Alkynyl triphosphine copper complexes: Synthesis and photophysical studies

Article abstract of DOI:10.1039/c5dt01870f

A rigid triphosphine PPh₂C₆H₄–PPh–C₆H₄PPh₂ (P³) reacted with Cu⁺ and a stoichiometric amount of terminal alkyne under basic conditions to give a family of copper(I) alkynyl compounds [Cu(P³)CuCR]. The number of terminal –CuCH groups in the starting ligand determines the nuclearity of the resulting complexes giving mono- (1, R = Ph; 2, R = C₆H₄OMe; 3, R = C₆H₄NO₂; 4, R = C₆H₄CF₃; 5, R = 2-pyridyl), di- (R = -(C₆H₄)_n-, n = 1 (6), n = 2, (7), n = 3 (2)) and trinuclear complexes (9, R = 1,3,5-(C₆H₄)₃-C₆H₃; 10, R = 1,3,5-(C₆H₄-4-C₂C₆H₄)₃-C₆H₃). In all the complexes the Cu(I) centers are found in a distorted tetrahedral environment that is achieved by tridentate coordination of the P³ ligand and σ-bonding to the alkynyl function. The crystal structures of 1, 3 and 5 were estimated by single crystal X-ray diffraction analysis. The ³¹P, ¹H and ¹H–¹H COSY NMR spectroscopy confirms that all the molecules remain intact in solution. The photophysical studies carried out in the solid state at 298 and 77 K revealed moderate to weak orange luminescence (Φ_em up to 19%), tentatively assigned to thermally activated delayed fluorescence for the mononuclear complexes. The quantum yields of emission of 1–10 demonstrated strong dependence on the nature of the alkynyl ligand, the role of which in the electronic transitions was elucidated by TD-DFT computational studies.

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Alkynyl triphosphine copper complexes: synthesis
and photophysical studies†
Cite this: DOI: 10.1039/c5dt01870f
Gomathy Chakkaradhari,a Andrey A. Belyaev,b Antti J. Karttunen,c Vasily Sivchik,a
Sergey P. Tunik*b and Igor O. Koshevoy*a
A rigid triphosphine PPh2C6H4–PPh–C6H4PPh2 (P3) reacted with Cu+ and a stoichiometric amount of
terminal alkyne under basic conditions to give a family of copper(I) alkynyl compounds [Cu(P3)CuCR].
The number of terminal –CuCH groups in the starting ligand determines the nuclearity of the resulting
complexes giving mono- (1, R = Ph; 2, R = C6H4OMe; 3, R = C6H4NO2; 4, R = C6H4CF3; 5, R = 2-pyridyl),
di- (R = -(C6H4)n-, n = 1 (6), n = 2, (7), n = 3 (2)) and trinuclear complexes (9, R = 1,3,5-(C6H4)3-C6H3; 10,
R = 1,3,5-(C6H4-4-C2C6H4)3-C6H3). In all the complexes the Cu(I) centers are found in a distorted tetra-
hedral environment that is achieved by tridentate coordination of the P3 ligand and σ-bonding to the
alkynyl function. The crystal structures of 1, 3 and 5 were estimated by single crystal X-ray diffraction ana-
lysis. The 31P, 1H and 1H–1H COSY NMR spectroscopy confirms that all the molecules remain intact in
solution. The photophysical studies carried out in the solid state at 298 and 77 K revealed moderate to
weak orange luminescence (Φem up to 19%), tentatively assigned to thermally activated delayed fluor-
escence for the mononuclear complexes. The quantum yields of emission of 1–10 demonstrated strong
dependence on the nature of the alkynyl ligand, the role of which in the electronic transitions was eluci-
dated by TD-DFT computational studies.
Received 18th May 2015,
Accepted 18th June 2015
DOI: 10.1039/c5dt01870f
www.rsc.org/dalton
of OLEDs copper(I) compounds are considered to be promising
emitting materials as, in a favorable case, they are able to
Introduction
The luminescent copper(I) complexes have been extensively exhibit thermally activated delayed fluorescence (TADF) that
investigated for nearly forty years since the pioneering reports stems from a very fast intersystem crossing between S1 and T1
on their photophysical properties.1 During the last decade par- excited states and, consequently, utilizing both singlet and
ticular attention was paid to systematic modulation of ligand triplet excitons via a singlet harvesting mechanism12,14,20,21
architecture of copper-containing species due to the (i) low thus
cost of the corresponding metal; (ii) facile coordination chem- efficiency.5,6,12,22,23
istry of the Cu(I) ion that allows for stereochemically controlled A rational choice of the ligands to optimize luminescence
offering
an
improved
electroluminescence
high yield preparation of a wide variety of complexes; and (iii) efficiency of Cu(I) species was considerably facilitated since a
their capability of efficiently generating intense luminescence number of experimental approaches supported by theoretical
under ambient conditions.2,3–9 This attractive photophysical investigations shed light on the details of structural rearrange-
feature, which comprises high quantum yield in the solid state ment and electronic processes, which occur in the excited
and tunable emission energy,7–14 has found applications in state.24 One of the main shortcomings of Cu(I) complexes is
technologically important areas such as chemical sensing,15 structural relaxation from tetrahedral to a pseudo-planar geo-
light-emitting electrochemical cells (LEC)16,17 and, immensely, metry as a result of a formal oxidation to Cu(II) that takes place
in organic light-emitting diodes (OLED).3,5–7,18,19 In the field upon metal to ligand charge transfer (MLCT). Consequently, it
increases the probability of non-radiative decay pathways
leading to a dramatic drop of the emission efficiency. Thus
one of the main trends in the design of Cu(I) luminophores
aUniversity of Eastern Finland, Department of Chemistry, 80101, Joensuu, Finland.
E-mail: igor.koshevoy@uef.fi
bSt. Petersburg State University, Department of Chemistry, Universitetskii pr. 26,
involves the use of relatively bulky ligands to suppress solvent-
induced exciplex quenching,25 to increase structural
rigidity3,6,26 and prevent flattening of the tetrahedral ligand
arrangement around Cu(I) centres.
