Synthesis, characterization and luminescent properties of three-coordinate copper(I) halide complexes containing diphenylamino monodentate phosphine ligand

Article abstract of DOI:10.1080/00958972.2017.1364373

Three-coordinate copper halide complexes with a bidentate phosphine ligand have received much attention. Here, a series of three-coordinate dinuclear copper halide complexes containing a diphenylamino monodentate phosphine ligand, [CuX(dpnp)]₂

Full text of DOI:10.1080/00958972.2017.1364373

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis, characterization and luminescent
properties of three-coordinate copper(I)
halide complexes containing diphenylamino
monodentate phosphine ligand
Bu-Lin Chen, Li Liu, Xin-Xin Zhong, Abdullah M. Asiri, Khalid A. Alamry, Fa-
Bao Li, Nian-Yong Zhu, Wai-Yeung Wong & Hai-Mei Qin
To cite this article: Bu-Lin Chen, Li Liu, Xin-Xin Zhong, Abdullah M. Asiri, Khalid A. Alamry, Fa-
Bao Li, Nian-Yong Zhu, Wai-Yeung Wong & Hai-Mei Qin (2017): Synthesis, characterization
and luminescent properties of three-coordinate copper(I) halide complexes containing
diphenylamino monodentate phosphine ligand, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2017.1364373
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1364373
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Date: 08 August 2017, At: 09:50

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2017.1364373
Synthesis, characterization and luminescent properties of three-coordinate
copper(I) halide complexes containing diphenylamino
monodentate phosphine ligand
a
a
a
b
b
a
BU-LIN CHEN , LI LIU* , XIN-XIN ZHONG , ABDULLAH M. ASIRI , KHALID A. ALAMRY ,FA-BAO LI* ,
NIAN-YONG ZHU , WAI-YEUNG WONG* andHAI-MEI QINf
c
d,e
aHubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry of Education Key
Laboratory for the Synthesis and Application of Organic Functional Molecules, School of Chemistry and
Chemical Engineering, Hubei University, Wuhan 430062, P. R. China
bChemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
cInstitute of Molecular Functional Materials and Department of Chemistry and Institute of Advanced Materials,
Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
dDepartment of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom,
Hong Kong, P. R. China
eInstitute of Molecular Functional Materials, Hong Kong Baptist University, Waterloo Road,
Hong Kong, P. R. China
fFujian Provincial Key Lab of Theoretical and Computational Chemistry, and Department of Chemistry,
College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China
Three-coordinate copper halide complexes with a bidentate phosphine ligand have received
much attention. Here, a series of three-coordinate dinuclear copper halide complexes containing
a diphenylamino monodentate phosphine ligand, [CuX(dpnp)] (dpnp = N-[2-
2
*
Corresponding authors. Email: liulihubei@hubu.edu.cn (L. Liu); lfb0615@hubu.edu.cn (F.-B. Li);wai-
yeung.wong@polyu.edu.hk (W.-Y. Wong)
1

(diphenylphosphino)-4,5-dimethylphenyl]-N-phenylaniline, X = I (1), Br (2) and Cl (3)),were
synthesized, and their molecular structures and photophysical properties were investigated. The
structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form
a dinuclear structure with a four-membered Cu X ring. Crystal structures of 1-3 contain 1-D
2
2
supramolecular arrays constructed by intermolecular C–H···π interactions. These complexes
exhibit blue emission in the solid state at room temperature and have peak emission wavelengths
at 483-487 nm with microsecond lifetimes (τ = 13.9-38.1 μs) and low emission quantum yields
(< 0.01%). The emission of complex 1 mainly originates from intraligand (IL) transition,
whereas the emissions of complexes 2 and 3are from a combination of MLCT, XLCT and IL
transitions. The three complexes displayed good thermal stability.
Keywords: Copper complex; Synthesis; Characterization; Luminescent property
1
. Introduction
Photoluminescent metal complexes have attracted attention owing to their potential applications
as organic light-emitting diodes (OLEDs) [1], solar cells [2], and chemical sensors [3].As an
attractive alternative to expensive, less abundant, and more toxic heavy-metal-containing
electroluminescent materials, copper(I)-organic compounds have been reported over the past
decade [4-16].
Reactions of Cu(I) halides with monodentate aliphatic and aromatic phosphine donors
show a remarkable structural diversity, ranging from monomeric and dimeric to polymeric
networks [7]. The stereochemistry of copper(I) complexes is dominated by four-coordination,
whereas three-coordinate species are less common [8-20].
Recently, a highly efficient, green, three-coordinate Cu(I) halide coordinated by bidentate
1
,2-bis(o-ditolylphosphino)benzene with an external quantum efficiency (EQE)over 20% was
reported [19]. Compared to a large number of cationic Cu(I) compounds, neutral Cu(I)
2

