Synthesis, characterization, and photophysical properties of heteroleptic copper(I) complexes with functionalized 3-(2'-pyridyl)-1,2,4-triazole chelating ligands

Article abstract of DOI:10.1021/ic4002829

A new series of mononuclear copper(I) complexes (1-9) with functionalized 3-(2'-pyridyl)-1,2,4-triazole chelating ligands, as well as the halide and/or phosphine ancillary ligands, have been synthesized. Complexes 1-9 were fully characterized by elemental analysis, NMR spectroscopy, mass spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and X-ray crystallography (1-8). They adopt a distorted tetrahedral configuration, and are considerably air-stable in solid state and in solution. All these Cu(I) complexes display a comparatively weak low-energy absorption in CH₂Cl₂ solution, assigned to charge-transfer transitions with appreciable MLCT character, as supported by TD-DFT studies. Cu(I) halide complexes 1-4 each shows bright solid-state emission at room temperature, although they are nonemissive in fluid solutions, in which the emission markedly depends on the halide and the substituent on the 2-pyridyl ring. Complexes 5-9 bearing 2-pyridyl functionalized 1,2,4-triazole and phosphine exhibit good photoluminescence properties in solution and solid states at ambient temperature, which are well-modulated via the alteration of the auxiliary phosphine ligand and the structural modification of 3-(2'-pyridyl)-1,2,4- triazole. Interestingly, cationic complex 6 and neutral derivative 7 can readily be interconverted through the ring inversion of the 1,2,4-triazolyl regulated by the NH a? N^- transformation.

Full text of DOI:10.1021/ic4002829

Article
pubs.acs.org/IC
Synthesis, Characterization, and Photophysical Properties of
Heteroleptic Copper(I) Complexes with Functionalized 3‑(2′-Pyridyl)-
1,2,4-triazole Chelating Ligands
Jing-Lin Chen,*,†,‡ Xing-Fu Cao,† Jin-Yun Wang,*,‡ Li-Hua He,† Zong-Yong Liu,† He-Rui Wen,†
and Zhong-Ning Chen‡
†School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, People’s Republic
of China
‡State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, People’s Republic of China
S
* Supporting Information
ABSTRACT: A new series of mononuclear copper(I) complexes (1−
9) with functionalized 3-(2′-pyridyl)-1,2,4-triazole chelating ligands, as
well as the halide and/or phosphine ancillary ligands, have been
synthesized. Complexes 1−9 were fully characterized by elemental
analysis, NMR spectroscopy, mass spectroscopy, electronic absorption
spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and X-ray
crystallography (1−8). They adopt a distorted tetrahedral configuration,
and are considerably air-stable in solid state and in solution. All these Cu(I) complexes display a comparatively weak low-energy
absorption in CH2Cl2 solution, assigned to charge-transfer transitions with appreciable MLCT character, as supported by TD-
DFT studies. Cu(I) halide complexes 1−4 each shows bright solid-state emission at room temperature, although they are
nonemissive in fluid solutions, in which the emission markedly depends on the halide and the substituent on the 2-pyridyl ring.
Complexes 5−9 bearing 2-pyridyl functionalized 1,2,4-triazole and phosphine exhibit good photoluminescence properties in
solution and solid states at ambient temperature, which are well-modulated via the alteration of the auxiliary phosphine ligand
and the structural modification of 3-(2′-pyridyl)-1,2,4-triazole. Interestingly, cationic complex 6 and neutral derivative 7 can
readily be interconverted through the ring inversion of the 1,2,4-triazolyl regulated by the NH ↔ N− transformation.
emitters have been investigated.8 In 2005, Harkins and Peters
reported a dicopper(I) complex supported by a rigid, bulky
INTRODUCTION
■
There has been a rapidly growing interest in emissive
PNP ligand (PNP = bis(2-diisobutylphosphinophenyl)amide),
transition-metal complexes, because of their potential applica-
which exhibited an unusually high quantum yield and long-lived
tions in organic light-emitting devices (OLEDs), light-emitting
excited state.9 Recently, the OLED fabricated with the above
electrochemical cells (LECs), chemical sensors/probes, and
optimized analogue {(PNP-tBu)CuI}2 (PNP-tBu− = bis(2-
biological labeling.1 With a focus on developing various
diisobutylphosphino-4-tert-butylphenyl)amido) showed a 16%
luminous devices, great efforts have been devoted to the
external quantum efficiency.10 In 2011, Hashimoto and co-
design and synthesis of transition metal-based phosphors with
emission wavelengths in the entire visible spectral region,2
workers reported a series of highly emissive three-coordinate
copper(I) complexes Cu(dtpb)X (dtpb = 1,2-bis(o-
especially the luminophores based on late transition-metal
complexes. The most recognizable paradigms involve d6 and d8
ditolylphosphino)benzene; X = I, Br, Cl), in which a vapor-
deposited OLED doped with Cu(dtpb)Br exhibited a
complexes of the third-row transition series such as Os(II),
maximum external quantum efficiency of 21.3%.11
Ir(III), and Pt(II).3 However, because of the high cost and
limited availability of these noble metals, more and more
attention has been paid to the exploitation of inexpensive
alternatives over the past two decades.4 Copper(I) systems
currently have become an important class of luminescent metal
complexes, based on their relative abundance, low cost, and
ability to display the promising application perspectives in
optoelectronics.5 In this field, the phosphine-containing
copper(I) complexes are probably most widely studied,6
among which heteroleptic Cu(I) complexes with the bidentate
ligands (diimine and/or diphosphine) have attracted recent
interest,7 and a limited number of OLEDs doped with such
With respect to [Cu(N∧N)(P2)]+/0 system (N∧N = diimine,
P2 = diphosphine or two monophosphine),12 the highest
occupied molecular orbital (HOMO) has a dominant metal
d(Cu) character, probably mixed with some contribution of the
phosphine ligand, while the lowest unoccupied molecular
orbital (LUMO) is basically resident on the diimine ligand.
Thus, the emission corresponding to the lowest triplet excited
state is essentially ascribed to the metal-to-ligand charge
Received: February 3, 2013
© XXXX American Chemical Society
A
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transfer (3MLCT) transition, which is normally sensitive to
coordination environment and peripheral ligand. It is shown
that the use of sterically congested ligands forms a rigid
environment around the Cu(I) center, and hence effectively
suppresses the nonradiative processes caused by Jahn−Teller
distortion and ligand dissociation of emissive states as well as
solvent-induced exciplex formation.13 Furthermore, because of
the low oxidation potential of the Cu(I) core and the absence
of a higher-lying metal centered d−d state induced emission
quenching, Cu(I) complexes are thus able to yield efficient
emission and are highly desirable for the fabrication of both
OLEDs14 and LECs15 with relatively low cost, compared to
Ru(II), Os(II), Ir(III), and Pt(II) metal complexes. Another
important advantage of Cu(I) complexes, in comparison to the
late transition-metal complexes, is more environmentally
benign. It is worthy of note that ionic emissive species can be
utilized as the electronically active component of the
electroluminescent layers of LECs to generate efficient light
output.
Scheme 1. Structures of Mononuclear Cu(I) Complexes 1−9
complex 6 and neutral derivative 7 can be successfully achieved
via the ring inversion isomerism of the coordinated 1,2,4-
triazolyl modulated by the controllable NH ↔ N− trans-
formation. Complexes 6 and 7 show distinct photolumines-
cence properties in solution and in the solid state, in which
neutral derivative 7 displays a blue-shifted fluid emission and a
red-shifted solid-state emission, relative to the parent species 6.
