- Email: [email protected]
Two unusual cyclometalated dimeric Ir(III) complexes: Synthesis, crystal structure and phosphorescent properties
Inorganic Chemistry Communications 17 (2012) 113–115
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Two unusual cyclometalated dimeric Ir(III) complexes: Synthesis, crystal structure and phosphorescent properties Bihai Tong a, Jiayan Qiang a, Qunbo Mei b,⁎, Hengshan Wang c, Qianfeng Zhang a a
College of Metallurgy and Resources, Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Ma'anshan, Anhui 243002, P. R. China Jiangsu Key Lab of Organic Electronics & Information Displays, Institute of Advanced Materials (IAM), Nanjing University of Posts & Telecommunications (NUPT), Nanjing 210046, P. R. China c Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources, College of Chemistry & Chemical Engineering, Guangxi Normal University, Guilin 541004, P. R. China b
a r t i c l e
i n f o
Article history: Received 22 November 2011 Accepted 16 December 2011 Available online 24 December 2011 Keywords: Dimeric iridium complex Crystal structure Photoluminescence
a b s t r a c t Two cyclometalated dimeric Ir(III) complexes, [{Ir(μ-Cl)(μ-ppa)(dmppa)}2] (dimer 1) and (dmppa)Ir(μ-Cl) (μ-ppa)Ir(ppa) (dimer 2) (dmppa = 1-(2,6-dimethylphenoxy)-4-phenylphthalazine, ppa = 1-hydroxyl-4phenylphthalazine), containing the bridging phthalazine ligands and bridging chlorides have been synthesized and fully characterized. Dimer 1 can form a noncovalently linked crystalline porous frameworks. The emission wavelength of dimer 1 in CH2Cl2 solution was 596 nm and the further hydrolysis of phenolic groups red shift the emission of dimer 2 to 634 nm. Two dimers have relatively high quantum efficiency, i.e., ca. 0.21 for dimer 1 and 0.3 for dimer 2 in CH2Cl2 solution. © 2011 Elsevier B.V. All rights reserved.
Due to their relatively short excited state lifetime, high photoluminescence efficiency and excellent color tuning, luminescent cyclometalated iridium (III) complexes have been widely used in organic light-emitting diodes (OLEDs), luminescence sensitizers, and biological imaging [1]. At the same time, the cyclometalated iridium complexes also exhibited abundant variability in coordination chemistry. For example, a cyclometalated dimeric iridium complex containing an unsupported IrII―IrII bond has been reported [2], and crystalline porous systems with luminescent iridium complexes consisting of two metal complexes that are simply the counterion of each other have also been reported [3]. Recently, we have reported the direct synthesis of a series of highly efficient tris-cyclometalated iridium(III) complexes using phenylphthalazine derivatives as ligands [4-7]. Based on Mi's works, it has been found that the ligands with an sp 2-hybrid N-atom adjacent to the chelating N-atom, such as phenylpyridazine and phenylphthalazine derivatives [8], are beneficial for the iridium(III) complexes due to the shorter bonding length and the stronger bonding strength between the chelating N-atom and the Ir-atom, compared with analogs which have a C-atom instead of the nonchelating N-atom. At the same time, Li et al. theoretically investigated the origin of rare and highly efficient phosphorescent and electroluminescent Iridium(III) complexes based on C^N N ligands [9]. Their research indicated that the more promising photoluminescent (PL) and electroluminescent (EL) properties of our tris(1(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine) iridium (III)
⁎ Corresponding author. Tel./fax: + 86 25 85866396. E-mail address: [email protected] (Q. Mei). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.12.027