complexes still remain rare. To date, there are only a few reports of devices fabricated by
vacuum deposition containing neutral Cu(I) complexes [11, 19, 21-24].
Based on the high luminescent efficiency of the three-coordinate mononuclear [19] and
our previously reported four-coordinate dinuclear [25] Cu(I) halide with a bidentate phosphine
ligand, it is generally assumed that a rigid/congested structure is important to avoid structural
changes in the excited state and to obtain a good emission quantum yield and for this reason
bidentate ligands are often employed. Here, a new P, N-bidentate ligand was designed in which
the diphenylamino group was initially inserted hypothesizing a P, N bidentate coordination mode
to obtain mononuclear Cu(P,N)X complexes, and the steric hindrance of NPh was taken into
2
account to obtain a congested structure. Reported here are a series of three-coordinate dinuclear
copper halide complexes [CuX(dpnp)] (dpnp = N-[2-(diphenylphosphino)-4,5dimethylphenyl]-
2
N-phenylaniline), X = I (1), Br (2) and Cl (3)). Their molecular structures and photophysical
properties were investigated.
2
2
. Experimental
.1. General methods
All reagents and solvents are of commercial reagent grade and used without further purification
except where noted. Copper(I) halides and o-xylene were purchased from Aladdin Company and
used without purification. Tetrahydrofuran (THF) was distilled under nitrogen in the presence of
sodium chips by using benzophenone ketyl as an indicator. 1,2-Dibromo-4,5-dimethylbenzene
was synthesized according to the literature method [26].
1H NMR spectra were recorded on a Varian 600 MHz NMR spectrometer using
deuterated solvents as the lock and reference. Chemical shifts were reported in ppm relative to
1
SiMe for the H. High-resolution mass spectra reported as m/z were obtained on a Bruker
4
Autoflex MALDI-TOF mass spectrometer. C, H and N analyses were determined using a Vario
Micro Cube elemental analyzer. The single crystal structures of complexes 1-3were measured at
room temperature or low temperature using a Bruker APEX DUO or Bruker D8 Venture
3

