Copper(I) Phosphinooxazoline Complexes: Impact of the Ligand Substitution and Steric Demand on the Electrochemical and Photophysical Properties

Article abstract of DOI:10.1002/chem.201904379

A series of seven homoleptic Cu^I complexes based on hetero-bidentate P^N ligands was synthesized and comprehensively characterized. In order to study structure–property relationships, the type, size, number and configuration of substituents at the phosphinooxazoline (phox) ligands were systematically varied. To this end, a combination of X-ray diffraction, NMR spectroscopy, steady-state absorption and emission spectroscopy, time-resolved emission spectroscopy, quenching experiments and cyclic voltammetry was used to assess the photophysical and electrochemical properties. Furthermore, time-dependent density functional theory calculations were applied to also analyze the excited state structures and characteristics. Surprisingly, a strong dependency on the chirality of the respective P^N ligand was found, whereas the specific kind and size of the different substituents has only a minor impact on the properties in solution. Most importantly, all complexes except C3 are photostable in solution and show fully reversible redox processes. Sacrificial reductants were applied to demonstrate a successful electron transfer upon light irradiation. These properties render this class of photosensitizers as potential candidates for solar energy conversion issues.

Full text of DOI:10.1002/chem.201904379

A Journal of
Accepted Article
Title: Copper(I) Phosphinooxazoline Complexes: Impact of the Ligand
Substitution and Sterical Demand on the Electrochemical and
Photophysical Properties
Authors: Robin Giereth, Alexander K. Mengele, Wolfgang Frey,
Marvin Kloß, Andreas Steffen, Michael Karnahl, and Stefanie
Tschierlei
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Copper(I) Phosphinooxazoline Complexes: Impact of the Ligand
Substitution and Sterical Demand on the Electrochemical and
Photophysical Properties
Robin Giereth,[a] Alexander K. Mengele,[a] Wolfgang Frey,[b] Marvin Kloß,[c] Andreas Steffen,[c] Michael
Karnahl,*[b] and Stefanie Tschierlei*[a]
A series of seven homoleptic Cu(I) complexes based on hetero-
bidentate P^N ligands was synthesized and comprehensively
characterized. In order to study structure-property relationships
the type, size, number and configuration of substituents at the
phosphinooxazoline (phox) ligands were systematically varied.
H2,[6–11] as photoredoxcatalysts for organic transformations
[12–16]
or in devices like organic light-emitting diodes
(OLEDs),[17–22] dye-sensitized solar cells (DSSCs)[23–26] and
light-emitting
electrochemical
cells
(LECs).[27,28]
Unfortunately, a limited stability under operating conditions
still hampers their large-scale application in molecular solar
energy conversion schemes.[21,29–34] It is known, that in
particular heteroleptic Cu(I) complexes of the type
[(P^P)Cu(N^N)]+ (with P^P representing a diphosphine and
To this end,
spectroscopy,
a
combination of X-ray diffraction, NMR
steady-state absorption and emission
spectroscopy, time-resolved emission spectroscopy, quenching
experiments and cyclic voltammetry was used to assess the
photophysical and electrochemical properties. Furthermore,
time-dependent density functional theory calculations were
applied to also analyze the excited state structures and
N^N a diimine ligand) can undergo ligand exchange
[29,31,33–35]
reactions in solution upon light irradiation.
This is
mainly caused by the formation of thermodynamically more
[29,31,33–
characteristics. Surprisingly,
a
strong dependency on the
favored homoleptic bisdiimine complex [Cu(N^N)2]+.
chirality of the respective P^N ligand was found, whereas the
specific kind and size of the different substituents has only a
minor impact on the properties in solution. Most importantly, all
complexes except C3 are photostable in solution and show fully
reversible redox processes. Sacrificial reductants were applied
35] Hence, this drawback drove the search and development
of novel Cu(I) complexes with an increased stability, but also
having other desired properties like a broad absorption in the
visible and a reversible redoxchemistry.[4,36–40]
One possible option to achieve this aim is the replacement
of the original P^P ligand by a heterobidentate P^N-
ligand.[17,41] Particularly, the combination of a N-heteroaryl
moiety, which possesses a wide range of tunable electronic
properties and a soft phosphine donor seems promising.[41,42]
Several Cu(I) complexes based on different types of P^N
ligands, mainly as multinuclear cuprous halide complexes,
have already been prepared and investigated.[43–53] In these
examples the phosphine unit is either directly bound to the
to demonstrate
a successful electron transfer upon light
irradiation. These properties render this class of photo-
sensitizers as potential candidates for solar energy conversion
issues.
Introduction
N-heteroaryl
pyridine[46,49] or 8-(diphenylphosphino)-quinoline[44,45]
connected via an aliphatic spacer (e.g. 2-[2-
(diphenylphosphino)-ethyl]-pyridine[51,53]). Consequently, the
previous examples are typically bridging or only
monodentate ligands due to the small bite angle.[44–
46,49,51,53,54] Moreover, these systems still suffer from a limited
stability.[21,55,56]
In contrast, Zeng et al. found that 1,2-phenyl-bridged P^N-
ligands can form phosphorescent and stable Cu(I)
complexes in solution and in the solid state.[57] Nevertheless,
the impact of different substituents, steric effects and chirality
on the electrochemistry and photophysics of copper P^N
complexes has not been studied in detail yet.
In a previous study we showed for the first time, that a
phosphinooxazoline (phox) based P^N ligand enables stable
mononuclear Cu(I) complexes with interesting photophysical
properties.[41] Moreover, also the ability of these complexes to act
as photosensitizers for the light-driven production of H2 was
demonstrated.[41] Hence, the impact of the spatial arrangement
moiety
(e.g.
2-(diphenylphosphino)-
Photoactive Cu(I) complexes are considered as a highly
promising alternative to traditional systems based on noble
metals such as ruthenium, iridium, rhenium or platinum.[1–5]
Indeed, Cu(I) compounds were already successfully applied
as photosensitizers in the light-driven reduction of protons to
)
or
[a]
[b]
[c]
Ulm University, Institute of Inorganic Chemistry I, Albert-Einstein-
Allee 11, 89081 Ulm, Germany.
E-mail: stefanie.tschierlei@uni-ulm.de,
Website: www.tschierlei-group.de
University of Stuttgart, Institute of Organic Chemistry,
Pfaffenwaldring 55, 70569 Stuttgart, Germany.
E-mail: michael.karnahl@oc.uni-stuttgart.de,
Website: www.karnahl-group.de
Faculty of Chemistry and Chemical Biology, TU Dortmund
University, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
Supporting information for this article is given via a link at the end of
the document. This contains: general information on the
experimental and synthetic details, crystallographic data, NMR and
UV-vis spectra, cyclic voltammograms as well as results of the
(TD-)DFT calculations.
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and steric demand in such phox ligands on the properties of the
resulting Cu(I) complexes is of high interest. In consequence, a
systematic series of seven homoleptic Cu(I) complexes (Figure 1)
with different size, type and number of substituents at the
The synthesis of the ligands L1, L2, L5 and L6 was performed
following a synthesis procedure from literature,[41,58,59] starting
from the corresponding and commercially available chiral amino
alcohols (see Scheme 1). These amino alcohols were first reacted
in a Witte-Seeliger reaction[58] to the aryl-bromide precursor and
then converted to the corresponding phox ligands via an Ullman-
type coupling (Scheme 1).[59] In contrast, the preparation of L4
and L7 was done using the easily accessible amino acids (i.e. DL-
valine, (S)-phenylalanine) as natural feedstock, while for L3 a
commercially available amino acid (2,2-diphenylglycine) was
utilized. For these three ligands the required aryl-bromide
precursors were obtained from the respective amino acids in a
two-step reaction using LiAlH4 for reduction[60] followed by the acid
catalyzed reaction with bromo-benzoylchloride (Scheme 1).[59] In
the case of L4 a racemic mixture of the (R) and (S) configurated
isomer was obtained, while the ligands L5-L7 are chiral and the
stereochemical information of the educts was preserved This
means that L6 is (R) configurated and L5 as well as L7 possess
a (S) configuration at the stereocenter.
oxazoline moiety was prepared.
