Synthesis, structural characterization and luminescent properties of a series of Cu(i) complexes based on polyphosphine ligands

Article abstract of DOI:10.1039/c1dt10358j

A series of Cu(i) complexes with a [Cu(NN)(PP)]⁺ moiety, [Cu(phen)(pba)](BF₄) (1a), [Cu₂(phen)₂(pbaa)] (BF₄)₂ (2a), [Cu₂(phen)₂(pnaa)] (BF₄)₂ (3a), [Cu₂(phen)₂(pbbaa)] (BF₄)₂ (4a), [Cu(dmp)(pba)](BF₄) (1b), [Cu ₂(dmp)₂(pbaa)](BF₄)₂ (2b), [Cu ₂(dmp)₂(pnaa)](BF₄)₂ (3b) and [Cu₂(dmp)₂(pbbaa)](BF₄)₂ (4b) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, pba = N,N-bis((diphenylphosphino)methyl)benzenamine, pbaa = N,N,N′,N′- tetrakis((diphenylphosphino)methyl)benzene-1,4-diamine, pnaa = N,N,N′,N′-tetrakis((diphenylphosphino)methyl)naphthalene-1, 5-diamine and pbbaa = N,N,N′,N′-tetrakis((diphenylphosphino)methyl) biphenyl-4,4′-diamine), were rationally designed and synthesized. These complexes were characterized by ¹H and ³¹P NMR, electrospray mass spectrometry, elemental analysis and X-ray crystal structure analysis. Introduction of different central arene spacers (phenyl, naphthyl, biphenyl) into ligands, resulting in the size variation of these complexes, aims to tune the photophysical properties of the complexes. Each Cu(i) ion in these complexes adopts a distorted tetrahedral geometry constructed by the chelating diimine and phosphine groups. Intermolecular C-H...π and/or π...π interactions are involved in the solid states. The dmp-containing complex exhibits better emission relative to the corresponding phen complex due to the steric encumbrance of bulky alkyl groups. Furthermore, for complexes with identical diimine but different phosphine ligands, the tendency of increased emission lifetime as well as blue-shifted emission in the solid state follows with the decrease in size of complexes. Intermolecular C-H...π interactions have an influence on the final solid state photophysical properties through vibrationally relaxed non-radiative energy transfer in the excited state. Smaller-sized complexes show better photophysical properties due to less vibrationally relaxed behavior related to flexible C-H...π bonds. Nevertheless, the tendency for increased quantum yield and emission lifetime, as well as blue-shifted emission in dilute solution goes with the increase in size of complexes. The central arene ring (phenyl, naphthyl or biphenyl) has an influence on the final photophysical properties. The larger the π-conjugated extension of central arene ring is, the better the photophysical properties of complex are. The rigid and large-sized complex 3b, with a high quantum yield and long lifetime, is the best luminophore among these complexes. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10358j

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PAPER
Synthesis, structural characterization and luminescent properties of a series of
Cu(I) complexes based on polyphosphine ligands†
Ruobing Hou, Ting-Hong Huang, Xiu-Jian Wang,* Xuan-Feng Jiang, Qing-Ling Ni, Liu-Cheng Gui,
You-Jun Fan* and Yi-Liang Tan
Received 2nd March 2011, Accepted 19th May 2011
DOI: 10.1039/c1dt10358j
A series of Cu(I) complexes with a [Cu(NN)(PP)]+ moiety, [Cu(phen)(pba)](BF4) (1a),
[Cu2(phen)2(pbaa)](BF4)2 (2a), [Cu2(phen)2(pnaa)](BF4)2 (3a), [Cu2(phen)2(pbbaa)](BF4)2 (4a),
[Cu(dmp)(pba)](BF4) (1b), [Cu2(dmp)2(pbaa)](BF4)2 (2b), [Cu2(dmp)2(pnaa)](BF4)2 (3b) and
[Cu2(dmp)2(pbbaa)](BF4)2 (4b) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline,
pba = N,N-bis((diphenylphosphino)methyl)benzenamine, pbaa = N,N,N¢,N¢-tetrakis((diphenyl-
phosphino)methyl)benzene-1,4-diamine, pnaa = N,N,N¢,N¢-tetrakis((diphenylphosphino)methyl)-
naphthalene-1,5-diamine and pbbaa = N,N,N¢,N¢-tetrakis((diphenylphosphino)methyl)biphenyl-
4,4¢-diamine), were rationally designed and synthesized. These complexes were characterized by 1H and
31P NMR, electrospray mass spectrometry, elemental analysis and X-ray crystal structure analysis.