diffractometer. UV–vis spectra were recorded on a Unicam Heλios α spectrometer.
Photoluminescence spectra were recorded on a FLS920 steady state and time-resolved
fluorescence spectrometer. Solid-state Φ values were determined using a Hamamatsu system
PL
for absolute PL quantum yield measurements equipped with an integrating sphere with
Spectralon inner surface coating. The samples were carefully degassed by at least five freeze-
pump-thaw cycles. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer
Diamond TG/DTA thermal analyzer under nitrogen.
2
2
.2. Syntheses
.2.1. Synthesis of N-(2-bromo-4,5-dimethylphenyl)-N-phenylaniline.To a solution of 2.64 g
(10 mmol) of 1,2-dibromo-4,5-dimethylbenzene in 30 mL of toluene was added 2.05 g (12
mmol) of diphenylamine, 0.77 g (4 mmol) of copper(I) iodide, 0.47 g (4 mmol) of
tetramethylethylenediamine and 3.39 g (30 mmol) of potassium t-butoxide at ambient
temperature. The solution was stirred at 120 °C for 12 h, then allowed to cool to room
temperature. The solvents were removed under reduced pressure. After being purified by column
chromatography using hexane as the eluent, a white solid was obtained in 45% yield (1.59 g).
1
H NMR (400 MHz, d -DMSO) δ: 7.52 (s, 1H), 7.24 (t, J = 8 Hz, 4H), 7.11 (s, 1H), 6.93 (t, J =
6
8
6
Hz, 2H), 6.86 (d, 4H, J = 4 Hz), 2.24 (s, 3H), 2.15 (s, 3H). Anal. Calcd for C H BrN: C,
20 18
8.19; H, 5.15; N, 3.98. Found: C, 68.24; H, 5.13; N, 4.04.
2
.2.2. Synthesis of N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-
phenylaniline(dpnp).To a cooled (-78 °C) solution of 3.51 g (10 mmol) of N-(2-bromo-4,5-
dimethylphenyl)-N-phenylaniline in 30 mL of THF was added dropwise 4.2 mL (10 mmol) of a
2
.4 M solution of n-butyllithium in hexanes under nitrogen. The solution was stirred at -78 °C
for 1 h and then 2.43 g (11 mmol) of chlorodiphenylphosphine in THF (15 mL) was added
dropwise. The solution was allowed to warm to room temperature, and then dichloromethane
was added to the solution. The organic layer was washed with water and saturated sodium
4

chloride and then dried over magnesium sulfate. The solvents were removed under reduced
pressure. The crude product was purified by column chromatography using hexane as the eluent.
1
A white solid was obtained in 50% yield (2.29 g). H NMR (600 MHz, CDCl ) δ: 7.23-7.19 (m,
3
6
5
H), 7.10 (t, J = 6 Hz, 4H), 7.04 (t, J = 12 Hz, 4H), 7.00 (d, J = 6 Hz, 1H), 6.90 (d, J = 6 Hz,
3
1
H), 6.78 (t, J = 6 Hz, 2H), 2.19 (s, 3H), 2.15 (s, 3H). P NMR (240 M, CDCl ) δ:−17.88 (s).
3
Anal. Calcd for C H NP: C, 84.00; H, 6.17; N, 3.06. Found: C, 84.12; H, 6.20; N, 3.04.
3
2
28
2
.2.3. Synthesis of di(μ-iodo)bis{N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-
phenylaniline copper(I)} (1).A suspension of copper(I) iodide (0.040 g, 0.21 mmol) and dpnp
0.096 g, 0.21 mmol) in 30 mL of CH Cl was stirred for 5 h at room temperature to form a
(
2
2
greenish-yellow precipitate. The precipitate was filtered off, and complex 1 was crystallized
from the filtered solution after slow evaporation at room temperature to give greenish-yellow
1
crystals (Yield: 0.112 g, 82%). H NMR (600 MHz, CDCl ) δ: 7.46 (t, J = 6 Hz, 8H), 7.29-7.27
3
(m, 4H), 7.21-7.19 (m, 8H), 6.97 (d, J = 6 Hz, 2H), 6.93-6.90 (m, 8H), 6.86-6.85 (m, 8H), 6.80
3
1
(
d, J = 6 Hz, 2H), 6.66 (t, J = 12 Hz, 4H), 2.17 (s, 6H), 2.13 (s, 6H). P NMR (240 M, CDCl )
3
δ: −15.81 (s). Anal. Calcd for C H I Cu N P : C, 59.31; H, 4.36; N, 2.16. Found: C, 59.40; H,
6
4
56 2
2
2 2
+
4
.33; N, 2.18. MS (MALDI-TOF): m/z calcd for [C H NP + H] , 458.1993, found: 458.0202.
32 28
2
.2.4. Synthesis of di(μ-bromo)bis{N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-
phenylaniline copper(I)} (2). Complex 2was obtained by a similar method as described for
1
using copper(I) bromide (0.030 g, 0.21 mmol) in place of copper(I) iodide. Greenish-yellow
1
crystals of 2were obtained (Yield: 0.106 g, 84%). H NMR (600 MHz, CDCl ) δ: 7.36-7.32 (m,
3
1
2H), 7.26-7.20 (m, 10H), 6.99-6.96 (m, 8H), 6.93-6.91 (m, 8H), 6.78 (d, J = 12 Hz, 2H), 6.74 (t,
3
1
J = 6 Hz, 4H), 2.19 (s, 6H), 2.14 (s, 6H). P NMR (240 M, CDCl ) δ:−7.19 (s). Anal. Calcd for
3
C H Br Cu N P : C, 63.95; H, 4.70; N, 2.33. Found: C, 63.89; H, 4.67; N, 2.36. MS (MALDI-
6
4
56
2
2
2 2
+
TOF): m/z calcd for [C H NP + H] , 458.1993, found: 458.1021.
3
2
28
5