Figure 1. General structure of the ligands L1 to L7 and the resulting homoleptic
Cu(I) complexes C1 to C7.
Following, a combination of NMR spectroscopy, X-ray analysis,
cyclic voltammetry, absorption and emission spectroscopy as well
as density functional theory (DFT) calculations was used to
identify structure-property relationships. The presence of single
crystals of all compounds enabled a detailed discussion of their
solid state structures. In addition, time-resolved emission
spectroscopy and time-dependent DFT (TD-DFT) calculations
were applied to also examine excited state properties. Most
remarkably a dependence of the complex properties on the
chirality of the respective P^N ligand was found. Finally,
measurements with sacrificial reductants on representative
complexes were performed to demonstrate successful electron
transfer upon light irradiation. All in all, the gained knowledge
paves the way to improved photoactive Cu(I) complexes, which
might be used in solar energy conversion schemes in the future.
Scheme 1. Overview of the common synthesis procedure of the ligands L1 to
L7 either starting from the respective amino acids or the amino alcohols. i)
Reduction: LiAlH4, THF,[60] ii.a) Witte-Seeliger reaction: ZnCl2, PhCl,[58] ii.b) step
1: NaHCO3, H2O/DCM; step 2: TsCl, TEA, DCM,[59] iii) Ullman-type coupling:
CuI, DMEDA, Cs2CO3, toluene.[59]
The ligands L1-L7 were subsequently coordinated to a Cu(I)
center by a ligand substitution reaction using the [Cu(MeCN)4]PF6
adduct (MeCN = acetonitrile) as a precursor. Following a general
synthesis procedure [Cu(MeCN)4]PF6 (1 equiv.) and the
respective phox ligand (L1-L7, 2 equiv.) were suspended in dry
dichloromethane and heated to reflux for 5 h under argon
atmosphere. After isolation and purification, the homoleptic Cu(I)
complexes C1-C7 of the type [Cu(phox)2]PF6 were obtained as
yellow to orange crystals. The obtained yields differ in the range
from 11% for C3 to 60% for C2 (for further details see the
Supporting Information). The much lower yield of C3 significantly
differs from all other complexes and might be caused by steric
constraints (two adjacent phenyl groups) and hence kinetic
instability in solution. Such instability, e.g. substitution reactions
in solution, is well known from sterically congested homo- and
heteroleptic Cu(I) complexes.[29,31,33–35]
Results and Discussion
Synthesis and structural characterization
A broad variety of phox ligands were prepared (see Figure 1) to
allow for a comprehensive evaluation of the ligand impact on the
ground and excited state properties of the resulting Cu(I)
complexes. Main attention was given to the steric influence of the
different substituents at the 4-position of the 2-oxazoline (4,5-
dihydrooxazole) moiety. This position was chosen for modification
due to its proximity to the copper center, because this likely has a
strong impact on the geometry as well as excited state relaxation
processes. A special distinction has been made between
derivatives without any substituents (L1), with only one
substituent (L4-L7) and two substituents (L2-L3) at the 2-
oxazoline (Figure 1). Furthermore, phox ligands with aliphatic (Me,
iPr, iBu) and aromatic substituents (Ph, Bn) were prepared. While
L1, L2 and L4-7 are literature known, L3 was specifically
designed for this study. It is also worth noting, that the ligands L4-
L7 possess a chirality center at the 4-position of the 2-oxazoline.
In a next step the molecular composition and structures of all
complexes were confirmed by standard methods. In the 31P{1H}
NMR spectra all complexes display one single signal in the range
between -8.5 (C2) and -5.3 ppm (C6) (Figure S2), indicating a
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weak influence of the different substituents. A relatively small and
broadened 31P{1H} NMR signal of C3 is another indication for a
limited stability of this particular complex in solution.
of the aryl groups clearly indicates such interactions[62–64], which
are predominantly responsible for the asymmetric coordination
environment. The highly symmetrical structure of C7 also exhibits
pairwise π-stacking interactions, but these are located between
the substituents. Two neighboring benzyl units form an
intermolecular parallel face-centered π-stacking with a centroid
distance of 470 pm. Moreover, the DFT calculated ground state
structures (Table 3 and SI) show a good agreement to the
measured ones.
Single crystals suitable for X-ray crystallography of all complexes
C1-C7 were either obtained by common diffusion techniques or
directly from recrystallization in methanol. The crystallographic
data and depiction of all solid state structures can be found in the
supporting information (Chapter 4), while only a selection is
presented here. For instance, complex C4 crystallizes in the
centrosymmetric space group P 21/n. Consequently, C4 is
therefore invariant under the parity operation P (inversion through
a point), which prevents the specification of an absolute structure
(i.e. whether it is the R or the S enantiomer). This is in line with
the preparation conditions, where a racemic mixture of L4 was
used for complexation. In contrast, the crystal structures of C5-C7
(Figures 4 and S4), which contain the chiral ligands L5-L7, have
a valid absolute-structure determination (see Flack parameters,
Table 1). Structural analysis revealed that C5 and C7 possess a
(S) configuration, whereas C6 has a (R) configuration on the
stereogenic center, as depicted in Figure 1. Interestingly, complex
C7 crystallizes in the monoclinic crystal lattice in the space group
C2 and therefore possesses symmetry operations like a two-fold
rotation axis (see Figure 2).
Furthermore, all Cu(I) complexes display a strongly distorted
tetrahedral geometry around the copper center as a common
feature for this class of compounds.[4,61] In the solid state structure
of C1 the two phenyl-(2-oxazoline) moieties are almost
perpendicular oriented towards each other, without any
perturbation in the ligand backbone. This can be visualized by the
ligand plane intersection angle (lpia), which describes the angle
between the two ligand planes, that are spanned through the
chelating P^N-heteroatoms and the copper center (see Table
1).[4,61] This angle is 85.88° for complex C1 without any
substituents at the 4-position of the 2-oxazoline (Figure 3). The
observed lpia is also well represented by the DFT calculations
(BP86-D3(BJ)/def2-TZVP), which provide a value of 81.9° for C1
(Table 3). For C2-C7 the lpia significantly differs from the ideal 90°
arrangement, e.g. 71.09° (DFT, 75.4°) for C2 or 68.01° (DFT,
68.6°) for C6, and is strongly influenced by the various
substituents. However, a clear trend concerning the kind and size
of substituents cannot be observed. Instead, the individual
packing in the solid state seems to superimpose any general trend.
Figure 2. Solid state structures (ORTEP representation with thermal ellipsoids
at a probability level of 50 %) of complex C1 with atom labeling (top) and of
complex C7 highlighting the two-fold rotation symmetry (bottom). The hydrogen
atoms, counter anions and solvent molecules are omitted for clarity.
