Dicopper(I) Complexes Incorporating Acetylide-Functionalized Pyridinyl-Based Ligands: Synthesis, Structural, and Photovoltaic Studies

Article abstract of DOI:10.1021/acs.inorgchem.8b01684

Heteroaryl incorporated acetylide-functionalized pyridinyl ligands (L1-L6) with the general formula Py-C≡C-Ar (Py = pyridine and Ar = thiophene-2-yl, 2,2′-bithiophene]-5-yl, 2,2′:5′,2″-terthiophene]-5-yl, thieno[2,3-b]thiophen-2-yl, quinoline-5-yl, benzo[c][1,2,5]thiadiazole-5-yl) have been synthesized by Pd(0)/Cu(I)-catalyzed cross-coupling reaction of 4-ethynylpyridine and the respective heteroaryl halide. Ligands L1-L6 were isolated in respectable yields and characterized by microanalysis, IR spectroscopy, ¹H NMR spectroscopy, and ESI-MS mass spectrometry. A series of dinuclear Cu(I) complexes 1-10 have been synthesized by reacting L1-L6 with CuI and triphenylphosphine (PPh₃) (R1) or with an anchored phosphine derivative, 4-(diphenylphosphino) benzoic acid (R2)/2-(diphenylphosphino)benzenesulfonic acid (R3), in a stoichiometric ratio. The complexes are soluble in common organic solvents and have been characterized by analytical, spectroscopic, and computational methods. Single-crystal X-ray structure analysis confirmed rhomboid dimeric structures for complexes 1, 2, 4, and 5, and a polymeric structure for 6. Complexes 1-6 showed oxidation potential responses close to 0.9 V vs Fc^0/+, which were chemically irreversible and are likely to be associated with multiple steps and core oxidation. Preliminary photovoltaic (PV) results of these new materials indicated moderate power conversion efficiency (PCE) in the range of 0.15-1.56% in dye-sensitized solar cells (DSSCs). The highest PCE was achieved with complex 10 bearing the sulfonic acid anchoring functionality.

Full text of DOI:10.1021/acs.inorgchem.8b01684

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Dicopper(I) Complexes Incorporating Acetylide-Functionalized
Pyridinyl-Based Ligands: Synthesis, Structural, and Photovoltaic
Studies
†
†
†
†
†
Maharaja Jayapal, Ashanul Haque, Idris J. Al-Busaidi, Nawal Al-Rasbi, Mohammed K. Al-Suti,
,
†
‡
,§
⊥
⊥
Muhammad S. Khan,* Rayya Al-Balushi, Shahidul M. Islam,* Chenghao Xin, Wenjun Wu,
,
#
,∥
,∥
Wai-Yeung Wong,* Frank Marken,* and Paul R. Raithby*
†
Department of Chemistry, Sultan Qaboos University, P.O. Box 36, Al Khod 123, Sultanate of Oman
‡
Department of Basic Sciences, College of Applied and Health Sciences, A’Sharqiyah University, Ibra 400, Sultanate of Oman
§
Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, United States
⊥
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Centre for Computational Chemistry, Shanghai Key
Laboratory of Functional Materials Chemistry, School of Chemistry and Molecular Engineering, East China University of Science
and Technology, Shanghai 200237, China
#
Institute of Molecular Functional Materials and Department of Applied Biology and Chemical Technology, The Hong Kong
Polytechnic University, Hung Hom, Kowloon, Hong Kong
∥
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
S Supporting Information
*
ABSTRACT: Heteroaryl incorporated acetylide-functionalized
pyridinyl ligands (L1−L6) with the general formula Py-CC-
Ar (Py = pyridine and Ar = thiophene-2-yl, 2,2′-bithiophene]-5-yl,
2
,2′:5′,2″-terthiophene]-5-yl, thieno[2,3-b]thiophen-2-yl, quino-
line-5-yl, benzo[c][1,2,5]thiadiazole-5-yl) have been synthesized
by Pd(0)/Cu(I)-catalyzed cross-coupling reaction of 4-
ethynylpyridine and the respective heteroaryl halide. Ligands
L1−L6 were isolated in respectable yields and characterized by
1
microanalysis, IR spectroscopy, H NMR spectroscopy, and
ESI-MS mass spectrometry. A series of dinuclear Cu(I)
complexes 1−10 have been synthesized by reacting L1−L6
with CuI and triphenylphosphine (PPh ) (R1) or with an
3
anchored phosphine derivative, 4-(diphenylphosphino) benzoic
acid (R2)/2-(diphenylphosphino)benzenesulfonic acid (R3), in a stoichiometric ratio. The complexes are soluble in common
organic solvents and have been characterized by analytical, spectroscopic, and computational methods. Single-crystal X-ray
structure analysis confirmed rhomboid dimeric structures for complexes 1, 2, 4, and 5, and a polymeric structure for 6.
0
/+
Complexes 1−6 showed oxidation potential responses close to 0.9 V vs Fc , which were chemically irreversible and are likely
to be associated with multiple steps and core oxidation. Preliminary photovoltaic (PV) results of these new materials indicated
moderate power conversion efficiency (PCE) in the range of 0.15−1.56% in dye-sensitized solar cells (DSSCs). The highest
PCE was achieved with complex 10 bearing the sulfonic acid anchoring functionality.
INTRODUCTION
abundance, a diverse set of emission origins (metal-to-ligand
charge transfer MLCT, halide-to-ligand charge transfer XLCT,
ligand-to-ligand charge transfer LLCT, and ligand-centered
(LC) and cluster-centered (CC) states), the ability to harvest
singlet and triplet excitons via thermally activated delayed
fluorescence (TADF), enlarged exciton diffusion length with
reduced charge recombination, and the ability to form mono-
to polynuclear complexes are some of the intriguing features
■
Transition-metal complexes have attracted significant attention
because of their intriguing architectures, topologies, and
optoelectronic (OE) properties.
redox-active metal centers are responsible for different shapes,
1
−3
In these complexes, the
sizes, and geometries, while the organic part tunes and controls
4
,5
the photophysical and physicochemical properties. Further-
more, interaction between metal and conjugated organic
spacers imparts low-energy electronic transition to the
7
−9
offered by Cu(I) based complexes.
These features
6
molecules. Among different transition metals, the monovalent
copper (Cu(I)) ion has emerged as a potential candidate for
the development of a new generation of hybrid materials. High
Received: June 19, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01684
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Article
Scheme 1. Synthesis of Non-Fused and Fused Heteroarylethynylpyridinyl Ligands (L1−L6) and Their Corresponding
Dinuclear Cu(I) Complexes 1−10
2
1−23
prompted researchers to synthesize new Cu(I) complexes for
applications in organic light emitting diodes (OLEDs), light to
electricity conversion, light-emitting electrochemical cells,
qunecher.
Based on this notion, we and others reported
the PL properties and applications of several mono-, di- and
polynuclear pyridine-based Cu(I) complexes and decided to
replace the Fc moiety by conjugated spacers in the acetylide-
functionalized pyridinyl-ligands.