2
.2.5. Synthesis of di(μ-chloro)bis{N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-
phenylaniline copper(I)} (3).Complex 3was obtained by a similar method as described for
1
using copper(I) chloride (0.021 g, 0.21 mmol) in place of copper(I) iodide. Greenish-yellow
1
crystals of 3were obtained (Yield: 0.104 g, 89%). H NMR (600 MHz, CDCl ) δ: 7.38-7.36 (m,
3
4
H), 7.29-7.27 (m, 16H), 7.04-7.02 (m, 8H), 6.98 (d, J = 6 Hz, 2H), 6.95-6.94 (m, 8H), 6.85-6.79
3
1
(
m, 6H), 2.20 (s, 6H), 2.16 (s, 6H). P NMR (240 M, CDCl ) δ:−4.12 (s). Anal. Calcd for
3
C H Cl Cu N P : C, 69.06; H, 5.07; N, 2.52. Found: C, 69.10; H, 5.02; N, 2.55. MS (MALDI-
6
4
56
2
2
2 2
+
TOF): m/z calcd for [C H NP + H] , 458.1993, found 458.1251.
3
2
28
2
.3. X-ray crystallography
Greenish-yellow crystals of complexes 1-3 suitable for X-ray diffraction studies were grown by
slow evaporation of their respective solutions in dichloromethane at room temperature.
Geometric and intensity data were collected using graphite-monochromated Mo Kα radiation
(
λ = 0.71073Å) on a Bruker AXS APEX II CCD area detector. The collected frames were
processed with the software SAINT[27], and an absorption correction was applied (SADABS)
28] to the collected reflections. The structureswere solved by direct methods (SHELXTL) [29] in
[
conjunction with standard difference Fourier techniques and subsequently refined by full-matrix
2
least-squares analyses on F . All non-hydrogen atoms were assigned with anisotropic
displacement parameters.
The disorder in complex 1 was solved by direct method with the location of I atom. The
other atoms were located by the difference Fourier map and refined. The Cu, P and N atoms
were disordered, which was caused by similarity of the PPh and NPh fragments. The
2
2
disorderness is a flip of the P and N atoms, while keeping the five benzene groups positioned,
which makes the disorderness of the P-bound copper atom also. Free refinement of the
occupancies of the disordered atoms gave rise to a value close to 0.5, which physically sounds
right. Therefore, the occupancies of the disordered Cu, P and N were set to be 0.5. With this kind
6