In sharp contrast to the [Cu(N∧N)(P2)]+/0 species, neutral
heteroleptic complexes Cu(N∧N)(P)X (N∧N = diimine, P =
monophosphine, X = halogen or pseudo-halogen) have been
much less investigated,16 despite the fact that they should more
easily undergo the vacuum deposition process in the fabrication
of electroluminescence devices. In fact, only a limited number
of reports involving emissive properties of Cu(dipyrido[3,2,-
a:2′,3′-c]phenazine)(PPh3)I, Cu(N,N)(PR3)(NCS) (N,N =
phen, 2,2′-bpy, two py), Cu(6-cyano-2,2′-bipyridine)(PPh3)X
(X = I, Br), and Cu(2-{2-benzimidazoly}-6-methylpyridine)-
(PPh3)X (X = I, Br, Cl) complexes have been described.17
In pursuit of novel emissive Cu(I) complexes, structural
modification of commonly used ligands such as 2,2′-bipyridine
or phenanthroline is an effective approach, while another
alternative route involves the utilization of previously
unemployed ligands. Several studies on the coordination
chemistry of triazoles and their chelating derivatives have
been reported recently.18 The 1,2,3-triazole-based chelating
ligands have been employed most recently for the construction
of emissive Cu(I) complexes.19 Of 3,5-disubstituted-1,2,4-
triazole, 3-(2′-pyridyl)-1,2,4-triazoles have been used to
synthesize photoactive Ru(II), Os(II), Ir(III), and Pt(II)
metal complexes.20 However, to the best of our knowledge,
luminescent Cu(I) complexes bearing functionalized 3-(2′-
pyridyl)-1,2,4-triazole and phosphine ligands have not been
reported hitherto. Herein, we describe the synthesis, character-
ization, and photophysical properties of a novel class of
emissive heteroleptic copper(I) complexes with tailorable 3-(2′-
pyridyl)-1,2,4-triazole ligand (see Chart 1 and Scheme 1). It is
RESULTS AND DISCUSSION
■
Syntheses and Characterizations. Mononuclear copper-
(I) halide complexes 1−4 were first prepared by treatment of
cuprous halide with 2 equiv of PPh3 in CH2Cl2 solution,
followed by the addition of 1 equiv of 5-tert-butyl-3-(2-pyridyl)-
1H-1,2,4-triazole (bptzH) or 5-tert-butyl-3-(6-methyl-2-pyrid-
yl)-1H-1,2,4-triazole (bmptzH). Halide complexes 1−4 are
soluble in dimethylformamide (DMF) and dimethylsulfoxide
(DMSO), but only sparingly soluble in CH2Cl2, CHCl3, and
1
CH2ClCH2Cl. In the H NMR spectra of 1−4 in DMSO-d6,
besides the aromatic proton signals (δ 8.4−7.3 ppm) and the
C−H resonances from the tert-butyl at 1.3 ppm and the methyl
at 2.3 ppm as two singlet peaks, the characteristic N−H proton
of the 1,2,4-triazolyl occurs at ∼14.4 ppm as a broad singlet
peak, implying that the bmptzH and bptzH ligands coordinate
to the Cu(I) center as a neutral ligand without the cleavage of
the N−H bond, as revealed by X-ray crystallography. The
31P{1H} NMR spectra exhibit a broad singlet peak at −6.05,
−5.23, −4.69, and −7.91 ppm for 1−4, respectively, somewhat
varying with both the halide ligand and the substituent on the
2-pyridyl. For halide complexes 1−4, an intensive molecular
ionic peak fragment (m/z, 527 or 541, [M−X]+) is observed in
their ESI mass spectra.
Complexes 5 and 6 were prepared by reaction of
[Cu(PPh3)2(CH3CN)2](ClO4) with an equivalent amount of
ligand bptzH and 5-trifluoromethyl-3-(2-pyridyl)-1,2,4-triazole
(fptzH), respectively. Complexes 8 and 9 were accessible via
the reaction of [Cu(CH3CN)4](ClO4) with bptzH and
diphosphine (1,2-bis(diphenylphosphino)ethane (dppe) or
bis[2-(diphenylphosphino)phenyl]ether (DPEphos)) in a
1:1:1 molar ratio. Neutral complex 7 was accessed by reacting
[Cu(PPh3)2(CH3CN)2](ClO4) with 1 equiv of fptzH in the
presence of NaOH. Interestingly, complex 7 could be also
obtained by laying H2O over the acetone solution of 6 in
several days, suggesting that H2O perhaps promoted the N−H
bond cleavage. In addition, neutral complex 7 readily converted
back to cationic complex 6 upon the addition of slightly excess
40% HClO4 solution. In the 1H NMR spectra, the unique N−H
Chart 1
demonstrated that all these Cu(I) complexes with function-
alized 3-(2′-pyridyl)-1,2,4-triazole are considerably air-stable in
both solution and solid states, and they exhibit tunable emission
properties that are markedly influenced by the variation of the
ancillary ligand such as halide and phosphine as well as the
structural modification of 3-(2′-pyridyl)-1,2,4-triazole. Interest-
ingly, it is notable that the interconversion between cationic
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signals of the 1,2,4-triazole rings appear at 14.4−14.9 ppm as a
broad singlet peak for 5, 6, 8, and 9, indicating that bptzH and
fptzH are still a neutral chelate without the N−H bond
cleavage, as revealed by X-ray crystallography. Strikingly
different from the above-mentioned complexes, the character-
istic N−H proton signal of 7 derived from fptzH is not
observed in its 1H NMR spectrum, as a result of NH
deprotonation of the 1,2,4-triazolyl. In the 31P NMR spectra,
a broad singlet peak is observed at −0.19, −2.81, −1.11, −7.41,
and −13.53 ppm for 5−9, respectively, markedly depending on
both the phosphine ancillary ligand and the modification of 3-
(2′-pyridyl)-1,2,4-triazole. In the 19F NMR spectra, complexes
6 and 7 exhibit a singlet peak at −64.25 and −63.29 ppm,
respectively, which are attributable to a combination of the ring
inversion and the NH ↔ N− conversion of the 1,2,4-triazolyl.
Moreover, in the ESI mass spectra, all cationic complexes 5, 6,
8, and 9 give an intensive molecular ionic peak fragment [M−
ClO4]+, while neutral complex 7 displays a molecular ionic peak
fragment [M+1]+.
The structures of 1−8 were established by X-ray
crystallography (see Figures 1−3, as well as Figures S1−S5 in
Figure 2. Perspective drawing of the cation of 6 showing 30%
probability thermal ellipsoids and atom-labeling scheme. The ClO4
anion and hydrogen atoms except H2B are omitted for the sake of
clarity.
Figure 1. Perspective drawing of 1 showing 30% probability thermal
ellipsoids and atom-labeling scheme. Hydrogen atoms except H3A are
omitted for the sake of clarity.
Figure 3. Perspective drawing of 7 showing 30% probability thermal
ellipsoids and atom-labeling scheme. Hydrogen atoms are omitted for
the sake of clarity.
the Supporting Information). The crystallographic data and
structure refinement details of 1−4 and 5−8 are summarized in
Tables 1 and 2, respectively. The selected bond lengths and
angles are listed in Table 3 for 1−4 and Table 4 for 5−8.
Halide complexes 1−4 adopt an N2PX distorted tetrahedral
geometry around the Cu(I) center, in which bptzH or bmptzH
displays a neutral chelating coordination mode. The Cu−
1−3 has a stronger bonding to the Cu(I) ion with the
decreased electron-donating character of the halide. The Cu−X
lengths of 1−3 become shorter as the van der Waals radii of X
decreases. In sharp contrast to 1−3, the Cu−Npyridyl length
(2.268(8) Å) is much shorter than the Cu−Ntriazolyl length
(2.446(10) Å) in 4, revealing a stronger bonding of the Cu(I)
atom to the N atom of the pyridyl, which is due to the
introduction of the electron-donating methyl group. Compared
with 1−3, both Cu−N distances are markedly elongated and
the N1−Cu−N4 angle is obviously enlarged for 4, as a result of
the increased steric congestion by the methyl substituent.
