Synthesis, structures and aggregation-induced emissive properties of copper(I) complexes with 1H-imidazo[4,5-f][1,10]phenanthroline derivative and diphosphine as ligands

Article abstract of DOI:10.1016/j.ica.2015.05.019

Abstract Reaction of 4-bromo-2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol (BIPP), chelating diphosphine ligands and [Cu(MeCN)₄]ClO₄ afforded five mononuclear [Cu(BIPP)(PP)]ClO₄ (PP = dppe, 1; dppp, 2; bdpp, 3; POP, 4; xantphos, 5) complexes with good phosphorescent emission in the solid state. All the complexes are characterized by elemental analyses, electrospray Ionization mass spectra, ¹H and ³¹P NMR spectra and X-ray single crystallography. The photoluminescence quantum yields of complexes 1-5 are from less than 0.010 to 0.262 in the solid state under air atmosphere, which increase with the increasing rigidity of diphosphine ligands and the increasing strength of intermolecular and intramolecular π?π interactions. The aggregation-induced emission of complexes 4 and 5 at room temperature was investigated.

Full text of DOI:10.1016/j.ica.2015.05.019

Accepted Manuscript
Synthesis, Structures and Aggregation-Induced Emissive Properties of Cop-
per(I) Complexes with 1H-imidazo[4,5-f][1,10]phenanthroline Derivative and
Diphosphine as Ligands
Rong Liu, Miao-Miao Huang, Xi-Xi Yao, Hao-Huai Li, Feng-Lei Yang, Xiu-
Ling Li
PII:
S0020-1693(15)00281-9
http://dx.doi.org/10.1016/j.ica.2015.05.019
ICA 16549
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
19 April 2015
22 May 2015
22 May 2015
Please cite this article as: R. Liu, M-M. Huang, X-X. Yao, H-H. Li, F-L. Yang, X-L. Li, Synthesis, Structures and
Aggregation-Induced Emissive Properties of Copper(I) Complexes with 1H-imidazo[4,5-f][1,10]phenanthroline
Derivative and Diphosphine as Ligands, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.
2
015.05.019
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Synthesis, Structures and Aggregation-Induced Emissive Properties of Copper(I) Complexes with
H-imidazo[4,5-f][1,10]phenanthroline Derivative and Diphosphine as Ligands
1
Rong Liu, Miao-Miao Huang, Xi-Xi Yao, Hao-Huai Li, Feng-Lei Yang, Xiu-Ling Li*
School of Chemistry and Chemical Engineering & Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University,
Xuzhou, Jiangsu 221116, China
*
Corresponding author: E-mail: lxl@jsnu.edu.cn
Abstract
Reaction of 4-bromo-2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol (BIPP), chelating diphosphine
ligands and [Cu(MeCN)
4
]ClO
4
afforded five mononuclear [Cu(BIPP)(PP)]ClO (PP = dppe, 1; dppp, 2;
4
bdpp, 3; POP, 4; xantphos, 5) complexes with good phosphorescent emission in the solid state. All the
1
31
complexes are characterized by elemental analyses, electrospray Ionization mass spectra, H and P NMR
spectra and X-ray single crystallography. The photoluminescence quantum yields of complexes 1−5 are from
0.0067 to 0.2616 in the solid state under air atmosphere, which increase with the increasing rigidity of
diphosphine ligands and the increasing strength of intermolecular and intramolecular π⋅⋅⋅π interactions. The
aggregation-induced emission of complexes 4 and 5 at room temperature was investigated.
Keywords: Copper(I) complexes, 1H-imidazo[4,5-f][1,10]phenanthroline derivative, crystal structure,
aggregation-induced emission
1. Introduction
Luminescent materials with aggregation-induced emission (AIE) have attracted much attention since 2001
and have been developed into a novel class of fluorescent turn-on biosensors with superior sensitivity [1−3].
Most AIE systems focused on organic luminescent molecules [1−5], on the other hand, the heavy-metal
1

6
8
10
complexes that possess d [6−18], d [19−22], and d electron configurations showed strong spin−orbit
coupling, resulting in efficient phosphorescence emission. The relative long emission lifetimes of
phosphorescence provide these heavy-metal complexes a chance as bioimaging probes to eliminate
autofluorescence from biological sample through time-gated technique. Aggregation-induced
phosphorescence emission (AIPE) provides a good path to active the luminescent behaviour of the metal
complexes with twisting ligands in the solution. However, most reported AIPE systems were focused on
Ir(III) [7−18], Pt(II) [19−22], and Au(I) systems [23−29]. The limited availability, toxicity and the prices of
these systems will limit their wide application in bioimaging probes. Therefore, it is necessary and urgent to
explore, design and synthesize noble-metal-free AIPE complexes. In this purpose, copper(I) complexes
containing diimine and diphosphine ligands appear to be a good alternative [30].
Cu(I)-diimine-phosphine systems in luminescent family have received more and more attention in the past
36 years since the early work of McMilin’s group was reported [30−37]. It was found that some
Cu(I)-diimine-diphosphine complexes showed intense phosphorescent emission behavior in the solid state,
but they were non-emissive or weakly emissive in the fluid environment due to the emission cancellation
resulting from oxygen and intramolecular motions including rotation and vibration, especially within the
twisted diphosphine ligands, which served as a relaxation channel for the excited states to deactivate [30, 34d,
35c]. Therefore, AIE phenomenon provides a new way for the application of Cu(I)-diimine-diphosphine
systems as ‘‘turn-on’’ luminescent materials by taking the advantage of luminogenic aggregation through
restriction of intramolecular motion in the aggregated state. We reported a series of mononuclear and
binuclear Cu(I)-diimine-diphosphine complexes with good phosphorescent properties at room temperature
[
30, 34d, 35c], and the binuclear [Cu
2
(BrphenBr)
2
(Ph
2
P(CH
2
)
n
PPh
2
)
2
](ClO
4
)
2
(BrphenBr
=
3,8-dibromo-1,10-phenanthroline) complexes exhibited good AIPE behavior and were further used for living
2