Herein we report the synthesis, structural and photophysical
characterization of a series of new dinuclear Cu(I) complexes
−6 incorporating nonfused/fused heteroarylethynylpyridinyl-
based conjugated ligands. Among the heterocyclic spacers,
benzothiadiazole and thiophene-based materials have been
widely studied for making low band gap (E ) complexes/
polymers as a result of strong donor (D) and acceptor (A)
3
,9
etc. Among carbon (C), nitrogen (N), oxygen (O), and
phosphorus (P) based donor ligands/coligands, N-donating
bridging and terminal ligands are most commonly employed to
satisfy coordination sphere around Cu(I). This is, essentially,
attributed to the versatility, easy complexation (solid as well as
solution phase) and exceptional stability offered by N-
3
,9
1
1
0
donors. It has been demonstrated that by fine-tuning of
the coordinated ligands, a range of complexes could be
achieved with unique and controlled photophysical properties
g
16
3
,11
interactions in the hybrid spacer. Also, these spacers are
known to lower the polarity and enhance the solubility of the
polymer materials. In order to be used in DSSCs, the
complexes require anchoring groups in order to bind to the
and applications.
Furthermore, using designer ligands, the
photonic harvesting can be improved, and redox potential can
17
12
be modulated. Following the seminal work by Savage et al.,
significant research efforts have been dedicated to explore the
13−16
TiO and facilitate electron injection. For this purpose, Cu(I)
2
potential of Cu(I) complexes as sensitizer for DSSC.
complexes (7−10) of heteroarylethynylpyridinyl ligands (L1−
L3 and L6) incorporating sulfonic acid/carboxylic acid
anchored triphenylphosphine auxiliaries have also been
synthesized. DSSC devices have been fabricated with these
anchored Cu(I) complexes, and their performance has been
evaluated.
Cu(I) complexes are considered potential alternative to the
traditional expensive Ru(II) complexes owing to the similarity
in photophysical properties of Cu(I) complexes to the latter.
Such Cu complexes can also be used in an electrolyte based on
the redox potential and frontier orbital (HOMO and LUMO)
energy levels of the complexes with respect to the dye
1
7,18
materials.
However, the PCE of most Cu(I) complexes are
RESULTS AND DISCUSSION
still below the threshold for commercial application, and
therefore, the design and development of new Cu(I)
complexes for DSSC application are receiving intense interests
from researchers worldwide. Recently, we reported the unique
structure and electrochemical properties of Cu(I) dimers and
tetramers with ferrocene (Fc) appended ethynylpyridinyl
■
Synthesis and Spectroscopic Characterization. The
synthesis of heteroarylethynylpyridinyl ligands (L1−L6) and
the corresponding Cu(I) complexes was achieved by
adaptation of previously reported methods. Briefly, the key
protected ligand precursor 4-(trimethylsilylethynyl)pyridine
24
1
9,20
I
ligands.
Despite the fact that these dimers and tetramers
(P1) was obtained by the Pd(0)/Cu -catalyzed cross-coupling
are easy to synthesize, stable, and possess intriguing OE
properties, the presence of the Fc moiety was considered
disadvantageous in terms of photophysical properties for light
harvesting applications as Fc is a known luminescence
reaction of 4-iodopyridine with trimethylsilylacetylene
i
(TMSA) in Pr NH/THF (Scheme 1). The ligand precursor,
2
P1, was deprotected by aqueous KOH in MeOH/THF
followed by purification by silica gel column chromatography
B
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Figure 1. Crystal and molecular structures of 1, 2, 4, 5, and 6 showing the atomic labeling scheme.
yielding 4-ethynylpyridine (P2) as an off-white powder in a
respectable yield (85−86%). It should be noted that both the
trimethylsilyl-protected (P1) and the terminal ethynylpyridinyl
PPh (C H COOH)/ PPh (C H SO H) and CuI in dry
2 6 4 2 6 4 3
CH Cl , under argon atmosphere for 24 h. All the complexes
2
2
are stable to light and air at ambient temperature.
(
P2) ligand precursors are somewhat unstable, decomposing at
All the synthesized materials were characterized by IR, NMR
(1H, C, and P) spectroscopy, electron-impact/electrospray
13
31
room temperature and, therefore, were used quickly for the
next sequence of reactions. A Sonogashira cross-coupling
reaction between P2 and a heteroaryl halide (Ar-X) produced
heteroarylethynylpyridinyl ligands (L1−L6) as light to dark
yellow solids in good to moderate yields (75−88%). The
Cu(I) complexes (1−10) were synthesized by reacting
equimolar quantity of the ligands (L1−L6), coligand (PPh3/
ionization mass spectrometry (EI-MS/ESI-MS), and elemental
−
1
analysis. A sharp peak at around 2165 cm in the IR spectrum
indicated the formation of 4-(trimethylsilylethynyl)pyridine in
the initial cross-coupling reaction. Base-induced deprotection
in the second reaction step was confirmed by the expected
−
1
lowering of the -CC- stretching frequency (2096 cm ) as
C
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Table 1. Selected Bond Parameters for Compounds 1, 2, 4, 5, and 6 (Å and °)
a
b
c
d
e
e
1
2
4
5
6 (Cu dimer 1)
6 (Cu dimer 2)
Cu(1)−I(1)
Cu(1)−I(1#)
Cu(1)−P(1)
Cu(1)−N(1)
Cu(1)···Cu(1#)
2.6516(3)
2.6642(3)
2.2259(5)
2.0510(16)
2.9624(5)
67.736(10)
112.263(9)
2.6381(4)
2.7178(4)
2.2376(7)
2.060(2)
2.9191(8)
66.034(14)
2.6681(3)
2.6552(3)
2.2251(6)
2.0571(17)
2.9680(5)
67.771(10)
2.6360(3)
2.6914(3)
2.2327(6)
2.0531(18)
2.9731(5)
67.835(10)
112.166(10)
2.6832(13)
2.6743(9)
2.2339(13)
2.060(3)
3.315(2)
71.63(3)
2.6506(8)
2.6412(11)
2.2179(13)
2.052(4)
2.978(2)
68.48(3)
Cu(1)−I(1)−Cu(1#)
I(1)−Cu(1)−I(1#)
113.967(14)
112.230(10)
108.37(3)
111.52(3)
a
b
c
d
e
−
x, −y+1, −z+1. −x+1, −y+2, −z+1. −x, −y, −z+1. −x+2, −y, −z−1. −x+1, −y+1, −z.
Figure 2. A diagram of one strand of the polymer [Cu I (PPh ) (L6) ] , exhibiting weak π−π and S···HC interactions between the aromatic rings.
2
2
3
2
2 ∞
−
1
well as the presence of a new peak at 3223 cm ,
arylethynylpyridinyl-based ligands (L1−L6) showed only a
1
corresponding to free ethynyl proton stretching (-CC−H
small shift in their H NMR spectra compared to their
str.). The observed ν
stretching frequencies of the
precursors. Signals due to triphenylphosphine (PPh −H) were
(
CC)
3
25,26
acetylide-functionalized arylpyridine ligands L1−L6 are 2203,
observed in the δ7−9 ppm region as multiplets.