of disorderness, the right configuration of the dinuclear complex is the one with Cu I nearly in
2
2
plane.A disorderness for the I atom was not carried out, since the two positions were too close.
2
.4. Theoretical calculations
The structural parameters for the three complexes were obtained from the crystal data which are
listed in tables 1 and 2. The density functional theory (DFT) and time-dependent density
functional theory (TDDFT) calculations were then performed to compute the HOMO-LUMO
energy gap, the natural bond orbital (NBO) analysis as well as the properties of the excited
states. X-ray structures were not optimized by DFT prior to orbital and TDDFT calculations. All
calculations were manipulated by the Gaussian 09 suite [30] at the B3LYP/DGDZVP level.
3
3
. Results and discussion
.1. Description of syntheses and structures
The synthetic routes for the Cu(I) complexes are outlined in scheme 1. First, Br was used to
2
brominate the 1,2-position of o-xylene in high yield to furnish 1,2-dibromo-4,5-
dimethylbenzene. After amination of 1,2-dibromo-4,5-dimethylbenzene with diphenylamine,
copper(I) iodide as catalyst in the mixture of tetramethylethylenediamine (TMEDA) and
potassium t-butoxide, N-(2-bromo-4,5-dimethylphenyl)-N-phenylaniline was obtained in
moderate yield. Then the synthesis of N-(4,5-dimethylphenyl) lithium-N-phenylaniline was
carried out in a mixture with the mole ratio of 1:1 for N-(2-bromo-4,5-dimethylphenyl)-N-
phenylaniline and n-butyllithium. By the addition of chlorodiphenylphosphine to 2-
(diphenylamino)-4,5-dimethylphenyl lithium in THF at -78 °C under nitrogen, dpnp was
synthesized in 50% yield. Complexes 1-3 were prepared in 82-89% yield by mixing a suspension
of CuX (X = I for 1, Br for 2, Cl for 3) in dichloromethane with 1 equiv of dpnp. All the new
Cu(I) complexes were obtained as air stable solids in high purity and found to be generally
soluble in CH Cl . They all gave satisfactory analytical data and were characterized by NMR
2
2
spectroscopy, MALDI-TOF spectrometry and single crystal X-ray diffraction. The structures of
7

Cu(I) complexes 1-3 are not our expected Cu(P,N)X complexes in which P, N bidentate
coordinated with Cu(I). We speculate that low electron density of N atom and large steric
hindrance of NPh are the main reasons which result in the non-coordination with Cu(I).
2
Br
Li
Br
Br2
n-BuLi
HNPh , TMEDA
2
CH Cl
CuI, t-BuOK, toluene
Br
THF
2
2
NPh2
NPh2
Ph PCl THF
2
Ph
Ph
Ph
Ph
PPh2
NPh2
X
X
CuX
P
Cu
Cu
P
2
CH Cl2
NPh2
Ph N
2
dpnp
1
X= I
2
3
X= Br
X= Cl
Scheme 1. Synthetic pathways to ligand dpnp and their dinuclear copper(I) complexes.
3
.2. X-ray crystallographic study
Perspective views of complexes 1-3 are shown in figure 1. The structure of complex 1 has two
solvent CH Cl molecules. Crystallographic data and selected bond lengths and angles are given
2
2
in tables 1 and 2, respectively. X-ray crystallographic studies on 1-3reveal that two copper(I)
centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered
Cu X ring. Complexes 2 and3 have planar Cu X geometries, analogous to halogen-bridged
2
2
2
2
copper complexes which typically have a planar Cu X geometry [31-34]. The Cu X rings of
2
2
2
2
complex 1are significantly deformed by bending along the X···X axis [35], the dihedral angles
between two CuX triangles in Cu X is 158.8° (Cu1-Cu1’), 171.6° (Cu1-Cu1) and 147.6°
2
2
2
(Cu1’-Cu1’), similar with those observed in dinuclear Cu(I) halide with 1,2-
bis(diphenylphosphino)-4,5-dimethylbenzene(152.31–160. 92°)[25]. As listed in table 1, the Cu–
X distances of complexes 1, 2and3elongate with an increase in the van der Waals radius of X.
The Cu···Cu distances are 2.690, 2.859 and 2.462 Å for complex 1 and2.920 and 2.862 Å for
complexes 2and 3, respectively, indicating a weak interaction between two copper atoms, as
8