Introduction of different central arene spacers (phenyl, naphthyl, biphenyl) into ligands, resulting in the
size variation of these complexes, aims to tune the photophysical properties of the complexes. Each
Cu(I) ion in these complexes adopts a distorted tetrahedral geometry constructed by the chelating
diimine and phosphine groups. Intermolecular C–H ◊ ◊ ◊ p and/or p ◊ ◊ ◊ p interactions are involved in the
solid states. The dmp-containing complex exhibits better emission relative to the corresponding phen
complex due to the steric encumbrance of bulky alkyl groups. Furthermore, for complexes with
identical diimine but different phosphine ligands, the tendency of increased emission lifetime as well as
blue-shifted emission in the solid state follows with the decrease in size of complexes. Intermolecular
C–H ◊ ◊ ◊ p interactions have an influence on the final solid state photophysical properties through
vibrationally relaxed non-radiative energy transfer in the excited state. Smaller-sized complexes show
better photophysical properties due to less vibrationally relaxed behavior related to flexible C–H ◊ ◊ ◊ p
bonds. Nevertheless, the tendency for increased quantum yield and emission lifetime, as well as
blue-shifted emission in dilute solution goes with the increase in size of complexes. The central arene
ring (phenyl, naphthyl or biphenyl) has an influence on the final photophysical properties. The larger
the p-conjugated extension of central arene ring is, the better the photophysical properties of complex
are. The rigid and large-sized complex 3b, with a high quantum yield and long lifetime, is the best
luminophore among these complexes.
luminescent complexes, ligand strategy, which is dedicated to
Introduction
tuning steric, electronic and conformational effects, is popularly
The photoluminescent properties of transition metal complexes
used to mediate the photophysical and photochemical properties
of metal complexes.3 The destabilization between ligand and
central metal is imposed on slight structure changes, electronic
spectra and excited state energies.
have garnered much attention due to their potential applications in
dye-sensitized solar cells, light-emitting or electrochemical devices
and photochemical catalysts.1,2 Searching for highly efficient
Cu(I) complexes, as potentially inexpensive photofunctional
molecules, have been recently widely reported.4 The typical
example is the [Cu(NN)2]+ system (NN = diimine).5 However,
the emission signal from the charge transfer (CT) excited state
of the copper(I) complex is typically weak and short-lived
because the lowest-energy CT state involves excitation from
a metal–ligand ds* orbital. Furthermore, the excited state
of Cu(I) typically prefers a tetragonally flattened geometry,
Key Laboratory for the Chemistry and Molecular Engineering of Medicinal
Resources (Ministry of Education of China), School Chemistry and
Chemical Engineering, Guangxi Normal University, Guilin, 541004, China.
E-mail: wang1_xj@yahoo.com.cn, youjun_f@hotmail.com
† Electronic supplementary information (ESI) available: Fig. S1–S6 and
Tables S1 and S2. CCDC reference numbers 815811–815818. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt10358j
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deviating from the tetrahedral-like coordination geometry in
the ground state. An important consequence of the steric
encumbrance of the bulky substituents on the diimine ligands
is that they can restrict the pseudotetrahedral Cu(I) to be
flattened in the excited state and extend the lifetime for the
photoprocess, while intermolecular interactions mediated by the
bulky substituents could also make the ground-state geometry
distorted and favor photo-oxidation of the metal with little
structural change. Recently, the [Cu(POP)(NN)]+ family (POP =
bis[2-(diphenylphosphino)phenyl]ether) with highly effective
luminescence suggested that we should extensively investigate
these heteroleptic complexes.6 The introduction of bulky
phosphine groups effectively avoids the geometric relaxation
of the excited state, as well as solvent attack, exhibiting an
unprecedentedly high quantum yield and a long lifetime at
room temperature. Therefore, new functional organophosphine
ligands, such as angular bis[2-(diphenylphosphino)phenyl]ether
(POP),6a rigid 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene7
and 1,2-bis(diphenylphosphino)benzene,8 hetero-donor 8-
diphenylphosphanylquinoline9 and bis(2-(diisobutylphosphino)-
phenyl)amide10 were designed to explore highly efficient
photofunctional Cu(I) complexes and the photoluminescent
molecular mechanical system.11 The previous demonstration
and calculation show that the low-lying metal-to-ligand charge
transfer (MLCT) transition in the [Cu(NN)(PP)]+ system is
dominated by the d orbital of the copper(I) ion, mixed with a
contribution from the phosphorous and a small contribution from
the diimine ligand.12 The electron donating properties and the bite
angle of the phosphine moiety could be effective to destabilize
the electronic character of the copper–phosphine fragment.
