English

• 1. INTRODUCTION

  Copper(Ⅰ) complexes and clusters represent one of important classes of luminescent metal compounds based on a relatively abundant, inexpensive and non-toxic element showing interesting photophysic properties, and have been shown to be promising highly efficient electroluminescent emitters for the development of organic light-emitting diodes (OLED)^[1-5]. Cuprous emissive [Cu(NN)₂]⁺ complexes that contain two diimine ligands (NN = diimine ligand) have been investigated intensively since 1970^[6]. The influence of the steric factors on the emissive properties of [Cu(NN)₂]⁺ complexes has been demonstrated in many studies, but the emission performance of [Cu(NN)₂]⁺ complexes is generally poor. In 2002, McMillin and coworkers obtained a series of highly emissive Cu(N,N)(P,P)⁺ complexes (PP = diphosphine ligand) by using bulky substituted 2,10-phenthroline and POP as ligands^[7], and some of the complexes were used successfully in the OLEDs latterly^[8]. Since then, substantial investigations have been carried out to develop new highly luminescent Cu(Ⅰ) materials^[9]. Recently, many neutral dinuclear Cu(Ⅰ) complexes with halide bridges, [(L)Cu(μ-X)₂Cu(L)] (X = Cl, Br, I; L = P- and N-containing ligands) synthesized from the reactions of cuprous halides with various P- and N-containing ligands, have been reported^[10-16]. As for luminescent copper(Ⅰ) complexes with acridine-modified diimine ligands, to the best of our knowledge, there are only very few examples^{[17, 18]}, while luminescent copper(Ⅰ) halide complexes with such kind of ligands have not been studied in this field. In this paper, we report the synthesis, structure, spectroscopic characterization and DFT/TD-DFT calculations of a new Cu(Ⅰ) halide complex with acridine-modified diimine ligand, namely, [(mapypz)Cu(μ-I)₂Cu(mapypz)] (1).

  2. EXPERIMENTAL

  2.1 Materials and instruments

  All reactions were performed under air atmosphere unless specified. Chemicals were purchased from commercial sources and used without further purification. The mapypz ligand was prepared by literature procedures^[18]. Elemental analyses (C, H, N) were carried out with an Elemental Vario EL Ⅲ elemental analysis. Photoluminescence spectra and decay lifetime were recorded on a HORIBA Jobin-Yvon FluoroMax-4 SPECTROMETER. The PL quantum yields, which were defined as the number of photons emitted per photon absorbed by the system, were measured by FluoroMax-4-equipped with an integrating sphere.

  2.2 Synthesis of complex [(mapypz)Cu(μ-I)₂Cu(mapypz)] (1)

  A solution of mapypz (129.0 mg, 0.3 mmol) in 5 mL of CH₂Cl₂ was carefully layered on the top of a solution of CuI (57.0 mg, 0.3 mmol) in 10 mL of CH₃CN in a test tube. Orange crystals of the product grew gradually and were isolated after two weeks. Yield: 155.0 mg, 83%. Anal. Cacld.: C₅₈H₄₈Cu₂I₂N₈: C, 56.27; H, 3.91; N, 9.05%. Found: C, 56.32; H, 3.89; N, 9.07%.

  2.3 Structure determination

  X-ray crystallographic analysis An orange crystal of complex 1 with dimensions of 0.08mm × 0.02mm × 0.02mm was used for X-ray diffraction analysis. Diffraction data of the complex were collected on a SuperNova, Dual, Cu at zero, Atlas diffractometer equipped with graphite-monochromated CuKα radiation (λ = 1.54184 Å). A total of 11463 reflections were collected at 100 K in the range of 4.76≤θ≤70.65º by using an ω-scan mode, of which 4627 were unique with R_int = 0.0280 and 4132 were observed with I > 2σ(I). The structure was solved by direct methods with SHELXS-97 and refined by full-matrix least-squares methods with SHELXL-97 program package^[19]. All of the non-hydrogen atoms were located with successive difference Fourier synthesis. Hydrogen atoms were added in idealized positions, and non-hydrogen atoms were refined anisotropically. The final R = 0.0330, wR = 0.0740 (w = 1/[σ²(F_o²) + (0.1121P)² + 0.6970P], where P = (F_o² + 2F_c²)/3), S = 1.001, (Δ/σ)_max = 0.000, (Δρ)_max = 0.962 and (Δρ)_min = –0.868 e/ų. Selected bond lengths and bond angles from X-ray structure analysis are listed in Table 1.