compared with the sum of van der Waals radius of copper (2.8Å), resembling dinuclear, four-
coordinate Cu(I) halides with a bidentate ligand [31-33].
The coordination geometry of the copper centers in 1-3is closely trigonal-planar; the sum
of the angles around the Cu(I) center are 355.69, 358.99 and 359.08°, respectively, similar to the
reported mononuclear three-coordinate Cu(I) halide with a bidentate ligand (359.66°) [19]. In
complex 1, the distance from the halogen to the closest H atom, H···I is 3.156 Å, displaying a
potential hydrogen bond. Intermolecular hydrogen bonds can be observed in 2and 3, with the
closest Br-to-H and Cl-to-H distances of 2.911 and 2.806 Å, respectively. In the solid state,
1
and3show intermolecular C–H···π interactions between the phenyl ring attached to phosphorus
and phenyl ring attached to nitrogen with the closest H-to-H and C-to-H distances of 3.040 and
.786 Å for 1, 3.306 and 2.861 Å for 3, and dihedral angles of 82.24° for 1 and 89.80° for 3 are
2
observed. Similar intermolecular C–H···π interactions can be observed in 2 between phenyl rings
attached to nitrogen with the closest H-to-H and C-to-H distances of 2.689 and 2.987 Å and
dihedral angle of 61.66°. Overall, all these intermolecular interactions are incorporated into 1-D
tape-like arrays along the a-axis for 1-3 (Supporting Information figures S7-S9).
3
.3. Photophysical properties
The absorption spectra of complexes 1-3 and dpnp in CH Cl at room temperature are shown in
2
2
figure 2. The absorption spectrum of dpnp exhibits a broad, intense band at 295 nm (ε = 8.97 ×
4
-1
-1
1
0 M cm ), which is characteristic of an aryl phosphine and amine compound. As compared to
the absorption band at 282 nm of 1,2-bis(diphenylphosphino)-4,5-dimethylbenzene [25], the
absorption of dpnpis red-shifted by about 13 nm, due to the more intense electron-donating
conjugation effect of N than P. This band is assigned to a mixed transition of n→π* and
π→π*,analogous to those in related three-coordinate mononuclear Cu(I) complexes [19].
Complexes 1-3 have an intense absorption band with a maximum at 271 nm [ε = (5.29-7.93) ×
4
-1
-1
1
0 M cm ] and a broad shoulder at 304 nm and a weaker band tail at 340-380 nm. The weaker
band tail may be attributed to the electronic transition affected by the copper ions, the halide
9

ligands, or both,or ligand-to-ligand charge transfer character. As shown in figure 3, DFT
calculations carried out for complexes 1-3 reveal that the electrons in the highest occupied
molecular orbital (HOMO) are mainly distributed over the copper, halogen, ligand for 2 and 3,
and ligand for 1, while those in the lowest unoccupied molecular orbital (LUMO) are localized
on ligand. We can thus conclude that the lowest energy excited states of 2and3consist of a metal-
to-ligand charge transfer (MLCT), a halogen-to-ligand charge transfer (XLCT), and an
intraligand transfer, analogous to those in related tetrahedral complexes [19, 36]. The lowest
energy excited states of 1mainlyconsist of an intraligand transition. MLCT and XLCT are very
weak for complex 1.
The emission spectra of complexes 1-3 in the solid state measured at 298 and 77 K are
shown in figure 4. Summarized in table 3 are the emission maxima, lifetimes and quantum yields
of the complexes at 298 and 77 K, and TDDFT calculation data based on the structures obtained
by X-ray structural analysis. Complexes 1-3 show blue emission between 483 and 487 nm with
Φ < 0.01% at room temperature.
PL
At 77 K, the emission maxima of complexes 1-3 are located at 502, 507 and 507 nm,
respectively. The emission bands are red-shifted upon cooling because the thermal population of
a lower excited state (T ) dominates at low temperature.Observed long emission decay times
1
between 13.9 and 38.1 μs and blue-shifted band at 298 K, an occurrence of a TADF (thermally
activated delayed fluorescence),is indicated [37-42]. Natural bond orbital (NBO) calculations
and analysis indicate that the hole/electron pairs can be used to describe these transitions. The
hole is approximately in the HOMO and the electron is approximately in the LUMO. The energy
level of singlet and triplet state and ΔE(S -T ) of complexes 1-3 are summarized in table 3. The
1
1
energy gaps between S and T level of complexes 1-3 are small (0.076-0.105 eV), which
1
1
provide further evidence to prove that complexes1-3 exhibit TADF [19].
According to the calculated frontier orbitals shown in figure 3, for complexes 1-3, the
contribution from the Cu, halogen and ligand to the hole distribution is 5, 35, 33; 5, 23, 14; 90,
4
2 and 53%, respectively. The electron distribution is confined to the phenyl rings of
1
0