Additionally, in C1 the copper center is asymmetrically chelated
by the two L1 ligands. One ligand is more loosely bound and
exhibits a bite angle of 91.20(8)°, while for the second ligand the
Cu-P bond length is significantly shortened (Cu-P1: 2.2230(8) pm
vs. Cu-P2: 2.1860(8) pm) and the bite angle is 97.25(7)°. A similar
coordination behavior is also found for C4 and C5. The detailed
inspection of the extended crystal structures and crystal packing
effects revealed pairwise intermolecular π-stacking interactions
(Figure S4) for C1, C4, C5 and C7. In C4 and C5, one aryl ring of
adjacent PPh2 groups participates in a perpendicular T-shaped
stacking interaction, whereas in C1 the interaction takes place
between one PPh2 unit and the central aryl moiety in 2-position of
the oxazoline. A distance of about 500 pm between the centroids
Figure 3. Space-filling representation of C1 (left) and simplified solid state
structure (right) showing only the copper center and the chelating heteroatoms
(with thermal ellipsoids at a probability level of 90 %). The simplified structure
of C1 displays the two ligand planes, i.e. the plane through the atoms P1-Cu1-
N1 (yellow) and P2-Cu1-N2 (blue).
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Table 1. Selected crystallographic bond lengths (pm) and angles (°) of the complexes C1 - C7. For atom labelling also compare with Figure 2 and the SI‡. The
respective CCDC reference numbers are given in the supporting information. These data are provided free of charge by the Cambridge Crystallographic Data
Centre.
C1
C2
C3
C4
C5
C6
C7
space group
Flack parameter
Cu-P1
P 21/n
P 21/n
P 4 c c
--
P 21/n
P 21
P 212121
0.012(2)
2.2263(8)
2.2186(7)
2.071(2)
2.066(2)
86.88(7)
87.81(7)
68.01
C2
--
-
n.a. [a]
0.004(4)
2.2428(4)
2.2502(4)
2.0488(12)
2.0712(12)
91.54(4)
87.86(4)
78.48
0.007(6)
2.2628(15)
2.2629(15)
2.128(5)
2.128(5)
89.24(12)
89.24(12)
88.31
2.2230(8)
2.1860(8)
2.047(2)
2.007(2)
91.20(8)
97.25(7)
85.88
2.2640(8)
2.2726(7)
2.094(2)
2.070(2)
86.38(6)
86.98(7)
71.09
2.2143(10)
2.2160(10)
2.070(3)
2.061(3)
88.39(9)
88.56(9)
73.93
2.2428(4)
2.2502(4)
2.0488(12)
2.0712(12)
91.54(4)
87.86(4)
77.56
Cu-P2
Cu-N1
Cu-N2
P1-Cu-N1
P2-Cu-N2
plane angle [b]
[a] Not applicable, because of a centrosymmetric point group. [b] Determined ligand plane intersection angle (lpia) between the two ligand planes.
Figure 4. Simplified solid state structures (ORTEP representation) of C4-C7 highlighting the ligand orientation in the respective Cu(I) complexes. The substituents
in C4 and C6 point away from each other, whereas in C5 and C7 they point towards each other. Thermal ellipsoids are at a probability level of 50 %. The hydrogen
atoms, the phenyl groups of the PPh2 moiety, counter anions and solvent molecules are omitted for clarity.
Although significantly different it is difficult to rank the substituents
in terms of their steric requirements.[65] To have a more profound
definition and classification of the “size of the substituent” the
molecular surfaces were calculated with the GEPOL algorithm.[66]
By calculating a smaller model system, i.e. only considering the
4-substituted 2-oxazoline moiety (Figure S5, Table S4), the
L4 < L5 < L6 < L7, whereby the surface size is enlarged
according to the size of the respective substituent. The same
trend is observed for the case that R1 and R2 are similar. The
surface size for C1 < C2 < C3 increases with more steric
demanding substituents, i.e. H < Me < Ph. Interestingly, the
calculated surface values, and thus, the expansion of the
molecular volumes of C4 (R2 = iPr) and C6 (R2 = Ph) are almost
surface
size
follows
the
order
L1 < L2 < L3
and
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the same, but much smaller than those of C5 (R1 = iBu) and C7
(R1 = Bn). This observation can be explained by the different
configuration of the ligands, because in C4 and C6 ((S)
configurated) the substituents points towards each other,
whereas in C5 and C7 ((R) configurated) the substituent R2 points
to the outside of the complex (Figure 4). Hence, the steric demand
of the substituents is not the crucial factor for the molecular
surface. Instead the differences in chirality and the spatial
arrangement are most important.
To verify these findings, an analysis of the buried volume (%Vbur
)
using the SambVca 2.0 online software[67] was carried out. This
method developed by Cavallo et al. describes the space filling of
the first coordination sphere in transition metal complexes.[68–70]
The results (Table S5) are in line with the surface sizes obtained
by the GEPOL algorithm. This means, that the complexes C4 and
C6 employing (R) configured ligands are much more densely
packed around the copper center than the complexes C5 and C7
with (S) configured ligands.
Figure 5. Cyclic voltammograms of C1-C7 in acetonitrile solution referenced vs.
the ferrocene/ferricenium (Fc/Fc+) couple. Left: reductive scans. Right: oxidative
scans. C1/C2 (red, solid/dashed), C4/C6 (blue, solid/dashed), C5/C7 (green,
solid/dashed), Conditions: scan rate of 100 mVs-1, with 0.1 M n-Bu4NPF6 as
supporting electrolyte.
Electrochemical properties
Cyclic voltammograms (CVs) of the complexes C1-C7 were
recorded in acetonitrile solution. Apart from C3 all compounds
display a fully reversible reduction and oxidation event each
(Figure 4, Table 3). It needs to be mentioned, that the reduction
in C3 is only reversible at scan rates above 500 mV/s, whereas
the oxidation stays irreversible (Figure S6). The reduction of C1-
C6 occurs at potentials between -2.25 to -2.21 V and corresponds
to a one-electron reduction of the P^N-ligand.[41,44,71] DFT
calculations confirmed this assignment and revealed that the spin
density of the reduced complex is only located at the coordinating
atoms and the central aryl unit (Figure S8). Therefore, this
process is largely invariant from the different substituents at the
2-oxazoline moiety, because they are not part of the conjugated
system of the phox ligand. Solely in complex C7 the reduction is
slightly shifted by about 50 mV to more positive potentials.
In contrast, the reversible oxidation potentials, which formally can
be assigned to a metal-centered Cu+/Cu2+ oxidation process, are
influenced by the substituents. The oxidation potential of C2
(0.58 V) is shifted by 300 mV more anodic compared to that of C1
(0.29 V). Apparently, the Cu(II) center ([Ar] 3d9) in the oxidized
species favors a square planar coordination environment. This
flattening seems to be hampered in C2 through the steric impact
of the two methyl groups at the oxazoline moiety. This is in line
with findings on Cu(I) complexes with 2,9-substituted
phenanthroline ligands, e.g. in [Cu(N^N)(POP)]+ (POP = bis[2-
(diphenylphosphino)-phenyl]ether), where the complex with
N^N = 2,9-dimethyl-phenanthroline shows a shift of 150 mV
towards more positive potentials compared to the complex
without substituents at the diimine ligand.[72] Moreover, there is a
direct correlation between the oxidation potentials and the
different orientations of the substituents in the chiral ligands. The
complexes with a larger expansion of the molecular volumes C4
and C6 (0.49 V and 0.47 V) are oxidized at higher potentials
compared to C5 and C7 (0.41 V and 0.42 V). All in all, these
observations seem to be in relation to the entatic state principle,[73]
which describes a pre-organization of the ligand sphere in order
to stabilize a certain coordination mode. This structural pre-
distortion is known for Cu(I) complexes in a protein matrix,[74–76]
as well as for other synthetically Cu(I) complexes[77–81], e.g. Cu(I)
complexes with guanidine ligands[80,81] or heteroleptic Cu(I)
complexes with sterically demanding phenanthroline ligands.[78]
The diffusion coefficients (D, Table 2) were obtained from the
scan rate-dependent CVs and the baseline corrected forward-
Table 2. Summary of the electrochemical properties of the complexes C1-
C7 in acetonitrile solution at room temperature. Potentials are referenced to
the ferrocene/ferricenium (Fc/Fc+) redox couple. Diffusion coefficients D are
determined using the Randles-Sevcik equation (see SI).