cell
imaging
successfully
[30].
As
a
phenanthroline
(phen)
derivative,
4
-bromo-2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol (BIPP) not only possesses the chelating
phenanthroline (phen) coordination sites, but also possesses the possible intramolecular hydrogen bond
between hydroxyl group and nitrogen atom of the imidazole ring. Such intramolecular hydrogen bond
increases the rigidity of BIPP, which restricts the intramolecular rotations, and thus might improve the
luminescence behavior of its Cu(I) complexes. As our continuous effort to exploit the
Cu(I)-diimine-diphosphine luminescent systems, herein we report the syntheses, structures and AIE
properties of a series of copper(I) complexes with BIPP and diphosphine as ligands.
Scheme 1. Synthetic routes to complexes 1−5.
2. Experimental Section
2.1. Materials and reagents
The reagents 5,6-diamino-1,10-phenanthroline (dap), 1,2-bis(diphenylphosphino)ethane (dppe),
1,3-bis(diphenylphosphino)propane
(dppp),
1,2-bis(diphenylphosphino)benzene
(bdpp),
bis[(2-diphenylphosphino)phenyl] ether (POP) and 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene
3

(
3
4 4
xantphos) were commercially available and were used without further purification. [Cu(CH CN) ]ClO was
prepared by the published method [38]. All solvents were purified and distilled by suitable procedures before
use. All other reagents were of analytical grade and were used as received. All samples used for studying the
spectra and properties are powders from crystals which were milled and then dried under infrared light.
2.2. Instruments
1
31
H and P NMR spectra were obtained from the solutions in DMSO-d
6
using a Bruker-400 spectrometer
with Me Si as an internal standard and 85% H PO as an external standard, respectively (see Figures S1−S11).
4
3
4
UV-Vis absorption spectra were determined on a Purkinje General TU-1901 UV-vis spectrophotometer.
Electrospray Ionization Mass Spectra (ESI-MS) analyses were carried out with a Bruker-micro-TOFQ-MS
analyzer using a DCM/methanol mixture for the mobile phase. Elemental analyses (C, H, and N) were carried
out on a Perkin−Elmer model 240C elemental analyzer. Steady-state excitation and emission spectra were
obtained with a Hitachi F4500 fluorescence spectrophotometer. Emission lifetimes were measured on an
Edinburgh FLS920 fluorescence spectrometer under air atmosphere. The photoluminescence yields in the
solid state under air atmosphere at room temperature is defined as the ratio of number of photons emitted to
the number of photons absorbed by the system and was measured under air with pure solid and an empty
sphere on an Edinburgh analytical instrument FLS920 with an integrating sphere established by Wrighton et
al [39]. The excitation wavelengths used for emission lifetimes and photoluminescence yields were 355, 350,
350, 330 and 330 nm, respectively, for complexes 1−5. The emission wavelengths used for emission lifetimes
were 601, 570, 531, 552 and 544 nm, for complexes 1−5. The data of emission lifetimes were fitted basing on
−x/t
0
the single exponential fitting mode. The exponential function used for fitting the data was y = y + A . The
Chi-squares are 0.98549, 0.99813, 0.99705, 0.99786 and 0.99799, respectively, for complexes 1−5. The
4

emission wavelength range used for determining photoluminescence yields were 340−800 nm, 335−800 nm,
335−800 nm, 315−800 nm and 315−800 nm, for complexes 1−5, respectively.
2.3. Single Crystal X-Ray Determination
Suitable single crystals were picked from the hexane/DCM systems in diffusive equilibrium, and then they
2
were quickly wrapped in epoxy resin or petroleum jelly and transferred to a stream of cold N on Bruker
Smart APEX II diffractometer fitted with a CCD-type area detector. The data were collected using
graphite-monochromatised Mo-Kα radiation (λ = 0.71073 Å). The CrystalClear software package 2009,
Bruker SAINT was used for data reduction [40, 41]. The absorption corrections were applied using SADABS
supplied by Bruker [42]. In all cases the structures were solved by direct methods and refined by the
2
full-matrix least-squares method on F data using the SHELXTL–97 program package [43]. Heavy atoms
were found from the E-map, and the remaining non-hydrogen atoms were located in subsequent Fourier maps.
Non-hydrogen atoms of complexes 1−5 were refined with anisotropic thermal parameters, while hydrogen
atoms were generated geometrically and refined with isotropic thermal parameters riding on those of the
parent atoms.
2.4. Preparation of BIPP and complexes
All reactions for complexes were carried out under anaerobic conditions using standard Schlenk techniques
under an atmosphere of dry argon at room temperature.
2.4.1. BIPP
BIPP was prepared by a modified procedure [44, 45]. The mixture of 5-bromosalicylaldehyde (1.00 mmol,
1
equiv), dap (1.00 mmol, 1 equiv), five drops of hydrogen peroxide H
2
O
2
(30% aqueous) and three drops of
5