[Ir(MPCPPZ)3] complex result from the bulky phenolic group, which acts as a pendant at the periphery of the emitting core and protects the emitting core from the inhibitory intermolecular interaction of emitters and reduces luminescence quenching. As a sequel of our studies on the mechanism of preferentially forming triscyclometalated Ir(III) complexes and synthesis of highly efficient phosphorescent and electroluminescent Iridium(III) complexes, we replace the ligand 1-(2, 6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine with 1-(2, 6-dimethylphenoxy)-4-phenylphthalazine to synthesize new iridium(III) complexes. Herein, we report the preparation and characterization of two unusual cyclometalated dimeric iridium complexes with the new ligand. The two dimers are composed of two bis-cyclometalated Ir(III) structures linked by a Cl bridged bond and a N N bridged bond. A noncovalently bound porous structure is found in the dimer crystals. The photophysical properties of these two dimers were also studied. After exchange of the ligand 1-(2, 6-dimethylphenoxy)-4-(4chlorophenyl)phthalazine with 1-(2, 6-dimethylphenoxy)-4-phenylphthalazine, the corresponding triscyclometalated Ir(III) complex cannot be obtained as major product. The ligand undergoes a partial hydrolysis during the process of coordination. The dimer 1 and dimer 2 can be readily dissociated by dithiocarbamate ligands but can not be dissociated by N ΛN type ligands, such as 2, 2′-bipyridine. The molecular structures of the complexes dimer 1 and dimer 2 are depicted in Fig. 1. Dimer 1 consists of two octahedrally coordinated iridium(III) centers each ligated by a dmppa ligand, a bridging chlorides and two bridging ppa ligands produced from the hydrolyzation of the dmppa ligand. The chloride ligands occupy the sites trans to the metalated C atoms of the ppa ligand. The three N atoms reside in the same plane with the Cl―Ir bond perpendicular to it. The cis
114
B. Tong et al. / Inorganic Chemistry Communications 17 (2012) 113–115
Dimer 1
Dimer 2
Fig. 1. Perspective view of the dimer 1 and dimer 2 with selected displacement ellipsoids drawn at the 30% probability level, H-atoms omitted.
C―C chelate disposition implies that there is a stronger trans influence of the phenyl group over that of the phthalazine. The Ir―C bond lengths, ranging from 1.96(3) to 2.03(3) Å, are within the range reported for closely related complexes [10]. The Ir―N bond lengths of the Ir[C ΛN] moieties spanning from (1.994(18) to 2.069(18) Å, are within the range reported for other mononuclear complexes containing analogous Ir[C ΛN] moieties [11]. However, the Ir―N bond lengths (2.238(17) and 2.255(16) Å) between the Ir center and the N atom linked to the N atom of Ir[C ΛN] moieties in the bridging ppa ligand are longer than those in the Ir[C ΛN] moieties because of stronger donating and back-bonding interactions between aryl groups and the iridium atom [12]. Moreover, this Ir―N bond deviated obviously from the plane of the bridging phthalazine group. The Ir―Cl bond lengths 2.438(6) and 2.471(6) Å are slightly shorter than those (from 2.4823(16) to 2.4983(15) Å) reported for closely related Ir III-μ-chloro-bridged dimers [13]. The bond angles of Ir―Cl―Ir (89.13(17)°) are smaller than those in the Ir III-μ-chloro-bridged dimer (97.02(5)° and 97.35(5)°) and close to the idealized 90° value. Furthermore, the C―C, C―O and C―N bond lengths and angles are within normal ranges and are in agreement with the corresponding parameters described for similarly constituted complexes [13]. The packing motif reveals a crystalline porous system and its projection along the a axis is depicted in Fig. 2. The projection of pores form a parallelogram and the bridging chlorides are the two vertices with the longest distance of 23.6532(59) Å. This porous structure replicates along a axis. However, during the process of crystal data acquisition, the crystallinity decreases because the loss of solvent