ퟏ/ퟐ
퐫퐞퐝
ퟏ/ퟐ
퐨퐱
푬
푬
D [cm2/s]
C1
C2
C3
C4
C5
C6
C7
-2.25
-2.25
0.29
0.58
1.15·10-5
1.14·10-5
n.d. [d]
-2.14 [a,b]
-2.23
0.76 [a,c]
0.49
1.13·10-5
1.06·10-5
1.15·10-5
1.14·10-5
-2.25
0.41
-2.21
0.47
-2.19
0.42
scan peak potentials (ip, ) by using the Randles-Sevcik equation
f
[a] irreversible [b] anodic peak [c] cathodic peak [d] not determined
(Figure S7). As a result, there seems no direct correlation
between the diffusion constants and the chirality or the steric
demand, because D is always about 1.13·10-5 cm2/s. This is most
likely due to a similar globular shape in solution for C1-C7.
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shifted, e.g. [(POP)Cu(P^N)]+, where P^N
= 8-diphenyl-
Absorption and Emission properties
phosphanylquinoline only exhibits an absorption maxima
(shoulder) at 360 nm,[44] and [Cu2(PNNP)Br2], with PNNP = 1,3-
bis(1-(2-(diphenylphospanyl)phenyl)-1H-pyrazol-3-yl)benzene
has also only weak absorption bands in the 325 -375 nm
region.[82] This renders the present Cu(I) phosphinooxazoline
complexes more attractive for light-harvesting applications.
Nevertheless, the ability to harvest visible (sun)light is still inferior
compared to benchmark photosensitizers like [Ru(bpy)3]2+
The absorption spectra of C1-C7 in dichloromethane (Figure 6)
are dominated by strong ligand centered (LC) transitions (π-π*
and n-π*) in the wavelength range below 300 nm.[41] Notably, the
different substituents and substitution pattern have only a
marginal influence on the band shape and energy. Solely in C6
and C7 additional LC transitions below 270 nm, caused by the
aromatic substituents, increase the extinction coefficient to some
extend (ε250 nm = 30000 M-1 cm-1). In comparison, the complexes
C4 and C5 with aliphatic chains in 4-position at the 2-oxazoline
possess an extinction coefficient of ε250 nm = 25000 M-1 cm-1. The
comparably weak (ε400 nm = 1500-2300 M-1 cm-1) and broad tails
for C1-C5 and C7 in the range between 350 and 450 nm can be
attributed to metal-to-ligand charge transfer (MLCT) processes.[41]
The respective TD-DFT calculations of C1 also suggest that the
lowest-lying excitations are mainly involving the frontier orbitals
HOMO-n (n = 0, 1, 2) and LUMO+m (m = 0, 1, 2). The HOMO (as
well as the HOMO-1 and HOMO-2) of both complexes
corresponds to a Cu(I) d-orbital. The LUMO and LUMO+1 are
ligand-centered orbitals, where the electron density is distributed
over the coordinating nitrogen atoms and the joint of the 2-
oxazoline and the central aryl ring itself. The LUMO+2 is mostly
localized on one of the aryl substituents of the PPh2 moiety
(Figure S11b, Table S6). Consequently, the most dominant
electronic transition (HOMO  LUMO) can be assigned to a
charge-separation from the copper center to the π*-orbitals of the
ligand sphere.[41] This is also the case for C6, resulting in a far
more pronounced and clearly separated MLCT band from the
other optical transitions (Figure S11a, Tables S6 and S7).
Compared to the unsubstituted parent complex C1, the low-
(λmax,MLCT = 452 nm, ε = 13.000 M-1 cm-1) or [fac-Ir(ppy)3] (λmax
=
84]
375 nm, ε = 7.200 M-1 cm-1).[83,
The light absorption of
[Cu(P^N)2]+ complexescould possibly further improved by the use
of larger, stiffer and sterically more demanding hetero-bidentate
P^N ligands.
Only complexes C2 and C4-C7 show emission (Figure S9, Table
4) in deaerated dichloromethane solution at room temperature
(293 K), but of very low intensity so that reliable values for the
quantum yields could not be obtained. The spectra are broad and
structureless with a maximum at about 600 nm, which is indicative
for 3MLCT states.
Excited state structure
After excitation with light that corresponds to the wavelength of
the MLCT region Cu(I) is formally oxidized to Cu(II) and the
electron configuration changes from d10 to d9. In solution, this
charge transfer induces a structural reorganization from a
tetrahedral geometry in the ground state (S0) to a distorted
square-planar ligand field in the singlet excited state (S1). The
related triplet excited state (T1) exhibits a similar geometry.[41,85]
To get a deeper insight into the influence of the different
substituents on this flattening process, the geometries of S0 and
S1 of C1-C7 (Figures S10) were optimized at the B3LYP-
D3(BJ)//def2-SVP level of theory. As described in the discussion
of the crystal structures above, in the ground state the lpia of C1-
C7 is correlated to the steric information of the substituents, but
an impact of π-stacking effects and distortions within the ligands
is also present. All in all, the difference in lpia is directly associated
with the steric encumbrance of the ligand within the complex. For
C1, which does not contain substituents at the 2-oxazoline moiety,
a difference in lpia (lpia) between the S0 (83.50°) and the S1
state (45.72°) of 37.78° is the highest one of all complexes
(Table 3). Instead, the lpias are significantly lower for C2 (4,4’-
dimethyl, 16.15°) and C3 (4,4’-diphenyl, 16.45°), but practically
unaltered in these two complexes containing two substituents
each. However, the energy difference between the ground and
the excited-state is higher in the case of C3. This is due to an
increased steric repulsion, which limits the structural changes in
the ligand sphere.
energy transitions are bathochromically shifted with
a
simultaneous increase in extinction coefficients (Figure 6). This
observation is also reflected in the TD-DFT calculations, where
the S0  S1 and S0  S2 transitions are shifted to lower energy
compared to C1.
Figure 6. UV/vis absorption spectra of C1/C2/C3 (red, solid/dashed/dotted),
C4/C6 (blue, solid/dashed) and C5/C7 (green, solid/dashed) in dichloromethane
under inert conditions. The inset is an enlargement of the MLCT region.
Interestingly, for the unsymmetrically and singly substituted
complexes C4-C7 the estimated reorganization energy is almost
independent of the mass or size of the substituents, but strongly
depends on the (R) and (S) configuration. TD-DFT calculations of
the complexes with (R) configured ligands (i.e. C4 and C6) exhibit
a lpia of approx. 31° (Table 3). This is much larger compared to
the (S) configured complexes C5 and C7 with a lpia of approx.
In comparison to structurally related mono- and multinuclear Cu(I)
complexes bearing P^N, P^N^P, P^N^N^P or N^P^N ligands, the
low-energy bands of C1-C7 are generally bathochromically
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10.1002/chem.201904379
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16°. Hence, only in C5 and C7, where the substituents at adjacent
ligands are pointing towards each other, the flattening distortion
is hampered (for S0 and S1 structures see Figure S10). Another
promising alternative to prevent unwanted flattening upon
photoexcitation is the design of linear Cu(I) complexes based on
addition, emission lifetime measurements of crystalline samples
of the complexes C1-C7 were performed at room temperature.