−1
HOAc (2.00 mol⋅L ) was refluxed in ethanol (20 mL) for 12 h. After completion of the reaction, the mixture
was cooled to room temperature and the solvent was concentrated in vacuo. After filtration, the yellow
1
desired precipitate was washed by cold ethanol and dried in vacuo. Yield: 73%. H NMR (400 MHz,
DMSO-d
6
, δ, ppm): 13.997 (s, 1H, NH), 12.852 (s, 1H, OH), 9.064 (br, 2H), 8.879 (d, J = 7.6 Hz, 2H), 8.370
(
d, J = 2.4 Hz, 1H), 7.849 (s, 2H), 7.533 (dd, J = 8.8 Hz, J′ = 2.0 Hz, 1H), 7.061 (d, J = 8.4 Hz, 1H).
2
.4.2. [Cu(bipp)(dppe)]ClO
CN) ]ClO (32.6 mg, 0.100 mmol) was added to a degassed DCM solution (about 10 mL) of BIPP
39.1 mg, 0.100 mmol) and dppe (40.6 mg, 98%, 0.100 mmol). A pale yellow suspension was obtained
4 2 2 2 2
⋅CH Cl (1⋅CH Cl )
[
(
Cu(CH
3
4
4
quickly and then stirred for 2 h at room temperature. After filtration, layering n-hexane dropwise onto the
DCM solution carefully produced the product as pale yellow crystals a few weeks later in 52% yield (53.4
mg). Anal. Calcd for C45
N 5.81. ESI-MS (m/z): 853.0740 [Cu(BIPP)(dppe)] (calcd 853.0747). H NMR (400 MHz, DMSO-d
ppm): 14.100 (s, 1H, NH), 12.462 (s, 1H, OH), 9.151 (d, J = 6.4 Hz, 2H), 8.958 (d, J = 4.4 Hz, 2H), 8.122 (br,
4 5 2
H35BrClCuN O P (1) (950.025): C 56.84, H 3.71, N 5.90. Found: C 56.57, H 3.65,
+
1
6
, δ,
31
3
H), 7.544−7.344 (m, 19H), 7.271−7.098 (m, 2H), 6.654 (s, 1H), 2.826 (t, 4H, J = 6.2 Hz, PCH ). P NMR
2
1
{
H NMR} (400 MHz, DMSO-d
.4.3. [Cu(bipp)(dppp)]ClO ⋅2CH
This compound was prepared by the same synthetic procedure as that of 1 except for using dppp instead of
dppe. Color: pale yellow. Yield: 81%. Anal. Calcd for C46 37BrClCuN (2) (964.041): C 57.26, H 3.87,
N 5.81. Found: C 57.03, H 3.92, N 5.74. ESI-MS (m/z): 867.094 [Cu(BIPP)(dppp)] (calcd 867.090). H
NMR (400 MHz, DMSO-d , δ, ppm): 14.164 (s, 1H, NH), 12.477 (s, 1H, OH), 9.200−9.140 (m, 4H),
.238−8.137 (m, 3H), 7.383−7.185 (m, 21H), 6.757 (br, 1H), 2.900 (br, 4H, PCH ), 2.095 (m, 2H, PCH
6
, δ, ppm): −4.081.
2
4
3
CN (2⋅2CH CN).
3
H
4 5 2
O P
+
1
6
8
2
2
CH
2
).
3
1
1
6
P NMR { H NMR} (400 MHz, DMSO-d , δ, ppm): −12.511.
6