Different types of ligand environments have been probed
to achieve intense emission and robustness of the Cu(I)
198504, St Petersburg, Russia. E-mail: stunik@inbox.ru
cAalto University, Department of Chemistry, FI-00076 Aalto, Finland
†Electronic supplementary information (ESI) available: Synthesis of the
ligands; optimized Cartesian coordinates of the studied systems. CCDC
1401069–1401071 for 1, 3 and 5. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c5dt01870f
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complexes.4 They include thoroughly studied homo- and hetero- constituting ligand nature onto the physical characteristics of
leptic bis-diimine Cu(I) compounds [Cu(NN)2]+ (ref. 26 and these species.
27) typically displaying weak quantum efficiency below 1%.
More recently, research focus has largely shifted to the mixed
phosphine–diimine complexes [Cu(NN)(PP)]n+ (n = 0, 1) of
neutral and cationic nature, for which an impressive enhance-
Results and discussion
Synthesis and characterization
ment of quantum yield was demonstrated reaching as high as
90%.5,12,16,18,23,25,28 The emission observed originates mainly The title compounds were obtained according to a general syn-
from MLCT excited states that make possible tuning lumine- thetic route shown in Scheme 1. The reactions of the [Cu(P3)]+
scence parameters through electronic and stereochemical pro- species generated in situ with a stoichiometric amount of a
perties of the ligands that stimulated further development of terminal mono-, di- or trialkyne in the presence of a base
the preparative chemistry of the Cu(I) ion. Among the notable allowed for the isolation of the alkynyl–triphosphine copper
examples are the amidophosphine derivatives [Cu(PN)(PP)],10 complexes [Cu(P3)C2R] (1–10) as air and moisture stable yellow
which exhibit intense and tunable green to blue emission in solids. However, most of the compounds were found to be
solution (Φem = 16–70%); highly luminescent dinuclear halide unstable in chlorinated solvents, which induce formation of a
species [Cu2(PN)3X2] covering the visible spectrum from blue chloro derivative [Cu(P3)(Cl)]34 through the substitution of the
to red (Φem = up to 96%);7,8 families of three-coordinate com- alkyne ligands.
plexes featuring phosphine halides [Cu(PP)X],6 arylamido-
phosphines [Cu(PP)NAr2]11 and carbene–diimines [Cu(NN)- in the solid state by single crystal X-ray diffraction analysis
NHC].9,13
(Fig. 1, crystallographic data are given in Table S1, ESI†). The
The mononuclear complexes 1, 3 and 5 were characterized
A general common feature of the Cu(I) complexes men- selected structural parameters are listed in Table 1. The coordi-
tioned above is a conformationally rigid chelating bidentate nation sphere of the copper ion in 1, 3 and 5 contains chelat-
phosphine that brings steric bulkiness and minimizes ing tridentate P3 phosphine and the σ-bound alkynyl group,
the undesired excited state distortions. It has to be noted that which completes a pseudo-tetrahedral arrangement around
triphosphine ligands have been rarely used in the synthesis the metal center. The Cu–P distances are comparable to the
of Cu(I) species with only a few reports on luminescent corresponding values reported for the related phosphine
compounds.29–31 In particular, coordination chemistry of a copper(I) complexes.31,35,36 The central P(2)–Cu bond length is
tridentate chelating phosphine PPh2C6H4–PPh–C6H4PPh2 slightly longer than the distances to the lateral PPh2 groups
(P3, see Scheme 1) with coinage metals remains poorly presumably as a result of a relatively strained geometry of the
explored32 despite promising practical results, which were P3 ligand. Additionally, the strongly donating anionic –CuCR
reported for these inorganic materials.33,34 In the current work fragment may enhance this effect due to a rather large C(1)–
we employ the triphosphine ligand P3 in combination with a Cu(1)–P(2) angle (124 and 131°). The Cu–C (terminal alkyne)
series of mono-, di- and trialkynes for the preparation of a contacts are in the range of 1.921–1.927 Å and are expectedly
family of Cu(I) complexes of different nuclearity. The lumine- shorter than the bond lengths in oligomeric copper alkynyl
scence properties of the resulting compounds were systemati- complexes, which typically demonstrate μ2- or μ3-bridging
cally investigated in the solid state to discover the effect of the coordination mode of –CuCR ligands.37 Due to a pronounced
tendency of the alkynyl ligands to bind two or more Cu(I)
centers through σ–π coordination mode a significant number
of tri- and tetranuclear species have been described37,38 but
surprisingly no monomeric alkynyl complexes were character-
ized to date. In this context it is worth mentioning that a con-
gener alkynyl–phosphine compound bearing an aliphatic
tripod ligand, that was initially thought to be monomeric,30
which was later described as
a dimer {Cu(μ2-CuCPh)-
(triphos)}2 (triphos = (PPh2CH2)3CMe),35 with only two P atoms
involved in binding to the metal ion. The solution behavior of
the complexes 1–10 was investigated by H and 31P{1H} NMR
1
spectroscopy. All the compounds demonstrate a very similar
set of resonances in the 31P spectra (see the Experimental
section and Fig. 3 for examples) irrespective of their nuclearity
that is indicative of a symmetrical arrangement of the di- (6–8)
and trimetallic (9–10) species and equivalence of the constitut-
ing {CuP3} fragments. This A2B system observed for the free
ligand together with a downfield shift of the signals in 1–10
clearly points to the phosphorus atom coordination to the
copper ions in solution. A narrow range of the chemical shifts
Scheme 1 Synthesis of the complexes 1–10 (298 K, 10 h, acetone).
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Fig. 1 Molecular views of the complexes 1, 3, and 5; thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms are omitted for
clarity. One of two independent molecules found in the unit cells of 1 and 3 is shown.