molecules inside the channels. This noncovalently bond porous materials may show an application as light modulators and novel functional molecular devices [3] and related studies are currently underway. The dimer 2 has the similar coordination structure and geometry except for one more ppa ligand from the corresponding hydrolyzation of the dmppa ligand. UV–vis absorption spectra of dimer 1 and dimer 2 in CH2Cl2 solution are shown in Fig. 3. Both complexes have similar spectra. The intense absorption bands in the ultraviolet around 309 nm are assigned to a typical spin-allowed singlet ligand-centered ( 1LC) transition. The moderately intense band at 357 nm corresponds most likely to a spinallowed singlet metal-to-ligand charge-transfer ( 1MLCT) [14]. On the other hand, the weak absorptions at ca. 430–580 nm can be assigned to a spin-forbidden triplet metal-to-ligand charge-transfer ( 3MLCT). The room-temperature photoluminescence spectra of the new complexes in CH2Cl2 solution and in powder are shown in Fig. 4. Dimer 1 in CH2Cl2 solution emits intense luminescence with an emission wavelength at 596 nm. The full width at half maximum (FWHM) of this transition is 44 nm. However, the emission intensity of dimer 1 in powder was rather weak, the wavelength red-shifts to 634 nm and the FWHM is 97 nm. The red-shift of the emission spectra and dilated FWHM in solid state is related to strong intermolecular interactions, indicating strong excited-state quenching of this iridium complex in solid state. The emission wavelength of dimer 2 in CH2Cl2 solution is 626 nm with a FWHM of 75 nm. This results indicate that the partial hydrolysis of phenolic groups lead to the observation of a red shift. The solid emission of dimer 2 has a maximum emission wavelength of 666 nm and a FWHM of 80 nm featuring also a red shift compared to solution.
1.0 Dimer1 Dimer2
Absorbance (a.u.)
0.8
0.6
0.4
0.2
0.0 300
400
500
600
700
Wavelength (nm) Fig. 2. The porous crystal packing of the complex dimer 1 along a axis.
Fig. 3. UV absorption spectra of dimer 1 and dimer 2 in CH2Cl2 solutions.
B. Tong et al. / Inorganic Chemistry Communications 17 (2012) 113–115
300
Dimer 1 in solution Dimer 2 in solution Dimer 1 in solid Dimer 2 in solid
Intensity (a. u.)
250
115
exhibit unique reaction character, thus they can serve for the design of new type of probes. These new iridium complexes are orange or red emitters with short lifetime and high quantum efficiency which is desirable for example in OLED applications.
200
Acknowledgments 150
This project was supported by the National Natural Science Foundations of China (grant nos. 50903001 and 50803027), 973 project (No. 2011CB512005) and Guangxi Natural Science Foundation of China (No. 2011GXNSFD018010).
100
50
Appendix A. Supplementary material 0 550
600
650
700
750
800
Wavelength (nm) Fig. 4. The room-temperature photoluminescence spectra of the new complexes in CH2Cl2 solution and in powder (λex = 450 nm).
References
2000
Dimer1 Dimer2
1500
Intensity (a. u.)
CCDC 822166 and 822257 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2011.12.027.
1000
500
0 0
1000
2000
3000
4000
5000
Time (ns) Fig. 5. Luminescence decay curves of dimer 1 and dimer 2.