Furthermore, luminescence enhancement is also triggered by
molecular interactions in the solid state.13
For pursuing a highly efficient photoprocess, our efforts are de-
voted to designing a series of new functional ligands to mediate the
photophysical properties of the [Cu(NN)(PP)]+ system. Here, four
polyphosphine ligands, N,N-bis((diphenylphosphino)methyl)-
benzenamine (pba), N,N,N¢,N¢-tetrakis((diphenylphosphino)-
methyl)benzene-1,4-diamine (pbaa), N,N,N¢,N¢-tetrakis((di-
phenylphosphino)-methyl)naphthalene-1,5-diamine (pnaa) and
N,N,N¢,N¢-tetrakis-((diphenylphosphino)methyl)biphenyl-4,4¢-
diamine (pbbaa) were developed first from arene amines (Scheme
1). These ligands are expected to coordinate in a bidentate P,P
fashion and the bite angle of the phosphine moiety attached to the
Cu center could be confined by the conformation of the tertiary
amine. In addition, the tertiary N atoms of the arene amine can
donate their electron lone pairs to conjugate with the central arene
ring, resulting in the arene ring being an electron-rich p system
that can act as an acceptor for the C–H ◊ ◊ ◊ p weak interactions.14
The change of the central arene spacer in a ligand will be
anticipated to tailor intermolecular C–H ◊ ◊ ◊ p interactions and
the photophysical properties of the complex. Actually, the central
arene spacer can perform as an organic chromophore to influence
the final photophysical properties of complexes. Compounds
with multichromophores (organic and complex chromophores)
are popular candidates for harnessing light energy.15 Here, eight
complexes [Cu(phen)(pba)](BF4) (1a), [Cu2(phen)2(pbaa)](BF4)2
(2a), [Cu2(phen)2(pnaa)](BF4)2 (3a), [Cu2(phen)2(pbbaa)](BF4)2
(4a) [Cu(dmp)(pba)](BF4) (1b), [Cu2(dmp)2(pbaa)](BF4)2 (2b),
[Cu2(dmp)2(pnaa)](BF4)2 (3b) and [Cu2(dmp)2(pbbaa)](BF4)2
(4b) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-
phenanthroline) are reported. They are characterized by X-ray
diffraction, NMR, elemental analysis, UV-Vis and emissive
spectra. Complexes 1a and 1b are mononuclear, and the other six
complexes are dinuclear. All eight complexes contain a similar
structure moiety of [Cu(NN)(PP)]+ in which the polyphosphine
ligand acts in a chelating coordination mode to coordinate to the
Cu(I) ion.
Result and Discussion
X-ray single-crystal diffraction analyses show that both 1a and
1b contain a [Cu(NN)(PP)]+ moiety constructed by bidentate
pba, but each of the other six complexes (2a–4b) contains two
[Cu(NN)(PP)]+ moieties that are linked by the corresponding
bridging tetradentate phosphine pbaa, pnaa or pbbaa (Fig. 1–8).
The copper ion in the [Cu(NN)(PP)]+ moiety adopts a distorted
tetrahedral geometry. Selected structural data are summarized in
Table S1.† The Cu–P and Cu–N bond lengths, as well as the
N–Cu–N bond angles in these eight complexes are in the range
◦
˚
2.01–2.10 and 2.20–2.30 A, and 80–82 , respectively, which are
not significantly different to previously studied [Cu(NN)(PP)]+
systems.16,17 The P–Cu–P bond angles in the reported complexes
(in the range of 100–107◦) are smaller, which may be modulated
by the geometric configuration of the tertiary amine. The dihedral
angles between the NCuN and PCuP planes in [Cu(NN)(PP)]+
moieties are in the range of 89–98◦, exhibiting a flattened distorted
or rocked distorted tetrahedral geometry.5c
Except for complex 4a, all other three phen complexes exhibit
intermolecular p–p stacking interactions between phen ligands in
the solid states (Fig. 1, Fig. S1 and S2†), but dmp complexes are
not involved in intermolecular p–p stacking interactions between
dmp moieties, possibly due to steric encumbrance. In the crystal
structures of 2a, 2b and 3a, the central arene rings are involved in
intermolecular C–H ◊ ◊ ◊ p interactions with phenyl H atoms (Fig.