After excitation at 355 nm, C2-C7 possess luminescence lifetimes
in the sub-microsecond timescale (Table 4). C7 exhibits the
longest emission lifetime, with a long-lived component of about
2.8 µs (Table 4). The energy separation between the S1 and T1
state in C1-C7 is estimated to be around 130-170 meV (Table S8).
Thermally activated delayed fluorescence (TADF), however, is
therefore expected to be less dominant and the emission lifetime
is most likely only associated with the decay of a 3MLCT
state.[93,94]
e.g. cyclic alkyl(amino)carbenes, N-heterocyclic carbenes and
87, 88, 89
different pyridine or amide ligands.86,
The coplanar
arrangement of the ligands can suppress non-radiative decay and
reduce structural reorganization resulting in highly efficient Cu(I)
emitters.
Table 3. Compilation of the ligand plane intersection angle (lpia, °),
reorganization energies ΔES -S and energy differences between the S1 and
T1 state of the complexes C1-C7 assessed from their calculated structures.
Table 4. Photophysical data of C1-C7 in dichloromethane solution and in the
solid state at room temperature under argon. Relative photoluminescence
quantum yields in solution (φPLQY,l) were determined using [Ru(bpy)3]PF6 as
standard (φR = 0.095 in MeCN[95,96]). Absolute photoluminescence quantum
yields in the solid (φPLQY,s) were determined using an integrating sphere with
an experimental error of 5% of the obtained values. The excitation
wavelength in all experiments was λ = 355 nm.
1
0
C1
C2
C3
C4
C5
C6
C7
crystal
85.88
81.88
71.09
75.35
73.93
76.03
77.56
71.89
78.48
79.91
68.01
68.59
88.31
84.10
[a]
S0
퐬퐨퐥퐢퐝
FWHM[d]
흉
퐞퐦
퐃퐂퐌
퐞퐦
퐬퐨퐥퐢퐝
퐞퐦
흀
FWHM[d] ΦPLQY,l
흀
ΦPLQY,s
[b]
S0
83.50
45.72
37.78
84.45
0.15
73.13
56.98
16.15
68.85
0.17
75.86
59.41
16.45
58.85
0.13
72.24
41.03
31.21
93.94
0.17
82.82
66.09
16.73
64.84
0.16
69.12
38.53
30.59
95.95
0.17
83.22
68.24
15.00
58.41
0.15
[nm]
[ns]
[nm]
[nm]
[%]
[nm]
[%]
[b]
S1
[a]
[c]
[c]
[a]
[c]
[c]
C1
C2
-
-
-
-
-
0.3
8.5
-
[b]
S1-S0
Δlpia
[b]
S1-S0
603
122
1.4
549
585
550
557
574
519
99
110
95
1329 ± 5
666 ± 207
1457 ± 12
819 ± 3
ΔE
[b]
T1-S1
ΔE
507,
590[b]
[c]
[c]
C3
C4
C5
C6
C7
-
-
0.6
3.6
3.4
2.4
3.8
[a] BP86-D3(BJ)//def2-TZVP [b] B3LYP-D3(BJ)//def2-SVP
592
592
609
591
146
130
136
137
0.18
0.59
0.34
0.26
Solid state emission and lifetime
102
99
Unlike their behavior in solution the complexes C2 and C4-C7 are
clearly luminescent in the solid state (Figure S12b) with
luminescence quantum yields Φ between 0.3 to 8.5 % (Table 4).
Upon excitation in the MLCT regime the crystalline solids of C2
and C4-C7 exhibit structureless emission bands with a full width
at half maximum (FWHM) of about 100 nm (Table 4). Interestingly,
the emission maxima are significantly hypsochromically shifted of
up to 72 nm for C7 compared to the maxima in solution. This shift
can be explained by the luminescence rigodochromic effect[90] as
well as by the smaller changes of the molecular geometry in the
solid state upon excitation.[91] Linfoot et al. showed, that even in
the solid state it is highly important to maximize the steric
repulsion between the ligands and the metal center in order to
increase the photoluminescence quantum yield of Cu(I)
488 ± 6
104
2781 ± 7
[a] The emission intensity was below the detection limit. [b] Shoulder. [c] Not
determined. [d] Full width at half maximum of the emission. [e] The long-
lived major lifetime component is given. For further details, see ESI and ref.
[97].
Photostability and Photoreactivity
With respect to possible applications in solar energy conversion
complexes.[92]
[(POP)Cu(N^N)]+ complexes (with POP
They studied the solid state emission of
bis[2-(diphenyl-
schemes
a
high photostability in solution is essential.
Unfortunately, heteroleptic diimine–diphosphine Cu(I) complexes
frequently suffer from a limited stability in solution under
irradiation or catalytic conditions.[31–34,98] Irradiation of the
prototype photosensitizer [(P^P)Cu(N^N)]PF6 (P^P = xantphos
and N^N = bathocuproine) in acetonitrile with a solar light source
(i.e. a 150 W Xe arc lamp) leads to ligand dissociation and the
formation of the respective homoleptic complexes (Figure S14).
In contrast, a ligand exchange reaction in the related heteroleptic
complex [(L2)Cu(bathocuproine)]PF6 does not occur (Figure S14).
Furthermore, the homoleptic complexes C1-C7 are not prone to
changes in their molecular composition, which results in more
photostable (Figure S15) complexes compared to heteroleptic
=
phosphino)-phenylether) and N^N = 4,4’-dimethyl- or 4,4’,6,6’-
tetramethyl-2,2’-bipyridine) and found that already a methyl group
largely hinders the flattening in the solid state and therefore
increases the emission.[86] The same behavior is observed in our
case, when changing from C1 (no substituents) to C2 (two methyl
groups). Furthermore, the complexes C1-C7 display an
unexpected strong dependence of the solid state emission color
from the different substituents (Figure S12a). The emission
covers a spectral region ranging from 519 nm in C7 up to 585 nm
for C3. However, there seems no clear correlation between the
size or kind of the substituents and the emission maxima. In
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10.1002/chem.201904379
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Cu(I) complexes bearing a P^P ligand. The photostability
measurements in acetonitrile solution have also shown, that the
(S) configurated complexes display a slightly higher stability than
the (R) configurated, which can be explained by the reduced steric
constraints.
respective MLCT state undergoes a strong flattening distortion,
which is independent of the specific kind, size or number of
substituents. Instead, the specific properties are dictated by the
chirality of the ligands. Furthermore, the flattening distortion is the
main reason for the weak emission in solution. In contrast, all
complexes show a clear emission in the solid state with a
dependence of the emission color on the steric information.
Additionally, the successful interaction of C2 with sacrificial
reductants as well as with an iron carbonyl water reduction
catalyst was demonstrated. As another key advantage compared
to heteroleptic diimine–diphosphine Cu(I) photosensitizers these
novel [Cu(N^P)2]+ complexes were found to be quite photorobust
and do not suffer from photoinduced ligand exchange reactions in
solution.
All in all, this renders these class of compounds as suitable for
various applications within solar energy conversion schemes. At
the same time, this study highlights the importance of having
control over chirality and steric information in Cu(I) complexes. In
the future, multidentate N^N^P or P^N^N^P ligands[100] as well as
macrocyclic phenanthroline ligands[36] might be used as suitable
alternatives to P^N ligands to further improve Cu(I) based
photosensitizers.