Fig. 5 presents the typical luminescence decay curves of the two complexes in CH2Cl2. All the complexes demonstrated a double exponential decay. The short lifetime (τ1) of dimer 1 was 195 ns and its contribution was 69%, and the long short lifetime (τ2) was 526 ns and its contribution was 31%. Dimer 2 showed a longer value of τ1 (255 ns, 31%) and τ2 (548 ns, 69%) compared to dimer 1. In general, the typical radiative lifetime of cyclometalated iridium complexes falls in the microsecond and submicrosecond range [15] and our experimental decay times fit in this range. The phosphorescence quantum efficiency of dimer 1 and dimer 2 in CH2Cl2 solution is ca. 0.21 and 0.3, respectively, using an aqueous solution of [Ru(bpy)3]Cl2 (Φ = 0.042) as the standard solution [16]. The high quantum efficiencies are comparable with other known high-performance iridium(III) complexes, such as Ir(ppy)3 (Φ = 0.4) [17]. In summary, two novel dimeric iridium complexes containing bridging phthalazine ligands have been prepared and characterized. A noncovalently bond porous structure was found in the crystals of our dimeric iridium complexes. The dimeric iridium complexes
[1] Z.Q. Chen, Z.Q. Bian, C.H. Huang, Functional Ir III complexes and their applications, Adv. Mater. 22 (2010) 1534–1539. [2] H.P. Lee, Y.F. Hsu, T.R. Chen, A novel cyclometalated dimeric iridium complex, [(dfpbo)(2)Ir](2) [dfpbo=2-(3,5-difluorophenyl)benzoxazolato-N, C(2')], containing an unsupported Ir(II)―Ir(II) bond, Inorg. Chem. 48 (2009) 1263–1265. [3] M. Mauro, K.C. Schuermann, R. Pretot, Complex iridium(III) salts: luminescent porous crystalline materials, Angew. Chem. Int. Ed. 49 (2010) 1222–1226. [4] B.H. Tong, Q.B. Mei, S.J. Wang, Nearly 100% internal phosphorescence efficiency in a polymer light-emitting diode using a new iridium complex phosphor, J. Mater. Chem. 18 (2008) 1636–1639. [5] Y. Fang, B.H. Tong, S.J. Hu, A highly efficient tris-cyclometalated iridium complex based on phenylphthalazine derivative for organic light-emitting diodes, Org. Electron. 10 (2009) 618–622. [6] Y. Fang, S.J. Hu, Y.Z. Meng, Synthesis of a novel tris-cyclometalated iridium(III) complex containing triarylamine unit and its application in OLEDs, Inorg. Chim. Acta 362 (2009) 4985–4990. [7] Y. Fang, Y.H. Li, S.J. Wang, Synthesis, characterization and electroluminescence properties of iridium complexes based on pyridazine and phthalazine derivatives with C^N N structure, Synth. Met. 160 (2010) 2231–2238. [8] Z.Q. Gao, B.X. Mi, H.L. Tam, K.W. Cheah, High efficiency and small roll-off electrophosphorescence from a new iridium complex with well-matched energy levels, Adv. Mater. 20 (2008) 774–778. [9] X.N. Li, Z.J. Wu, X.J. Liu, H.J. Zhang, Origin of rare and highly efficient phosphorescent and electroluminescent iridium(III) complexes based on C boolean and N N ligands, A theoretical explanation, J. Phys. Chem. A 114 (2010) 9300–9308. [10] S.J. Lee, K.M. Park, K. Yang, Blue phosphorescent Ir(III) complex with high color purity: fac-tris(2′,6′-difluoro-2,3′-bipyridinato-N, C(4)′)iridium(III), Inorg. Chem. 48 (2009) 1030–1037. [11] B.H. Tong, F.H. Wu, Q.B. Mei, Synthesis, crystal structure and luminescence properties of a cyclometalated Ir(III) complex of 3,4-diphenylcinnoline, Z. Naturforsch. 65b (2010) 511–515. [12] B. Douglas, D. McDaniel, J. Alexander, Concepts and Models in Inorganic Chemistry, 3rd ed. John Wiley & Sons, Inc, New York, 1994. [13] M. Graf, M. Thesen, H. Krüger, P. Mayer, Synthesis and X-ray crystal structure of a bis-cyclometalated phosphorescent red-emitting iridium(III) complex, Inorg. Chem. Commun. 12 (2009) 701–703. [14] L.Q. Xiong, Q. Zhao, H.L. Chen, Phosphorescence imaging of homocysteine and cysteine in living cells based on a cationic iridium(III) complex, Inorg. Chem. 49 (2010) 6402–6408. [15] K.K. Lo, C. Chung, T.K. Lee, New luminescent cyclometalated iridium(III) diimine complexes as biological labeling reagents, Inorg. Chem. 42 (2003) 6886–6897. [16] J. van Houten, R.J. Watts, Temperature dependence of the photophysical and photochemical properties of the tris(2,2′-bipyridyl)ruthenium(II) ion in aqueous solution, J. Am. Chem. Soc. 98 (1976) 4853–4858. [17] M. Ikai, S. Tokito, Y. Sakamoto, T. Suzuki, Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer, Appl. Phys. Lett. 79 (2001) 156–158.