3, 4 and 5), and adjacent molecules are held together by these C–
H ◊ ◊ ◊ p interactions in one-dimensional chains. These chains in 2a
and 3a are further extended into 2-D supramolecular structures
through p–p stacking interactions between parallel phen planes
(Fig. S1 and S2†). However, the central arene rings in 3b and
4a are involved in intermolecular C–H ◊ ◊ ◊ p interactions with H
atoms of phen or dmp to build 2-D supramolecular structures in
which adjacent molecules are in a T-shaped orientation relative to
each other (Fig. 6, 7, Fig. S3 and S4†). Such a T-shaped packing
mode results in complex cations loosely arranged in the lattice.
Nevertheless, in the crystal structure of 4b, the central arene ring is
involved in intermolecular C–H ◊ ◊ ◊ p interactions with methylene
H atoms. No apparent C–H ◊ ◊ ◊ p interaction is involved for the
Scheme 1
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Fig. 1 (a) An ORTEP view of◦1a with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angle between the
˚
NCuN and PCuP planes is 90.5 . (b) The p ◊ ◊ ◊ p interaction of a pair of symmetry-related complexes with a ring central–central distance of 3.572 A.
exist in the crystal lattices, but they are not discussed here. The
biphenyl moieties in 4a and 4b exhibit twisted conformations with
twist angles between phenyl rings of 34.3 and 26.3◦, respectively.
But complexes with pbaa or pbbaa ligands exhibit relatively rigid
features.
Spectroscopic properties
The optical properties of the eight complexes are summarized
in Table 1. These complexes have intense absorption bands at
~240 and 280 nm, which are assigned to the p–p* transition of
intraligands. The less intense broad absorption bands at 350–
490 nm (e = 2500–6300 M-1 cm-1) are attributed to the dp–p*
MLCT absorption, whose magnitude of the extinction coefficient
is of the order expected for a dp–p* transition. Compared with
the previously investigated analogous [Cu(NN)(PP)]+ series,16 the
MLCT absorption maxima of the reported complexes occur at
slightly longer wavelengths. Accounting for this, selected DFT
calculations of 2a, 2b and 3b were undertaken. Calculation results,
similar to those previously reported,17 show that the HOMOs
in these complexes are dominated by the copper d-orbital with
admixed phosphine ligand character (Fig. 9, Fig. S5 and S6†),
while the LUMOs predominantly consist of the p-electron system
of phen or dmp. This fact confirms that the electron structures
and orbital couplings in this system should be modified by the
phosphine moiety, and the lowest energy CT excitation inevitably
stems from a metal–ligand ds* orbital. According to angular
Fig. 2 An ORTEP view of 1b with 30% thermal ellipsoids, showing the
local coordination environment of Cu+. The dihedral angle between the
NCuN and PCuP planes is 90◦.
phenyl amine moiety in 1a and 1b, maybe due to the relatively less
conjugated electrons of the phenyl amine moiety in pba. Of course,
the C–H ◊ ◊ ◊ F contacts between complex cations and anions surely
Fig. 3 (a) An ORTEP view of 2a with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angles between the
NCuN and PCuP planes around Cu1 and Cu2 are 97.4◦ and 97.4◦, respectively. (b) The 1D chain structure constructed by intermolecular C–H ◊ ◊ ◊ p
˚
˚
interactions between arene amine rings and phenyl H atoms (H29 ◊ ◊ ◊ pcentroid = 2.908 A, H57 ◊ ◊ ◊ pcentroid = 2.984 A).
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Fig. 4 (a) An ORTEP view of 2b with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angle between the
NCuN and PCuP planes is 91.9◦. (b) The 1D chain structure constructed by intermolecular C–H ◊ ◊ ◊ p interactions between arene amine rings and phenyl
˚
H atoms (H26 ◊ ◊ ◊ pcentroid = 2.868 A).