In a next step, the electron transfer properties of these novel
photosensitizers upon light irradiation were tested by the
interaction with commonly used sacrificial reductants as well as
with a water reduction catalyst.[99] For this purpose, an acetonitrile
solution containing C2 (0.1 mM) and either dimethylphenyl-
benzimidazoline (BIH, 0.5 mM) or triethylamine (TEA, 100 mM)
was irradiated. Simultaneous UV/vis measurements revealed the
constant build-up of a new band at 570 nm (Figure S16). The
speed and magnitude of interaction using TEA, however, is
substantially slower than with BIH, which is in accordance with the
lower oxidation potential of BIH.[99] The interplay of C2 with a
water reduction catalyst was probed with the commonly used iron
carbonyl complex [Fe3(CO)12][6,7,35,41] (Figure S17). From the
Stern-Volmer experiment, an apparent emission quenching can
be seen (KSV = 1.99 x 103 M-1). These spectroscopic observations
are in line with our previous results, where complex C2 was used
for the light-driven reduction of protons to hydrogen within a fully
noble-metal-free system composed of [Fe3(CO)12] as water
reduction catalyst and triethylamine as sacrificial reductant.[41]
There, C2 showed a low, but fairly constant production of H2 with
a turnover number of 53 within 24 h.[41]
Experimental Section
CCDC 1934742 (C1), 11561237 (C2), 1934740 (C3), 1934739 (C4),
1947485 (C5), 1947486 (C6), 1934741 (C7) contain the crystallographic
data for this paper. These data are provided free of charge by the
Cambridge Crystallographic Data Centre. All further experimental and
synthetic details can be found in the Supporting Information.
Conclusions
Based on the phosphinooxazoline ligand a systematic series of
sterically modified P^N ligands L1-L7, without any substituents
(L1), with only one substituent (L4-L7) and two substituents (L2-
L3) at the 2-oxazoline moiety, were prepared. These
heterobidentate P^N ligands were then used to design a new
class of homoleptic Cu(I) photosensitizers C1-C7 and to study
their impact on the photophysical and electrochemical properties.
The different ligands are either available by a two-step procedure
starting from the commercially available amino alcohols or via a
three-step synthesis using natural amino acids. The complexes
C1-C7 (yellow to orange solids) were mostly obtained in good
Acknowledgements
This work was supported by the Deutsche Forschungs-
gemeinschaft (DFG, Priority Program SPP 2102 “Light-controlled
reactivity of metal complexes” (TS 330/4-1 and KA 4671/2-1)) and
the DFG project TS 330/3-1. M.K. and S.T. are grateful to the
Fonds der Chemischen Industrie (FCI) for funding. The authors
also acknowledge support by the state of Baden-Württemberg
through bwHPC and by the DFG (INST 40/467-1 FUGG). We
thank Benedikt Bagemihl for assistance in the lab.
yields with
a
remarkably photostability in solution.
A
comprehensive X-ray analysis revealed a uniform coordination
behavior around the copper center and exposed major
differences of the ligand arrangement in (S) and (R) substituted
complexes.
Keywords: copper complexes • P^N ligands • X-ray structures •
photophysics • structure-property relations
The redox processes of all complexes (except C3) are fully
reversible, which is in strong contrast to most of the conventional
heteroleptic diamine-diphosphine Cu(I) photosensitizers. While
the reduction potentials are not affected by the different
substituents or substitution pattern, the oxidation of C2-C7 occurs
at higher potentials compared to C1, which does not bear any
substituents. The absorption spectra are largely unaffected by the
different substituents, with only complex C6 having a phenyl
substituent exhibiting a pronounced bathochromic shift of the
MLCT band. (TD-)DFT calculations corroborate the findings and
were used to determine the excited state structures. The
[1]
[2]
Y.-J. Yuan, Z.-T. Yu, D.-Q. Chen, Z.-G. Zou, Chem. Soc. Rev. 2017, 46,
603–631.
Y. Liu, S.-C. Yiu, C.-L. Ho, W.-Y. Wong, Coord. Chem. Rev. 2018, 375,
514–557.
[3]
[4]
M. S. Lazorski, F. N. Castellano, Polyhedron 2014, 82, 57–70.
Y. Zhang, M. Schulz, M. Wächtler, M. Karnahl, B. Dietzek, Coord. Chem.
Rev. 2018, 356, 127–146.
[5]
[6]
M. Sandroni, Y. Pellegrin, F. Odobel, C. R. Chim. 2016, 19, 79–93.
S.-P. Luo, E. Mejía, A. Friedrich, A. Pazidis, H. Junge, A.-E. Surkus, R.
Jackstell, S. Denurra, S. Gladiali, S. Lochbrunner, M. Beller, Angew.
Chem. Int. Ed. 2013, 52, 419–423.
This article is protected by copyright. All rights reserved.

10.1002/chem.201904379
Chemistry - A European Journal
FULL PAPER
[7]
E. Mejía, S.-P. Luo, M. Karnahl, A. Friedrich, S. Tschierlei, A.-E. Surkus,
H. Junge, S. Gladiali, S. Lochbrunner, M. Beller, Chem. Eur. J. 2013, 19,
15972–15978.
[37] E. Leoni, J. Mohanraj, M. Holler, M. Mohankumar, I. Nierengarten, F.
Monti, A. Sournia-Saquet, B. Delavaux-Nicot, Jean-Francois
Nierengarten, N. Armaroli, Inorg. Chem. 2018, 57, 15537–15549.
[38] M. Alkan-Zambada, S. Keller, L. Martínez-Sarti, A. Prescimone, J. M.
Junquera-Hernández, E. C. Constable, H. J. Bolink, M. Sessolo, E. Ortí,
C. E. Housecroft, J. Mater. Chem. C 2018, 6, 8460–8471.
[39] N. S. Murray, S. Keller, E. C. Constable, C. E. Housecroft, M. Neuburger,
A. Prescimone, Dalton Trans. 2015, 44, 7626–7633.
[40] R. Molteni, K. Edkins, M. Haehnel, A. Steffen, Organometallics 2016, 35,
629–640.
[8]
[9]
J. Kim, D. R. Whang, S. Y. Park, ChemSusChem 2017, 10, 1883–1886.
S. Saeedi, C. Xue, B. J. McCullough, S. E. Roe, B. J. Neyhouse, T. A.
White, ACS Appl. Energy Mater. 2019, 2, 131–143.
[10] J. Windisch, M. Orazietti, P. Hamm, R. Alberto, B. Probst,
ChemSusChem 2016, 9, 1719–1726.
[11] R. S. Khnayzer, C. E. McCusker, B. S. Olaiya, F. N. Castellano, J. Am.
Chem. Soc. 2013, 135, 14068–14070.
[12] K. Matsuo, E. Yamaguchi, A. Itoh, Asian J. Org. Chem. 2018, 7, 2435–
2438.
[41] R. Giereth, W. Frey, H. Junge, S. Tschierlei, M. Karnahl, Chem. Eur. J.
2017, 23, 17432–17437.
[13] O. Reiser, Acc. Chem. Res. 2016, 49, 1990–1996.
[14] S. Paria, O. Reiser, ChemCatChem 2014, 6, 2477–2483.
[15] B. M. Hockin, C. Li, N. Robertson, E. Zysman-Colman, Catal. Sci.
Technol. 2019, 9, 889–915.
[42] M. K. Rong, F. Holtrop, J. C. Slootweg, K. Lammertsma, Coord. Chem.
Rev. 2019, 382, 57–68.
[43] E. I. Musina, A. V. Shamsieva, I. D. Strelnik, T. P. Gerasimova, D. B.
Krivolapov, I. E. Kolesnikov, E. V. Grachova, S. P. Tunik, C. Bannwarth,
S. Grimme, S. A. Katsyuba, A. A. Karasik, O. G. Sinyashin, Dalton Trans.
2016, 45, 2250–2260.