For [Cu(N∧N)(P2)](ClO4) complexes 5, 6, and 8, the Cu(I)
atom is located in an N2P2 distorted tetrahedral environment,
in which bptzH or fptzH serves as a neutral chelating ligand.
Analogous to 1−3, complexes 5 and 6 have two distinctive
Cu−N bonds with the Cu−Ntriazolyl distances (2.095(4) Å for 5
N
pyridyl lengths (2.1818(19), 2.189(3), and 2.195(4) Å for 1, 2,
and 3, respectively) are much longer than the Cu−Ntriazolyl
lengths (2.0751(18), 2.082(3), and 2.087(4) Å for 1, 2, and 3,
respectively), showing a stronger bonding of the Cu(I) center
to the N4 atom of the 1,2,4-triazolyl. Both Cu−Npyridyl and
Cu−Ntriazolyl bonds of 1−3 are slightly elongated with the
decrease of electron-donating ability of the halide (I− > Br− >
Cl−), implying that the halide possibly has some impact on the
entire 3-(2′-pyridyl)-1,2,4-triazole ligand, and not simply on the
pyridyl or 1,2,4-triazolyl fragment. Moreover, the Cu−P
distances follow a ranking of 1 (2.2047(6) Å) > 2
(2.2022(11) Å) > 3 (2.1978(14) Å), suggesting that PPh3 of
C
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Table 1. Crystal Data and Structure Refinement for the Halide Compounds 1−4
compound
1
2
3
4
formula
fw
C29H29ICuN4P
654.97
296(2)
monoclinic
Cc
C29H29BrCuN4P
607.98
296(2)
monoclinic
Cc
C29H29ClCuN4P
563.52
296(2)
monoclinic
Cc
C30H31ICuN4P
669.00
296(2)
monoclinic
Cc
T [K]
crystal system
space group
a [Å]
10.8694(2)
17.0146(3)
16.0390(3)
90
10.69550(10)
16.9158(2)
15.7249(2)
90
10.5931(4)
16.8769(6)
15.5198(6)
90
10.7879(10)
17.1097(17)
16.297(2)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
99.9750(10)
90
97.9500(10)
90
97.240(2)
90
98.3540(10)
90
2921.39(9)
4
2817.65(6)
4
2752.49(18)
4
2976.1(5)
4
Z
ρcalcd [mg m−3
]
1.489
1.433
1.360
1.493
μ [mm−1
]
1.883
2.274
0.973
1.850
no. reflections collected
no. unique reflections
Rint
13648
10550
10582
6466
6041
4854
4212
3306
0.0183
6041
0.0360
4854
0.0471
4212
0.0356
3306
no. observed reflections
no. parameters
goodness of fit (GOF) on F2
325
325
325
334
1.023
0.889
0.979
1.040
R1 (I > 2σ(I))
0.0214
0.0490
0.0326
0.0654
0.0426
0.0563
0.0515
0.1300
wR2
Table 2. Crystal Data and Structure Refinement for Compounds 5−8
compound
5
6
7
8
formula
fw
C47H44ClCuN4O4P2
889.79
C132H105Cl3Cu3F9N12O12P6·3CHCl3
C44H34CuF3N4P2
801.23
C37H38ClCuN4O4P2
763.64
3063.17
153(2)
triclinic
T [K]
296(2)
monoclinic
C2/c
296(2)
monoclinic
P21/n
296(2)
monoclinic
P21/n
crystal system
space group
a [Å]
P1
̅
32.625(4)
15.5875(19)
21.406(2)
90
15.6798(15)
16.7611(16)
27.175(3)
85.433(2)
84.598(3)
74.193(2)
6830.3(11)
2
13.0571(2)
21.9601(3)
14.3551(2)
90
12.1535(3)
15.9763(3)
19.9227(4)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
124.976(2)
90
106.3010(10)
90
106.2740(10)
90
8919.7(18)
8
3950.65(10)
4
3713.35(14)
4
Z
ρcalcd [mg m−3
]
1.325
1.489
1.347
1.366
μ [mm−1
]
0.669
0.845
0.684
0.790
no. reflections collected
no. unique reflections
Rint
31492
79940
15839
29489
11090
30856
9096
8487
0.0928
0.0284
0.0377
0.0329
no. observed reflections
no. parameters
goodness of fit (GOF) on F2
11090
30856
9096
8487
548
1820
487
442
0.968
1.066
1.007
1.031
R1 (I > 2σ(I))
0.0698
0.0450
0.0496
0.0429
wR2
0.1620
0.1248
0.1166
0.1099
and avg. 2.0994(17) Å for 6) being shorter than the Cu−Npyridyl
distances (2.177(4) Å for 5 and avg. 2.1319(16) Å for 6).
Because of the steric effect of dppe in 8, an unfavorable
repulsion between the Cu(I) center and one adjacent methyl
group of the tert-butyl substituent appears, as supported by the
splitting behavior of the methylene and tert-butyl signals in the
1H NMR spectrum. As a result, the Cu−Npyridyl bond of 8 is
obviously shorter (2.061(2) Å) than those of 5 (2.177(4) Å)
and 6 (av. 2.1319(16) Å), although the Cu−Ntriazolyl and Cu−P
distances are still within the normal range. The N−Cu−N angle
of 8 is somewhat greater, 82.01(8)°, because of the reduced
steric congestion of dppe relative to PPh3.21 The P−Cu−P
angles vary dramatically from 125.41(5)° for 5 and avg.
126.80(2)° for 6 to 91.97(3)° for 8. For neutral species 7, the
Cu(I) ion is also in an N2P2 distorted tetrahedral arrangement
with the Cu−Ntriazolyl length (2.016(2) Å) being obviously
shorter than the Cu−Npyridyl distance (2.207(2) Å). The Cu−
Ntriazolyl length (2.016(2) Å) of 7 is much shorter than those
(2.0751(18)−2.119(2) Å) of 1−3, 5, 6, and 8, indicative of the
D
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the lowest-lying transition of 1−9 are ascribed as Cu(3d) →
N∧N and phosphine → N∧N charge transfer (1MLCT/1LLCT)
transitions, mixed with some halide-to-ligand charge transfer
(1XLCT) character for 1−4 and a small amount of intraligand
(1IL) charge transition inside the anionic fptz chelate for 7.
In degassed CH2Cl2 solution at ambient temperature,
complexes 5−9 show a broad single emission band (Figure
5) centered at 504, 547, 529, 581, and 525 nm with moderate
quantum yields of 0.097, 0.048, 0.027, 0.016, and 0.140,
respectively. The emission intensity is drastically quenched by
oxygen in aerated solution. This, together with the emission
lifetime (from several to a dozen microseconds), indicates that
the emission may be phosphorescent in origin. However, any
detectable solution emission is unobserved for the halide
complexes 1−4 at room temperature, most likely as a result of
fast structural relaxation occurring in the low-viscosity solution,
as supported by the fact that complexes 1−4 display strong
solid-state emissions (Table 5) due to the retardation of
structural relaxation in the solid state. Hence, the rigid-
ochromism, which has been reported for other photoactive
transition-metal complexes,22 appears for Cu(I) halide
complexes 1−4.