The
−
1
31
2
197, 2194, 2198, 2217, and 2215 cm , respectively. This
trend clearly shows the impact of employing fused and
nonfused thiophene spacers on the values of ν( stretching
complexes were further characterized by P NMR. All
3
1
complexes exhibited P NMR peaks between δ 29.09−29.24
ppm, which are well documented for ethynylpyridinyl based
CC)
19
frequencies. For example, a decrease in the values of ν
Cu(I) complexes bearing phosphine auxiliaries.
(
CC)
stretching frequency on going from L1 → L3 can be attributed
to increased conjugation and hence the donacity (i.e., the order
of donacity: L3 > L2 > L1). It is notable that L4 bearing fused
Structural Characterization. Spectroscopic results were
further complemented by the analysis of the crystal and
molecular structures of complexes 1, 2, 4, 5, and 6 (Figure 1).
The crystals were grown by slow diffusion of hexane in
dichloromethane. Key bond parameter data are summarized in
Table 1.
thiophene (thieno[2,3-b]thiophene) has ν(
frequency value close to its structural analogue L2 (nonfused
stretching
CC)
system). Comparatively higher values of ν( frequency in
CC)
the case of L5 and L6 can be ascribed to electron-withdrawing
“acceptor”) ability of quinoline and benzo[c][1,2,5]-
thiadiazole units. Upon complexation, the single sharp peak
in the IR spectrum due to ν( in the ligand (L) showed
As shown in Figure 1, the crystal structure determinations of
the dimeric complexes [Cu I (PPh ) (L1) ],
(
2
2
3
2
2
[Cu I (PPh ) (L2) ], [Cu I (PPh ) (L4) ], and
2
2
3
2
2
2
2
3
2
2
[Cu I (PPh ) (L5) ] establish that they have a similar Cu I
CC)
2 2
3 2
2
2 2
only a minor change, possibly due to the large distance
core and a trans arrangement of the two phosphine and the
two L ligands. Each Cu(I) center is in a tetrahedral
coordination environment consisting of two bridging iodo
1
9
between -CC- and Cu(I) coordination center. All
anchored complexes displayed a ν stretching frequency
(
CC)
−
1
in the range of 2193−2214 cm . Complexes C7−C10 showed
ligands, one PPh and the nitrogen atom of 4′-pyridinyl
3
−
1
a sharp peak in the range of 1701−1723 cm , owing to the
substituent of L1, L2, L4, or L5, respectively. Each molecule
sits on a crystallographic center of inversion at the center of the
Cu I parallelepiped so that there is half a molecule in the
-
3
CO functionality. In addition, a broad peak in the range of
−
1
057−3061 cm corresponding to −OH carboxylic or
2
2
sulfonic acid moiety (in case of R2 or R3) was also observed.
Similarly, sharp peaks were observed in the range of 1158−
asymmetric unit. Within each dimer, the two unique Cu−I
distances show a variation between 0.01 and 0.08 Å, with a
range from 2.6360(3) to 2.7178(4) Å across the series. The
angles at Cu are obtuse with a range of 112.166(1) −
113.967(14)°, while, as required, the angle at the iodine center
is acute with a range of 66.034(14) − 67.835(10)°, as is
observed in other complexes containing a Cu I core. The
−
1
1
482 cm corresponding to SO groups of R3 in complexes
C9 and C10.
1
The H NMR spectrum of P1 showed doublets at δ7.22, and
δ7.28 ppm corresponding to the α and β protons of the
pyridinyl unit, respectively. As expected, for trimethylsilyl
2
2
(
TMS) groups, the singlet appeared at δ0.27 ppm. Both α and
Cu···Cu separations in the dimers show only a small variation
β protons of pyridinyl unit in the nonfused/fused hetero-
from 2.9191(8) to 2.9731(5) Å, which is too long a distance
D
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Figure 3. (a) UV−vis spectra of complexes 1−6 and (b) anchored Cu(I) complexes 7−10.
for a formal Cu−Cu bonding interaction. The average Cu−N
and Cu−P distances for the series of dimeric complexes are
Table 2. UV−vis and PL Spectral Data of Complexes 1−10
in Dichloromethane at Room Temperature
2
.06 and 2.21 Å, respectively, and show little variation across
luminescence
the series. Generally, these values for the bond parameters
around the Cu(I) center are comparable to those reported
absorption profile
profile
3
12
λmax/nm (ε x 10
optical band gap
λex
λem
previously in other dimeric Cu I systems. However, it is
−1
−1
o
2
2
complex
M
cm
)
(E , eV)
(nm) (nm)
g
apparent that the different coordinating pyridines (L1, L2, L4,
and L5) have little effect on the Cu−N bond lengths
suggesting that the differing electronic properties of the
ligands do not extend to the environment around the Cu(I)
centers.
1
2
3
4
5
308 (11.7), 323 (11)
280 (22), 369 (6.8)
274 (22.9), 397 (6.2)
331 (5.7)
3.36
2.90
2.63
3.20
3.30
310
380
420
350
335
358
435
479
486
398
269 (19.9), 282 (18.6),
An examination of the crystal structures of the four dimeric
complexes shows that there are no strong intermolecular
interactions except in the case of [Cu I (PPh ) (L5) ] 5,
3
19 (14.9)
6
270 (15.4), 284 (16.5),
337 (10.7)
3.03
355
395
2
2
3 2
2
where there is a π···π stacking interaction between the
quinoline groups on adjacent molecules. The centroid−
centroid distance is 3.926 Å and the offset is 1.849 Å. The
incorporation of the benzothiadiazole ligand, L6, into the
copper complex 6 has a major effect on its solid-state structure.
The bidentate L6 acts as a bridging ligand by linking of two
Cu I cores through pyridine and benzothiadiazole units. This
7
8
9
307 (18.9), 325 (17.5)
260 (9.6), 362 (23.1)
326 (18), 341 (17.6)
293 (8.9), 368 (16)
2.78
2.80
2.27
2.52
310
370
345
380
368
434
386
465
10
respectively, essentially due to extended conjugation. In
contrast, complex 4 bearing the fused thieno[2,3-b]thiophene
spacer showed λmax at 331 nm (ε = 5.7 × 10 M cm ), much
lower than its nonfused bithienyl analogue 2. This can be
attributed to the decreased number of double bonds in the
fused systems compared to nonfused systems. The onset of
absorption for anchored Cu(I) complexes 7−10 was found to
be red-shifted compared with their PPh analogues (Table 2).
Another interesting feature was the similarity of band shapes of
nonanchored (1, 2, and 3) complexes with anchored (7, 8, and
9) counterparts. A similar trend has been observed in the
optical band gap (E ) of the complexes. These observations
were complemented by theoretical calculations (vide infra).
Trends similar to those in the IR data were also observed in
the PL studies. It has been established that the emission
properties of Cu(I) complexes depend on the organic ligands
(type, rigidity, and conjugation), the size of the complex as
2
2
3
−1
−1
leads to the formation of a 1D polymer with the formula:
Cu I (PPh ) (L6) ] . Again, each of the Cu I units sits
[
2
2
3 2
2 ∞
2 2
around a crystallographic center of symmetry so that the
parallelepipeds are required to be planar. In this instance, there
are two independent “Cu I ” in the polymer and they exhibit
2
7
2
2
somewhat different parameters (see Table 1) with the Cu···Cu
distance for one of the unique centers being 3.315(2) Å while
the other is 2.978(2) Å. This is reflected in the variation in the
Cu−I−Cu and I−Cu−I angles which show a difference of ca.