Table 1 Selected bond lengths and angles for complexes 1, 3, and 5
(two values for 1 and 3 correspond to the independent molecules found
in the unit cell)
1
3
5
Bond lengths, Å
P(1)–Cu(1)
2.2798(9)
2.2840(9)
2.3003(9)
2.2622(9)
2.2988(10)
2.2899(9)
1.925(4)
1.930(3)
1.195(5)
1.198(5)
2.3049(7)
2.3029(6)
2.2751(6)
2.2708(7)
2.2690(6)
2.2961(6)
1.927(2)
1.934(3)
1.213(3)
1.199(4)
2.2864(15)
2.2965(14)
2.2869(15)
1.921(5)
P(2)–Cu(1)
P(3)–Cu(1)
C(1)–Cu(1)
C(1)–C(2)
1.199(8)
Bond angles, °
C(2)–C(1)–Cu(1)
171.7(3)
177.2(3)
171.8(2)
171.2(2)
115.25(7)
116.78(7)
129.12(7)
130.85(7)
118.22(7)
118.42(7)
113.69(2)
112.11(2)
87.32(2)
86.48(2)
87.77(2)
85.82(2)
172.1(5)
120.2(2)
132.3(2)
114.1(2)
113.7(6)
85.36(5)
84.73(5)
C(1)–Cu(1)–P(1)
C(1)–Cu(1)–P(2)
C(1)–Cu(1)–P(3)
P(1)–Cu(1)–P(3)
P(1)–Cu(1)–P(2)
P(3)–Cu(1)–P(2)
113.21(10)
118.86(10)
131.53(11)
124.17(11)
121.94(11)
116.82(11)
114.07(3)
115.20(3)
85.18(3)
Fig. 2 1H–1H COSY NMR spectra of the complex 3 (acetone-d6, 298 K).
88.21(3)
84.01(3)
86.62(3)
the phosphine and alkynyl ligands generate four well-separ-
ated multiplets in the region 7.4–7.8 ppm, while the PPh frag-
ment displays a non-resolved group of signals around 7.2 ppm.
Further analysis of the 1H spectroscopic data for other com-
pounds allows for an easy identification of the resonances of
the alkyne ligands. The 1H–1H COSY spectrum of the tri-
nuclear complex 10 given in Fig. 3 shows the assignment of
the trialkynyl protons that confirm the C3v symmetry point
group of the idealized molecule. Relative intensities and multi-
plicities of the proton NMR signals observed for all the title
compounds fit well with the composition and structures
suggested in Scheme 1.
observed for 1–10 (δA from 1.1 to −0.5 ppm and δB from −1.8
to −3.1 ppm) implies a relatively small effect of the alkynyl
substituents onto electronic properties of the metal centre that
is also in line with the photophysical characteristics (see
below).
A complete assignment of the proton spectra was done on
the basis of the 1D and 2D 1H–1H COSY experiments (Fig. 2
1
and 3). Analogous to 31P data, the H signals of the P3 phos-
phine protons do not demonstrate significant alterations upon
variation of the alkynyl ligands to give essentially similar
spectroscopic patterns with satisfactorily resolved resonances,
which are clearly seen in the spectrum (see for example Fig. 2).
The phenyl protons of the terminal PPh2 groups appear as two
sets of “ortho–meta–para” signals. The phenylene spacers of
Photophysical characteristics
The complexes 1–10 do not demonstrate detectable photo-
luminescence in solution. Therefore, the photophysical investi-
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Fig. 4 Normalized solid state excitation (left) and emission (right)
spectra of 1 and 5 at 298 K (dashed lines) and 77 K (solid lines).
lowering the temperature to 77 K being red shifted by
6–10 nm. The room temperature excited state lifetime of the
complexes under study fall in a microsecond domain and are
comparable to the corresponding values of other mononuclear
Cu(I) phosphine complexes.6,12,20,21,39,40 However, the lifetime
values of 1, 2, and 4 demonstrate a very significant up to 130-
fold increase upon cooling down to 77 K. Together with the
small red-shift of the emission energy (5–10 nm) the lumine-
scence behavior of these complexes might be considered as
thermally activated delayed fluorescence (TADF).12,20,21 Conse-
quently, the emission at 77 K can be considered as the one
from the triplet state, while at room temperature thermal equi-
librium between the nearest S1 and T1 states leads to a popu-
lation of higher lying singlets causing a blue shift of emission
maximum and a considerable decrease of the τ values, which
is in fact a derivative of the triplet (μs) and singlet (ns) decay
lifetimes. The double exponential treatment of the lumine-
scence decay for the solid state emission is not surpris-
ing21,40,41 and may be attributed to similar electronic
transitions, which differ in relaxation rates due to the local dis-
order in the crystal cell or to the presence of two molecules
Fig. 3 31P{1H} (top) and 1H–1H COSY (bottom) NMR spectra of the
complex 10 (CD2Cl2, 298 K).
gation was carried out in the solid state only, and the data are
given in Table 2. Upon photoexcitation the mononuclear com-
plexes 1–5 (except for 3) exhibit yellow emission of a moderate
intensity (Φem ranges from 6 to 19%). Fig. 4 and S2† show exci-
tation and emission spectra of the solid powders at 298 and
77 K. The compounds 1, 2, 4 and 5 show broad structureless
bands, the maxima of which are only slightly influenced by
Table 2 Photophysical properties of the complexes 1–10 in the solid state
298 K
77 K
λex, nm
λem, nm a
τav, μs b
Φ, %
kr, s−1 c
knr, s−1 d
λex, nm
λem, nm
τav, μs b
1
2
3
4
5
6
7
8
9
10
415
415
580
340, 415
415
602
602
722
573
573
603
616
629
638
560
1.8
2.1
—
2.5
3.8
1.6
2.2
2.2
1.0
0.3
6.3
7.9
∼0.1
11
3.4 × 104
3.8 × 104
5.1 × 105
4.4 × 105
415
415
415
370
415
401
426
426
426
442
612
612
717
579
246
73
—
59
149
50
13
—
166
—
4.3 × 104
5 × 104
3.5 × 105
2.2 × 105
6 × 105
19
579
424
2.6
1.4
0.6
2
1.6 × 104
6.3 × 103
2.8 × 103
2 × 104
540sh, 581, 635
556, 642
574, 622, 683
530, 575sh, 640
524, 570, 607, 647sh
341, 441
347, 441
393
4.4 × 105
4.6 × 105
1 × 106
312, 483
∼0.1
3.5 × 103
3.5 × 106
a λexc = 420 nm for 1, 2, 4–9; λexc = 550 nm for 3; λexc = 490 nm for 10. b Average emission lifetime for the two exponential decay determined by the
equation τav = (A1τ12 + A2τ12)/(A1τ1 + A2τ1). c kr were estimated by Φ/τav. d knr were estimated by kr(1 − Φ)/τav.