For complexes 5, 8, and 9 involving the same bptzH and
different phosphine ligands, the emission peak shifts toward
lower energy with λmax ≈ 504 nm for 5, 525 nm for 9, and 581
nm for 8. The emission energy trend in fluid solutions of 5, 9,
and 8 is largely in accord with that of their weak low-energy
absorptions mentioned above, suggesting that both may
originate from the same electronic excited states markedly
affected by the phosphine ligand. The tendency of the emission
peaks for 5, 9, and 8 is consistent with those for the
[Cu(phen)(P2)]+, [Cu(dmp)(P2)]+, and [Cu(ppb)(P2)]+
systems (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-
1,10-phenanthroline, ppb = 2-(2-pyridylbenzimidazolyl)-
benzene; P2 = 2PPh3, DPEphos, and dppe).21a,23 The sequence
of the emission energy is contrary to the electron-donating
ability of the phosphine ligands (PPh3 < DPEphos < dppe).24
Besides, it has been reported that a larger P−Cu−P angle can
reduce the dσ* interactions and increase the energy required
for MLCT.23 Thus, it is likely that the P−Cu−P angle plays a
partial role on the emission variation of 5, 9, and 8, and virtually
the P−Cu−P angle of 5 (125.41°), 9 (110−120° in Cu(I)
complexes),23,25 and 8 (91.97°) follows the reverse order of the
Table 3. Selected Bond Lengths and Angles of Compounds
1−4
Bond Lengths [Å]
1
2
3
4
Cu1−N1
Cu1−N4
Cu1−P1
Cu1−X1
2.1818(19)
2.0751(18)
2.2047(6)
2.5886(3)
2.189(3)
2.082(3)
2.195(4)
2.268(8)
2.087(4)
2.446(10)
2.171(3)
2.2022(11)
2.1978(14)
2.2962(13)
2.4293(6)
2.2063(14)
Bond Angles [deg]
1
2
3
4
N1−Cu1−N4
N1−Cu1−X1
N1−Cu1−P1
N4−Cu1−P1
N4−Cu1−X1
P1−Cu1−X1
79.59(7)
79.04(12)
109.23(9)
110.87(9)
123.34(9)
110.06(9)
117.26(3)
78.19(16)
108.32(11)
111.16(11)
122.14(10)
110.64(10)
118.48(5)
86.9(3)
110.00(6)
109.57(5)
123.59(6)
110.48(6)
116.83(2)
111.3(2)
116.5(3)
130.1(2)
107.6(2)
103.55(9)
significant effect of the anionic 1,2,4-triazolate, resulting from
the NH deprotonation.
Photophysical and Electrochemical Properties in
Fluid Solution. The absorption and emission spectra of
three free ligands (fptzH, bptzH, and bmptzH) and their
respective Cu(I) complexes 1−9 were investigated in CH2Cl2
solution at ambient temperature. All pertinent photophysical
data are summarized in Table 5. The free ligands display
multiple absorption bands in the UV region (<310 nm),
1
attributed to the ligand-centered π−π* transitions, showing a
certain red-shifting (fptzH < bptzH < bmptzH) with the
increased electron-donating ability of the substituents on 3-(2′-
pyridyl)-1,2,4-triazole. As shown in Figure 4 and Table 5,
complexes 1−9 exhibit several absorption peaks in the 230−
1
330 nm region (ε > 104 M−1 cm−1), because of the π−π*
transitions of both N∧N and phosphine ligands, which are
slightly red-shifted, because of the more-extended π-conjuga-
tion, relative to the free ligands. Moreover, complex 8 exhibits a
clear low-energy absorption band centered at ∼366 nm, despite
only a relatively weak low-energy absorption shoulder or tail (ε
< 5500 M−1 cm−1) being observed in the range of 330−400 nm
for 1−7 and 9, suggesting that these weak low-energy
absorptions appearing at 330−400 nm are affected more
significantly by the phosphine ligand than the N∧N chelate and
halide ligands. As suggested by TD-DFT studies (vide infra),
Table 4. Selected Bond Lengths and Angles of Compounds 5−8
Bond Lengths [Å]
a
5
6
7
8
a
Cu1−N1 (Cu2−N5, Cu3−N9)
2.177(4)
2.1405(16), 2.1275(16), 2.1276(16)
2.1001(17), 2.0934(17), 2.1046(17)
2.2731(5), 2.2436(5), 2.2472(5)
2.2357(5), 2.2581(5), 2.2705(6)
2.207(2)
2.016(2)
2.2666(8)
2.2578(8)
2.061(2)
2.119(2)
2.2586(8)
2.2781(8)
a
Cu1−N4 (Cu2−N8, Cu3−N12) (Cu1−N2)
2.095(4)
a
Cu1−P1 (Cu2−P3, Cu3−P5)
2.2677(14)
2.2776(15)
a
Cu1−P2 (Cu2−P4, Cu3−P6)
Bond Angles [deg]
a
5
6
7
8
a
N1−Cu1−N4 (N5−Cu2−N8, N9−Cu3−N12) (N1−Cu1−N2)
79.87(15)
105.88(11)
104.64(11)
112.54(10)
116.63(11)
125.41(5)
79.36(6), 79.70(6), 79.33(6)
98.06(4), 114.60(5), 115.65(5)
117.60(4), 102.57(5), 106.32(5)
103.48(5), 111.18(5), 109.29(5)
116.29(5), 115.75(5), 109.52(5)
129.81(2), 123.93(2), 126.67(2)
79.13(9)
82.01(8)
129.60(6)
119.23(6)
115.32(6)
122.31(6)
91.97(3)
a
N1−Cu1−P1 (N5−Cu2−P3, N9−Cu3−P5)
N1−Cu1−P2 (N5−Cu2−P4, N9−Cu3−P6)
108.63(7)
100.39(7)
113.00(8)
117.36(8)
125.37(3)
a
a
N4−Cu1−P1 (N8−Cu2−P3, N12−Cu3−P5) (N2−Cu1−P1)
N4−Cu1−P2 (N8−Cu2−P4, N12−Cu3−P6) (N2−Cu1−P2)
a
a
P1−Cu1−P2 (P3−Cu2−P4, P5−Cu3−P6)
a
There are three independent molecules in the asymmetric unit of complex 6.
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Table 5. Photophysical and Electrochemical Data of Pyridyl Triazole Ligands and Their Compounds 1−9
a
b
compound
bmptzH
medium
CH2Cl2
λabs [nm] (ε [M−1 cm−1])
λem [nm]
τ [μs]
Φem [%]
Eox [V]
247 (17300), 284 (19660), 294 (15140)
343
bptzH
fptzH
1
CH2Cl2
CH2Cl2
248 (15910), 280 (15640), 290sh (11590)
238 (20890), 278 (14840), 285 (11820)
274 (22620), 309 (8010), 353 (2100)
322
432
CH2Cl2
solid
0.56
0.61
0.61
0.55
1.45
1.61
1.58
1.27
1.37
c
c
547 (590)
551
21.7 (98)
18.2
17.1
47.6
17.2
35.3
2
3
4
5
6
7
8
9
CH2Cl2
solid
274 (20730), 360 (1825)
274 (20980), 316 (5620), 361 (1160)
279 (21290), 364 (1220)
265 (40930), 341 (3780)
258 (41510), 343 (3930)
249 (44550), 345 (1500)
274 (34670), 366 (4660)
272 (36930), 348 (5170)
CH2Cl2
solid
571
20.5
CH2Cl2
solid
499
18.0
CH2Cl2
solid
504
456
12.0
107
9.7
41.8
CH2Cl2
solid
547
7.9
4.8
c
c
c
472 (536)
20.2 (163)
67.1
CH2Cl2
solid
529
6.9
2.7
c
496 (500)
30.3 (95)
53.3
CH2Cl2
solid
581
525
7.8
1.6
15.9
49.1
CH2Cl2
solid
525
15.0
26.9
14.0
40.4
468
a
b
Values shown in parentheses in this column represent the absorption peak data. Potentials were quoted versus the ferrocenium/ferrocene
c
reference (Fc+/0 = 0.51 V); oxidation potentials were measured in dry DMF (for 1−4) and CH2Cl2 (for 5−9). Value shown in parentheses
represents data measured in the solid state at 77 K.
Figure 4. Absorption spectra of three free ligands and their respective
complexes 1−9 in diluted CH2Cl2 solution at ambient temperature.