2.4.4. [Cu(bipp)(bdpp)]ClO
4 2 2 2 2
⋅CH Cl (3⋅CH Cl )
This compound was prepared by the same synthetic procedure as that of 1 except for using bdpp instead of
dppe. Color: orange yellow. Yield: 35%. Anal. Calcd for C49
H35BrClCuN
4
O
5
P
2
(3) (998.025): C 58.92, H
+
1
3
.53, N 5.61. Found: C 59.03, H 3.61, N 5.68. ESI-MS (m/z): 901.067 [Cu(BIPP)(bdpp)] (calcd 901.075). H
NMR (400 MHz, DMSO-d , δ, ppm): 14.042 (s, 1H, NH), 12.314 (s, 1H, OH), 9.069 (s, 2H), 8.640 (s, 1H),
6
8
7
2
.592 (s, 1H), 8.044−7.993 (m, 3H), 7.819−7.797 (m, 2H), 7.650−7.628 (m, 2H), 7.513−7.422 (m, 12H),
31
1
.343−7.137 (m, 8H), 6.998−6.539 (m, 2H). P NMR { H NMR} (400 MHz, DMSO-d
.4.5. [Cu(bipp)(POP)]ClO ⋅2.5CH Cl (4⋅2.5CH Cl
This compound was prepared by the same synthetic procedure as that of 1 except for using POP instead of
dppe. Color: yellow. Yield: 73%. Anal. Calcd for C55 39BrClCuN (4) (1090.051): C 60.55, H 3.61, N
.14. Found: C 60.23, H 3.70, N 5.06. ESI-MS (m/z): 993.095 [Cu(BIPP)(POP)] (calcd 993.101). H NMR
400 MHz, DMSO-d , δ, ppm): 14.218 (s, 1H, NH), 12.504 (s, 1H, OH), 9.119 (d, J = 7.6 Hz, 2H), 8.883 (d,
J = 4.4 Hz, 2H), 8.373 (s, 1H), 7.945 (s, 2H), 7.512−6.976 (m, 28H), 6.701−6.663 (m, 2H). P NMR { H
NMR} (400 MHz, DMSO-d , δ, ppm): −11.667.
.4.6. [Cu(bipp)(xantphos)]ClO ⋅2CH Cl (5⋅2CH
This compound was prepared by the same synthetic procedure as that of 1 except for using xantphos instead
of dppe. Color: yellow. Yield: 53%. Anal. Calcd for C58 43BrClCuN (5) (1130.08): C 61.59, H 3.83, N
.96. Found: C 61.72, H 3.81, N 4.89. ESI-MS (m/z): 1033.11 [Cu(BIPP)(xantphos)] (calcd 1033.13). H
6
, δ, ppm): −3.725.
4
2
2
2
2
)
H
4
O
P
6 2
+
1
5
(
6
31
1
6
2
4
2
2
2 2
Cl )
H
4 6 2
O P
+
1
4
NMR (400 MHz, DMSO-d , δ, ppm): 14.236 (s, 1H, NH), 12.466 (s, 1H, OH), 9.108 (d, J = 8.0 Hz, 2H),
6
8.546 (d, J = 4.4 Hz, 2H), 8.389 (s, 1H), 7.940−7.889 (m, 4H), 7.588−7.522 (m, 1H), 7.314−7.234 (m, 6H),
3
1
1
7
.138−7.017 (m, 9H), 6.942−6.930 (m, 8H), 6.598−6.580 (m, 2H), 1.775 (s, 6H, CH
, δ, ppm): −12.822.
3
). P NMR { H NMR}
(
400 MHz, DMSO-d
6
7

3. Results and discussion
3.1. Syntheses of the ligand BIPP and the Cu(I) complexes
Biswas’s group reported the synthesis of 2-substituted benzimidazoles at ambient temperature from various
alkyl and aryl aldehydes using 3,6-di(pyridine-2-yl)-1,2,4,5-tetrazine (pytz) as catalyst and aerial oxygen as
oxidants under visible light irradiation [44]. Chen et al synthesized BIPP by refluxing the mixture of
5
,6-diamino-1,10-phenanthroline (dap) and 5-bromosalicylaldehyd in ethanol for 12h [45]. Here, BIPP was
prepared by a modified procedure using dap and 5-bromosalicylalde as starting materials, hydrogen peroxide
) as the oxidant and HOAc as the catalyst without light irradiation. Complexes 1−5 (Scheme 1) were
synthesized in good yields by reaction of an equimolar BIPP, diphosphine ligands (dppe =
2 2
(H O
1
1
9
,2-bis(diphenylphosphino)ethane, dppp
,2-bis(diphenylphosphino)benzene, POP
=
1,3-bis(diphenylphosphino)propane (dppp), bdpp
bis[(2-diphenylphosphino)phenyl] ether, xantphos
=
=
=
3 4 4
,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene) and [Cu(CH CN) ]ClO in dichloromethane (DCM)
solution. All the complexes crystallized with solvent molecules. Once formed, they are stable to air and
moisture in the solid state.
3.2. Crystallographic studies
The corresponding crystallographic data and selected refinement details of all the complexes are presented
in Table 1. Selected bond lengths and angles are listed in Table 2. ORTEP drawings of the cations for
complexes 1−5 are depicted in Figures 1−5, respectively. All the Cu(I) centers in complexes 1−5 adopt
distorted tetrahedral coordinated geometries completed by N
2
2
P donor atoms with two N atoms from BIPP
and two P atoms from chelating diphosphine ligands. Such distortion mainly originates from the rigid BIPP
ligand, which restricts the N−Cu−N bite angles to 81.62(11)°, 80.60(17)°, 82.08(14)°, 80.93(15)° and
81.10(15)°, and 80.52(10)° for complexes 1−5, respectively. The corresponding P−Cu−P angles are 90.61(4)°,
8