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Two unusual cyclometalated dimeric Ir(III) complexes: Synthesis, crystal structure and phosphorescent properties Bihai Tong a, Jiayan Qiang a, Qunbo Mei b,⁎, Hengshan Wang c, Qianfeng Zhang a a
College of Metallurgy and Resources, Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Ma'anshan, Anhui 243002, P. R. China Jiangsu Key Lab of Organic Electronics & Information Displays, Institute of Advanced Materials (IAM), Nanjing University of Posts & Telecommunications (NUPT), Nanjing 210046, P. R. China c Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources, College of Chemistry & Chemical Engineering, Guangxi Normal University, Guilin 541004, P. R. China b
a r t i c l e
i n f o
Article history: Received 22 November 2011 Accepted 16 December 2011 Available online 24 December 2011 Keywords: Dimeric iridium complex Crystal structure Photoluminescence
a b s t r a c t Two cyclometalated dimeric Ir(III) complexes, [{Ir(μ-Cl)(μ-ppa)(dmppa)}2] (dimer 1) and (dmppa)Ir(μ-Cl) (μ-ppa)Ir(ppa) (dimer 2) (dmppa = 1-(2,6-dimethylphenoxy)-4-phenylphthalazine, ppa = 1-hydroxyl-4phenylphthalazine), containing the bridging phthalazine ligands and bridging chlorides have been synthesized and fully characterized. Dimer 1 can form a noncovalently linked crystalline porous frameworks. The emission wavelength of dimer 1 in CH2Cl2 solution was 596 nm and the further hydrolysis of phenolic groups red shift the emission of dimer 2 to 634 nm. Two dimers have relatively high quantum efficiency, i.e., ca. 0.21 for dimer 1 and 0.3 for dimer 2 in CH2Cl2 solution. © 2011 Elsevier B.V. All rights reserved.
Due to their relatively short excited state lifetime, high photoluminescence efficiency and excellent color tuning, luminescent cyclometalated iridium (III) complexes have been widely used in organic light-emitting diodes (OLEDs), luminescence sensitizers, and biological imaging [1]. At the same time, the cyclometalated iridium complexes also exhibited abundant variability in coordination chemistry. For example, a cyclometalated dimeric iridium complex containing an unsupported IrII―IrII bond has been reported [2], and crystalline porous systems with luminescent iridium complexes consisting of two metal complexes that are simply the counterion of each other have also been reported [3]. Recently, we have reported the direct synthesis of a series of highly efficient tris-cyclometalated iridium(III) complexes using phenylphthalazine derivatives as ligands [4-7]. Based on Mi's works, it has been found that the ligands with an sp 2-hybrid N-atom adjacent to the chelating N-atom, such as phenylpyridazine and phenylphthalazine derivatives [8], are beneficial for the iridium(III) complexes due to the shorter bonding length and the stronger bonding strength between the chelating N-atom and the Ir-atom, compared with analogs which have a C-atom instead of the nonchelating N-atom. At the same time, Li et al. theoretically investigated the origin of rare and highly efficient phosphorescent and electroluminescent Iridium(III) complexes based on C^N N ligands [9]. Their research indicated that the more promising photoluminescent (PL) and electroluminescent (EL) properties of our tris(1(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine) iridium (III)
⁎ Corresponding author. Tel./fax: + 86 25 85866396. E-mail address: [email protected] (Q. Mei). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.12.027
[Ir(MPCPPZ)3] complex result from the bulky phenolic group, which acts as a pendant at the periphery of the emitting core and protects the emitting core from the inhibitory intermolecular interaction of emitters and reduces luminescence quenching. As a sequel of our studies on the mechanism of preferentially forming triscyclometalated Ir(III) complexes and synthesis of highly efficient phosphorescent and electroluminescent Iridium(III) complexes, we replace the ligand 1-(2, 6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine with 1-(2, 6-dimethylphenoxy)-4-phenylphthalazine to synthesize new iridium(III) complexes. Herein, we report the preparation and characterization of two unusual cyclometalated dimeric iridium complexes with the new ligand. The two dimers are composed of two bis-cyclometalated Ir(III) structures linked by a Cl bridged bond and a N N bridged bond. A noncovalently bound porous structure is found in the dimer crystals. The photophysical properties of these two dimers were also studied. After exchange of the ligand 1-(2, 6-dimethylphenoxy)-4-(4chlorophenyl)phthalazine with 1-(2, 6-dimethylphenoxy)-4-phenylphthalazine, the corresponding