Figure 5. Emission spectra of complexes 5−9 in CH2Cl2 solution at
ambient temperature.
emission maximum. Therefore, the emissions of 5, 9, and 8 are
markedly affected by both the electronic properties of the
phosphines and the P−Cu−P angles.21a Complex 6 shows a
single, broad emission band at 547 nm with a 43 nm (1560
cm−1) red-shift, relative to that of 5 (504 nm), as a
consequence of the replacement of tert-butyl by electron-
withdrawing trifluoromethyl on the 1,2,4-triazolyl, which lowers
the energy level of the LUMO of 6 and thus reduces HOMO−
LUMO gap. Complex 7 shows a broad emission at 529 nm
with 18 nm (622 cm−1) of blue-shift, compared with cationic
complex 6. This is perhaps due to NH deprotonation of the
fptzH, in which the negative charge significantly raises the
LUMO level and slightly influences the HOMO level, leading
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to a larger HOMO−LUMO gap and thus a higher energy of
emission.
The electrochemical behavior of the 1,2,4-triazole-based
Cu(I) complexes has been investigated by cyclic voltammetry
in dry DMF (for 1−4) and CH2Cl2 (for 5−9) using ferrocene
as the internal standard, and the electrochemical data are
presented in Table 5. During the anodic scan in DMF solution,
halide complexes 1−4 display an irreversible oxidation peak
with Epa values of ∼0.56, 0.61, 0.61, and 0.55 V, respectively,
ascribed to the oxidation of Cu(I) to Cu(II). For 5−9, an
irreversible oxidation peak is also observed in CH2Cl2 solution
with Epa values of ∼1.45, 1.61, 1.58, 1.27, and 1.37 V,
respectively. It is noted that the oxidation potentials of 5−9 are
much higher than those of 1−4, which is mainly due to the
replacement of the electron-donating halide by the good π-
acceptor phosphine, which markedly decreases the electron
density on the copper center, thus stabilizing the HOMO level.
The oxidation potential sequence is 5 (1.45 V) > 9 (1.37 V) >
8 (1.27 V), which is contrary to the electron-donating ability of
the phosphine ligands (PPh3 < DPEphos < dppe), which
implies that the HOMO orbital involves the contributions from
the phosphine ligand. Moreover, the oxidation potentials of 5−
7 appear to show that the HOMO level is also affected by the
electronic nature of the N∧N chelate.
Figure 7. Emission spectra of complexes 5, 6, 8, and 9 in the solid
state at ambient temperature.
Luminescence Properties in Solid State. The solid-state
emission spectra of complexes 1−9 at ambient temperature and
three representative complexes 1, 6, and 7 at 77 K were
measured using powder samples (see Figures 6−9), and
Figure 8. Emission spectra of complexes 6 and 7 in CH2Cl2 solution
(dashed lines) and in the solid state (solid lines) at ambient
temperature.
Figure 6. Emission spectra of complexes 1−5 in the solid state at
ambient temperature.
relevant luminescence data are listed in Table 5. It is found that
these Cu(I) complexes (1−9) are highly emissive in the solid
state at ambient temperature. Halide complexes 1−3 with
bptzH show an emission band centered at 547, 551, and 571
nm with the quantum yields of 0.171, 0.476, and 0.172,
respectively. The emission maxima (λmax) show the order of 1 <
2 < 3, implying that the luminescence is influenced by the
ligand-field strength of the halide (I− < Br− < Cl−).11 It is thus
believed that the electronic nature of the emissive excited states
of 1−3 is affected to some degree by X− → π*(N∧N) charge-
transfer transitions. It is noted that the emission of 3 exhibits a
20 nm (636 cm−1) red-shift, whereas that of 1 exhibits only a 4
nm (133 cm−1) blue-shift, compared to that of 2, suggesting
that the emission is also affected by the electron-donating
nature of the halide (I− > Br− > Cl−), thus influencing the
Figure 9. Excitation and emission spectra of complexes 1, 6, and 7 in
the solid state at 77 K.
HOMO level localized at the Cu(I) center. Complex 4 gives a
solid-state emission with the maximum at 499 nm and a good
quantum yield of 0.353 with remarkable blue-shift (∼48 nm,
1759 cm−1), relative to that of 1 (547 nm). The blue-shift may
be due to the introduction of the electron-donating methyl on
the 2-pyridyl of 1, which raises the LUMO level, thus increases
the HOMO−LUMO gap.
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Figure 10. Plots of frontier orbitals involved in the lowest-lying electronic absorption transitions of complexes 1, 6, and 7.
Similarly, complexes 5−9 in solid-state show a broad and
unstructured emission profile with maxima at 456, 472, 496,
525, and 468 nm and quantum yields of 0.418, 0.671, 0.533,
0.491, and 0.404, respectively. The emission maxima, to some
extent, are blue-shifted, relative to their corresponding
solutions, as a result of the rigid medium. Moreover, the
solid emission maxima of 5, 9, and 8 are in agreement with
those in solution (5 < 9 < 8). The solid emission of 6 (472 nm)
is red-shifted by 16 nm (743 cm−1), relative to that of 5 (456
nm), because of the substitution of the tert-butyl group by a
trifluoromethyl group. Interestingly, the solid emission of 7
shows a 24 nm (1025 cm−1) red-shift, whereas the solution
emission exhibits an 18 nm (622 cm−1) blue-shift, relative to
that of 6. Such an anomaly can be rationalized in terms of a less
rigid molecular structure of 7 than that of 6 upon the ring
inversion of the 1,2,4-triazolyl mediated by NH deprotonation,
under a basic medium.
Upon cooling to 77 K, the emission spectra (λmax) for three
representative complexes1 (590 nm), 6 (536 nm), and 7
(500 nm)exhibit a bathochromic shift of 4−64 nm (161−
2530 cm−1), relative to those at ambient temperature, along
with a marked increase in emission lifetime (95−163 μs). Such
a luminescence behavior is frequently observed for emissive
Cu(I) complexes with small singlet−triplet energy gaps
ΔE(S1−T1) and is generally assigned to a decrease in thermally
activated delayed fluorescence (TADF).8d,10,13e,18k,26 At low
temperatures, thermally activated population of the higher-lying
state with faster radiative rate is suppressed, resulting in a red-
shifted emission and a longer excited-state lifetime. Moreover,
the solid emission peak of 6 (472 nm) at room temperature is
remarkably blue-shifted, with respect to that (536 nm)
measured at 77 K, whereas the solid emission profile of 7 at
ambient temperature resembles that recorded at 77 K,
indicating that the ring inversion and NH deprotonation of
the 1,2,4-triazolyl have a significant impact on the emissive
properties.
complexes, the time-dependent density functional theory
(TD-DFT)27/PBE1PBE28 calculations were performed. The
calculated lowest-lying absorptions of 1−8 and emission
transition properties of 5−8 in CH2Cl2 media are summarized
in Table 6. The frontier molecular orbitals involved in the
lowest-lying electronic absorption transitions of 1, 6, and 7 are
depicted in Figure 10. More figures and tables on TD-DFT
studies of 1−8 are provided in the Supporting Information (see
Tables S1−S10 and Figures S6−S25).
As shown in Figure 10, Table 6, and Table S1 in the
Supporting Information, the HOMO of 1, as an example of the
halide complexes 1−4, has contributions from Cu(3d)
(42.86%), PPh3 (26.95%), and I (26.76%), while the LUMO
is basically localized on bptzH (96.58%). Hence, the calculated
lowest-energy absorption at 377 nm from HOMO → LUMO
transition is attributable to the 1MLCT/1XLCT/1LLCT
(Cu(3d)/I/PPh3 → bptzH) state, which is in reasonable
agreement with the experimentally measured one at 353 nm.