  Table 1

  

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  DownLoad: CSV

  Bond	Dist.		Angle	(°)
  Cu(1)–N(1)	2.113(3)		N(1)–Cu(1)–N(3)	78.0(1)
  Cu(1)–N(3)	2.089(3)		I(1)–Cu(1)–I(1A)	119.16(2)
  Cu(1)–I(1)	2.5858(5)		Cu(1)–I(1)–Cu(1A)	60.84(2)
  Cu(1)–I(1A)	2.5862(5)		N(1)–Cu(1)–I(1)	106.72(7)
  Cu(1)–Cu(1A)	2.6189(9)		N(3)–Cu(1)–I(1A)	109.09(7)
  Symmetric code: A: –x+1, –y, –z+2

  2.4 Computational methodology

  The DFT and TD-DFT calculations were performed based on the X-ray structure at the hybrid Becke three-parameter Lee-Yang-Parr (B3LYP) functional^{[20, 21]} level. The vertical excitation energies in gas state were obtained by calculating 50 singlet and 10 triplet excited states with TD-DFT^[22-24] method. In all calculations, the relativistic effective core potential (RECP) and the associated basis set Lanl08 (f) and Lanl08(d)^[25], which are the revised version of original Hay-Wadt basis set, were employed for the Cu(Ⅰ) atoms, and all-electron basis set of 6-31G* was used for other non-metal atoms of P, S, N, C, and H. All the calculations were implemented using Gaussian 09 program package^[26]. Visualization of the optimized structures and frontier molecular orbitals were performed by GaussView.

  3. RESULTS AND DISCUSSION

  The studied complex (1) was prepared by the reaction of CuI and equivalent amount of the acridine-modified diimine ligand. The reaction of CuI and the diimne ligand happens quickly to give orange amorphous product. In order to get crystals of the product with good crystallinity, it is crucial to control the mixing speedy of the reactants in reaction media. After trials, we found that the crystalline product can be obtained from the procedure described in the experimental section. Complex 1 is insoluble in common organic solvents, including CH₂Cl₂, CHCl₃ and DMF. It is stable in solid state. The crystals obtained are suitable for X-ray diffraction.

  The crystal structure of complex 1 was determined by X-ray single-crystal analysis. Its ORTEP plot is shown in Fig. 1. Complex 1 crystallizes in P2₁/c space group with an inversion center located at the center of the molecule (Z = 2). The molecular structure of 1 can be viewed as containing a Cu₂I₂ central unit and two diimine terminal ligands. The copper atoms are four-coordinated in a distorted tetrahedral geometry defined by two N atoms from a diimine ligand and two iodide anions. The angles of Ⅰ-Cu-Ⅰ and N–Cu–N largely deviate from the usual tetrahedral value of 109.5°^[27]. The N–Cu–N angles of the complex are 78.0(1)° because of the small bite angle of the diimine ligand. The Ⅰ-Cu-Ⅰ angles of 119.16(2)° are due to the structure constraint of the four-membered ring formed by the copper atoms and the I bridging anions. The Cu₂I₂ center is essentially planar. The Cu−I and Cu–N bond distances in these complexes fall in normal ranges. The Cu···Cu distance is 2.6189(9) Å, which is obviously shorter than those observed in [PPh₂PAr₂Cu(μ-X)₂CuPPh₂PAr₂]^[14]. The Cu···Cu distance in complex 1 is smaller than the sum of van der Waals radii (about 2.8 Å), implying the contribution of Cu···Cu interaction.

  Figure 1

  

  Figure 1.  ORTEP structure of complex 1. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity

  DownLoad: Full-Size Img PowerPoint

  The emission spectra of complex 1 were measured with powder samples. The studied complex shows intense orange luminescence under UV excitation. Its emission spectrum at ambient temperature is shown in Fig. 2. The complex exhibits broad and unstructured emission band, which is typical for intramolecular charge-transfer (CT) transitions. At room temperature, the photoluminescence quantum yield (PLQY) of the complex is 22%. The transient photoluminescence decay characteristics of the complex show one component decay with the decay lifetime of 16 μs. It is noteworthy to point out that there is no prompt fluorescence with nanosecond decay lifetime observed for this complex. According to k_r = Φ_PLτ^-1, the corresponding radiative rate k_r for complex 1 at room temperature can be calculated to be 1.4 × 10⁴. The magnitudes of the emission lifetime and radiative rate indicate that the photoluminescence has a triplet nature.