3
o
g
3
° compared to a difference of only 1° for the dimeric
complexes discussed above. Figure 2 shows one strand of the
polymer [Cu I (PPh ) (L6) ] which is stabilized through
2
2
3 2
2 ∞
weak π−π interactions between the aromatic rings. S···HC
intermolecular interactions of 2.9 Å are also evident. A
molecule of dichloromethane of crystallization is also present
in the lattice.
9
well as Cu···Cu bond distances. Photoemission of non-
Optical Spectroscopy. The electronic spectra of com-
plexes 1−10 were collected in dichloromethane at room
temperature (Figure 3a,b) and the data are compiled in Table
anchoring ligand based complexes 1−6 in dichloromethane
solution is shown in Figure 4a, while nonanchored ligand-
based complexes 7−10 are depicted in Figure 4b. Almost all
2
. As can be seen, all complexes showed a strong high energy
complexes exhibited a broad green to blue emission (λ
=
em
(
HE) bands with λmax within 300−400 nm attributed to π−π*
358−486 nm) in solution without any vibronic progression at
transition in organic group(s). A trend similar to the variation
in IR bands was observed in the UV spectra. Complex 1 having
one thienyl ring showed a band at 323 nm (ε = 11 × 10
M cm ), which shifted significantly to the red (369 nm, ε =
room temperature (RT), which is consistent with related
28
Cu(I) complexes. The emission wavelength of the complexes
shifted bathochromically on moving from complex 1 (358 nm)
through 2 (435 nm) to 3 (479 nm). The nature and extent of
shifting unarguably indicated conjugation-directed lumines-
cence control in these complexes.
3
−
1
−1
3
−1
−1
3
−1
−1
6
.8 × 10 M cm and 397 nm ε = 6.2 × 10 M cm ) for
complexes 2 and 3 bearing bithienyl and terthienyl,
E
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Figure 4. (a) PL spectra of complexes 1−6 and (b) anchored Cu(I) complexes 7−10.
Computational Modeling. In order to obtain an insight
into the optical spectroscopic results, we performed quantum-
chemical calculations using hybrid density functional theory
Supporting Information), which agrees well with those
obtained experimentally (308 and 369 nm, respectively, Figure
3). Contrarily, complex 3 showed λmax at 315 nm in the TD-
DFT calculation (Figure S3, Supporting Information), which
was found at 397 nm experimentally (Figure 3). Similarly,
complex 4 showed a λmax at 335 nm (Figure S3, Supporting
Information), which agrees very well with the experimental
value of 331 nm (Figure 3). In addition to matching
absorption values, simulated spectra also showed the similar
trend as the experimental spectra (viz., bathochromic shift in
absorption peaks with increasing conjugation, i.e., 1 → 3,
Figure S3, Supporting Information). The electrical transport
properties of a molecule depend on the energy gap between
HOMO and LUMO orbitals. It is interesting to note that the
values of calculated HOMO−LUMO energy gap, although
different (lower) from the experimental one, followed the same
trend as experimental ones (Table 3). Both the experimental
and computational studies showed the lowering of the band
gap on moving from complexes 1 → 3.
(
DFT). The computational methodology is described in detail
in the Experimental Section. The optimized geometries of the
complexes were obtained at the B3LYP level of theory with the
Lanl2dz for iodine and 6-31G(d) for all other atoms (Figure
S1, Supporting Information). Figures S2 and S3 (Supporting
Information) depict frontier molecular orbital diagrams and
simulated absorption spectra of the complexes, respectively.
The Cartesian coordinates of the optimized geometries are
provided in Table ST1 (Supporting Information), while
c
g
theoretically calculated band gaps (E , eV) are given in
Table 3.
Table 3. Theoretical and Experimental Values of the
Frontier Molecular Orbital Energies and Band Gaps of the
Cu(I) Complexes
a
b
theoretical
experimental
Electrochemical Studies. Cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) data were obtained in
anhydrous acetonitrile (ACN) solution to provide comple-
mentary information about redox reactivity for metal
c
o
complex
HOMO (eV)
LUMO (eV)
(E , eV)
(E , eV)
g
g
1
2
3
4
5
6
7
8
9
−4.53
−4.41
−4.40
−4.44
−4.56
−4.67
−4.68
−4.50
−4.53
−4.64
−2.12
−2.20
−2.29
−2.15
−2.26
−2.92
−2.20
−2.26
−2.32
−2.41
2.40
2.21
2.11
2.29
2.29
1.75
2.47
2.24
2.21
2.22
3.36
2.90
2.63
3.20
3.30
3.03
2.78
2.80
2.27
2.52
complexes 1 to 6. All the materials exhibit oxidation responses
0/+
(
all chemically irreversible) close to 0.9 V vs Fc , which are
likely to be associated at least initially with the oxidation of the
Cu I core. Complexes 2−5 showed very similar values of the
2
2
oxidation potentials (see Table 4, DPV data) because of their
close HOMO energy levels. Complex 6 showed the highest
oxidation potential values of 0.99 V consistent with its HOMO
energy level being very low (−4.67 eV). The oxidation
potential value of complex 1 and 6 are found to be very similar
though there are significant energy difference between their
HOMO levels. This is likely to be due to fast and irreversible
reaction steps. Because of the limited information that can be
extracted from these data and the multistep character of
processes, ligand contributions are possible. In the CV data
1
0
a
c
g
Energy levels and calculated band gap (E , eV) of Cu(I) complexes
obtained at the B3LYP/6-31G(d)+Lanl2dz level of theory. Optical
band gap (E , eV) was calculated from the onset of absorption from
dicholoromethane solution spectra using the formula E = [1240/
b
o
g
o
g
λonset] (eV).
The frontier molecular orbitals (HOMOs/LUMOs) togeth-
er with simulated absorption spectra of two representative
examples (complexes 7 and 10) are shown in Figure 5a−d. As
expected, the HOMO of the complexes was mainly localized
over metal center with little contribution of triphenylphos-
phine coligand. On the other hand, LUMO was mainly
delocalized over ethynylpyridine-based ligands (Figure 5a,b).
The main trends in the simulated spectra compare reasonably
well with the corresponding solution spectra (Figure 5c,d),
although simulated spectra show more than one peak for all
complexes. For example, complexes 1 and 2 showed λmax at
(
Figure S4, Supporting Information), all oxidation peak
currents are chemically irreversible (without a back-reduction
peak in this time domain) and therefore likely to be associated
with fast follow-up chemical steps, which may affect both the
ligands or the core of the complex. This redox reactivity of the
oxidized form of the metal complexes could be relevant to
characteristics in DSSCs, as photoexcitation is likely to lead to
electron injection and a period of “hole reactivity” on the metal
complex (vide infra).