The calculated lowest-energy absorption wavelengths follow a
ranking of
4 (369 nm) < 1 (377 nm) < 2 (381 nm) < 3 (391 nm)
(see Table 6), which agrees with that of the measured emission
4 (499 nm) < 1 (547 nm) < 2 (551 nm) < 3 (571 nm)
(see Table 5). As an example of cationic complexes 5, 6, and 8,
the HOMO of 6 is primarily composed of Cu(3d) (31.05%)
and two PPh3 (66.46%), while the LUMO is essentially
centered on fptzH (94.60%) (see Table S6 in the Supporting
Information). Thus, the calculated lowest-lying absorption of 6
is assigned to a mixed 1MLCT/1LLCT (Cu(3d)/PPh3 →
fptzH) character. However, for 7 bearing deprotonated fptz, the
LUMO is predominantly located on the anionic fptz, whereas
the HOMO, HOMO-1, HOMO-2, and HOMO-3 are almost
resident on Cu(3d), PPh3, and fptz (see Table S7 in the
Supporting Information). Hence, its calculated lowest-energy
absorption at 318 nm is typical of a significant 1MLCT
(Cu(3d) → fptz) character mixed with a certain degree of the
Theoretical Investigations. To gain insight into the
photophysical properties of the 1,2,4-triazole-based Cu(I)
I
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1LLCT transition (PPh3 → fptz) and the intraligand (1IL)
transition inside fptz.
formation, in which they exhibit distinct emission properties
in both solution and solid states. The results presented herein
might provide new insight into the synthesis of blue
phosphorescent materials of the 3-(2′-pyridyl)-1,2,4-triazole-
based copper(I) complexes with potentially high luminescence
efficiency.
The emissive properties of 5−8 in CH2Cl2 media were
investigated by TD-DFT/PBE1PBE calculations, according to
the optimized lowest triplet excited-state T1 geometries. As
depicted in Table 6, as well as Table S9 and Figures S16−S20
in the Supporting Information, the triplet emissive states of 6
and 8 corresponding to the HOMO→LUMO transitions are
attributed to the 3MLCT transitions mixed with some
3LLCT/3IL characters, while the triplet excited state of 7
from the HOMO → LUMO and HOMO-1 → LUMO tran-
sitions can be assigned as a mixed 3MLCT/3LLCT/3IL
character. However, despite the fact that the lowest singlet
EXPERIMENTAL SECTION
■
General Procedures and Materials. All reactions were
performed under a N2 atmosphere, using anhydrous solvents or
solvents treated with an appropriate drying reagent. Commer-
cially available reagents were used without further purification
unless otherwise stated. [Cu(CH3CN)4](ClO4)29 and [Cu-
(PPh3)2(CH3CN)2](ClO4)30 were prepared according to the
literature methods. The functionalized 3-(2′-pyridyl)-1,2,4-
triazole ligands including 5-trifluoromethyl-3-(2-pyridyl)-1,2,4-
triazole (fptzH), 5-tert-butyl-3-(2-pyridyl)-1H-1,2,4-triazole
(bptzH), and 5-tert-butyl-3-(6-methyl-2-pyridyl)-1H-1,2,4-tria-
zole (bmptzH) were synthesized using previously reported
procedures.31
1
(S1) absorption of 5 has a substantial MLCT transition (see
Table S5 in the Supporting Information), its lowest triplet-state
3
(T1) is identified as the IL transition inside bptzH. Such a
phenomenon can be rationalized via a larger difference between
3
3
the IL level and the MLCT/3LLCT levels of 5, relative to
those of 6−8, which leads to a relatively complete energy
3
transfer from the higher MLCT/3LLCT level to the lower 3IL
Caution! The perchlorate salts are potentially explosive and
should be handled carefully in small amounts.
level for 5.
The solid emission properties of 1 and 4−6 were also
calculated using the TD-DFT/PBE1PBE method, based on
their single-crystal structures (see Table S10 and Figures S21−
S25 in the Supporting Information). The lowest triplet excited
Preparation of Cu(bptzH)(PPh3)I (1). A mixture of CuI
(36.2 mg, 0.190 mmol) and PPh3 (100.2 mg, 0.382 mmol) was
stirred in CH2Cl2 (ca. 15 mL) for 30 min at ambient
temperature to give a colorless solution. A solution of bptzH
(38.7 mg, 0.191 mmol) in CH2Cl2 (ca. 6 mL) was added, and
the mixture was stirred for 3 h, affording a yellow precipitate.
The precipitate (1, 109.5 mg, 0.167 mmol, 88%) was collected
by filtration, washed with CH2Cl2 and diethyl ether, and dried
under vacuum. X-ray-quality yellow crystals were grown via the
slow diffusion of methanol into the DMF solution of 1 after 4
3
state of 1 in the solid state is assigned as the MLCT/3XLCT
characters, while the solid-state emission of 4 is attributable to
the 3(MLCT/LLCT/XLCT) transitions. The calculated
HOMO−LUMO gaps are 1 (3.33 eV) < 4 (3.42 eV), which
is consistent with that of the measured solid emission energies.
For 5, the calculated solid emission displays mixed transition
3
properties of IL/3LLCT/3MLCT, which is distinctly different
1
days. ESI-MS: m/z 527 [M−I]+. H NMR (DMSO-d6, 400
from that (3IL) of its calculated solution emission. This may be
due to the effect of the rigid medium retarding the structural
relaxation being favorable to the energy transfer from
3MLCT/3LLCT state to 3IL state for 5 in solution. The
MHz): δ 14.49 (s, 1H), 8.38 (s, 1H), 8.19 (d, 1H, J = 7.6 Hz),
8.05 (t, 1H, J = 6.4 Hz), 7.65−7.60 (m, 3H), 7.58−7.53 (m,
3H), 7.40−7.38 (m, 10H), 1.31 (s, 9H). 31P{1H} NMR
(DMSO-d6, 202.3 MHz): δ −6.05 (s, PPh3). Anal. Calcd for
C29H29ICuN4P: C, 53.18; H, 4.46; N, 8.55. Found: C, 53.32; H,
4.58; N, 8.43.
3
calculated solid emission of 6 is assigned as a mixed (MLCT/
LLCT) character. The calculated HOMO−LUMO gaps follow
5 (4.55 eV) > 6 (3.84 eV), which is in reasonable agreement
with that of the experimentally measured solid emissions of 5
(456 nm) and 6 (472 nm).
Preparation of Cu(bptzH)(PPh3)Br (2). Complex 2 was
prepared following the procedure for 1, using CuBr (32.6 mg,
0.227 mmol), PPh3 (119.3 mg, 0.455 mmol), and bptzH (46.1
mg, 0.228 mmol), which resulted in the formation of a light
yellow precipitate (2, 112.3 mg, 0.185 mmol, 81%). Light
yellow crystals were afforded via the slow diffusion of diethyl
ether into the DMF solution of 2 after 3 days. ESI-MS: m/z
CONCLUSIONS
■
We have designed and synthesized a new series of luminescent
monometallic Cu(I) complexes with functionalized 3-(2′-
pyridyl)-1,2,4-triazole ligands. Their structural features and
photophysical properties have been fully investigated. These
1,2,4-triazole-based Cu(I) complexes 1−9 are fairly air-stable
both in solution and in the solid state. They show a relatively
weak low-energy absorption in CH2Cl2 solution, ascribed to the
charge-transfer transitions with appreciable MLCT character as
supported by TD-DFT calculations. Complexes 5−9 have a
good luminescence properties in degassed CH2Cl2 solution,
despite the halide complexes 1−4 being nonemissive in fluid
solution, In contrast, complexes 1−9 are all strongly emissive in
the solid state at ambient temperature, and the emissive
properties are well-modulated via the structural modification of
3-(2′-pyridyl)-1,2,4-triazole and the change of the ancillary
ligands such as phosphine and halide. The interconversion
between cationic complex 6 and neutral derivative 7 has been
successfully achieved through the ring inversion of the 1,2,4-
triazolyl regulated by the controllable NH ↔ N− trans-
1
527 [M−Br]+. H NMR (DMSO-d6, 400 MHz): δ 14.45 (s,
1H), 8.35 (s, 1H), 8.19 (s, 1H), 8.05 (s, 2H), 7.65−7.60 (m,
1H), 7.58−7.54 (m, 2H), 7.45−7.37 (m, 12H), 1.31 (s, 9H).