Fig. 5 (a) An ORTEP view of 3a with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angle between NCuN
and PCuP planes is 91.6◦. (b) Showing 1D chain structure constructed by intermolecular C–H ◊ ◊ ◊ p interactions between arene amine rings and phenyl
˚
˚
H atoms (H59 ◊ ◊ ◊ pcentroid = 2.631 A, H15 ◊ ◊ ◊ pcentroid = 2.566 A).
Fig. 6 (a) An ORTEP view of 3b with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angle between the
NCuN and PCuP planes is 96.8◦. (b) The intermolecular T-shaped structure induced by intermolecular C—H ◊ ◊ ◊ p interactions between arene amine
˚
˚
rings and phenyl H atoms (H38 ◊ ◊ ◊ pcentroid = 2.615 A, H40 ◊ ◊ ◊ pcentroid = 2.697 A).
Fig. 7 (a) An ORTEP view of 4a with 30% thermal ellipsoids, showing the local coordination environment of Cu+. The dihedral angles between the
NCuN and PCuP planes around Cu1 and Cu2 are 91.4◦ and 91.3◦ respectively. (b) The intermolecular T-shaped structure induced by intermolecular
˚
˚
˚
C–H ◊ ◊ ◊ p interactions between arene amine rings and phenyl H atoms (H67 ◊ ◊ ◊ pcentroid = 2.819 A, H70 ◊ ◊ ◊ pcentroid = 2.948 A, H79 ◊ ◊ ◊ pcentroid = 2.797 A).
orbital model considerations, the destabilization of the copper
d-orbital can be minimized by increasing the angle q between the
Cu-center and the two s-donor ligands situated at the corners
of the tetrahedron. That is to say, a smaller bite angle of the
phosphine in the [Cu(NN)(PP)]+ moiety can induce a larger
orbital overlap integral between the P-localized lone-pairs and
one of the occupied dp–orbitals of the copper center, resulting
in lower MLCT transitions. Therefore, the longer-wavelength
absorption maxima in the reported complexes are attributed to
the destabilization effect of smaller P–Cu–P bite angles.
Upon excitation at 425 nm, the solid state emission spectra
of 1a–4b from the MLCT excited states occur in the visible
region 513–595 nm at room temperature (Fig. 10). Comparing
complexes with different NN ligands, incorporating bulky alkyl
groups in the 2 and 9 positions of phenanthroline ligand leads to
increased excited state lifetime as well as a blue-shifted emission
7554 | Dalton Trans., 2011, 40, 7551–7558
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Table 1 The photophysical properties of eight complexes at room temperature
Emission
Solution (in CH2Cl2)
Solid state
Complex
lmax (e) (nm)
lmax (nm)
Uem
t (ms)
Kr (s-1)
knr (s-1)
lmax (nm)
t (ms)
1a
2a
3a
4a
1b
2b
3b
4b
412 (2400)
422 (5000)
425 (5200)
418 (4900)
397 (2900)
400 (6200)
389 (5200)
395 (3400)
620
618
610
612
637
615
596
583
0.00093
0.00215
0.00162
0.00991
0.00305
0.03520
0.31300
0.07150
4.14
6.77
5.56
8.15
7.55
14.90
18.95
15.21
2.25 ¥ 102
3.18 ¥ 102
1.54 ¥ 102
1.21 ¥ 103
4.04 ¥ 102
2.36 ¥ 103
1.65 ¥ 104
4.50 ¥ 103
2.41 ¥ 105
1.47 ¥ 105
9.48 ¥ 104
9.67 ¥ 104
1.32 ¥ 105
6.48 ¥ 104
3.62 ¥ 104
6.10 ¥ 104
563
582
572
595
513
529
566
589
19.95
15.82
15.83
14.57
50.94
34.28
28.57
14.82
Fig. 8 An ORTEP view of 4b with 30% thermal ellipsoids, showing
the local coordination environment of Cu+. The dihedral angles between
the NCuN and PCuP planes around Cu1 and Cu2 are 96.6◦ and 89.8◦
respectively.
Fig. 10 The emission spectra of complexes in the solid state at room
temperature, upon excitation at 425 nm.