Table 4 summarizes the peak potential data. Figure 6 shows
a typical set of differential pulse voltammetry data sets for
3
20 and 360 nm, respectively in TD-DFT study (Figure S3,
F
DOI: 10.1021/acs.inorgchem.8b01684
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Inorganic Chemistry
Article
Figure 5. (a,b) Frontier orbitals and (c,d) simulated absorption spectra from TD-DFT calculations in dichloromethane (black line) compared to
solution absorption spectra (shaded area) of complexes 7 and 10. Each plot shows the simulated absorption profile obtained from the spin-allowed
29
singlet states (blue line). These plots were prepared using the GaussView 6 visualization software.
Table 4. Summary of Electrochemical Data for Cu(I)
Complexes 1−6
methods are sometimes shifted in potential but there is
generally a good correlation.
Photovoltaic Performance. To underpin the photo-
voltaic performance of the developed materials, we have
fabricated DSSCs of complexes 7−10 (bearing anchoring
cyclic voltammetry (CV)
differential pulse voltammetry
0/+
0
/+
materials
E
(V vs Fc
)
(DPV) E
(V vs Fc )
ox,peak
ox,peak
1
2
3
4
5
6
0.94, 1.17
0.96, 1.13
0.96, 1.08, 1.24
0.99, 1.09
0.99
0.98, 1.20
groups). The TiO photoanodes based on different dyes were
2
0.91, 1.03, 1.09
0.96, 1.10, 1.27
0.95, 1.12
0.90, 1.01
0.99, 1.21
used to assemble DSSCs with platinized counter electrodes
−
−
and a classical I /I based redox couple. Although low in
3
efficiency, the devices showed performances comparable to
3
many other homoleptic Cu(I)-based DSSCs. Figure 7a shows
0.96, 1.17
that the current density−voltage (J−V) curves of the DSSCs
measured under irradiation of AM1.5 simulated solar light
−
2
(
100 mW cm ), and the corresponding parameters are
summarized in Table 5. TiO films with a 10-based device
2
showed the highest photoelectric conversion efficiency (PCE =
2
1
.56%), with improved Voc = 0.52 V, J = 4.43 mA/cm , and
sc
FF = 69%. To the contrary, the DSSCs based on the dye 7
showed the lowest photovoltaic performance (PCE = 0.15%)
2
with V of 0.41 V, J = 0.53 mA/cm , and FF = 68%. Complex
7
oc
sc
30
has a lower PCE than the reported thiophene-function-
alized 2,2′-bipyridine incorporated Cu(I) complex bearing
carboxylic acid anchoring group (C1), which showed a PCE of
1
.16%. Similarly, C1 showed better solar cell performance
compared to the Cu(I) complex having no thiophene
12
moiety. This can be attributed to the bathochromic shift of
MLCT band and a higher HOMO energy level of C1, which
suggest that the solar cell performance can be improved by
incorporating the thiophene moiety into the ligand. For
example, V , J , FF, and PCE rise on going from 7 → 9, which
Figure 6. Differential pulse voltammetry (DPV) data (modulation
time = 0.1 s, interval time = 0.5 s and modulation amplitude = 0.05 V)
obtained at a 3 mm diameter glassy carbon disc electrode for
complexes 1, 2, 3, 4, 5, and 6, approximately 1 mM in anhydrous
ACN with 0.1 M NBu PF electrolyte.
oc sc
can be attributed to the increasing number of thienyl units
3
attached to pyridine. As reported in other studies, we also
noted that complex bearing carboxyl functionality as an
anchoring unit showed inferior performance compared with
the sulfonated analogue. A sudden rise in the performance on
using complex 10 can be attributed to synergistic effect of
terthiophene spacer in combination with anchoring group. For
an efficient electron transfer between the sensitizer, the
semiconductor, and the electrolyte, it is important to match
energy levels (HOMO and LUMO) of the complexes with the
4
6
complexes 1, 2, 3, 4, 5, and 6. Complexes 2 and 4 appear to be
slightly more sensitive to oxidation but all complexes show
+
/0
activity at approximately 0.9 V vs Fc . A comparison of cyclic
voltammetry data and differential pulse voltammetry data
suggests similar trends. Oxidation peaks in differential pulse
G
DOI: 10.1021/acs.inorgchem.8b01684
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Inorganic Chemistry
Article
−
−
Figure 7. (a) J−V curves and (b) IPCE spectra for DSSCs based on different dyes with I /I redox electrolyte.
3
Table 5. Photovoltaic Parameters of DSSCs Based on
CONCLUSIONS
■
−
2
Different Dyes under an Illumination of 100 mW cm , AM
.5 G condition
A series of new neutral Cu(I) complexes 1−10 of nonfused/
fused heteroarylethynylpyridinyl ligands (L) with CuI and the
coligand including PPh3 (R1) or a nchored
PPh (C H COOH)/ PPh (C H SO H) (R2/ R3) have been
1
Voc (V) Jsc (mA cm−2
device
)
FF (%) PCE (%) IPCE (%)
2
6
4
2
6
4
3
7
8
9
0.41
0.42
0.45
0.52
0.55
0.53
0.92
2.32
4.43
2.95
68
60
68
69
71
0.15
0.23
0.72
1.56
1.16
42.05
42.51
37.53
58.14
14−17
synthesized. The absorption was found to be red-shifted with
the presence of an increasing number of thienyl units in
complexes 1−3, whereas the onset absorption of complex 4
was found to be blue-shifted compared to the complex 2 which
may be attributed to a reduced number of double bonds in the
fused system. The absorption of anchored Cu complexes 7−10
was found to be red-shifted in comparison with complexes 1−
. Rhomboid dimeric structures for complexes 1, 2, 4, and 5
and polymeric structure for 6 have been established by single
crystal X-ray structure analysis. All the complexes exhibit
oxidation potential responses close to 0.9 V vs Fc which are
associated with follow-up chemical and electrochemical
reaction steps. The anchored Cu-complexes 7−10 displayed
PCE in the range of 0.15−1.56% in DSSCs. Complex 10
containing the sulfonic acid functionality showed the highest
PCE of 1.56%. The structures of all the Cu complexes have
been optimized, and their HOMO and LUMO energy levels
have been determined by DFT and TD-DFT calculations. The
LUMO energy level of dye materials was found to be higher
1
0
C1 (ref 30)
6
conduction band of TiO2 and redox potential of the
electrolyte. We found that the LUMO orbital (−2.20 eV,
−
2.26 eV, −2.32 eV, −2.41 eV for 7, 8, 9, and 10, respectively,
0
/+
Table 3) was above the conduction band of TiO (E = −4.0
2
CB
3
1
eV). Interestingly, the gap between LUMO and ECB follows
the order: 7 (1.80 eV) > 8 (1.74 eV) > 9 (1.68 eV) > 10 (1.59
eV), providing enough power for electron injection (>0.3
eV). Close HOMO energy level of 10 (−4.64 eV) with redox
potential of the electrolyte (I /I = −4.80 eV) might have
3
2
−
−
31
3
also contributed. For the complexes 9 and 10 with L3, 10 has a
higher dye regeneration power of 4.16 eV (−4.80 eV HOMO),
which is beneficial to the improvement of its PCE and
suppression of electronic recombination. Furthermore, higher
light to energy conversion by complex 10 may also be linked to
its absorption profile, which was most bathochromically
shifted. The incident photon-to-current conversion efficiency
than that of the conduction band of the TiO , which facilitated
2
effective electron transport. Theoretical calculations have
complemented the optical absorption and photovoltaic
characteristics of these complexes.