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Fig. 6 Normalized solid state excitation (left) and emission (right)
spectra of 10 at 298 K and 77 K.
Fig. 5 Normalized solid state excitation (left) and emission (right)
spectra of 8 at 298 K and 77 K.
with slight variations in structural characteristics (see e.g. the
structures of 1 and 3).
species 9 and 10 pointing to an ascending role of effective
quenching processes for the compounds with star-like
trialkynes.
It is worth noting that the complex 3, containing an alkyne
functionalized with the NO2 group, displays photophysical
characteristics very different from those of other mononuclear
congeners. Its emission band is considerably red shifted that
is accompanied by a dramatic decrease of quantum efficiency
(Φem is ca. 0.1%). The computational results (vide infra) show a
significant contribution of the nitro functionality to the triplet
excited state that is contrasting with electronic structures of
other monometallic compounds. This delocalization of the
electron density might account for the observed red shift of
luminescence and appearance of non-radiative decay pathways,
which cause a dramatic decrease of the quantum efficiency. At
room temperature the dinuclear species 6–8 demonstrate
broad emission bands (Fig. 5), whereas at 77 K (Fig. S3†) these
bands start to show the structure with a clear vibronic pro-
gression (ν = 1307 and 1463 cm−1) in the case of 8, which can
be assigned to intraligand transitions located at the alkynyl
ligand. This observation is consistent with theoretical results
that clearly point to the intraligand T1 → S0 transition as the
origin of the triplet luminescence at 77 K (Fig. 5).
Computational results
The photophysical properties of the Cu(I) complexes 1–10 were
also investigated using quantum chemical methods. The geo-
metries of the studied complexes were fully optimized at the
DFT-PBE0 level of theory and the lowest energy singlet and
triplet excited states were studied by means of time-dependent
TD-DFT-PBE0 calculations (see the Experimental section for
full computational details). The optimized geometries of the
complexes 1, 3, and 5 are in good agreement with the available
X-ray structures (the coordinates of the optimized structures
are included in the ESI†). Table 3 lists the wavelengths pre-
dicted for the S0 → S1 and T1 → S0 electronic transitions of all
studied complexes, while the corresponding electron density
difference plots are shown in Fig. 7 for complexes 1, 6, and 9
(the other complexes are illustrated in the ESI†). For the
A rather similar behavior is detected for trinuclear com-
plexes 9 and 10, which show featureless bands at 298 K.
Appearance of a fine structure is observed at 77 K for 10
having the most extended alkyne ligand in this series (Fig. 6
and S4†) that testifies to the alkynyl ligand-centered nature of
photoemission.
Table 3 Computational photophysical results for the Cu(I) complexes
1–10 in the gas phase (TD-DFT-PBE0)a
λ (S0 → S1) (nm)
λ (T1 → S0) (nm)
A severe drop of emission intensity for the di- and trinuc-
lear complexes with extended alkynyl backbones (7, 8, 10) is
reflected by radiative decay rate constants kr (derived from the
relationship Φem = kr/kobs), which demonstrate a 5–10 times
decrease in comparison with the mononuclear congeners
(Table 2). This trend is particularly illustrated by the dinuclear
compounds, for which the radiative decay rate gets slower with
elongation of the phenylene spacers u-(C6H4)n-u: 1.6 × 104
s−1 (6, n = 1), 6.3 × 103 s−1 (7, n = 2), 2.8 × 103 (8, n = 3). Accord-
Theor.
Exp.a
Theor.
Exp.a
1
2
3
4
5
6
7
8
9
10
421
424
409
415
418
494
467
453
451
438
415
415
415
370
415
401
426
426
426
442
614
600
673
621
610
768
807
803
634
685
612
612
717
579
579
635
642
683
640
647
ingly, the nonradiative decay rate constants (defined as knr
=
a Excitation and emission wavelengths from the solid state, 77 K.
kobs − kr, kobs = 1/τav) are visibly larger for the trinuclear
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majority of the studied complexes, the predicted S0 → S1 exci- In a similar fashion, the T1 → S0 emission wavelengths are
tation wavelengths are in reasonable agreement with the also clearly overestimated for the complexes 6–8. For the
experimental excitation energies obtained in the solid state at mononuclear compounds 1–5, the predicted emission wave-
77 K. For the complexes 4, 6–8, the predicted excitation wave- lengths are rather well in line with the experimental values. In
lengths are overestimated in comparison with the experiment. particular, the emission wavelength for the complex 3 is
clearly larger in comparison with the other mononuclear com-
plexes that are in line with experimental observations.
In the case of mononuclear complexes 1–5, the S0 → S1
transition can be assigned to IL charge transfers involving the
phosphine and alkynyl ligands, possibly mixed with MLCT/
LLCT contributions (Fig. 7). The T1 → S0 emission turned out
to be completely different from the S0 → S1 transitions. For
1 and 4 it is practically an intraligand transition of the alkynyl
ligand, while the complexes 2 and 3 also show a minor contri-
bution from the Cu atom. In complex 5 with alkynyl–pyridine
functionality the phosphine ligand together with the Cu atom
participate in charge transfer processes. The reason for a
lower emission energy of the complex 3 with respect to the
other mononuclear congeners is not completely clear. A major
difference in comparison with 1, 2, and 4 is that the nitro
group in 3 contributes significantly to the T1 → S0 emission in
contrast to the X groups of the other complexes (X = OMe, H,
CF3), suggesting a more significant effect on the energy levels
of the alkynyl ligand.