[16] B. Wang, D. P. Shelar, X.-Z. Han, T.-T. Li, X. Guan, W. Lu, K. Liu, Y.
Chen, W.-F. Fu, C.-M. Che, Chem. Eur. J. 2015, 21, 1184–1190.
[17] M. Wallesch, D. Volz, D. M. Zink, U. Schepers, M. Nieger, T. Baumann,
S. Bräse, Chem. Eur. J. 2014, 20, 6578–6590.
[44] L. Qin, Q. Zhang, W. Sun, J. Wang, C. Lu, Y. Cheng, L. Wang, Dalton
Trans. 2009, 9388 - 9391.
[18] B. Jiao, J. Wang, J. Huang, M. Cao, C. Liu, G. Yin, Y. Zhu, B. Zhang, C.
Du, Org. Electron. 2019, 64, 158–165.
[45] T. Suzuki, H. Yamaguchi, A. Hashimoto, K. Nozaki, M. Doi, N. Inazumi,
N. Ikeda, S. Kawata, M. Kojima, H. D. Takagi, Inorg. Chem. 2011, 50,
3981–3987.
[19] E. Cariati, E. Lucenti, C. Botta, U. Giovanella, D. Marinotto, S. Righetto,
Coord. Chem. Rev. 2016, 306, 566–614.
[46] D. M. Zink, M. Bächle, T. Baumann, M. Nieger, M. Kühn, C. Wang, W.
Klopper, U. Monkowius, T. Hofbeck, H. Yersin, S. Bräse, Inorg. Chem.
2013, 52, 2292–2305.
[20] M. Wallesch, A. Verma, C. Fléchon, H. Flügge, D. M. Zink, S. M.
Seifermann, J. M. Navarro, T. Vitova, J. Göttlicher, R. Steininger, L.
Weinhardt, M. Zimmer, M. Gerhards, C. Heske, S. Bräse, T. Baumann,
D. Volz, Chem. Eur. J. 2016, 22, 16400–16405.
[47] D. M. Zink, T. Baumann, J. Friedrichs, M. Nieger, S. Bräse, Inorg. Chem.
2013, 52, 13509–13520.
[21] F. Dumur, Org. Electron. 2015, 21, 27–39.
[48] A. J. M. Miller, J. L. Dempsey, J. C. Peters, Inorg. Chem. 2007, 46, 7244–
7246.
[22] C. Bizzarri, E. Spuling, D. M. Knoll, D. Volz, S. Bräse, Coord. Chem. Rev.
2018, 373, 49–82.
[49] A. Neshat, R. B. Aghakhanpour, P. Mastrorilli, S. Todisco, F. Molani, A.
Wojtczak, Polyhedron 2018, 154, 217–228.
[23] S. Y. Brauchli, E. C. Constable, C. E. Housecroft, Dyes Pig. 2015, 113,
447–450.
[50] R. Mondal, I. B. Lozada, R. L. Davis, J. A. G. Williams, D. E. Herbert, J.
Mater. Chem. C 2019, 7, 3772–3778.
[24] E. Schönhofer, B. Bozic-Weber, C. J. Martin, E. C. Constable, C. E.
Housecroft, J. A. Zampese, Dyes Pig. 2015, 115, 154–165.
[25] C. E. Housecroft, E. C. Constable, Chem. Soc. Rev. 2015, 44, 8386–
8398.
[51] F. Wei, X. Liu, Z. Liu, Z. Bian, Y. Zhao, C. Huang, CrystEngComm 2014,
16, 5338–5344.
[52] D. M. Zink, D. Volz, T. Baumann, M. Mydlak, H. Flügge, J. Friedrichs, M.
Nieger, S. Bräse, Chem. Mater. 2013, 25, 4471–4486.
[53] Z. Liu, P. I. Djurovich, M. T. Whited, M. E. Thompson, Inorg. Chem. 2012,
51, 230–236.
[26] B. Bozic-Weber, E. C. Constable, C. E. Housecroft, Coord. Chem. Rev.
2013, 257, 3089–3106.
[27] R. D. Costa, D. Tordera, E. Ortí, H. J. Bolink, J. Schönle, S. Graber, C.
E. Housecroft, E. C. Constable, J. A. Zampese, J. Mater. Chem. 2011,
21, 16108–16118.
[54] S. Maggini, Coord. Chem. Rev. 2009, 253, 1793–1832.
[55] D. Volz, M. Nieger, J. Friedrichs, T. Baumann, S. Bräse, Inorg. Chem.
Commun. 2013, 37, 106–109.
[28] E. Fresta, R. D. Costa, J. Mater. Chem. C 2017, 5, 5643–5675.
[29] A. J. J. Lennox, S. Fischer, M. Jurrat, S.-P. Luo, N. Rockstroh, H. Junge,
R. Ludwig, M. Beller, Chem. Eur. J. 2016, 22, 1233–1238.
[30] A. Barbieri, G. Accorsi, N. Armaroli, Chem. Commun. 2008, 2185–2193.
[31] M. Nishikawa, D. Kakizoe, Y. Saito, T. Ohishi, T. Tsubomura, Bull. Chem.
Soc. Jpn. 2017, 90, 286–288.
[56] M. Wallesch, M. Nieger, D. Volz, S. Bräse, Inorg. Chem. Commun. 2017,
86, 232–240.
[57] C. Zeng, N. Wang, T. Peng, S. Wang, Inorg. Chem. 2017, 56, 1616–
1625.
[58] J. Sedelmeier, T. Hammerer, C. Bolm, Org. Lett. 2008, 10, 917–920.
[59] K. Tani, D. C. Behenna, R. M. McFadden, B. M. Stoltz, Org. Lett. 2007,
9, 2529–2531.
[32] Y. Zhang, M. Heberle, M. Wächtler, M. Karnahl, B. Dietzek, RSC Adv.
2016, 6, 105801–105805.
[33] S. Fischer, D. Hollmann, S. Tschierlei, M. Karnahl, N. Rockstroh, E.
Barsch, P. Schwarzbach, S.-P. Luo, H. Junge, M. Beller, S. Lochbrunner,
R. Ludwig, A. Brückner, ACS Catal. 2014, 4, 1845–1849.
[34] A. Kaeser, M. Mohankumar, J. Mohanraj, F. Monti, M. Holler, J.-J. Cid,
O. Moudam, I. Nierengarten, L. Karmazin-Brelot, C. Duhayon, B.
Delavaux-Nicot, N. Armaroli, J.-F. Nierengarten, Inorg. Chem. 2013, 52,
12140–12151.
[60] D. A. Dickman, A. I. Meyers, G. A. Smith, R. E. Gawley, Org. Synth. 1985,
63, 136.
[61] N. Armaroli, G. Accorsi, F. Cardinali, A. Listorti, Top. Curr. Chem. 2007,
280, 69–115.
[62] C. R. Martinez, B. L. Iverson, Chem. Sci. 2012, 3, 2191–2201.
[63] M. O. Sinnokrot, C. D. Sherrill, J. Am. Chem. Soc. 2004, 126, 7690–7697.
[64] S. K. Burley, G. A. Petsko, Science 1985, 229, 23–28.
[65] M. K. Eggleston, D. R. McMillin, K. S. Koenig, A. J. Pallenberg, Inorg.
Chem. 1997, 36, 172–176.
[35] M. Heberle, S. Tschierlei, N. Rockstroh, M. Ringenberg, W. Frey, H.
Junge, M. Beller, S. Lochbrunner, M. Karnahl, Chem. Eur. J. 2017, 23,
312–319.