(
IPCE) values of DSSCs based on 10 are higher than those of
EXPERIMENTAL SECTION
General Procedures. All reactions were performed under a dry
argon atmosphere using the standard Schlenk line technique. Solvents
were predried and distilled before use by standard procedures. All
chemicals, except where stated otherwise, were obtained from Sigma-
Aldrich and TCI Chemicals and used as received. The key starting
material 4-(trimethylsilylethynyl)pyridine (P1) and 4-ethynylpyridine
(P2) were synthesized by adaptation of the literature method.
Elemental analyses were performed in the microanalysis laboratory of
the Department of Chemistry, University of Cambridge, U.K. NMR
■
other dyes from 300 to 800 nm (Figure 7b). The IPCE values
of 10 are above 50% within a wider range of wavelengths,
which demonstrates that 10 is a better photosensitizer for
DSSCs. Consequently, DSSC based on 10 dye has more
efficient charge collection efficiency than other dyes. This fact
is further supported by higher short current density (Jsc)
obtained from the J−V curves. Compared with other Cu(I)-
13
33
3
1
based complexes, our homoleptic systems demonstrated
lower performance. Since there are several compositional and
device related factors that control overall performance of the
device, it would be too early to blame any single factor for the
overall low device performance. However, we attribute
comparatively low performance to increased rigidity (and
thus enhanced the π−π interaction) of the molecule, leading to
spectra were recorded in CDCl using a Bruker Advance III HD 700
3
MHz spectrometer equipped with 5 mm TCI H/C/N cryoprobe. The
1
3
13
H and C NMR spectra were referenced to solvent resonances, and
1
1
P{ H} NMR spectra were referenced to external phosphoric acid. IR
spectra were recorded directly on the sample as attenuated total
reflectance (ATR) on Diamond using Cary 630 FT-IR spectrometer.
UV−vis spectra were recorded with an Agilent Cary 5000 UV−visible
spectrophotometer using a quartz cuvette with a 1 cm path length.
the formation of aggregates of the dyes on the surface of TiO .
2
H
DOI: 10.1021/acs.inorgchem.8b01684
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Mass spectra were acquired using a Kratos MS 890 spectrometer
using electron-impact (EI) and electrospray-ionization (ESI)
techniques. Preparative thin-layer chromatography was carried out
on commercial Merck plates with a 0.25 mm layer of silica. Column
chromatography was performed using silica gel (230−400 mesh).
Caution! All chemicals used in the current work are irritants to skin,
eyes and the respiratory system. Therefore, all reactions were
performed in a well-ventilated fume hood. Inhalation of silica/
alumina and low boiling point solvents like dichloromethane and
hexane may cause injuries to internal organs. Safety glasses, gloves,
masks and lab coats were worn during the experiments.
= 7.0 Hz, 1H). 13C NMR (700 MHz, CDCl ):δ/ppm149.78, 140.45,
3
136.37, 134.19, 131.02, 128.06, 125.48, 125.09, 124.65, 123.68,
120.39 (Aromatic C), 91.41, 87.37 (−CC−).ESI-MS: m/z 267.9.
Anal. Calc. for C H NS : C, 67.38; H, 3.39; N, 5.24%; found: C,
1
5
9
2
67.43; H, 3.41; N, 5.25%.
4-([2,2′:5′,2″-Terthiophene]-5-ylethynyl)pyridine, L3. This com-
pound was synthesized following the procedure described for L1
using 5-bromo-2,2′:5′,5″-terthiophene (0.28 g, 0.86 mmol).The
compound L3 was obtained as a dark yellow solid (0.27 g, 90%).
−
1
1
IR (ATR, diamond): ν/cm 2194 (−CC−). H NMR 7.36 (dd, J
= 8.1, 1.5 Hz, 1H), 7.24 (d, J = 0.42 Hz, 1H), 7.20 (d, J = 1.1 Hz,
1H), 7.19 (d, J = 1.1 Hz, 1H), 7.13 (d, J = 3.7 Hz, 2H), 7.11 (d, J =
Ligand Synthesis. 4-(Trimethylsilylethynyl)pyridine, P1. To a
i
13
solution of 4-iodopyridine (4 g, 19.51 mmol) in Pr NH/THF (150
5.2 Hz, 2H), 7.09 (d, J = 3.8 Hz, 2H), 7.04 (d, J = 3.6 Hz, 1H). C
2
3
cm , 1:4 v/v) were added catalytic amounts of Pd(OAc) (44 mg),
NMR (700 MHz, CDCl ):δ/ppm 149.87, 140.28, 137.57, 136.88,
2
3
CuI (46 mg), and PPh (256 mg) under an Ar atmosphere. After
135.12, 134.43, 131.21, 128.13, 124.60, 124.40, 124.21, 124.23,
124.09, 123.69, 120.54 (Aromatic C), 91.79, 87.58 (−CC−). ESI-
MS: m/z 347.8. Anal. Calc. for C H NS : C, 65.30; H, 3.17; N,
3
stirring for 30 min, trimethylsilylacetylene(3.3 mL, 23.41 mmol) was
added dropwise followed by overnight reflux. The completion of the
reaction was confirmed by silica TLC and IR spectroscopy. The
reaction mixture was concentrated under reduced pressure, and the
crude residue was subjected to silica gel column chromatography
using hexane/CH Cl (1:1, v/v) as eluent to yield the title compound
1
9
11
3
4.01%;found: C, 65.43; H, 3.19; N, 4.05%.
4-(Thieno[2,3-b]thiophen-2-ylethynyl)pyridine, L4. This com-
pound was synthesized following the procedure described for L1
using 2-bromothieno[3,2-b]thiophene (0.21 g, 0.96 mmol). The
compound L4 was obtained as a yellow solid (0.19 g, 86%). IR (ATR,
2
2
−
1
as an orange oil (3.05 g, 89%). IR (ATR, diamond):ν/cm 2165
1
−1
1
(
(
−CC−). H NMR: δ/ppm 7.28 (d, J = 5.0 Hz, 2H, Hβ‑pyr), 7.22
diamond): ν/cm
2198 (−CC−). H NMR (700 MHz,
1
3
d, J = 5.0 Hz, 2H, H ), 0.27 (s, 9H, SiMe ). C NMR (700 MHz,
CDCl ):δ/ppm 7.69 (dd, J = 3.8, 1.3 Hz, 2H), 7.68 (t, J = 1.6 Hz,
α‑pyr
3
3
CDCl , ppm):δ/ppm 150. 29, 126.41, 128.79, (Aromatic C) 90.63,
2H), 7.57−7.56 (m, 1H), 7.55 (dd, J = 2.8, 1.4 Hz, 1H), 7.28 (s, 1H).
3
1
3
8
9.21 (−CC−), 0.15 (C of Si(CH ) ). ESI-MS m/z 175.30. Anal.