  Figure 2

  

  Figure 2.  Emission spectrum of complex 1 in powder state at 298 K. The excitation wavelength for the emission spectra is 366 nm

  DownLoad: Full-Size Img PowerPoint

  The emission spectrum of complex 1 in the solid state was also measured at 77 K. With temperature increasing from 77 to 298 K, a blue shift of the emission maximum by 5 nm complexes was observed. To further understand the emission proprieties of the complex, the observed lifetime (τ_obs) of complex 1 at varied temperature from 77 to 298 K was investigated and the temperature-dependent results are shown intuitively in Fig. 3. The observed lifetime reduced drastically by six times from 96 μs at 77 K to 16 μs at 293 K. The severe decrease of the emission lifetime indicates that the emissions of these complexes may arise from two inter-convertible excited states in thermal equilibrium. The change of emission lifetime along with the blue shift of the emission maxima with increasing temperature indicates that the complex at room temperature emits via thermally activated delayed fluorescence (TADF), which has been observed often from emissive Cu(Ⅰ) complexes and organic donor-acceptor compounds with small S₁-T₁ energy gaps^[28-35]. For thermally equilibrated states, the observed decay time (τ_obs) of the two excited states can be expressed as a function of the temperature as shown in Eq. (1) that has been used generally in literature^{[18b, 23a]}.

  $ {\tau _{{\rm{obs}}}} = \frac{{1 + \frac{1}{3}\exp \left( { - \frac{{\Delta {{\rm{E}}_{ST}}}}{{{{\rm{k}}_{\rm{B}}}{\rm{T}}}}} \right)}}{{\frac{1}{{\tau \left( {{{\rm{T}}_1}} \right)}} + \frac{1}{{\tau \left( {{{\rm{S}}_1}} \right)}}\exp \left( { - \frac{{\Delta {{\rm{E}}_{ST}}}}{{{{\rm{k}}_{\rm{B}}}{\rm{T}}}}} \right)}} $

  (1)

  Figure 3

  

  Figure 3.  (a) Temperature-dependent emission lifetime of complex 1. The solid line is a fit curve according to Eq. 1. (b) Energy levels for ground-state and the lowest excited state of complex 1. Herein, τ_DF, τ_P, and ΔE_st represent the decay time of the delayed fluorescence at room temperature, the decay time of the transition of T₁→S₀ (phosphorescence), and the energy gap between S₁ and T₁ states, respectively

  DownLoad: Full-Size Img PowerPoint

  From a weighted linear least-squares fitting procedure using Eq. 1, important photophyscical parameters for compound 1, τ_T, τ_S, and ΔE_ST are determined and summarized in the inset of Fig. 3. An analysis of these data allows us to have a better understanding of the emission process. For complex 1, the τ_T fitted value of 95 μs is close to the measured of 96 μs at 77 K. The fit value of ΔE_ST of 79 meV is in good agreement with 19 meV determined from the emission spectra. The small energy gap between S₁ and T₁ states facilitates thermally activated conversion of T₁ → S₁ and therefore leads to pronounced TADF at ambient temperature. The fit τ_S value of 290 ns is 3 orders of magnitude smaller than the fit values of τ_T. These results support the presented model in which the higher- and lower-energy states are assigned to a spin-allowed S₁ and a spin-forbidden T₁ states, respectively.

  DFT/TD-DFT calculations were carried out at the B3LYP functional^{[20, 21]} level of theory for the crystal structural geometry to give the NTOs (natural transition orbitals). In Fig. 4, we only reproduce the NTOs for the S1 state, since those referring to the T1 state are almost identical. TD-DFT calculations show that the transition between NTOs represents a charge transfer (CT) transition with dominant charge arrangements from Cu (56%) and I (29%) to the diimine ligands. We abbreviate this type of CT transition shortly as the metal-to-ligand charge transfer (MLCT) transition. The TD-DFT calculations reveal that the resulting MLCT (T1) and MLCT (S1) states are 98% and 96% of HOMO → LUMO+1 character, respectively. Therefore, the corresponding NTOs essentially represent HOMO (hole) and LUMO+1 (electron), respectively. Moreover, the two excited states exhibit an energy difference of 40 meV.

  Figure 4

  

  Figure 4.  Natural transition orbitals of the S₁ state for complex 1 based on the X-ray structure

  DownLoad: Full-Size Img PowerPoint

  In summary, a new neutral binuclear emissive cuprous complex 1 was obtained. It is a rare example of emissive binuclear copper complexes with an acridine-modified diimine ligand. The luminescent properties of the complex have been studied experimentally and theoretically, indicating that the complex displays TADF at room temperature.