103.08(6)°, 90.43(5)°, 113.00(5)° and 114.97(5)°, and 121.55(3)° for complexes 1−5, respectively, showing
much variation to each other with different diphosphine ligands. The dihedral angles between N−Cu−N and
P−Cu−P planes are 86.61(8)°, 86.93(12)°, 76.81(12)°, 85.19(11)° and 85.64(11)°, and 80.76(8) for complexes
1−5, respectively. Both the larger P−Cu−P angles and the smaller dihedral angles between N−Cu−N and
P−Cu−P planes imply that the PPh groups in the corresponding complexes are sterically much closer to the
2
BIPP ligands [30, 37g].
2 2 3 2 2 2 2 2 2
Table 1. Crystallographic data and select refinement details for 1⋅CH Cl , 2⋅2CH CN, and 3⋅CH Cl , 4⋅2.5CH Cl and 5⋅2CH Cl .
1
⋅CH
2
Cl
2
2⋅2CH
3
CN
3⋅CH
2
Cl
2
4⋅2.5CH
2
Cl
2
2 2
5⋅2CH Cl
Empirical formula
Formula weight
T (K)
C
46
H
37BrCl
3
CuN
4
O
5
P
2
C
50
H
43BrClCuN
6
O
5
P
2
C
50
H
37BrCl
3
CuN
4
O
5
P
2
C
57.5
H
44BrCl
6
CuN
4
O
6
P
2
C
60
H
47BrCl CuN O P P
5 4 6 2 2
1037.54
150(2)
0.71073
triclinic
P−1
1048.74
150(2)
1085.58
150(2)
1305.06
150(2)
1302.66
150(2)
0.71073
triclinic
P−1
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P2(1)/c
13.0541(4)
13.6044(5)
15.3763(5)
106.348(2)
111.353(2)
104.241(2)
17.7043(5)
13.7292(4)
21.2556(6)
11.2997(4)
17.9383(7)
24.5882(8)
20.2683(3)
15.6090(3)
39.8830(6)
12.2897(3)
14.9638(4)
17.2244(4)
b (Å)
c (Å)
α (°)
105.9040(10)
109.7680(10)
97.3010(10)
2781.01(12)
2
β (°)
107.899(2)
115.968(2)
117.5540(10)
γ (°)
3
V (Å )
2247.26(13)
2
4916.4(2)
4
4480.8(3)
4
11186.5(3)
8
Z
−
3
)
Dcalc (mg⋅m
1.533
1.417
1.609
1.550
1.556
–
1
µ (mm )
1.676
1.429
1.685
1.504
1.466
F(000)
1052
2144
2200
5287
1324
Reflections collected
33095
7875
35993
6891
34092
7860
86057
19660
15736
19660/12/1416
1.063
39921
Independent reflections
Reflections with I > 2σ(I)
Data/restraints/parameters
9734
6295
4711
6176
8802
7875/0/559
1.045
6891/32/619
1.013
7860/0/590
1.027
9734/0/712
1.030
2
Goodness-of-fit (GOF) on F
Final R indices [I > 2σ(I)]
0.0483
0.1353
0.0621
0.1462
0.0578
0.1512
0.0907
0.1759
0.0578
0.1454
0.0784
0.1601
0.0655
0.1603
0.0834
0.1725
0.0497
wR
R indices (all data)
wR (all data)
2
[I > 2σ(I)]
0.1408
0.0544
2
0.1456
9

2 2
Fig. 1. ORTEP drawings of complex 1⋅CH Cl with the atom labelling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity.
(d(O1−H1⋅⋅⋅N3) = 2.564 Å, ∠ O1−H1⋅⋅⋅N3 = 149°)
2 2 3 2 2 2 2 2 2
Table 2. Selected bond lengths (Å) and angles (º) for 1⋅CH Cl , 2⋅2CH CN, and 3⋅CH Cl , 4⋅2.5CH Cl and 5⋅2CH Cl .
1
⋅CH
2
Cl
2
2⋅2CH
3
CN
3⋅CH
2
Cl
2
4⋅2.5CH
2
Cl
2
2 2
5⋅2CH Cl
Cu1−N1
2.044(3)
2.051(3)
2.071(4)
2.048(4)
2.021(4)
2.049(4)
2.091(4)
2.044(4)
2.058(4)
2.079(4)
2.211(1)
2.304(1)
2.307(1)
2.211(1)
2.105(3)
2.052(3)
Cu1−N2
Cu2−N5
Cu2−N6
Cu1−P1
2.243(1)
2.244(1)
2.239(2)
2.221(2)
2.245(1)
2.228(1)
2.314(1)
2.250(1)
Cu1−P2
Cu2−P3
Cu2−P4
N1−Cu1−N2
N5−Cu2−N6
P1−Cu1−P2
P3−Cu2−P4
N1−Cu1−P1
N1−Cu1−P2
N2−Cu1−P1
N2−Cu1−P2
N5−Cu2−P3
N5−Cu2−P4
N6−Cu2−P3
N6−Cu2−P4
81.62(11)
90.61(4)
80.60(17)
103.08(6)
82.08(14)
90.43(5)
80.93(15)
81.10(15)
113.00(5)
114.97(5)
133.77(11)
97.67(11)
122.06(11)
102.28(11)
101.57(11)
120.57(11)
97.81(11)
133.16(11)
80.52(10)
121.55(3)
122.88(9)
123.11(9)
124.80(9)
117.81(9)
115.88(13)
129.34(13)
105.25(13)
119.94(13)
115.01(11)
134.18(11)
125.29(12)
114.69(11)
96.13(8)
124.16(8)
109.10(8)
117.14(8)
10