C NMR (700 MHz, CDCl ):δ/ppm 145.89, 139.42, 132.25, 131.97,
3
3
3
Calc. for C H NSi: C, 68.51; H, 7.47; N, 7.99%; found: C, 68.53; H,
129.17, 128.56, 125.87, 124.37, 120.03(Aromatic C), 90.94, 87.72
10
13
7
.45, N, 7.97%.
-Ethynylpyridine, P2. P1 (3.0 g, 17.11 mmol) was proto-
(−CC−). ESI-MS: 241.9. Anal. Calc. for C H NS : C, 64.70; H,
1
3
7
2
4
2.92; N, 5.80%; found: C, 64.63; H, 2.88; N, 5.85%.
desilylated in THF/methanol (20 mL, 4:1, v/v) using aqueous
KOH (1.92 g, 34.21 mmol). The reaction mixture was stirred at room
temperature for 1.5 h. during which time TLC and IR revealed that all
protected compound has been converted to the terminal alkyne
ligand. The solvent mixture was then removed, and the residue was
dissolved in a small amount of CH Cl and subjected to column
5-(Pyridin-4-ylethynyl)quinoline, L5. This compound was synthe-
sized by adapting the procedure described for L1 using 5-
bromoquinoline (0.2 g, 0.96 mmol). The compound L5 was obtained
−
1
as a yellow solid (0.18 g, 81% yield). IR (ATR, diamond): ν/cm
1
2217 (−CC−). H NMR (700 MHz, CDCl ): δ/ppm 8.59 (d, J =
3
2
2
8.3 Hz, 2H, H ), 8.11 (d, J = 8.4 Hz, 2H, H ), 7.35−7.78 (m,
α‑pyr
β‑pyr
1
3
chromatography on silica using hexane/CH Cl (1:1, v/v) as eluent to
6H, Aromatic H). C NMR (700 MHz, CDCl ): δ/ppm 151.02,
2
2
3
give 4-ethynylpyridine as an off-white solid (1.52 g, 86%). IR (ATR,
149.69, 147.85, 131.42, 130.92, 128.92, 128.72, 128.50, 128.48,
126.39, 122.01, 120.01 (Aromatic C), 91.99, 80.25 (−CC−). ESI-
MS: 230.9. Anal. Calc. for C H N : C, 83.46; H, 4.38; N, 12.17%;
−
1
1
diamond): ν/cm : 3223 (ν
) and 2109 (ν
). H
(
R‑CC−H)
(R‑CC−)
NMR (700 MHz, CDCl , ppm): δ/ppm 7.55 (d, J = 6.0 Hz, 2H,
3
16 10
2
H
β‑pyr), 7.40 (d, J = 5.4 Hz, 2H, Hα‑pyr), and 4.00 (s, 1H, CC-H).
found: C, 83.63; H, 4.31; N, 12.21%.
13
C NMR (700 MHz, CDCl , ppm): δ/ppm 132.3, 128.4, 128.3,
5-(Pyridin-4-ylethynyl)benzo[c][1,2,5]thiadiazole, L6. This com-
pound was synthesized by adapting the procedure described for L1
using 5-bromobenzo[c][1,2,5]thiadiazole (0.15 g, 0.70 mmol). The
compound was obtained as a yellow solid (0.14 g, 84%, yield). IR
3
1
22.7 (Aromatic C), 89.6, 85.4(−CC−). ESI-MS: m/z 103.09.
Anal. Calc. for C H N: C, 81.53; H, 4.89; N, 13.58%; found: C,
7 5
8
1.59; H, 4.86; N, 13.61%.
-(Thiophene-2-ylethynyl)pyridine, L1. To a solution of 4-
−
1
1
4
(ATR, diamond): ν/cm 2215 (−CC−). H NMR (700 MHz,
CDCl ): δ/ppm 8.21 (d, J = 1.4 Hz, 2H), 7.99 (d, J = 1.4 Hz, 1H),
7.67 (d, J = 1.5 Hz 2H), 7.44 (br s, 1H), 7.26 (s, 1H). C NMR (700
MHz, CDCl ): δ/ppm 154.56, 154.47, 149.93, 132.68, 128.58,
126.13, 125.29, 123.63, 121.78 (Aromatic C), 92.63, 89.80 (−C
C−). ESI-MS: 236.59. Anal. Calc. for C13 S: C, 65.80; H, 2.97;
N, 17.71%; found: C, 65.63; H, 2.87; N, 17.75%.
Synthesis of Cu(I) Complexes. [(L1) (CuI)
complexes were prepared by adapting the recently reported literature
i
3
ethynylpyridine, P1 (0.12 g, 1.16 mmol) in Pr NH/THF (120 cm ,
3
2
1
3
1
:4 v/v) under an Ar atmosphere were added catalytic amounts of
Pd(OAc) (26 mg), CuI (27 mg), and PPh (15.2 mg). The solution
3
2
3
was stirred for 0.5 h and 2-iodothiophene (0.24 g, 1.16 mmol) was
added. The reaction mixture was allowed to stir at reflux overnight at
H N
7 3
∼
70 °C. Silica TLC and IR spectroscopy were performed from time
to time in order to follow the completion of the reaction. After drying
the reaction mixture under vacuum, the crude residue was subjected
to a silica gel column chromatography using hexane/CH Cl (2:8, v/
2
(PPh ) ], 1. Cu(I)
2 3 2
19
method. The ligand L1 (0.1 g, 0.54 mmol) dissolved in 10 mL of
degassed dichloromethane (CH Cl ) was added to a solution of CuI
(102 mg) and triphenylphosphine (142 mg) in 15 mL CH Cl . The
2
2
v) to afford L1 as a yellow solid (0.18 g, 84%, mp 125.9 °C). IR
2
2
1
1
(
ATR, diamond): ν/cm− 2203 ν(
.
H NMR (700 MHz,
2
2
−CC−)
CDCl ):δ/ppm 7.68 (d, J = 7.00 Hz, 2H,Hα‑pyr,), 7.65 (d, J = 7.00 Hz,
mixture was allowed to stir for 24 h at room temperature. The crude
product obtained on the removal of solvent under reduced pressure
3
2
H, Hβ‑pyr), 7.38 (d, J = 1.12 Hz, 1H), 7.35 (d, J = 1.12 Hz, 1H), 7.47
13
(
d, J = 2.8 Hz,1H). C NMR (700 MHz, CDCl , ppm): δ/ppm
was redissolved in CH
Cl and passed through a plug of Celite.
2 2
3
1
1
2
49.92, 125.53, 128.87 (C’s of pyridine), 122.08, 132.08, 127.49,
27.72 (C of thiophene), 90.53, 87.64 (−CC−). ESI-MS: m/z
85.00. Anal. Calc. for C H NS: C, 71.32; H, 3.81; N, 7.52%; found:
Finally, the solvent was removed under reduced pressure to afford 1 as
−
1
a dark yellow solid (0.25 g, 73%). IR (ATR, diamond): ν/cm 2199
1
(−CC−). H NMR (700 MHz, CDCl
Hz, 1.9 Hz, 4H, Hα‑pyr), 7.66−7.40 (m, 34H, PPh
= 1.5 Hz, 2H), 7.37 (dd,, J = 1.1 Hz, 2H), 7.35 (d,, J = 1.1 Hz, 2H).