31P{1H} NMR (DMSO-d6, 202.3 MHz): δ −5.23 (s, PPh3).
Anal. Calcd for C29H29BrCuN4P: C, 57.29; H, 4.81; N, 9.22.
Found: C, 57.13; H, 4.75; N, 9.33.
Preparation of Cu(bptzH)(PPh3)Cl (3). Complex 3 was
prepared following the procedure for 1, using CuCl (29.3 mg,
0.296 mmol), PPh3 (155.4 mg, 0.592 mmol), and bptzH (60.0
mg, 0.297 mmol), which led to the formation of a light yellow
precipitate (3, 130.2 mg, 0.231 mmol, 78%). Light yellow
crystals were obtained by slow diffusion of diethyl ether into
the DMF solution of 3 after 3 days. ESI-MS: m/z 527 [M−
Cl]+. 1H NMR (DMSO-d6, 400 MHz): δ 14.39 (s, 1H), 8.30 (s,
1H), 8.16 (d, 1H, J = 7.6 Hz), 8.00 (t, 1H, J = 7.4 Hz), 7.65−
7.56 (m, 1H), 7.45−7.32 (m, 15H), 1.29 (s, 9H). 31P{1H}
NMR (DMSO-d6, 202.3 MHz): δ −4.69 (s, PPh3). Anal. Calcd
J
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for C29H29ClCuN4P: C, 61.81; H, 5.19; N, 9.94. Found: C,
61.94; H, 5.23; N, 9.89.
in CH2Cl2 (8 mL) was stirred for 30 min at room temperature.
A solution of bptzH (22.7 mg, 0.112 mmol) in CH2Cl2 (5 mL)
was added, and this admixture was stirred for another 3 h to get
a yellow solution. The solvent was evaporated to dryness at
reduced pressure. The residue was dissolved in CH2Cl2, and a
slow diffusion of diethyl ether into the above solution gave
yellow crystals of 8 (75.3 mg, 0.099 mmol, 88%). ESI-MS: m/z
664 [M−ClO4]+. 1H NMR (DMSO-d6, 400 MHz): δ 14.81 (s,
1H), 8.42 (d, 1H, J = 8.0 Hz), 8.23 (t, 2H, J = 7.6 Hz), 7.63 (t,
1H, J = 6.2 Hz), 7.44−7.34 (m, 16H), 7.27−7.20 (m, 4H), 2.79
(s, 3H), 2.54 (s, 1H), 1.21 (s, 2H), 0.92 (s, 7H). 31P{1H} NMR
(DMSO-d6, 202.3 MHz): δ −7.41 (s, dppe). Anal. Calcd for
C37H38ClCuN4O4P2: C, 58.19; H, 5.02; N, 7.34. Found: C,
58.13; H, 4.95; N, 7.41.
Preparation of Cu(bmptzH)(PPh3)I (4). Complex 4 was
prepared following the procedure for 1, using CuI (38.1 mg,
0.200 mmol), PPh3 (105.3 mg, 0.401 mmol), and bmptzH
(43.5 mg, 0.201 mmol), which resulted in the generation of a
light yellow precipitate (4, 101.7 mg, 0.152 mmol, 76%). Light
yellow crystals were grown by slow diffusion of diethyl ether
into the DMF solution of 4 after 3 days. ESI-MS: m/z 541 [M−
1
I]+. H NMR (DMSO-d6, 400 MHz): δ 14.48 (s, 1H), 8.05−
7.96 (m, 2H), 7.65−7.53 (m, 3H), 7.44−7.33 (m, 13H), 2.34
(s, 3H), 1.24 (s, 9H). 31P{1H} NMR (DMSO-d6, 202.3 MHz):
δ −7.91 (s, PPh3). Anal. Calcd for C30H31ICuN4P: C, 53.86; H,
4.67; N, 8.37. Found: C, 53.95; H, 4.72; N, 8.41.
Preparation of [Cu(bptzH)(PPh3)2](ClO4) (5). A CH2Cl2
solution (10 mL) of bptzH (18.6 mg, 0.092 mmol) and
[Cu(PPh3)2(CH3CN)2](ClO4) (70.2 mg, 0.091 mmol) was
stirred at ambient temperature for 4 h to give a light yellow
solution. The solvent was then removed at reduced pressure.
The resultant residue was again dissolved in a mixture of
CH2ClCH2Cl/CH2Cl2 (1:5 v/v), and slow diffusion of
petroleum ether into the above solution yielded creamy crystals
of 5 (64.5 mg, 0.072 mmol, 79%). ESI-MS: m/z 790 [M−
ClO4]+. 1H NMR (DMSO-d6, 400 MHz): δ 14.72 (s, 1H), 8.23
(d, 1H, J = 8.0 Hz), 8.04 (t, 1H, J = 7.6 Hz), 7.91 (s, 1H), 7.46
(t, 6H, J = 7.4 Hz), 7.41−7.33 (m, 13H), 7.13 (t, 12H, J = 8.0
Hz), 1.16 (s, 9H). 31P{1H} NMR (DMSO-d6, 202.3 MHz): δ
−0.19 (s, PPh3). Anal. Calcd for C47H44ClCuN4O4P2: C, 63.44;
H, 4.98; N, 6.30. Found: C, 63.26; H, 4.74; N, 6.47.
Preparation of [Cu(bptzH)(DPEphos)](ClO4) (9). A
solution of [Cu(CH3CN)4](ClO4) (35.4 mg, 0.108 mmol)
and bis[2-(diphenylphosphino)phenyl]ether (DPEphos) (58.3
mg, 0.108 mmol) in CH2Cl2 (10 mL) was stirred for 30 min at
room temperature. A solution of bptzH (21.9 mg, 0.108 mmol)
in CH2Cl2 (5 mL) was added, and this mixture was stirred for
another 3 h to afford a nearly colorless solution. The solvent
was evaporated to dryness at reduced pressure. The residue was
dissolved in CH2Cl2, and slow diffusion of diethyl ether into the
above solution gave white crystals of 9 (81.2 mg, 0.090 mmol,
1
83%). ESI-MS: m/z 804 [M−ClO4]+. H NMR (DMSO-d6,
400 MHz): δ 14.65 (s, 1H), 8.26 (d, 1H, J = 8.0 Hz), 8.07−
8.00 (m, 2H), 7.47−7.25 (m, 18H), 7.13 (t, 5H, J = 7.6 Hz),
6.82−6.75 (m, 6H), 1.04 (s, 9H). 31P{1H} NMR (DMSO-d6,
202.3 MHz): δ −13.53 (s, DPEphos). Anal. Calcd for
C47H42ClCuN4O5P2: C, 62.46; H, 4.68; N, 6.20. Found: C,
62.35; H, 4.57; N, 6.31.
Preparation of [Cu(fptzH)(PPh3)2](ClO4) (6). Complex 6
was prepared following the procedure for 5, using [Cu-
(PPh3)2(CH3CN)2](ClO4) (72.4 mg, 0.094 mmol) and fptzH
(20.2 mg, 0.094 mmol). The resulting residue was again
dissolved in CH2Cl2, and slow diffusion of petroleum ether into
the above solution afforded light yellow crystals of 6 (69.6 mg,
Crystal Structural Determination. Data collections for
compounds 1−8 were performed on a Bruker SMART Apex II
CCD diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). The datasets were corrected for
Lorentz and polarization factors as well as for absorption by
SADABS program. The structures were solved by direct
methods and refined on F2 by full-matrix least-squares methods
using the SHELXTL-97 program package.32 The heavy atoms
were located from E-map, and other non-hydrogen atoms were
found in subsequent difference Fourier syntheses. All non-
hydrogen atoms were refined anisotropically, while the
hydrogen atoms were generated geometrically with isotropic
thermal parameters.