diphenylphosphine and dimethylphenyl rings in dpnp. These indicate that the luminescence
arises from the MLCT, XLCT and intraligand transitions. Compared with complexes 2 and 3,
MLCT and XLCT transitions for complex 1 are much weaker, intraligand charge transfer
dominates emissive state for complex 1. We speculated that halogens and structures of
complexes including intermolecular interactions are the reasons for this difference. We found
that the lifetimes of luminescence in the solid state at 298 K for 1-3 (13.9-38.1 μs) are 2 orders of
magnitude shorter than those at 77 K (3954-7457 μs), which is also consistent with TADF.
3
.4. Thermal properties
Since good thermal stabilities of the complexes are important for OLED applications, the onset
decomposition temperatures (T ) of complexes 1-3 were determined by thermogravimetric
dec
analysis (TGA) under a stream of nitrogen. From the onset of the TGA curves (figure 5), all
complexes show good thermal stabilities with their Tdec values ranging from 372 to 395 °C. A
sharp one-step weight loss for all the complexes of ca. 71~82% was observed between 395 and
6
45 °C, which can be ascribed to the removal of dpnp ligand. These data render the materials
suitable for the fabrication of OLEDs by using the vacuum thermal deposition method.
4
. Conclusion
A series of three-coordinate dinuclear copper halide complexes 1-3were synthesized. These
complexes exhibit blue emission in the solid state at room temperature and have peak emission
wavelengths at 483-487 nm. Small S –T energy gaps in the solid state indicate that the emission
1
1
occurred from a thermally activated excited singlet state at ambient temperature. The low
emission quantum yields (< 0.01%) are attributed to the poor rigid environment around the
copper center, which results in radiationless deactivations. The introduction of more rigid ligands
to the Cu(I) complexes is in progress.
1
1

Acknowledgements
This work was supported by the National Natural Science Foundation of China [grant number
2
2
1671061]; Natural Science Foundation of Hubei Province of China [grant number
013CFA087]; Hubei Province High-End Talent Training Program and the Natural Science
Fund for Creative Research Groups of Hubei Province of China [grant number 2014CFA015].
W.-Y.W. acknowledges the financial support from the Areas of Excellence Scheme, University
Grants Committee of HKSAR, China (AoE/P-03/08) and the Hong Kong Polytechnic University.
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1
5

1
2
3
Figure 1. ORTEP diagrams of complexes 1-3.
1
6

Figure 2. Absorption spectra of complexes 1-3 and dpnp in CH Cl at 298K. The inset shows a
2
2
magnified view of the absorption edges.
1
7

HOMO E=5.024656 eV
LUMO E= 0.943568 eV
1
HOMO E=4.940608 eV
2
LUMO E= 0.828512 eV
LUMO E= 0.892432 eV
HOMO E=4.976784 eV
3
Figure 3. Molecular orbitals of complexes 1-3 as calculated by DFT.
1
8

a
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
400
500
600
700
800
Wavelength (nm)
b
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
400
500
600
700
800
Wavelength (nm)
Figure 4. Normalized emission spectra of complexes 1-3 in the solid state at (a) 298 K and (b)
7 K. λexc = 417 nm.
7
1
9

1
2
3
1
00
8
6
4
2
0
0
0
0
0
0
100 200 300 400 500 600 700 800
o
Temperature ( C)
Figure 5. TGA traces of complexes 1-3.
2
0