  
  
• 1. [1]

     Di, D.; Romanov, A. S.; Yang, L.; Richter, J. M.; Rivett, J. P. H.; Jones, S.; Thomas, T. H.; Abdi Jalebi, M.; Friend, R. H.; Linnolahti, M.; Bochmann, M.; Credgington, D. High-performance light-emitting diodes based on carbene-metal-amides. Science 2017, 356, 159–163. doi: 10.1126/science.aah4345

  2. [2]

     Hamze, R.; Peltier, J. L.; Sylvinson, D.; Jung, M.; Cardenas, J.; Haiges, R.; Soleilhavoup, M.; Jazzar, R.; Djurovich, P. I.; Bertrand, G. Eliminating nonradiative decay in Cu(Ⅰ) emitters: > 99% quantum efficiency and microsecond lifetime. Science 2019, 363, 601–606. doi: 10.1126/science.aav2865

  3. [3]

     Shi, S.; Jung, M. C.; Coburn, C.; Tadle, A.; Sylvinson M. R. D.; Djurovich, P. I.; Forrest, S. R.; Thompson, M. E. Highly efficient photo- and electroluminescence from two-coordinate Cu(Ⅰ) complexes featuring nonconventional N-heterocyclic carbenes. J. Am. Chem. Soc. 2019, 141, 3576–3588. doi: 10.1021/jacs.8b12397

  4. [4]

     Chen, X. L.; Yu, R.; Zhang, Q. K.; Zhou, L. J.; Wu, X. Y.; Zhang, Q.; Lu, C. Z. Rational design of strongly blue-emitting cuprous complexes with thermally activated delayed fluorescence and application in aolution-processed OLEDs. Chem. Mater. 2013, 25, 3910–3920. doi: 10.1021/cm4024309

  5. [5]

     Zhang, Q.; Komino, T.; Huang, S.; Matsunami, S.; Goushi, K.; Adachi, C. Triplet exciton confinement in green organic light-emitting diodes containing luminescent charge-transfer Cu(Ⅰ) complexes. Adv. Funct. Mater. 2012, 22, 2327–2336. doi: 10.1002/adfm.201101907

  6. [6]

     Laviecambot, A.; Cantuel, M.; Leydet, Y.; Jonusauskas, G.; Bassani, D.; McClenaghan, N. Improving the photophysical properties of copper(Ⅰ) bis(phenanthroline) complexes. Coordin. Chem. Rev. 2008, 252, 2572–2584. doi: 10.1016/j.ccr.2008.03.013

  7. [7]

     Cuttell, D. G.; Kuang, S. M.; Fanwick, P. E.; McMillin, D. R.; Walton, R. A. Simple Cu(Ⅰ) complexes with unprecedented excited-state lifetime. J. Am. Chem. Soc. 2002, 124, 6–7. doi: 10.1021/ja012247h

  8. [8]

     Zhang, Q. S.; Zhou, Q. G.; Cheng, Y. X.; Wang, L. X.; Ma, D. G.; Jing, X. B.; Wang, F. S. Highly efficient green phosphorescent organic light-emitting diodes based on Cu-Ⅰ complexes. Adv. Mater. 2004, 16, 432–436. doi: 10.1002/adma.200306414

  9. [9]

     Chou, P. T.; Chi, Y.; Chung, M. W.; Lin, C. C. Harvesting luminescence via harnessing the photophysical properties of transition metal complexes. Coordin. Chem. Rev. 2011, 255, 2653–2665. doi: 10.1016/j.ccr.2010.12.013

  10. [10]

      Tsuboyama, A.; Kuge, K.; Furugori, M.; Okada, S.; Hoshino, M.; Ueno, K. Photophysical properties of highly luminescent copper(Ⅰ) halide complexes chelated with 1,2-bis(diphenylphosphino)benzene. Inorg. Chem. 2007, 46, 1992–2001. doi: 10.1021/ic0608086

  11. [11]

      Zink, D. M.; Baumann, T.; Friedrichs, J.; Nieger, M.; Brase, S. Copper(Ⅰ) complexes based on five-membered P^N heterocycles: structural diversity linked to exciting luminescence properties. Inor. Chem. 2013, 52, 13509–20. doi: 10.1021/ic4019162

  12. [12]