1
0.077 mmol, 82%). ESI-MS: m/z 802 [M−ClO4]+. H NMR
(CD2Cl2, 400 MHz): δ 14.47 (s, 1H), 8.57 (d, 1H, J = 8.8 Hz),
8.10−8.08 (m, 2H), 7.45 (t, 7H, J = 6.8 Hz), 7.29 (t, 12H, J =
7.6 Hz), 7.18 (d, 12H, J = 7.2 Hz). 19F{1H} NMR (CD2Cl2,
376.5 MHz): δ −64.25 (s, CF3). 31P{1H} NMR (DMSO-d6,
202.3 MHz): δ −2.81 (s, PPh3). Anal. Calcd for
C44H35ClCuF3N4O4P2: C, 58.61; H, 3.91; N, 6.21. Found: C,
58.73; H, 4.12; N, 6.25.
Preparation of Cu(fptz)(PPh3)2 (7). A methanol solution
(10 mL) of fptzH (25.8 mg, 0.121 mmol) and [Cu-
(PPh3)2(CH3CN)2](ClO4) (92.5 mg, 0.120 mmol) was stirred
at room temperature for 2 h, generating a light yellow solution.
Powdered NaOH (5.2 mg, 0.130 mmol) was added, and this
admixture was stirred for another 3 h, yielding an almost
colorless suspension. After the solvent was evaporated at
reduced pressure, the solid residue was extracted with CH2Cl2.
Subsequent diffusion of n-hexane into the CH2Cl2 solution gave
nearly colorless crystals of 7 (75.2 mg, 0.094 mmol, 78%). ESI-
1
Physical Measurements. H, 19F{1H}, and 31P{1H} NMR
spectra were recorded on Bruker Avance III (400 MHz)
spectrometer with SiMe4 as the internal reference and 85%
H3PO4 as the external reference. Elemental analyses (C, H, and
N) were conducted on a Perkin−Elmer Model 240C elemental
analyzer. UV−vis absorption spectra in CH2Cl2 solution were
measured on a Shimadzu Model UV-2550 spectrometer.
Electrospray ionization mass spectrometry (ESI-MS) was
recorded on a Finnigan Model DECAX-30000 LCQ mass
spectrometer, using DMF−methanol or dichloromethane−
methanol as the mobile phase. The photoluminescence
properties in CH2Cl2 solution and in the solid state were
determined on an Edinburgh analytical instrument (Model
F900 fluorescence spectrometer) with a thermoelectrically
cooled Hamamatsu Model R3809 photomultiplier tube. The
emission quantum yields (Φem) of 5−9 in CH2Cl2 solution at
room temperature were calculated by Φs = Φr(Br/Bs)(nr/
1
MS: m/z 802 [M+1]+. H NMR (CD2Cl2, 400 MHz): δ 8.11
(d, 1H, J = 8.0 Hz), 7.91 (s, 1H), 7.79 (t, 1H, J = 6.8 Hz),
7.34−7.38 (m, 6H), 7.22 (d, 24H, J = 4.4 Hz), 7.06 (s, 1H).
19F{1H} NMR (CD2Cl2, 376.5 MHz): δ −63.29 (s, CF3).
31P{1H} NMR (DMSO-d6, 202.3 MHz): δ −1.11 (s, PPh3).
Anal. Calcd for C44H34CuF3N4P2: C, 61.81; H, 5.19; N, 9.94.
Found: C, 61.93; H, 5.26; N, 9.87.
Preparation of [Cu(bptzH)(dppe)](ClO4) (8). A solution
of [Cu(CH3CN)4](ClO4) (36.7 mg, 0.112 mmol) and 1,2-
bis(diphenylphosphino)ethane (dppe) (44.8 mg, 0.112 mmol)
ns)2(Ds/Dr) using fluorescein in H2O as the standard (Φem
=
0.79), where the subscripts “r” and “s” denote reference
K
dx.doi.org/10.1021/ic4002829 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
standard and the sample solution, respectively, and n, D, and Φ
are the refractive index of the solvents, the integrated intensity,
and the luminescence quantum yield, respectively.33 The
quantity B is calculated by B = 1−10−AL, where A is the
absorbance at the excitation wavelength and L is the optical
path length. An integrating sphere (Labsphere) was applied to
measure the quantum yields of 1−9 in the solid state. The
cyclic voltammogram were carried out in a Princeton Applied
Research Model 263A potentiostat/galvanostat analyzer using a
glassy carbon disk working electrode, a platinum counter
electrode, and a Ag/AgCl reference electrode. All experiments
were performed in dry DMF (for 1−4) and CH2Cl2 (for 5−9)
solvents with 0.1 M tertrabutylammonium hexafluorophosphate
as the supporting electrolyte. The potentials are quoted versus
the ferrocenium/ferrocene couple (Fc+/0 = 0.51 V).
AUTHOR INFORMATION
Corresponding Author
*E-mail: gzchenjinglin@126.com (J.-L.C.), jy_wang@fjirsm.ac.
■
cn .
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the financial support from the NSFC (Nos.
21163009, 21001057, and 21161008), the Key Project of
Chinese Ministry of Education (No. 211088), the Advanced
Program for the Retuned Overseas Chinese Scholars of
MOHRSS (No. 474[2011]), the Training Program for Jiangxi
Provincial Young Scientists (No. 20122BCB23016), the Key
Project of Education Department of Jiangxi Province (No.
GJJ13436), the Foundation of State Key Laboratory of
Structural Chemistry (No. 20110015), and the Scientific
Research Foundation of Jiangxi University of Science and
Technology (No. JXXJ12072).
Computational Methodology. All the calculations were
carried out by using the Gaussian 03 program package34 to get
insight into the photophysical properties of these 1,2,4-triazole-
based Cu(I) complexes 1−8. First, the density functional
theory (DFT)35 at the gradient-corrected correlation functional
PBE1PBE28 and unrestricted PBE1PBE (UPBE1PBE) levels,
respectively, was used to optimize the ground-state (S0)
geometries of complexes 1−8 and the triple excited-state
(T1) geometries of complexes 5−8 without symmetry
constraint. The initial structures were extracted from the
crystallographically determined geometries. During the opti-
mization processes, the convergent values of maximum force,
root-mean-square (RMS) force, maximum displacement, and
RMS displacement are set by default. To analyze the
spectroscopic properties, 60 singlet excited states for 1−8 and
6 triplet excited states for 5−8 in CH2Cl2 solution were
calculated by the time-dependent DFT (TD-DFT)27 method at
the same functional used in the geometrical optimization,
respectively, based on the optimized ground-state S0 and
lowest-energy triplet excited-state T1 geometries. The solvent
effects in CH2Cl2 media were taken into account by performing
the self-consistent reaction field (SCRF) calculations using the
polarizable continuum model method (PCM).36 To analyze the
emission properties in the solid states, the TD-DFT/PBE1PBE
calculations were carried out on the model structures derived
from the crystallographic data with all C−H bond length sets
by 1.09 Å and N−H ones by 1.01 Å.37 In these calculations, the
Hay−Wadt double-ζ with a Los Alamos relativistic effect basis
set (LANL2DZ)38 consisting of the effective core potentials
(ECP) was employed for the Cu, P, I, Br, and Cl atoms, and the
6-31G(p,d) basis set39 was used for the remaining atoms. To
precisely describe the molecular properties, one additional f-
type polarization function was implemented for the Cu atom
(αf = 0.24), and a d-type polarization function was employed
for the P (αd = 0.34), I (αd = 0.266), Br (αd = 0.389), and Cl
(αd = 0.514) atoms.40 Visualization of the optimized structures
and frontier molecular orbitals were performed by GaussView.
The Ros and Schuit method (C-squared population analysis
method, SCPA)41 is supported to analyze the partition orbital
composition, using the Multiwfn 2.4 program.42
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ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic data (CIF file) of 1−8. Perspective drawings
of 2−4 and the cations of 5 and 8, tables and figures regarding
the TD-DFT calculations of 1−8, and characterization data of
1−9 (PDF file). This material is available free of charge via the
Internet at http://pubs.acs.org.
L
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