triscyclometalated Ir(III) complex cannot be obtained as major product. The ligand undergoes a partial hydrolysis during the process of coordination. The dimer 1 and dimer 2 can be readily dissociated by dithiocarbamate ligands but can not be dissociated by N ΛN type ligands, such as 2, 2′-bipyridine. The molecular structures of the complexes dimer 1 and dimer 2 are depicted in Fig. 1. Dimer 1 consists of two octahedrally coordinated iridium(III) centers each ligated by a dmppa ligand, a bridging chlorides and two bridging ppa ligands produced from the hydrolyzation of the dmppa ligand. The chloride ligands occupy the sites trans to the metalated C atoms of the ppa ligand. The three N atoms reside in the same plane with the Cl―Ir bond perpendicular to it. The cis
114
B. Tong et al. / Inorganic Chemistry Communications 17 (2012) 113–115
Dimer 1
Dimer 2
Fig. 1. Perspective view of the dimer 1 and dimer 2 with selected displacement ellipsoids drawn at the 30% probability level, H-atoms omitted.
C―C chelate disposition implies that there is a stronger trans influence of the phenyl group over that of the phthalazine. The Ir―C bond lengths, ranging from 1.96(3) to 2.03(3) Å, are within the range reported for closely related complexes [10]. The Ir―N bond lengths of the Ir[C ΛN] moieties spanning from (1.994(18) to 2.069(18) Å, are within the range reported for other mononuclear complexes containing analogous Ir[C ΛN] moieties [11]. However, the Ir―N bond lengths (2.238(17) and 2.255(16) Å) between the Ir center and the N atom linked to the N atom of Ir[C ΛN] moieties in the bridging ppa ligand are longer than those in the Ir[C ΛN] moieties because of stronger donating and back-bonding interactions between aryl groups and the iridium atom [12]. Moreover, this Ir―N bond deviated obviously from the plane of the bridging phthalazine group. The Ir―Cl bond lengths 2.438(6) and 2.471(6) Å are slightly shorter than those (from 2.4823(16) to 2.4983(15) Å) reported for closely related Ir III-μ-chloro-bridged dimers [13]. The bond angles of Ir―Cl―Ir (89.13(17)°) are smaller than those in the Ir III-μ-chloro-bridged dimer (97.02(5)° and 97.35(5)°) and close to the idealized 90° value. Furthermore, the C―C, C―O and C―N bond lengths and angles are within normal ranges and are in agreement with the corresponding parameters described for similarly constituted complexes [13]. The packing motif reveals a crystalline porous system and its projection along the a axis is depicted in Fig. 2. The projection of pores form a parallelogram and the bridging chlorides are the two vertices with the longest distance of 23.6532(59) Å. This porous structure replicates along a axis. However, during the process of crystal data acquisition, the crystallinity decreases because the loss of solvent
molecules inside the channels. This noncovalently bond porous materials may show an application as light modulators and novel functional molecular devices [3] and related studies are currently underway. The dimer 2 has the similar coordination structure and geometry except for one more ppa ligand from the corresponding hydrolyzation of the dmppa ligand. UV–vis absorption spectra of dimer 1 and dimer 2 in CH2Cl2 solution are shown in Fig. 3. Both complexes have similar spectra. The intense absorption bands in the ultraviolet around 309 nm are assigned to a typical spin-allowed singlet ligand-centered ( 1LC) transition. The moderately intense band at 357 nm corresponds most likely to a spinallowed singlet metal-to-ligand charge-transfer ( 1MLCT) [14]. On the other hand, the weak absorptions at ca. 430–580 nm can be assigned to a spin-forbidden triplet metal-to-ligand charge-transfer ( 3MLCT). The room-temperature photoluminescence spectra of the new complexes in CH2Cl2 solution and in powder are shown in Fig. 4. Dimer 1 in CH2Cl2 solution emits intense luminescence with an emission wavelength at 596 nm. The full width at half maximum (FWHM) of this transition is 44 nm. However, the emission intensity of dimer 1 in powder was rather weak, the wavelength red-shifts to 634 nm and the FWHM is 97 nm. The red-shift of the emission spectra and dilated FWHM in solid state is related to strong intermolecular interactions, indicating strong excited-state quenching of this iridium complex in solid state. The emission wavelength of dimer 2 in CH2Cl2 solution is 626 nm with a FWHM of 75 nm. This results indicate that the partial hydrolysis of phenolic groups lead to the observation of a red shift. The solid emission of dimer 2 has a maximum emission wavelength of 666 nm and a FWHM of 80 nm featuring also a red shift compared to solution.