Fig. 2. ORTEP drawings of complex 2⋅2CH
3
CN with the atom labelling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity.
(d(O1−H1⋅⋅⋅N4) = 2.613 Å, ∠ O1−H1⋅⋅⋅N4 = 146°)
2 2
Fig. 3. ORTEP drawings of complex 3⋅CH Cl with the atom labelling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity.
(d(O1−H1⋅⋅⋅N4) = 2.597 Å, ∠ O1−H1⋅⋅⋅N4 = 148°)
11

2 2
Fig. 4. ORTEP drawings of two asymmetric cations of complex 4⋅2.5CH Cl with the atom labelling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms
and some phenyl rings are omitted for clarity. (d(O1−H1⋅⋅⋅N3) = 2.641 Å, ∠ O1−H1⋅⋅⋅N3 = 148°; d(O3−H3⋅⋅⋅N8) = 2.648 Å, ∠ O3−H3⋅⋅⋅N8 = 148°)
2 2
Fig. 5. ORTEP drawings of complex 5⋅2CH Cl with the atom labelling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity.
(d(O1−H1⋅⋅⋅N4) = 2.602 Å, ∠ O1−H1⋅⋅⋅N4 = 148°)
12

The Cu−N and Cu−P bond distances fall in range of 2.021(4) − 2.105(3) Å and 2.211(1) − 2.314(1) Å,
respectively, which are comparable to those observed in other Cu(I)-diimine-diphosphine complexes [30,
32−37]. The average Cu−N distances are 2.048, 2.060, 2.035, 2.068 and 2.079 Å for complexes 1−5,
respectively, with the shortest average Cu−N distance occurring at complex 3 and the longest average
distance occurring at complex 5. While the average Cu−P bond lengths are 2.244, 2.230, 2.237, 2.258 and
2
.282 Å for complexes 1−5, respectively, with the shortest average Cu−P distance occurring at complex 1 and
the longest average distance occurring at complex 5. The longest Cu−N and Cu−P bond lengths for complex
among the series indicate that the largest repulsion between BIPP and diphosphine ligands occurs in
5
complex 5 because of the bulky xantphos. The ligand BIPP in each copper(I) cation keeps good coplanity
with dihedrals between phenyl ring and 1H-imidazo[4,5-f][1,10]phenanthroline plane being 3.6° for complex
1, 5.3° for complex 2, 7.0° for complex 3, 1.7° and 2.4° for complex 4, 3.8° for complex 5, respectively. In
addition, in all complexes, phenolic hydroxyl groups link with the N atoms through O−H⋅⋅⋅N hydrogen bonds
with O ⋅⋅⋅N distances in the range of 2.564 − 2.648 Å and O−H⋅⋅⋅N angles in the range of 146° − 149° (see
Figures 1−5 and Table S1). The N−H bonds in the imidazole rings link with perchlorate ions through
N−H⋅⋅⋅O hydrogen bonds with N ⋅⋅⋅O distances in the range of 2.830 − 2.882 Å and N−H⋅⋅⋅O angles in the
range of 156° − 171° (see Table S1). Such intramolecular hydrogen bonds improve the rigidity of BIPP.
13

Fig. 6. The cation dimer of complex 4 formed through intermolecular and intramolecular π⋅⋅⋅π interactions. (a) Ball-and-stick model (Most hydrogen atoms are
omitted for clarity. symmetry code for A: x, y + 1, z); (b) the space-fillings (C and H atoms of pop are shown with green color and those of BIPP are shown with
grey color for clarity).
Fig. 7. The cation dimer of complex 5 formed through intermolecular π⋅⋅⋅π interactions. (a) Ball-and-stick model (Most hydrogen atoms are omitted for clarity.
symmetry code for B: −x, −y + 1, −z + 1); (b) the space-fillings (C and H atoms of xantphos are shown with green color and those of BIPP are shown with grey color
for clarity).
14

On the other hand, as shown in Figures 6−7, Figures S12−S14 and Table S2, intermolecular π⋅⋅⋅π
interactions widely exist between BIPP molecules, leading to the formation of the cation dimers. Quadruple,
triple, quintuple, quintuple and quintuple intermolecular π⋅⋅⋅π interactions were observed in complexes 1−5,
respectively, between phenyl rings and phen rings, and between imidazole rings, with the distances between
ring centroids in the range of 3.458−3.781 Å. Furthermore, double intramolecular π⋅⋅⋅π interactions were
also observed between phen rings and phenyl rings of POP in complex 4 with the distances between ring
centroids in the range of 3.495−3.639 Å. The copper(I) centers can be more effectively protected by BIPP and
diphosphine ligands from the attack of oxygen and solvent molecules due to such intermolecular and
intramolecular π⋅⋅⋅π interactions along with the larger P−Cu−P angles and the smaller dihedral angles
between N−Cu−N and P−Cu−P planes. The well protected Cu(I) centers can also be seen from the
space-fillings of cation dimers of complexes 1−5 in Figures 6 and 7 and Figures S12−S14 (see supporting
information). The best protected Cu(I) centers are suggested to be in complexes 4 and 5. Such good
protection make complexes 1−5 are very stable to air and moisture in the solid state.
3
.3. Photophysical Properties
.3.1. Absorption spectra
3
Table 3. Photophysical data of complexes 1–5 at room temperature.
λ
em/nm
τem/µs
−
1
−1
compd
λ
abs/nm (ε/M cm ) (CH
2
Cl
2
)
Φ
em (solid)
(solid)
(solid)
1
2
3
4
5
229 (68400), 280 (60920), 339 (27480), 354 (24440), 428 (8520)
229 (69240), 280 (65800), 340 (29400), 354 (27080), 421 (8320)
230 (78160), 281 (66040), 339 (30200), 352 (26960), 431 (9640)
230 (78600), 280 (76080), 339 (33560), 352 (30960), 411 (9040)
230 (79280), 280 (85080), 340 (32520), 353 (30520), 411 (8840)
601
570
531
552
544
4.55±0.04
7.25±0.02
7.67±0.03
14.24±0.05
17.70±0.06
<1.0%
<1.0%
(12.4±1.0)%
(9.0±1.1)%
(26.2±1.0)%
15

