Ni, L.-C. Gui, Y.-J. Fan, Y.-L. Tan, Synthesis, structural characterization and luminescent properties of a series of Cu(I) complexes based on polyphosphine ligands, Dalton Trans. 40 (2011) 7551–7558. [8] S. Rau, B. Schäfer, D. Gleich, E. Anders, M. Rudolph, M. Friedrich, H. Görls, W. Henry, J.G. Vos, A supramolecular photocatalyst for the production of hydrogen and the selective hydrogenation of tolane, Angew. Chem. Int. Ed. 45 (2006) 6215–6218. [9] P. Sun, A. Krishnan, A. Yadav, S. Singh, F.M. MacDonnell, D.W. Armstrong, Enantiomeric separations of ruthenium(II) polypyridyl complexes using high-
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performance liquid chromatography (HPLC) with cyclodextrin chiral stationary phases (CSPs), Inorg. Chem. 46 (2007) 10312–10320. E. Ishow, A. Gourdon, J.-P. Launay, C. Chiorboli, F. Scandola, Synthesis, mass spectrometry, and spectroscopic properties of a dinuclear ruthenium complex comprising a 20 Å long fully aromatic bridging ligand, Inorg. Chem. 38 (1999) 1504–1510. J. Frey, C. Tock, J.-P. Collin, V. Heitz, J.-P. Sauvage, K. Rissanen, Cyclic [2] pseudorotaxane tetramers consisting of two rigid rods threaded through two bis-macrocycles: copper(I)-templated synthesis and X-ray structure studies, J. Am. Chem. Soc. 130 (2008) 11013–11022. [Cu2(pz)(pda)2(CH3CN)2](BF4)2 (1): A mixture of [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol) and pda (0.0490 g, 0.10 mmol) in 6 ml CH3CN/CH2Cl2 (2:4) was stirred at room temperature for 0.5 h and then pz (0.0040 g, 0.05 mmol) was added. This reaction mixture was stirred for an additional 1 h and filtered. The resulted yellow solution was diffused by diethyl ether. Four days later, yellow block crystals were afforded. Yield: 0.0430 g (60%). Anal. calcd for C72H68N6B2F8P4Cu2: C, 59.92; H, 4.72; N, 5.83. Found: C, 60.21; H, 4.50; N, 5.52. IR (cm− 1): 1594(s), 1498(s), 1482(s), 1436(s), 1418(s), 1203(s), 1053(vs), 856(s), 747(s), 696(s), 504(m). ESI-MS: m/z = 552 [Cu(dpa)]+.[Cu2(tpphz)(pda)2] (BF4)2(CH3CN)4 (2): Similar to 1, using [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol), pda (0.0490 g, 0.10 mmol) and tpphz (0.020 g, 0.05 mmol) in 6 ml CH3CN/CH2Cl2/DMF (2:1:3) to yield orange block crystals. Yield: 0.0590 g (65%). Anal. calcd for C96H82N12B2F8P4Cu2: C, 63.12; H, 4.49; N, 9.19. Found: C, 63.41; H, 4.74; N, 9.47. IR (cm− 1): 1594(s), 1502(s), 1481(s), 1435(s), 1394(s), 1372(s), 1124(s), 1083(vs), 1063(vs), 1037(vs), 851(m), 737(vs), 693(vs), 508(m). ESI-MS: m/z = 745 [Cu2(tpphz)(pda)2]2 +.[Cu2(bfimbz)(pda)2](BF4)2 (3): Similar to 1, using [Cu(CH3CN)4]BF4 (0.0316 g, 0.10 mmol), pda (0.0490 g, 0.10 mmol), and bfimbz (0.026 g, 0.05 mmol) in 7 ml CH3CN//DMF (2:5) to yield yellow block crystals. Yield: 0.0450 g (50%). Anal. calcd for C96H76N10B2F8P4Cu2: C, 64.21; H, 4.24; N, 7.80. Found: C, 65.61; H, 4.34; N, 7.62. IR (cm− 1): 1593(m), 1502(m), 1474(m), 1450(m), 1434(m), 1372(m), 1120(m), 1083(vs), 854(m), 737(m), 493(m). ESI-MS: m/z = 552 [Cu(dpa)]+, 809 [Cu2(bfimbz)(pda)2]2 +. Reflection intensity data for 1, 2 and 3 were collected at 293 K on a Oxford ‘Xcalibur, Sapphire3, Gemini ultra’ diffractometer using the ω technique with Enhance Ultra (Mo) X-ray Source (λ = 0.7107 Å) for 1 and 3, and with Enhance Ultra (Cu) X-ray Source (λ = 1.54184 Å) for 2. All the structures were solved by direct methods and refined with the full-matrix least-squares on F2 using SHELXTL. Most of the hydrogen atoms were introduced into the last cycle of the refinement from geometrical calculations and refined by using a riding model. Crystal data for 1: C72H68N6B2F8P4Cu2, Mr= 1441.90, Triclinic, space group P − 1, a = 8.757(3)Å, b = 12.304(6)Å, c = 16.129(6)Å, α = 84.71(4)° β = 80.51(3)° γ = 76.59(4)° V= 1664.79(1)Å3, Z = 1, F(000)= 742, GOF = 0.979, R1= 0.0349, wR2= 0.0797 [I> 2σ(I)]. Crystal data for 2: C96H88N10B2F8O2P4Cu2, Mr= 1838.34, Monoclinic, space group P21/c, a = 14.659(2)Å, b = 18.033(3)Å, c = 17.259(3)Å, β = 105.594(2)° V = 4394.42(1)Å3, Z = 2, F(000)= 1900, GOF = 1.079, R1 = 0.0582, wR2 = 0.1667 [I> 2σ(I)]. Crystal data for 3: C96H76N10B2F8P4Cu2, Mr= 1794.25, Monoclinic, space group P21/c, a = 9.460(3)Å, b = 16.326(7)Å, c = 27.189(1)Å, β = 105.90(4)° V = 4038.4(3)Å3, Z = 2, F(000)= 1844, GOF = 0.821, R1 = 0.0717, wR2= 0.1342 [I> 2σ(I)].