For the di- and trinuclear complexes 6–10, the S0 → S1 tran-
sition is rather similar to that of mononuclear compounds 1–5
and is mainly composed of metal-perturbed ILCT shared with
some mixed MLCT/LLCT. The complex 6 is the only multi-
nuclear compound showing significant contributions from the
metal atom and the phosphine ligands in the T1 → S0 emis-
sion. In the case of species 7–10 with extended alkynyl back-
bones the T1 → S0 emission is very clearly centered on the
alkynyl ligand. Analysis of electron difference density plots
(Fig. 7 and S5†) implies significant ligand to ligand charge
transfers for 7–10 during the S1 → T1 transition that might
result in the appearance of efficient nonradiative pathways of
the excited state relaxation, which account for lower quantum
yields of the di- and trinuclear compounds.
Conclusions
To sum up, chelating triphosphine PPh2C6H4–PPh–C6H4PPh2
(P3) was successfully used for the preparation of a series of
copper(I) alkynyl compounds. Depending on the number of
terminal –CuCH groups, mono- (1–5), di- (6–8) and trinuclear
(9 and 10) complexes were obtained. In all the title species Cu
centers adopt a distorted tetrahedral geometry, which is pro-
vided by the tridentate coordination of P3 and σ-bonding of
the alkyne moiety. The complexes 1, 3 and 5 were character-
ized by single crystal X-ray diffraction measurements, while the
composition and structures of other species were estimated by
Fig. 7 Electron density difference plots for the lowest energy singlet
excitation (S0 → S1) and the lowest energy triplet emission (T1 → S0) of
the Cu(I) complexes 1, 6, and 9 (isovalue 0.002 a.u.). During the elec-
means of 31P, 1H and 1H–1H COSY NMR spectroscopy. The
title compounds exhibit moderate to weak room temperature
luminescence in the solid state with quantum yields reaching
19%. Analysis of the photoemission characteristics obtained at
tronic transition, the electron density increases in the blue areas and
decreases in the red areas. Hydrogen atoms are omitted for clarity.
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298 and 77 K for the mononuclear species reveals a dramatic yellow solid (41 mg, 62%). 31P NMR (162 MHz, acetone-d6,
increase of lifetime values (up to 130-fold) upon temperature 298 K, δ): AB2 system −0.5 (2P), −3.1 (1P) J(P–P) 136 Hz. 1H
decrease accompanied by a small red shift of the emission NMR (400 MHz, acetone-d6, 298 K, δ): PPh2 groups 8.35 (m,
energy (5–10 nm). These observations indicate that lumine- 4H, ortho-H), 7.42 (m, 4H, meta-H), 7.41 (m, 2H, para-H), 7.28
scence of the complexes under consideration might demon- (m, 2H, J(H–H) 7.4 Hz, para-H), 7.10 (dd, 4H, J(H–H) 7.4 Hz,
strate thermally activated delayed fluorescence (TADF), recently 7.2 Hz, meta-H), 6.54 (m, 4H, J(H–H) 7.2 Hz, ortho-H); C6H4
described for a number of copper(I) compounds. Following the groups 7.81 (m, 2H, J(H–H) 7.3 Hz, ortho-H), 7.59 (dd, 2H,
hypothesis, low temperature emission is therefore governed J(H–H) 7.2 Hz, 7.3 Hz, meta-H), 7.49 (dd, 2H, J(H–H) 7.4 Hz,
by T1 → S0 transition, while at 298 K a thermal equilibrium 7.2 Hz, meta-H), 7.42 (m, 2H, J(H–H) 7.4 Hz, ortho-H);
between S1 and T1 levels results in a significant contribution 4-OCH3C6H4C2 group 7.28 (d, 2H, J(H–H) 8.1 Hz, ortho-H),
of S1 → S0 relaxation into the radiative decay pathway. Theore- 6.77 (d, 2H, J(H–H) 8.1 Hz, meta-H), 3.76 (s, 3H); PPh group
tical calculations of the electronic structures of 1–10 elucidated 7.29–7.33 (m, 5H). Anal. Calcd for C51H40CuOP3: C, 74.21;
the photophysical properties, which are strongly dependent on H, 4.88; found: C, 73.81; H, 5.16.
the nature of constituting alkynyl groups.
Cu(P3)(C2-4-NO2C6H4) (3). Prepared analogously to 1 start-
ing from P3 (30 mg, 0.047 mmol), [Cu(NCMe)4](BF4) (15 mg,
0.048 mmol), 4-nitrophenylacetylene (7 mg, 0.048 mmol) and
KOH (2.7 mg, 0.048 mmol). Recrystallization by gas-phase
diffusion of pentane into a toluene solution of 3 at room tem-
Experimental
General comments
(2-Bromophenyl)diphenylphosphine,42
perature gave a yellow-red crystalline material (33 mg, 83%).
4,4′-HC2(C6H4)2C2H 31P NMR (162 MHz, acetone-d6, 298 K, δ): AB2 system 1.1 (2P),
(L3),43 4,4″-HC2(C6H4)3C2H (L4),44 and 1,3,5-(4-HC2-C6H4)3- −1.3 (1P) J(P–P) 133 Hz. 1H NMR (400 MHz, acetone-d6,
C6H3 (L5)45 were prepared according to the reported pro- 298 K, δ): PPh2 groups 8.22 (dm, 4H, J(H–H) 7.6 Hz, ortho-H),
cedures. Tetrahydrofuran was distilled over Na–benzophenone- 7.44 (m, 4H, J(H–H) 7.6 Hz, meta-H), 7.43 (m, 2H, para-H),
ketyl under a nitrogen atmosphere prior to use. Other reagents 7.31 (dm, 2H, J(H–H) 7.5 Hz, para-H), 7.12 (dd, 4H, J(H–H)
were used as received. The solution 1H, 31P{1H} NMR and 7.5 Hz, 7.3 Hz, meta-H), 6.57 (dm, 4H, J(H–H) 7.3 Hz, ortho-H);
1H–1H COSY spectra were recorded on Bruker 400 MHz Avance C6H4 groups 7.83 (dm, 2H, J(H–H) 7.4 Hz, ortho-H), 7.6 (dd,
and AMX 400 spectrometers. Microanalyses were carried out at 2H, J(H–H) 7.5 Hz, 7.4 Hz, meta-H), 7.51 (dd, 2H, J(H–H)
the analytical laboratory of the University of Eastern Finland.