At room temperature, the luminescence spectra of complexes
in dilute CH2Cl2 solution were also recorded upon excitation at
425 nm (Fig. 11). Similar to the solid state luminescence, the
dmp-containing complex exhibits an increased quantum yield and
excited-state lifetime, as well as blue-shifted emission relative to
the corresponding phen complex, due to the steric encumbrance
of the bulky alkyl group, which will moderate the structural re-
laxation/reorganization that attends formation of the CT excited
state in solution. In fact, the structural relaxation/reorganization
will narrow the gap between the ground and excited state, enhance
the coupling between the two states, and shorten the excited state
lifetimes. Generally, phen complexes exhibit similar luminescence
in solution. Concerning complexes with identical dmp ligands
but different phosphine ligands, the tendency toward increased
quantum yield and lifetime, as well as the blue-shifted emission,
goes with the size increase of complexes. It seems that the central
arene rings (phenyl, naphthyl or biphenyl) have an influence on
the final photophysical properties of complexes. The larger the
p-conjugated extension of the central arene ring is, the better the
photophysical properties of the complex are. So it can be deduced
that the central arene ring performs as an organic chromophore,
and the cooperative effect of the complex chromophore is related
to the central metal and the central organic chromophore results
in the final photophysical properties of the complex. 3b with a
Fig. 9 Contour plots of the HOMO (left) and LUMO (right) of complex
3b.
band. The reason for these is that bulky substituents can sterically
prevent structural relaxation in the MLCT states, and decrease
non-radiative decay. Furthermore, for complexes with identical
diimine but different phosphine ligands, the tendency toward an
increased lifetime, as well as for a blue-shifted emission, goes
with the decrease in size of the phosphine ligands. Intermolecular
C–H ◊ ◊ ◊ p interactions can trigger vibrationally relaxed energy
transfer in the excited state, and subsequently result in non-
radiative decay. A larger-sized central arene ring is favorable
for forming intermolecular C–H ◊ ◊ ◊ p interactions (see the above-
discussed crystal structure). Therefore smaller-sized complexes
exhibit longer lifetimes and blue-shifted emissions in the solid
state due to less vibrationally relaxed behavior related to flexible
C–H ◊ ◊ ◊ p bonds. Complexes 4a and 4b exhibit the lowest intensity
luminescence and the shortest lifetime, maybe due to the biphenyl
moiety in dppaa, which can be rotated, enhancing the vibrationally
relaxed CT excited state.
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solid state photophysical properties. For complexes with identical
diimine but different phosphine ligands, smaller-sized complexes
show better photophysical properties due to less vibrationally
relaxed behavior related to flexible C–H ◊ ◊ ◊ p bonds. Nevertheless,
in dilute solution, the backbone (phenyl, naphthyl or biphenyl)
has an influence on the final photophysical properties. The larger
the p-conjugated extension of the central arene ring is, the better
the photophysical properties of the complex are. The rigid and
large complex 3b exhibits extraordinary emission. Intermolecular
C–H ◊ ◊ ◊ p interactions are very weak in dilute solution.
Experimental Section
General
All chemicals were of reagent grade and were used as received
without further purification. Elemental analyses were performed
with a Carlo ERBA 1106 analyzer; 1H and 31P{ H} spectra were
1
Fig. 11 The emission spectra of complexes in CH2Cl2 solution (5 ¥ 10-4 M)
at room temperature, upon excitation at 425 nm.
recorded on a Bruker 500 spectrometer at 500.13 and 202.46 MHz,
respectively. Electrospray mass spectra were recorded on a Bruck
HCT ESI spectrometer. Absorption spectra were measured with
a Varian CARY-100UV spectrophotometer. The luminescence
spectra and emission lifetimes were measured at room temperature
on a FL3-P-TCSPC spectrophotometer with a xenon lamp as
the light source. The absorption and luminescence spectra of
complexes were measured in CH2Cl2. Emission quantum yield,
U, was measured with the use of [Ru(bpy)3](PF6)2 in MeCN as
a standard (U = 0.09). Ligands pba, pbaa, pnaa and pbbaa are
reported first here and synthesized according to references.20
rigid naphthalene ring exhibits the best emission with the largest
quantum yield (0.313) and the longest emission lifetime (18.95 ms).