1.0 Dimer1 Dimer2
Absorbance (a.u.)
0.8
0.6
0.4
0.2
0.0 300
400
500
600
700
Wavelength (nm) Fig. 2. The porous crystal packing of the complex dimer 1 along a axis.
Fig. 3. UV absorption spectra of dimer 1 and dimer 2 in CH2Cl2 solutions.
B. Tong et al. / Inorganic Chemistry Communications 17 (2012) 113–115
300
Dimer 1 in solution Dimer 2 in solution Dimer 1 in solid Dimer 2 in solid
Intensity (a. u.)
250
115
exhibit unique reaction character, thus they can serve for the design of new type of probes. These new iridium complexes are orange or red emitters with short lifetime and high quantum efficiency which is desirable for example in OLED applications.
200
Acknowledgments 150
This project was supported by the National Natural Science Foundations of China (grant nos. 50903001 and 50803027), 973 project (No. 2011CB512005) and Guangxi Natural Science Foundation of China (No. 2011GXNSFD018010).
100
50
Appendix A. Supplementary material 0 550
600
650
700
750
800
Wavelength (nm) Fig. 4. The room-temperature photoluminescence spectra of the new complexes in CH2Cl2 solution and in powder (λex = 450 nm).
References
2000
Dimer1 Dimer2
1500
Intensity (a. u.)
CCDC 822166 and 822257 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2011.12.027.
1000
500
0 0
1000
2000
3000
4000
5000
Time (ns) Fig. 5. Luminescence decay curves of dimer 1 and dimer 2.
Fig. 5 presents the typical luminescence decay curves of the two complexes in CH2Cl2. All the complexes demonstrated a double exponential decay. The short lifetime (τ1) of dimer 1 was 195 ns and its contribution was 69%, and the long short lifetime (τ2) was 526 ns and its contribution was 31%. Dimer 2 showed a longer value of τ1 (255 ns, 31%) and τ2 (548 ns, 69%) compared to dimer 1. In general, the typical radiative lifetime of cyclometalated iridium complexes falls in the microsecond and submicrosecond range [15] and our experimental decay times fit in this range. The phosphorescence quantum efficiency of dimer 1 and dimer 2 in CH2Cl2 solution is ca. 0.21 and 0.3, respectively, using an aqueous solution of [Ru(bpy)3]Cl2 (Φ = 0.042) as the standard solution [16]. The high quantum efficiencies are comparable with other known high-performance iridium(III) complexes, such as Ir(ppy)3 (Φ = 0.4) [17]. In summary, two novel dimeric iridium complexes containing bridging phthalazine ligands have been prepared and characterized. A noncovalently bond porous structure was found in the crystals of our dimeric iridium complexes. The dimeric iridium complexes