7.7 Hz, 7.5 Hz, meta-H), 7.41 (m, 2H, J(H–H) 7.7 Hz, ortho-H);
Cu(P3)C2C6H5 (1). P3 (100 mg, 0.159 mmol), [Cu(NCMe)4]- 4-NO2C6H4C2 group 8.08 (d, 2H, J(H–H) 8.9 Hz, ortho-H), 7.48
(BF4) (50 mg, 0.159 mmol) and phenylacetylene (16 mg, (d, 2H, J(H–H) 8.9 Hz, meta-H); PPh group 7.29–7.36 (m, 5H).
0.157 mmol) were suspended in acetone (10 mL) and the reac- Anal. Calcd for C50H37CuNO2P3: C, 71.46; H, 4.43; N, 1.66;
tion mixture was stirred for 10 min at room temperature to found: C, 71.36; H, 4.71; N, 1.57.
give a nearly clear pale-green solution. Addition of KOH
Cu(P3)(C2-4-CF3C6H4) (4). Prepared analogously to 1 starting
(9.2 mg, 0.164 mmol) changed its color to brown. The reaction from P3 (100 mg, 0.159 mmol), [Cu(NCMe)4](BF4) (50 mg,
mixture was stirred for additional 10 h, then it was filtered, 0.158 mmol), 4-(trifluoromethyl)phenylacetylene (26 mg,
evaporated and the crude solid was recrystallized by gas-phase 0.153 mmol) and KOH (9.2 mg, 0.164 mmol). Recrystallization
diffusion of pentane into a THF solution of 1 at room tempera- by gas-phase diffusion of pentane into a toluene solution of 4
ture to give a pale yellow crystalline material (65 mg, 54%). 31P at room temperature gave a yellow solid (83 mg, 63%).
NMR (162 MHz, acetone-d6, 298 K, δ): AB2 system −0.1 (2P), 31P NMR (162 MHz, acetone-d6, 298 K, δ): AB2 system 0.5 (2P),
−2.6 (1P) J(P–P) 134 Hz. 1H NMR (400 MHz, acetone-d6, 298 K, −2.0 (1P) J(P–P) 133 Hz. 1H NMR (400 MHz, acetone-d6, 298 K,
δ): PPh2 groups 8.34 (m, 4H, ortho-H), 7.43 (m, 4H, meta-H), δ): PPh2 groups 8.28 (m, 4H, ortho-H), 7.44 (m, 6H, meta-H+
7.41 (m, 2H, para-H), 7.28 (t, 2H, J(H–H) 7.5 Hz, para-H), 7.10 para-H), 7.32 (t, 2H, J(H–H) ca. 7.3 Hz, para-H), 7.12 (dd, 4H,
(dd, 4H, J(H–H) 7.5 Hz, 7.2 Hz, meta-H), 6.54 (m, 4H, J(H–H) J(H–H) ca. 7.3, 7.0 Hz, meta-H), 6.56 (m, 4H, J(H–H) 7.0 Hz,
7.2 Hz, ortho-H); C6H4 groups 7.82 (m, 2H, J(H–H) 7.1 Hz, ortho-H); C6H4 groups 7.84 (m, 2H, J(H–H) 7.1 Hz, ortho-H),
ortho-H), 7.59 (dd, 2H, J(H–H) 7.3, 7.0 Hz, meta-H), 7.50 (dd, 7.61 (dd, 2H, J(H–H) 7.1 Hz, meta-H), 7.50 (m, 2H, J(H–H)
2H, J(H–H) ca. 7.3 Hz, 7.1 Hz, meta-H), 7.42 (m, 2H, J(H–H) 7.6 Hz, meta-H), 7.44 (m, 2H, J(H–H) 7.6 Hz, ortho-H);
7.0 Hz, ortho-H); C2Ph group 7.35 (m, 2H, J(H–H) 7.7 Hz, 4-CF3C6H4C2 group 7.48–7.50 (m, 4H); PPh group 7.31–7.33
ortho-H), 7.17 (dd, 2H J(H–H) 7.7 Hz, 7.1 Hz, meta-H), 7.02 (t, (m, 5H). Anal. Calcd for C51H37CuF3P3: C, 70.95; H, 4.32;
1H, J(H–H) 7.1 Hz, para-H); PPh group 7.22–7.41 (m, 5H). found: C, 70.68; H, 4.49.
Anal. Calcd for C50H38CuP3: C, 75.51; H, 4.81; found: C, 75.31;
H, 5.02.
Cu(P3)(C2-2-C5H4N) (5). Prepared analogously to 1 starting
from P3 (130 mg, 0.206 mmol), [Cu(NCMe)4](BF4) (65 mg,
Cu(P3)(C2-4-OCH3C6H4) (2). Prepared analogously to 1 start- 0.207 mmol), 2-ethynylpyridine (21 mg, 0.203 mmol) and KOH
ing from P3 (50 mg, 0.079 mmol), [Cu(NCMe)4](BF4) (25 mg, (11 mg, 0.196 mmol). The crude solid was dissolved in toluene
0.080 mmol), 4-ethynylanisole (10.5 mg, 0.080 mmol) and (10 mL) and precipitated with excess of hexane to give a yellow
KOH (4.8 mg, 0.085 mmol). The crude solid was dissolved in solid (68 mg, 42%). 31P NMR (162 MHz, CD2Cl2, 298 K, δ): AB2
1
toluene (5 mL) and precipitated with excess of hexane to give a system 0.5 (2P), −1.8 (1P) J(P–P) 132 Hz. H NMR (400 MHz,
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CD2Cl2, 298 K, δ): PPh2 groups 8.13 (dm, 4H, J(H–H) 7.5 Hz ortho-H), 7.41 (m, 12H, meta-H+ para-H), 7.24 (t, 4H, J(H–H)
ortho-H), 7.39 (m, 6H, J(H–H) 7.5 Hz, meta-H+ para-H), 7.25 (t, 7.5 Hz, para-H), 7.05 (dd, 8H, J(H–H) 7.5 Hz, 7.6 Hz, meta-H),
2H, J(H–H) 7.6 Hz, para-H), 7.05 (dd, 4H, J(H–H) 7.6 Hz, 6.59 (dm, 8H, J(H–H) 7.6 Hz, ortho-H); C6H4 groups 7.73 (dm,
7.0 Hz, meta-H), 6.58 (dm, 4H, J(H–H) 7.0 Hz, ortho-H); C6H4 4H, J(H–H) 7.1 Hz, ortho-H), 7.50 (dd, 4H, J(H–H) 7.5 Hz,
groups 7.70 (dm, 2H, J(H–H) 7.2 Hz, ortho-H), 7.47 (dd, 2H, meta-H), 7.41 (m, 4H, J(H–H) 7.1 Hz, meta-H), 7.36 (dm, 4H,
J(H–H) 7.2 Hz, meta-H), 7.39 (m, 2H, J(H–H) 7.0 Hz, meta-H), J(H–H) ca. 7.5 Hz, ortho-H); C2(C6H4)3C2 group 7.70 (s, 4H),
7.35 (dm, 2H, J(H–H) ca. 7.0 Hz, ortho-H); C6H4N group 8.43 7.55 (d, 4H, J(H–H) 8.2 Hz), 7.51 (d, 4H, J(H–H) 8.2 Hz); PPh
(dm, 1H, J(H–H) 5.1 Hz, 1.8 Hz, 6-H), 7.51 (ddd, 1H, J(H–H) group 7.26–7.28 (m, 10H). Anal. Calcd for C106H78Cu2P6:
7.8 Hz, 7.7 Hz, 1.8 Hz, 4-H), 7.35 (dm, 1H, J(H–H) 7.8 Hz, 3-H), C, 76.47; H, 4.72; found: C, 76.14; H, 4.90.
6.97 (ddd, 1H, J(H–H) 7.7 Hz, 5.1 Hz, 5-H); PPh group
7.20–7.36 (m, 5H). Anal. Calcd for C49H37CuNP3: C, 73.90; to 1 using stoichiometric ratios of the reagents starting
H, 4.68; N, 1.75; found: C, 73.62; H, 5.06; N, 1.57.
from P3 (150 mg, 0.238 mmol), [Cu(NCMe)4](BF4) (75 mg,
Cu3(P3)3(1,3,5-(C2C6H4)3C6H3) (9). Prepared analogously
Cu2(P3)2(1,4-C2C6H4C2) (6). Prepared analogously to 1 using 0.238 mmol), 1,3,5-trisubstituted benzene (27 mg,
stoichiometric ratios of the reagents starting from P3 (150 mg, 0.071 mmol) and KOH (13 mg, 0.232 mmol). The crude solid
0.238 mmol), [Cu(NCMe)4](BF4) (75 mg, 0.238 mmol), 1,4-di- was dissolved in THF (10 mL) and precipitated with an excess
ethynylbenzene (15 mg, 0.119 mmol) and KOH (13.8 mg, of diethyl ether to give a yellow solid (62 mg, 37%). 31P NMR
0.246 mmol). Recrystallization by gas-phase diffusion of (162 MHz, CD2Cl2, 298 K, δ): AB2 system 0.0 (2P), −2.3 (1P)
diethyl ether into a dichloromethane solution of 6 at room J(P–P) 133 Hz. 1H NMR (400 MHz, CD2Cl2, 298 K, δ): PPh2
temperature gave a yellow solid (65 mg, 39%). 31P NMR groups 8.21 (dm, 12H, J(H–H) ca. 7.5 Hz, ortho-H), 7.42 (m,
(162 MHz, CD2Cl2, 298 K, δ): AB2 system −0.4 (2P), −2.9 (1P) 18H, J(H–H) 7.5 Hz, meta-H+ para-H), 7.23 (t, 6H, J(H–H)
J(P–P) 133 Hz. 1H NMR (400 MHz, CD2Cl2, 298 K, δ): PPh2 7.4 Hz, para-H), 7.05 (dd, 12H, J(H–H) 7.8 Hz, 7.4 Hz, meta-H),
groups 8.19 (m, 8H, ortho-H), 7.40 (m, 12H, meta-H+ para-H), 6.58 (dm, 12H, J(H–H) 7.8 Hz, ortho-H); C6H4 groups 7.73 (dm,
7.22 (t, 4H, J(H–H) 7.2 Hz, para-H), 7.04 (dd, 8H, J(H–H) 6H, J(H–H) ca. 7.0 Hz, ortho-H), 7.48 (dd, 6H, J(H–H) 7.0 Hz,
7.2 Hz, 6.7 Hz, meta-H), 6.57 (dm, 8H, J(H–H) ca. 6.7 Hz, ortho- meta-H), 7.39 (dm, 6H, J(H–H) ca. 7.3 Hz, meta-H), 7.37 (dm,
H); C6H4 groups 7.71 (dm, 4H, J(H–H) ca. 7.2 Hz, ortho-H), 6H, J(H–H) ca. 7.3 Hz, ortho-H); (C6H4)C2 group 7.64 (d, 6H,
7.46 (dd, 4H, J(H–H) 7.7 Hz, 7.2 Hz, meta-H), 7.38 (m, 8H, J(H–H) 8.3 Hz), 7.54 (d, 6H, J(H–H) 8.3 Hz); C6H3 group 7.82
J(H–H) 7.7 Hz, meta-H+ ortho-H); C2C6H4C2 group 7.40 (s, 4H); (s, 3H); PPh group 7.28–7.31 (m, 15H). Anal. Calcd for
PPh group 7.26–7.27 (m, 10H). Anal. Calcd for C94H70Cu2P6:
C, 74.64; H, 4.66; found: C, 74.91; H, 4.87.
C
156H114Cu3P9: C, 76.22; H, 4.67; found: C, 75.94; H, 4.65.