The influence of intermolecular interactions on luminescent
properties is much weaker in dilute solution. It should be noted
that complexes 4a and 4b have relatively better emissions in
solution, maybe due to the increasing coplanarity of two phenyl
rings in the biphenyl moiety in solution leading to extended
intraligand electron delocalization and minimized excited state
distortion of the corresponding complex.18 Nevertheless, the fact
that the emission of 4b is similar to 2b, but not as good as that of
rigid complex 3b, shows that the rotating/vibrating behavior of the
biphenyl moiety is still not ignored in solution. The emission yields
of our phen-complexes are similar to that of Cu(phen)(POP)]+,
but their lifetimes are longer than that of the latter. However, the
lifetimes of dmp complexes in our system are comparable with
those of [Cu(dmp)(POP)]+ or [Cu(dbp)(POP)]+,6a but the yields
are a little lower than those of the latter complexes. Complex 3b is
exceptional, its emission yield is higher than [Cu(dmp)(POP)]+,
even comparable with that of [Cu(POP)(DMPP)]+ (DMPP =
2,9-dimethyl-4,7-phenylphenanthroline), which was reported as
a good luminophore with the highest quantum yield in the
[Cu(NN)(PP)]+ system.19
The experimentally measured t and U values were used to
calculate the radiative, kr and the nonradiative, knr, rate constants.
The kr values of dmp complexes exhibit a marked increase with
size increase, but the knr values of phen complexes slightly decrease
with size increase, showing that the bulkiness of ligand preventing
complexes from distorting in the excited states plays a dominant
role in solution. The knr values of 2b and 4b are similar, though
their sizes are very different. The highest kr value, as well as the
low nonradiative decay of 3b results from the cooperative effects
of structural rigidity and steric encumbrance.
X-ray crystallography
Reflection intensity data for 1a, 1b, 2b and 4a were collected (1a
and 1b at a temperature of 296 K, 2b and 4a at 173 K) on a
Bruker APEX CCD diffractometer with graphite monochromated
˚
Mo-Ka radiation (l = 0.71073 A) using the w technique, and
data for 2a, 3a, 3b and 4b were collected at 150 K on a Oxford
‘Xcalibur, Sapphire3, Gemini ultra’ diffractometer with Enhance
˚
Ultra (Cu) X-ray Source (l = 1.5418 A) using the w technique. All
the structures were solved by direct methods and refined with the
full-matrix least-squares on F2 using SHELXTL. The structure
3
˚
of 2a contains solvent accessible voids of 205 A , indicating
that there may be solvents occupied in the voids. However,
they cannot be found in the crystal structure. Maybe they are
likely too diffuse/disordered to be resolved. During the structure
refinement of 4b, an unidentified and badly disordered solvent
molecule (probably DMF) was removed with the squeeze option in
PLATON.21 No hydrogen atoms were assigned on water molecules
O1 and O2. Crystal and structure refinement data are summarized
in Table S2.†
Computational details
The Gaussian03 program22 was used in the molecular orbital
calculations on the basis of corresponding coordinates of the
X-ray crystal structures. All calculations were performed with the
B3LYP method and the 6-311++G(d,p) basis sets.23
In conclusion, the crystal structures and photophysical prop-
erties of these eight complexes are discussed in detail. Results
show that the steric encumbrance of bulky substitutes in the 2
and 9 positions of phenanthroline plays a dominant role in the lu-
minescent properties of the [Cu(NN)(PP)]+ system. Furthermore,
intermolecular C–H ◊ ◊ ◊ p interactions have an influence on the final
[Cu(phen)(pba)](BF4) (1a)
A typical procedure is as follows. A mixture of [Cu(CH3CN)4]BF4
(0.016 g, 0.05 mmol) and phosphine ligand (0.0245 g, 0.05 mmol)
7556 | Dalton Trans., 2011, 40, 7551–7558
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in 4 ml CH3CN was stirred at room temperature for 0.5 h and then
phen (0.009 g, 0.05 mmol) was added. This reaction mixture was
stirred for an additional 1 h and filtered. The vapor diffusion of
diethyl ether into the resulting clear yellow filtrate afforded yellow
crystals of the complex. The complex was obtained by filtration,
washed by diethyl ether and dried in vacuo. Yield: 0.034 g (83%).
Anal. calcd for C44H37N3BF4P2Cu: C, 64.39; H, 4.51; N, 5.12.