      Zink, D. M.; Bachle, M.; Baumann, T.; Nieger, M.; Kuhn, M.; Wang, C.; Klopper, W.; Monkowius, U.; Hofbeck, T.; Yersin, H.; Brase, S. Synthesis, structure, and characterization of dinuclear copper(Ⅰ) halide complexes with P^N ligands featuring exciting photoluminescence properties. Inorg. Chem. 2013, 52, 2292–305. doi: 10.1021/ic300979c

  13. [13]

      Volz, D.; Wallesch, M.; Grage, S. L.; Gottlicher, J.; Steininger, R.; Batchelor, D.; Vitova, T.; Ulrich, A. S.; Heske, C.; Weinhardt, L.; Baumann, T.; Brase, S. Labile or stable: can homoleptic and heteroleptic PyrPHOS-copper complexes be processed from solution? Inorg. Chem. 2014, 53, 7837–47. doi: 10.1021/ic500135m

  14. [14]

      Kang, L.; Chen, J.; Teng, T.; Chen, X. L.; Yu, R.; Lu, C. Z. Experimental and theoretical studies of highly emissive dinuclear Cu(Ⅰ) halide complexes with delayed fluorescence. Dalton Trans. 2015, 44, 11649–59. doi: 10.1039/C5DT01292A

  15. [15]

      Zink, D. M.; Volz, D.; Baumann, T.; Mydlak, M.; Flügge, H.; Friedrichs, J.; Nieger, M.; Bräse, S. Heteroleptic, dinuclear copper(Ⅰ) complexes for application in organic light-emitting diodes. Chem. Mater. 2013, 25, 4471–4486. doi: 10.1021/cm4018375

  16. [16]

      Liu, Z.; Qiu, J.; Wei, F.; Wang, J.; Liu, X.; Helander, M. G.; Rodney, S.; Wang, Z.; Bian, Z.; Lu, Z.; Thompson, M. E.; Huang, C. Simple and high efficiency phosphorescence organic light-emitting diodes with codeposited copper(Ⅰ) emitter. Chem. Mater. 2014, 26, 2368–2373. doi: 10.1021/cm5006086

  17. [17]

      Liang, D.; Jia, J. H.; Liao, J. Z.; Yu, R.; Lu, C. Z. Synthesis, crystal structure and photoluminescence of a TADF cuprous complex. Chin. J. Struct. Chem. Comm. 2017, 36, 82–88.

  18. [18]

      Liang, D.; Chen, X. L.; Liao, J. Z.; Hu, J. Y.; Jia, J. H.; Lu, C. Z. Highly efficient cuprous complexes with thermally activated delayed fluorescence for solution-processed organic light-emitting devices. Inorg. Chem. 2016, 55, 7467–7475. doi: 10.1021/acs.inorgchem.6b00763

  19. [19]

      Sheldrick, G. M. SHELXL-97, Program for Solution of Crystal Structures. Institute for Inorganic Chemistry, University of Göttingen: Göttingen. Germany 1997.

  20. [20]

      Lee, C. T.; Yang, W. T.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. doi: 10.1103/PhysRevB.37.785

  21. [21]

      Becke, A. D. Density-functional thermochemistry. Ⅲ. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648–5652. doi: 10.1063/1.464913

  22. [22]

      Bauernschmitt, R.; Ahlrichs, R. Treatment of electronic excitations within the adiabatic approximation of time dependent density functional theory. Chem. Phys. Lett. 1996, 256, 454–464. doi: 10.1016/0009-2614(96)00440-X

  23. [23]

      Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. Molecular excitation energies to high-lying bound states from time-dependent density-functional response theory: characterization and correction of the time-dependent local density approximation ionization threshold. J. Chem. Phys. 1998, 108, 4439–4449. doi: 10.1063/1.475855

  24. [24]

      Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An efficient implementation of time-dependent density-functional theory for the calculation of excitation energies of large molecules. J. Chem. Phys. 1998, 109, 8218–8224. doi: 10.1063/1.477483

  25. [25]

      Roy, L. E.; Hay, P. J.; Martin, R. L. Revised basis sets for the LANL effective core potentials. J. Chem. Theory Comput. 2008, 4, 1029–1031. doi: 10.1021/ct8000409

  26. [26]

      Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.; Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, Gaussian 09, Revision D. 01 2009.