Fig. 8. UV-vis absorption spectra of 1–5 in DCM at room temperature.
−5
−1
UV-vis absorption data of complexes 1−5 in DCM solutions with concentrations at 2.500 × 10 mol⋅L at
room temperature are summarized in Table 3, while the corresponding electronic absorption spectra are
depicted in Figure 8. The molar extinction coefficients are calculated basing on the UV-vis absorption spectra
−5
−5
−1
−5
of the solutions with 1.000 × 10 and 2.500 × 10 mol⋅L . The maximum absorbance of 2.500 × 10
−1
mol⋅L solutions are at about 2.000. Too low concentration results in the increase of the dissociation of the
complexes, and too high concentration won’t obey Beer-Lambert’s Law. For this series, the solutions obey
−5
−5
−1
Beer-Lambert’s Law with the concentration in the range of 1.000×10 −2.500×10 mol⋅L . All the
4
−1
−1
complexes display strong absorption peaks (molar extinction coefficient ε > 10 M cm ) with wavelengths
shorter than 360 nm that can be assigned to intraligand π→π* transitions of both BIPP and diphosphine
ligands. The lower-energy absorption bands with maximum wavelengths in the range of 411−431 nm and ε in
−1
−1
the range of 8320−9640 M cm are assigned to dπ(Cu)→π*(diimine) metal-to-ligand charge transfer
MLCT) transitions, mixing with some charge transfer character from diphosphine ligand to diimine ligands
within the cation. Such assignments base on the results of density functional theory (DFT) calculation of
(
16

complex [Cu(dmbpm)(POP)]BF
orbitals of [Cu(dmbpm)(POP)]BF
HOMO−1 were mainly centered on the copper and POP [46].
.3.2. Photoluminescence (PL) in the Solid State
4
(dmbpm = 4,4′-dimethyl-2,2′-bipyrimidine), which showed the frontier
4
, LUMO and LUMO+1 were located mainly at dmbpm, and HOMO and
3
The excitation and emission spectra of complexes 1−5 in the crystalline state were investigated at room
temperature (see Figure 9), and the corresponding spectral data, including emission wavelengths, emission
lifetimes, and the photoluminescence quantum yields in the solid state under air atmosphere are listed in
Table 3. Complexes 1−5 display moderate to intense emission bands with λmax = 601, 570, 531, 552 and 544
nm, respectively. The emission bands span a wide wavelength range resulting in rich emission color. The
3
microsecond range lifetimes are consistent with dπ(Cu)→π*(diimine) ( MLCT) transitions as the origin of
the emission bands [30, 34c, 35d]. The replacement flexible dppe, dppp and POP by more rigid diphosphine
ligands bdpp and xantphos leads to the obvious enhancement of emission quantum yields from 0.0067
(
complex 1), 0.0106 (complex 2), 0.0895 (complex 4) to 0.1239 (complex 3) and 0.2616 (complex 5). The
richer intermolecular and intramolecular π⋅⋅⋅π interactions in complex 4 along with a larger P−Cu−P bite
angle may play a key role for the enhancement of the luminescence behavior compared with complexes 1 and
2
since π⋅⋅⋅π interactions and large P−Cu−P bite angles provide good protection for the Cu(I) centers from the
attack of oxygen [30, 35c].
17

Fig. 9. The PL excited (left) and emission spectra of complexes 1−5 (right) in the solid state at room temperature.
3.3.3. Aggregation-Induced Emission
In pure DCM solutions, only was complex 5 observed with weak emission under the radiation at 365 nm in
air atmosphere, and all other complexes shows no obvious emission. The non-emissive behavior of
complexes 1−4 and the weak emission of complex 5 in DCM solutions are suggested to arise from the
luminescence quenching caused by oxygen and the active intramolecular motions (rotation and vibration) [1,
30, 47]. Both the very weak emission in the solution and intense luminescent behavior in the solid state
suggest that complexes 1−5 may show AIE behavior. Here, complexes 4 and 5 were selected for AIE studies.
In order to investigate their AIE attributes, different amounts of hexane, a poor solvent for complexes 4 and 5,
were added to the DCM solutions by defining the hexane volume fractions (f
h
) of 0−90% and keeping the
concentrations constant at 5.000× 10 mol⋅L . Figure 10 shows the AIE spectra of complexes 4 and 5 for
different f with the excitation wavelength at 330 nm with optical filter at 395 nm. The AIE luminescent
images of 4 and 5 with different f and those in the solid state under 365 nm radiation are shown in Figure 11.
−5
−1
h
h
18