[66] J. L. Pascual-ahuir, E. Silla, I. Tuñon, J. Comput. Chem. 1994, 15, 1127–
1138.
[36] M. Mohankumar, M. Holler, E. Meichsner, J. F. Nierengarten, F. Niess,
J. P. Sauvage, B. Delavaux-Nicot, E. Leoni, F. Monti, J. M. Malicka, M.
Cocchi, E. Bandini, N. Armaroli, J. Am. Chem. Soc. 2018, 140, 2336–
2347.
[67] L. Falivene, R. Credendino, A. Poater, A. Petta, L. Serra, R. Oliva, V.
Scarano, L. Cavallo, Organometallics 2016, 35, 2286–2293.
[68] A. Poater, F. Ragone, S. Giudice, C. Costabile, R. Dorta, S. P. Nolan, L.
Cavallo, Organometallics 2008, 27, 2679–2681.
This article is protected by copyright. All rights reserved.

10.1002/chem.201904379
Chemistry - A European Journal
FULL PAPER
[69] A. Poater, F. Ragone, R. Mariz, R. Dorta, L. Cavallo, Chem. Eur. J. 2010,
16, 14348–14353.
[85] S. Tschierlei, M. Karnahl, N. Rockstroh, H. Junge, M. Beller, S.
Lochbrunner, ChemPhysChem 2014, 15, 3709–3713.
[86] D. Di, A. S. Romanov, L. Yang, J. M. Richter, J. P. H. Rivett, S. Jones, T.
H. Thomas, M. A. Jalebi, R. H. Friend, M. Linnolahti, M. Bochmann, D.
Credgington, Science 2017, 356, 159-163.
[70] H. Clavier, S. P. Nolan, Chem. Commun. 2010, 46, 841-861.
[71] J.-J. Cid, J. Mohanraj, M. Mohankumar, M. Holler, F. Monti, G. Accorsi,
L. Karmazin-Brelot, I. Nierengarten, J. M. Malicka, M. Cocchi, B.
Delavaux-Nicot, N. Armaroli, J.-F. Nierengarten, Polyhedron 2014, 82,
158–172.
[87] M. Gernert, U. Meller, M. Haehnel, J. Pflaum, A. Steffen, Chem. Eur. J.
2017, 23, 2206-2216.
[72] D. G. Cuttell, S.-M. Kuang, P. E. Fanwick, D. R. McMillin, R. A. Walton,
J. Am. Chem. Soc. 2002, 124, 6–7.
[88] R. Hamze, J. L. Peltier, D. Sylvinson, M. Jung, J. Cardenas, R. Haiges,
M. Soleilhavoup, R. Jazzar, P. I. Djurovich, G. Bertrand, M. E. Thompson,
Science 2019, 363, 601-606.
[73] P. Comba, Coord. Chem. Rev. 2000, 200–202, 217–245.
[74] R. J. P. Williams, Inorganica Chim. Acta Rev. 1971, 5, 137–155.
[75] R. J. P. Williams, J. Mol. Catal. 1985, 30, 1–26.
[89] J. Föller, C. Ganter, A. Steffen, C. M. Marian, Inorg. Chem. 2019, 58,
5446-5456.
[76] L. B. LaCroix, S. E. Shadle, Y. Wang, B. A. Averill, B. Hedman, K. O.
Hodgson, E. I. Solomon, J. Am. Chem. Soc. 1996, 118, 7755–7768.
[77] G. Chaka, J. L. Sonnenberg, H. B. Schlegel, M. J. Heeg, G. Jaeger, T. J.
Nelson, L. A. Ochrymowycz, D. B. Rorabacher, J. Am. Chem. Soc. 2007,
129, 5217–5227.
[90] A. J. Lees, Comments Inorg. Chem. 1995, 17, 319–346.
[91] A. Stoïanov, C. Gourlaouen, S. Vela, C. Daniel, J. Phys. Chem. A 2018,
122, 1413–1421.
[92] C. L. Linfoot, M. J. Leitl, P. Richardson, A. F. Rausch, O. Chepelin, F. J.
White, H. Yersin, N. Robertson, Inorg. Chem. 2014, 53, 10854–10861.
[93] R. Czerwieniec, M. J. Leitl, H. H. H. Homeier, H. Yersin, Coord. Chem.
Rev. 2016, 325, 2–28.
[78] L. Kohler, R. G. Hadt, D. Hayes, L. X. Chen, K. L. Mulfort, Dalton Trans.
2017, 46, 13088–13100.
[79] B. Dicke, A. Hoffmann, J. Stanek, M. S. Rampp, B. Grimm-Lebsanft, F.
Biebl, D. Rukser, B. Maerz, D. Göries, M. Naumova, M. Biednov, G.
Neuber, A. Wetzel, S. M. Hofmann, P. Roedig, A. Meents, J. Bielecki, J.
Andreasson, K. R. Beyerlein, H. N. Chapman, C. Bressler, W. Zinth, M.
Rübhausen, S. Herres-Pawlis, Nat. Chem. 2018, 10, 355–362.
[80] A. Hoffmann, S. Binder, A. Jesser, R. Haase, U. Flörke, M. Gnida, M. S.
Stagni, W. Meyer-Klaucke, B. Lebsanft, L. E. Grünig, S. Schneider, M.
Hashemi, A. Goos, A. Wetzel, M. Rübhausen, S. Herres-Pawlis, Angew.
Chem. Int. Ed. 2014, 53, 299–304.
[94] R. Czerwieniec, H. Yersin, Inorg. Chem. 2015, 54, 4322–4327.
[95] H. Ishida, S. Tobita, Y. Hasegawa, R. Katoh, K. Nozaki, Coord. Chem.
Rev. 2010, 254, 2449–2458.
[96] K. Suzuki, A. Kobayashi, S. Kaneko, K. Takehira, T. Yoshihara, H. Ishida,
Y. Shiina, S. Oishi, S. Tobita, Phys. Chem. Chem. Phys. 2009, 11, 9850
- 9860.
[97] M.-A. Schmid, M. Rentschler, W. Frey, S. Tschierlei, M. Karnahl,
Inorganics 2018, 6, 134.
[98] M. Holler, B. Delavaux-Nicot, J.-F. Nierengarten, Chem. Eur. J. 2019, 25,
4543–4550.
[81] D. F. Schrempp, S. Leingang, M. Schnurr, E. Kaifer, H. Wadepohl, H.-J.
Himmel, Chem. Eur. J. 2017, 23, 13607–13611.
[99] Y. Pellegrin, F. Odobel, C. R. Chim. 2017, 20, 283–295.
[100] H. Chen, L.-X. Xu, L.-J. Yan, X.-F. Liu, D.-D. Xu, X.-C. Yu, J.-X. Fan, Q.-
A. Wu, S.-P. Luo, Dyes Pigm. 2019, doi: 10.1016/j.dyepig.2019.108000
[82] J.-H. Jia, X.-L. Chen, J.-Z. Liao, D. Liang, M.-X. Yang, R. Yu, C.-Z. Lu,
Dalton Trans. 2019, 48, 1418–1426.
[83] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. Von
Zelewsky, Coord. Chem. Rev. 1988, 84, 85-277.
[84] L. Flamigni, A. Barbieri, C. Sabatini, B. Ventura, F. Barigelletti, V. Balzani,
S. Campagna, Top. Curr. Chem. , 281, 143-203.
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Robin Giereth, Alexander K. Mengele,
Wolfgang Frey, Marvin Kloß, Andreas
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Tschierlei*
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Copper(I) Phosphinooxazoline
Complexes: Impact of the ligand
substitution and sterical demand on
the electrochemical and
photophysical properties
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