[1] Z.Q. Chen, Z.Q. Bian, C.H. Huang, Functional Ir III complexes and their applications, Adv. Mater. 22 (2010) 1534–1539. [2] H.P. Lee, Y.F. Hsu, T.R. Chen, A novel cyclometalated dimeric iridium complex, [(dfpbo)(2)Ir](2) [dfpbo=2-(3,5-difluorophenyl)benzoxazolato-N, C(2')], containing an unsupported Ir(II)―Ir(II) bond, Inorg. Chem. 48 (2009) 1263–1265. [3] M. Mauro, K.C. Schuermann, R. Pretot, Complex iridium(III) salts: luminescent porous crystalline materials, Angew. Chem. Int. Ed. 49 (2010) 1222–1226. [4] B.H. Tong, Q.B. Mei, S.J. Wang, Nearly 100% internal phosphorescence efficiency in a polymer light-emitting diode using a new iridium complex phosphor, J. Mater. Chem. 18 (2008) 1636–1639. [5] Y. Fang, B.H. Tong, S.J. Hu, A highly efficient tris-cyclometalated iridium complex based on phenylphthalazine derivative for organic light-emitting diodes, Org. Electron. 10 (2009) 618–622. [6] Y. Fang, S.J. Hu, Y.Z. Meng, Synthesis of a novel tris-cyclometalated iridium(III) complex containing triarylamine unit and its application in OLEDs, Inorg. Chim. Acta 362 (2009) 4985–4990. [7] Y. Fang, Y.H. Li, S.J. Wang, Synthesis, characterization and electroluminescence properties of iridium complexes based on pyridazine and phthalazine derivatives with C^N N structure, Synth. Met. 160 (2010) 2231–2238. [8] Z.Q. Gao, B.X. Mi, H.L. Tam, K.W. Cheah, High efficiency and small roll-off electrophosphorescence from a new iridium complex with well-matched energy levels, Adv. Mater. 20 (2008) 774–778. [9] X.N. Li, Z.J. Wu, X.J. Liu, H.J. Zhang, Origin of rare and highly efficient phosphorescent and electroluminescent iridium(III) complexes based on C boolean and N N ligands, A theoretical explanation, J. Phys. Chem. A 114 (2010) 9300–9308. [10] S.J. Lee, K.M. Park, K. Yang, Blue phosphorescent Ir(III) complex with high color purity: fac-tris(2′,6′-difluoro-2,3′-bipyridinato-N, C(4)′)iridium(III), Inorg. Chem. 48 (2009) 1030–1037. [11] B.H. Tong, F.H. Wu, Q.B. Mei, Synthesis, crystal structure and luminescence properties of a cyclometalated Ir(III) complex of 3,4-diphenylcinnoline, Z. Naturforsch. 65b (2010) 511–515. [12] B. Douglas, D. McDaniel, J. Alexander, Concepts and Models in Inorganic Chemistry, 3rd ed. John Wiley & Sons, Inc, New York, 1994. [13] M. Graf, M. Thesen, H. Krüger, P. Mayer, Synthesis and X-ray crystal structure of a bis-cyclometalated phosphorescent red-emitting iridium(III) complex, Inorg. Chem. Commun. 12 (2009) 701–703. [14] L.Q. Xiong, Q. Zhao, H.L. Chen, Phosphorescence imaging of homocysteine and cysteine in living cells based on a cationic iridium(III) complex, Inorg. Chem. 49 (2010) 6402–6408. [15] K.K. Lo, C. Chung, T.K. Lee, New luminescent cyclometalated iridium(III) diimine complexes as biological labeling reagents, Inorg. Chem. 42 (2003) 6886–6897. [16] J. van Houten, R.J. Watts, Temperature dependence of the photophysical and photochemical properties of the tris(2,2′-bipyridyl)ruthenium(II) ion in aqueous solution, J. Am. Chem. Soc. 98 (1976) 4853–4858. [17] M. Ikai, S. Tokito, Y. Sakamoto, T. Suzuki, Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer, Appl. Phys. Lett. 79 (2001) 156–158.