Table 1. Crystallographic data and details for 1-3.
• 2CH Cl
1
2
3
2
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C H I Cu N P •2CH Cl
C H Br Cu N P
C H Cl Cu N P
2 2
6
4
56 2
2
2
2
2
2
64 56
2
2
2
2
64 56
2
2
1465.80
173(2)
1201.94
1113.09
301(2)
173(2)
0.71073
0.71073
0.71073
Monoclinic
C2/c
Monoclinic
P2(1)/n
16.513(2)
9.3929(11)
19.211(3)
2806.9(6)
2
Monoclinic
P2(1)/n
16.357(7)
9.267(4)
19.041(9)
2711(2)
2
23.441(3)
14.0826(17)
19.019(2)
6223.7(14)
4
b (Å)
c (Å)
V (Å3)
Z
-
3
ρ (g cm )
1.564
1.422
1.364
-
1
μ (mm )
1.940
2.279
0.985
F (0 0 0)
2928
1224
1152
θ range for data collection (°)
Index ranges
1.691 to 24.736
2.823 to 27.569
21 ≤ h ≤ 21
9 ≤ k ≤ 12
2.278 to 27.529
18 ≤ h ≤ 21
12 ≤ k ≤ 12
24 ≤ l ≤ 24
21 ≤ h ≤ 27


16 ≤ k ≤ 16
22 ≤ l ≤ 22
24 ≤ l ≤ 24
Independent reflections
Completeness to θ = 25.242°
Max. and min. transmission
Gof
5302 [R(int)=0.0890]
99.6%
6453 [R(int)=0.0371]
99.7%
6213 [R(int)=0.0217]
99.7%
0.7451 and 0.5863
1.039
0.796 and 0.727
1.018
0.7456 and 0.6238
1.022
Final R indices [I> 2σ(I)]
R1= 0.0740
R1= 0.0414
R1= 0.0309
wR = 0.1569
wR = 0.1059
wR = 0.0818
2
2
2
R (all data)
R1= 0.1515
R1= 0.0679
R1= 0.0387
wR = 0.1817
wR = 0.1196
wR = 0.0864
2
2
2
Max/min (e Å3)
0.824 and 1.535
0.607 and 0.933
0.721 and 0.376
2
1

Table 2. Selected bond lengths (Å) and angles (°) for complexes 1-3.
Complex
1• 2CH Cl
2
3
2
2
CuX
2.454(7), 2.455(6)
.628(7), 2.690(7)
2.3909(5), 2.4168(6)
2.2907(11), 2.3068(9)
2
CuP
2.176(7), 2.232(8)
2.1919(8)
2.9200(8)
2.1739(10)
2.8615(13)
Cu···Cu
2.859(11), 2.690(7),
2
.462(11)
XCuX
CuXCu
PCuX
112.2(2), 114.4(2)
67.3(2), 57.8(2)
105.203(19)
103.02(3)
74.796(19)
76.98(3)
128.8(3), 115.7(3)
126.16(3), 127.63(3)
126.77(3), 129.29(3)
1
18.7(3), 125.1(3)
2
2

Table 3. Photophysical data of complexes 1-3 in the solid state.
λmax (nm)a
98 K
τ (μs)b
Фc
S1 (eV)d T1 (eV)d ΔE(S -T ) (eV)
d
1
1
2
77 K 298 K
77 K
298 K
1
2
3
483
487
487
502
507
507
13.9
29.0
38.1
b
3954
7457
6733
< 0.01
< 0.01
< 0.01
2.567
2.551
2.546
2.470
2.446
2.470
0.097
0.105
0.076
a
c
Emission peak wavelength. Emission lifetime. Experimental errors are ± 5%. Absolute emission
d
quantum in the solid state. Experimental errors are ± 5%. Determined results (S and T energy
1
1
levels, and energy gap between S and T ) obtained from the emission spectra at 77 K and 298 K.
1
1
2
3

Graphical abstract
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
Ph
Ph
Ph
X
X
P
Cu
Cu
P
Ph
2
NPh2
Ph N
1
2
3
X= I
X= Br
X= Cl
400
500
600
700
800
Wavelength (nm)
2
4