Found: C, 64.21; H, 4.70; N, 5.52. 1H NMR (CD3SOCD3, 25 ◦C,
TMS): d = 5.0 (4H, –CH2–), 6.4–6.8 (5H, C6H5–N), 7.2–7.4 (20H,
diffusion of diethyl ether into solution of complex in mixture of
MeCN-toluene.
[Cu2(phen)2(pbbaa)](BF4)2 (4a)
Yield: 0.031 g (38%). Anal. calcd for C88H72N6B2F8P4Cu2, C, 64.47;
1
H, 4.40; N, 5.13. Found: C, 64.83; H, 4.21; N, 5.58. H NMR
(CD3SOCD3, 25 ◦C, TMS): d = 5.1 (8H, –CH2–), 6.5–6.9 (8H,
N–C6H4–C6H4–N), 7.3–7.5 (40H, C6H5–P), 7.7–8.8 ppm (16H,
1
phen). 31P{ H}–NMR (CDCl3): -14.85. ESI–MS (+): m/z 732
1
C6H5–P), 7.8–8.8 ppm (8H, H–phen). 31P{ H}–NMR (CDCl3):
[Cu2(phen)2(pnaa)]2+.
-14.95. ESI–MS (+): m/z 733 [Cu(pda)(phen)]+.
The procedures for the synthesis of 1b–4b were essentially
identical to that described in 1a, only different ligands are used.
[Cu2(dmp)2(pbbaa)](BF4)2 (4b)
Yield: 0.035 g (41%). Anal. calcd for C92H80N6B2F8P4Cu2, C, 65.17;
[Cu(dmp)(pba)](BF4) (1b)
1
H, 4.72; N, 4.96. Found: C, 65.52; H, 4.97; N, 5.05. H NMR
(CD3SOCD3, 25 ◦C, TMS): d = 2.4–2.5 (12H, CH3–), 5.1–5.3 (8H,
Yield: 0.032 g (76%). Anal. calcd for C46H41N3BF4P2Cu: C, 65.09;
1
–CH2–), 7.5–7.8 (8H, N–C6H4–C6H4–N), 7.8–8.0 (40H, C6H5–P),
H, 4.83; N, 4.95. Found: C, 64.82; H, 4.91; N, 5.12. H NMR
1
8.2–9.1 ppm (12H, H–phen). 31P{ H}–NMR (CDCl3): -20.77.
(CD3SOCD3, 25 ◦C, TMS): d = 2.7 (6H, CH3–), 5.3 (4H, –CH2–),
ESI–MS (+): m/z 760 [Cu2(dmp)2(pnaa)]2+. Single crystals were
collected by vapor diffusion of diethyl ether into DMF solution
of complex.
7.4–7.6 (5H, C6H5–N), 7.7–7.9 (20H, C6H5–P), 8.2–9.1 ppm (6H,
1
H–phen). 31P{ H}–NMR (CDCl3): -19.83. ESI–MS (+): m/z 761
[Cu(pda)(dmp)]+.
[Cu2(phen)2(pbaa)](BF4)2 (2a)
Acknowledgements
Yield: 0.045 g (58%). Anal. calcd for C82H68N6B2F8P4Cu2, C,
This work is financially sponsored by the National Natural
Foundation of China (No. 20463001, 20863001), the Natu-
ral Foundation of Guangxi Province (2011GXNSFA018041,
2010GXNSFF013001), and the Programme for Excellent Talents
in Guangxi Higher Education Institutions.
1
63.00; H, 4.35; N, 5.38. Found: C, 63.45; H, 4.68; N, 5.41. H
NMR (CD3SOCD3, 25 ◦C, TMS): d = 4.7 (8H, –CH2–), 6.2
(4H, N–C6H4–N), 7.2–7.4 (40H, C6H5–P), 7.0–8.8 ppm (16H, H–
1
phen). 31P{ H}–NMR (CDCl3): -16.08. ESI–MS (+): m/z 694
[Cu2(pbaa)(phen)2]2+.
References
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[Cu2(phen)2(pnaa)](BF4)2 (3a)
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1
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8.9 ppm (62H, (6H, N–C10H6–N) + (40H, C6H5–P) + (16H, H–
1
phen)). 31P{ H}–NMR (CDCl3): -16.25. ESI–MS (+): m/z 719
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◦
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©