  27. [27]

      Czerwieniec, R.; Yu, J.; Yersin, H. Blue-light emission of Cu(Ⅰ) complexes and singlet harvesting. Inorg. Chem. 2011, 50, 8293–8301. doi: 10.1021/ic200811a

  28. [28]

      Linfoot, C. L.; Leitl, M. J.; Richardson, P.; Rausch, A. F.; Chepelin, O.; White, F. J.; Yersin, H.; Robertson, N. Thermally activated delayed fluorescence (TADF) and enhancing photoluminescence quantum yields of [Cu(Ⅰ)(diimine)(diphosphine)](+) complexes-photophysical, structural, and computational studies. Inorg. Chem. 2014, 53, 10854–61. doi: 10.1021/ic500889s

  29. [29]

      Hofbeck, T.; Monkowius, U.; Yersin, H. Highly efficient luminescence of Cu(Ⅰ) compounds: thermally activated delayed fluorescence combined with short-lived phosphorescence. J. Am. Chem. Soc. 2015, 137, 399–404. doi: 10.1021/ja5109672

  30. [30]

      Osawa, M.; Hoshino, M.; Hashimoto, M.; Kawata, I.; Igawa, S.; Yashima, M. Application of three-coordinate copper(Ⅰ) complexes with halide ligands in organic light-emitting diodes that exhibit delayed fluorescence. Dalton Trans 2015, 44, 8369–78. doi: 10.1039/C4DT02853H

  31. [31]

      Osawa, M.; Kawata, I.; Ishii, R.; Igawa, S.; Hashimoto, M.; Hoshino, M. Application of neutral d10 coinage metal complexes with an anionic bidentate ligand in delayed fluorescence-type organic light-emitting diodes. J. Mater. Chem. C 2013, 1, 4375. doi: 10.1039/c3tc30524d

  32. [32]

      Zhang, Q.; Kuwabara, H.; Potscavage, W. J. Jr.; Huang, S.; Hatae, Y.; Shibata, T.; Adachi, C. Anthraquinone-based intramolecular charge-transfer compounds: computational molecular design, thermally activated delayed fluorescence, and highly efficient red electroluminescence. J. Am. Chem. Soc. 2014, 136, 18070–81. doi: 10.1021/ja510144h

  33. [33]

      Xu, S.; Liu, T.; Mu, Y.; Wang, Y. F.; Chi, Z.; Lo, C. C.; Liu, S.; Zhang, Y.; Lien, A.; Xu, J. An organic molecule with asymmetric structure exhibiting aggregation-induced emission, delayed fluorescence, and mechanoluminescence. Angew Chem. Int. Ed. Engl. 2015, 54, 874–8. doi: 10.1002/anie.201409767

  34. [34]

      Nakanotani, H.; Higuchi, T.; Furukawa, T.; Masui, K.; Morimoto, K.; Numata, M.; Tanaka, H.; Sagara, Y.; Yasuda, T.; Adachi, C. High-efficiency organic light-emitting diodes with fluorescent emitters. Nat. Commun. 2014, 5, 4016. doi: 10.1038/ncomms5016

  35. [35]

      Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 2012, 492, 234–8. doi: 10.1038/nature11687

• 

  Figure 1  ORTEP structure of complex 1. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity

  下载: 全尺寸图片 幻灯片
  

  Figure 2  Emission spectrum of complex 1 in powder state at 298 K. The excitation wavelength for the emission spectra is 366 nm

  下载: 全尺寸图片 幻灯片
  

  Figure 3  (a) Temperature-dependent emission lifetime of complex 1. The solid line is a fit curve according to Eq. 1. (b) Energy levels for ground-state and the lowest excited state of complex 1. Herein, τ_DF, τ_P, and ΔE_st represent the decay time of the delayed fluorescence at room temperature, the decay time of the transition of T₁→S₀ (phosphorescence), and the energy gap between S₁ and T₁ states, respectively

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Natural transition orbitals of the S₁ state for complex 1 based on the X-ray structure

  下载: 全尺寸图片 幻灯片

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  Bond	Dist.		Angle	(°)
  Cu(1)–N(1)	2.113(3)		N(1)–Cu(1)–N(3)	78.0(1)
  Cu(1)–N(3)	2.089(3)		I(1)–Cu(1)–I(1A)	119.16(2)
  Cu(1)–I(1)	2.5858(5)		Cu(1)–I(1)–Cu(1A)	60.84(2)
  Cu(1)–I(1A)	2.5862(5)		N(1)–Cu(1)–I(1)	106.72(7)
  Cu(1)–Cu(1A)	2.6189(9)		N(3)–Cu(1)–I(1A)	109.09(7)
  Symmetric code: A: –x+1, –y, –z+2

  下载: 导出CSV
•