h
No obvious emission in the DCM–hexane mixture with a hexane fraction (f ) less than 70% for complex 4
and 75% for complex 5, respectively, was observed. Raising the hexane content to 70% and 75% for
complexes 4 and 5 induces the complexes to aggregate obviously and leads to dramatic luminescence
enhancement (Figures 10 and 11). As shown in Figure 10, complexes 4 and 5 exhibit good AIE behavior with
the most intense emission appearing at f = 80% and 85%, respectively. Since complexes 4 and 5 were
h
insoluble in hexane, increasing the hexane fraction in the mixed solvent would change their existing forms
from a solution in DCM to the aggregated particles in the DCM/hexane mixed solvent, so enhanced emission
intensity was observed due to aggregation. The further addition of hexane to 85% for complex 4 and 90% for
complex 5, however, resulted in a lowering of the luminescence intensity, which may be attributed to an
increase of the particle size since the increase of the particle size would prevent the formation of the
well-disperse aggregation state and lead to the precipitation. Complexes 4 and 5 exhibit various AIE colors
changing from yellow-green to yellow. Similar AIE effect was also observed for the binuclear
[
2 2 2 2 n 2 2 4 2
Cu (BrphenBr) (Ph P(CH ) PPh ) ](ClO ) (BrphenBr = 3,8-dibromo-1,10-phenanthroline) complexes with
common features of twisted structures and freely rotatable peripheral aromatic moieties [30]. It's worth
mentioning that yellow-green AIE luminescence of complex 4 contrasts markedly with the yellow emission
in the solid state (see Figure 11), indicating that AIE colors depend on the different aggregation states
dramatically. Here, the restriction of intramolecular motion (RIM), which includes rotation and vibration, is
proposed to be the main cause for the AIE behavior of complexes 1−5.
19

Fig. 10. AIE spectra of 4 and 5 in DCM/hexane mixed solvents (up) and the change of peak intensity (down) with different f
h
with the excitation at 330 nm.
−5
−1
Fig. 11. AIE luminescent images of 4 and 5 in hexane-DCM mixed solvents with the concentration kept at 5.000 × 10 mol⋅L and luminescence images of
complexes 1−5 in the solid state radiated with an ultraviolet light at 365 nm.
20

4. Conclusions
Five mononuclear [Cu(BIPP)(PP)]ClO
4
complexes with good phosphorescent emission in the solid state were
synthesized and characterized. The photoluminescence quantum yields of complexes 1−5 in the solid state
under air atmosphere increase with the increasing rigidity of diphosphine ligands and the increasing strength
of intermolecular and intramolecular π⋅⋅⋅π interactions. Complexes 4 and 5 displayed good
aggregation-induced emission behaviour at room temperature.
Acknowledgements
This work is supported financially by the National Natural Science Foundation of China (21271091 and
21401086), the Major Basic Research Project of Natural Science Foundation of the Jiangsu Higher Education
Institutions (11KJA430009), and PAPD of Jiangsu Higher Education Institutions.
Appendix A. Supplementary material
CCDC 1046965−1046969 contains the supplementary crystallographic data for complexes 1⋅CH
⋅2CH CN, 3⋅CH Cl , 4⋅2.5CH Cl and 5⋅2CH Cl . These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre,
2 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
2 2
Cl ,
2
3
2
2
2
2
2
2
1
Supplementary data associated with this article can be found, in the online version, at ??????.
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24

Synthesis, Structures and Aggregation-Induced Emissive Properties of Copper(I) Complexes with
1H-imidazo[4,5-f][1,10]phenanthroline Derivative and Diphosphine as Ligands
Rong Liu, Miao-Miao Huang, Xi-Xi Yao, Hao-Huai Li, Feng-Lei Yang, Xiu-Ling Li*
4
Five mononuclear [Cu(BIPP)(PP)]ClO (PP = dppe, 1; dppp, 2; bdpp, 3; POP, 4; xantphos, 5) complexes with good
phosphorescent emission were synthesized. Their photoluminescence quantum yields in the solid state increase with the
increasing rigidity of diphosphine ligands and the increasing strength of intermolecular and intramolecular π⋅⋅⋅π interactions.
The aggregation-induced emission of complexes 4 and 5 was investigated.
25

Synthesis, Structures and Aggregation-Induced Emissive Properties of Copper(I)
Complexes with 1H-imidazo[4,5-f][1,10]phenanthroline Derivative and Diphosphine as
Ligands
Highlights
1
2
3
. Synthesized five Cu(I) complexes with good luminescence behaviour.
. Analysized why such complexes are stable to air and moisture from crystallography.
. Studied the luminescence lifetimes, quantum yields and aggregation-induced emission.
26