Cu3(P3)3(1,3,5-(C2C6H4C2C6H4)3C6H3) (10). Prepared ana-
Cu2(P3)2(4,4′-C2(C6H4)2C2) (7). Prepared analogously to logously to 1 using stoichiometric ratios of the reagents start-
1 using stoichiometric ratios of the reagents starting from P3 ing from P3 (150 mg, 0.238 mmol), [Cu(NCMe)4](BF4) (75 mg,
(150 mg, 0.238 mmol), [Cu(NCMe)4](BF4) (75 mg, 0.238 mmol), 1,3,5-trisubstituted benzene (48 mg,
0.238 mmol), 4,4″-di-ethynylbiphenyl (24 mg, 0.119 mmol) 0.071 mmol) and KOH (13 mg, 0.232 mmol). The crude solid
and KOH (13.8 mg, 0.246 mmol). The crude solid was dis- was dissolved in toluene (10 mL) and precipitated with excess
solved in toluene (10 mL) and precipitated with excess of of pentane to give an orange solid (46 mg, 23%). 31P NMR
hexane to give a yellow solid (65 mg, 34%). 31P NMR (162 MHz, (162 MHz, CD2Cl2, 298 K, δ): AB2 system 0.3 (2P), −1.9 (1P)
CD2Cl2, 298 K, δ): AB2 system −0.1 (2P), −2.5 (1P) J(P–P) J(P–P) 132 Hz. 1H NMR (400 MHz, CD2Cl2, 298 K, δ): PPh2
133 Hz. 1H NMR (400 MHz, CD2Cl2, 298 K, δ): PPh2 groups groups 8.17 (dm, 12H, J(H–H) 7.9 Hz, ortho-H), 7.43 (m, 18H,
8.21 (m, 8H, ortho-H), 7.43 (m, 12H, meta-H+ para-H), 7.24 (t, J(H–H) ca. 7.9 Hz, meta-H+ para-H), 7.25 (t, 6H, J(H–H) 7.0 Hz,
4H, J(H–H) 7.4 Hz, para-H), 7.06 (dd, 8H, J(H–H) 7.4 Hz, para-H), 7.05 (dd, 12H, J(H–H) 7.5 Hz, 7.0 Hz, meta-H), 6.58
7.2 Hz, meta-H), 6.58 (m, 8H, J(H–H) 7.2 Hz, ortho-H); C6H4 (dm, 12H, J(H–H) ca. 7.5 Hz, ortho-H); C6H4 groups 7.73 (dm,
groups 7.73 (dm, 4H, J(H–H) 7.6 Hz, ortho-H), 7.49 (dm, 8H, 6H, J(H–H) 7.5 Hz, ortho-H), 7.48 (dd, 6H, J(H–H) 7.5 Hz,
J(H–H) ca. 6.8 Hz, 7.6 Hz, meta-H), 7.39 (m, 4H, J(H–H) meta-H), 7.40 (dm, 6H, J(H–H) ca. 7.6 Hz, meta-H), 7.34 (m,
ca. 6.8 Hz, 7.5 Hz, meta-H), 7.35 (m, 4H, J(H–H) 7.5 Hz, ortho-H); 6H, J(H–H) 7.6 Hz, ortho-H); (C6H4C2)2 group AB system 7.77
C2(C6H4)2C2 and PPh groups 7.26–7.50 (unresolved m, 18H). (d, 6H, J(H–H) 8.4 Hz), 7.68 (m, 6H, J(H–H) 8.4 Hz); 7.43 (m,
Anal. Calcd for C100H74Cu2P6: C, 75.60; H, 4.69; found: 6H), 7.27 (m, 6H); C6H3 group 7.90 (s, 3H); PPh group
C, 75.31; H, 4.77.
7.27–7.31 (m, 15H). Anal. Calcd for C180H126Cu3P9: C, 78.37;
Cu2(P3)2(4,4″-C2(C6H4)3C2) (8). Prepared analogously to 1 H, 4.60; found: C, 78.49; H, 4.76.
using stoichiometric ratios of the reagents starting from P3
X-ray structure determination
(30 mg, 0.047 mmol), [Cu(NCMe)4](BF4) (15 mg, 0.048 mmol),
4,4″-diethynyl-p-terphenyl (6.6 mg, 0.024 mmol) and KOH The crystals of 1, 3 and 5 were immersed in cryo-oil, mounted
(2.7 mg, 0.048 mmol). Recrystallization by gas-phase diffusion in a nylon loop, and measured at a temperature of 120 K. The
of pentane into a THF solution of 9 at room temperature to diffraction data were collected with a Bruker Kappa Apex II
give a yellow solid (30 mg, 75%). 31P NMR (162 MHz, CD2Cl2, Duo diffractometer using Mo Kα radiation (λ = 0.71073 Å). The
298 K, δ): AB2 system 0.0 (2P), −2.3 (1P) J(P–P) 132 Hz. 1H APEX246 program package was used for cell refinements and
NMR (400 MHz, CD2Cl2, 298 K, δ): PPh2 groups 8.20 (m, 8H, data reductions. The structures were solved by direct methods
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using the SHELXS-201347 program with the WinGX48 graphical
Acknowledgements
user interface.
(SADABS)49 was applied to all data. Structural refinements Financial support was provided from the University of Eastern
were carried out using SHELXL-2013.47
Finland (Russian–Finnish collaborative project), the Academy
A
semiempirical absorption correction
One of the phenyl rings of an alkynyl ligand in 1 was of Finland (grant 268993, I. O. K.), the Alfred Kordelin Foun-
disordered between two positions and was refined with dation (A. J. K.), St. Petersburg State University (grants
occupation factors 0.52/0.48. The aromatic rings of both com- 0.37.169.2014 and 12.42.1272.2014), and the Russian Foun-
ponents were geometrically idealized. Displacement con- dation for Basic Research (grants 14-03-00970 and 13-04-
straints and restraints were applied to these moieties.
40342/13-04-40343). Computational resources were provided by
Some of the crystallized tetrahydrofuran (1) and water (5) CSC – the Finnish IT Center for Science (A. J. K.). The work
molecules were partially lost and these moieties were refined was carried out using equipment of the Centers for Chemical
with a 0.5 occupancy at each site. A series of geometry and dis- Analysis and Materials Research and for Optical and Laser
placement constraints and restraints were applied to the THF Materials Research (St. Petersburg State University).
solvent molecules. Additionally, some of the lost solvent in 1
could not be resolved unambiguously. The missing solvent
was taken into account by using a SQUEEZE routine of
References
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