): δ/ppm 7.76 (dd,, J = 3.2
1
1
7
3
C, 71.42; H, 3.83; N, 7.55%.
3
, Hβ‑pyr), 7.48 (d,, J
4
-([2,2′-Bithiophene]-5-ylethynyl)pyridine, L2. This compound
1
3
was synthesized following the procedure described for L1 using 5-
bromo-2,2′-bithiophene (0.26 g, 1.06 mmol).The compound L2 was
obtained as a brownish yellow solid (0.20 g, 71%). IR (ATR,
C NMR (700 MHz, CDCl
3
):δ/ppm 150.16, 135.39, 134.33, 134.25,
132.94, 131.63, 130.38, 128.69, 127.79, 127.76, 122.01 (Aromatic C),
3
1
90.48, 88.12 (−CC−). P NMR (121.53 MHz, CDCl ): δ = 29.10
3
diamond): ν/cm− 2197 (−CC−). H NMR (700 MHz, CDCl ):
1
1
(s, PPh ) ppm. ESI-MS: m/z 1227.0. Anal. Calc. for
3
3
δ/ppm 7.28 (dd, J = 1.1 Hz, 2H, H ), 7.27 (d, J = 1.3 Hz, 2H,
C H Cu I N P S : C, 54.60; H, 3.48; N, 2.20%; found: C, 54.63;
58 44 2 2 2 2 2
α‑pyr
Hβ‑pyr), 7.23 (d, J = 3. 57 Hz, 1H), 7.10 (d, J = 3.85 Hz,1H), 7.04 (t, J
H, 3.53; N, 2.25%.
I
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Inorganic Chemistry
Article
[
(L2) (CuI) (PPh ) ], 2. This compound was synthesized by
0.70 mmol), CuI (134 mg), and 4-(diphenylphosphino)benzoic acid
2
2
3 2
following a procedure similar to that described above for 1 using
L2 (0.15 g, 0.56 mmol), CuI (107 mg), and triphenylphosphine (147
mg) yielding 2 as a dark yellow solid (0.27 g, 67%). IR (ATR,
(215 mg), yielding 7 as a brown solid (0.31 g, 64%). IR (ATR,
−
1
1
diamond): ν/cm 2204 (−CC−), 1701 (-CO(OH)). H NMR
(700 MHz, CDCl ): δ/ppm 9.60 (s, 2H of COOH), 7.73−7.67 (m,
3
diamond): ν/cm− 2199 (−CC−). H NMR (700 MHz, CDCl ):
1
1
4H, H ), 7.59−7.48 (m, 32H, PPh , H ), 7.23 (m, J = 6.0 Hz,
3
α‑pyr
3
β‑pyr
1
3
δ/ppm 8.36 (d, J = 6.1 Hz, 4H, H ), 7.80−7.38 (m, 34H, PPh ,
2H), 7.15 (d, J = 3.8 Hz, 4H). C NMR (700 MHz, CDCl ): δ/ppm
α‑pyr
3
3
1
3
Hβ‑pyr), 7.28−7.32 (m, 6H), 7.05 (d, J = 5.6 Hz, 4H). NMR C NMR
169.3 (C of COOH), 149.4, 136.1, 135.9, 134.0, 132.0, 131.5, 130.7,
130.3, 128.8, 127.9, 127.7, 127.2, 126.2, 122.4 (Aromatic C), 94.01,
(
1
1
700 MHz, CDCl ):δ/ppm 150.22, 141.43, 136.44, 134.52, 132.90,
3
3
1
31.96, 129.64, 128.76, 127.64, 126.28, 125.08 (Aromatic C), 123.83,
88.97(−CC−). PNMR (121.53 MHz, CDCl ): δ = 29.20 (s,
3
31
24.82 (−CC−). PNMR (121.53 MHz, CDCl ): δ = 29.10 (s,
PPh ) ppm. ESI-MS: m/z 1366.5. Anal. Calc. for
3
3
PPh ) ppm. ESI-MS: m/z 1332.3. Anal. Calc. for C H Cu I N P S :
C H Cu I N O P S : C, 52.83; H, 3.25; N, 2.05%; found: C,
3
66 48
2 2
2
2
4
60 44
2 2
2
4 2 2
C, 55.04; H, 3.36; N, 17.62%; found: C, 65.63; H, 2.87; N, 17.75%.
(L3) (CuI) (PPh ) ], 3. This compound was synthesized by
52.71; H, 3.23; N, 2.08%.
[
[(CuI) (L2) (R2) ], 8. This compound was synthesized by following
2
2
3 2
2
2
2
following a procedure similar to that described above for 1 using
L3 (0.17g, 0.49 mmol), CuI (92 mg), and triphenylphosphine (127
mg), yielding 3 as an orange solid (0.25 g, 63%) IR (ATR, diamond):
a procedure similar to that described above for 1 using L2 (100 mg,
0.37 mmol), CuI (71 mg), and 4-(diphenylphosphino)benzoic acid
(115 mg), yielding 8 as light yellow solid (0.20 g, 71%). IR (ATR,
−
1
1
−1
1
ν/cm 2195 (−CC−). H NMR (700 MHz, CDCl ): δ/ppm 8.63
diamond): ν/cm 2196 (−CC−), 1723(-CO(OH)). H NMR
3
(
dd, J = 4.4, 1.6 Hz, 4H), 7.71−7.37 (m, 34H, PPh , H ), 7.22 (dd, J
3.6, 1.1 Hz, 4H), 7.15 (d, J = 3.8 Hz, 4H), 7.12 (dd, J = 7.0, 3.8 Hz,
H), 7.06 (dd, J = 5.1, 3.6 Hz, 2H). C NMR (700 MHz, CDCl ):δ/
(700 MHz, CDCl ): δ/ppm 9.48 (s, 2H of COOH), 7.71 (dd, J = 5.6,
3
py
3
=
4
3.3 Hz, 4H, Hα‑pyr), 7.55−7.34 (m, 32H, PPh , Hβ‑pyr), 7.34 (s, 2H),
7.23 (d, J = 3.6 Hz, 4H), 7.29 (s, 2H), 7.10 (d, J = 3.8 Hz, 2H), 7.05
(dd, J = 5.1, 3.7 Hz, 2H). C NMR (700 MHz, CDCl ): δ/ppm
3
1
3
3
1
3
ppm 149.89, 149.84, 140.16, 137.44, 136.75, 134.99, 134.30, 132.85,
3
1
1
32.26, 132.15, 132.09, 131.96, 131.94, 131.07, 128.55, 128.48,
28.00, 125.27, 125.08, 124.96, 124.47, 124.11, 123.56, 120.41
169.8 (C of COOH), 149.81, 138.54, 136.90, 136.22, 135.90, 134.26,
132.91, 131.53, 130.83, 130.44, 128.82, 128.01, 127.91, 126.45,
124.83, 124.11, 123.54, 122.31(Aromatic C), 95.12, 90.03(−C
3
1
(
Aromatic C), 91.66, 87.47 (−CC−). PNMR (121.53 MHz,
3
1
CDCl ): δ = 29.24 (s, PPh ) ppm. ESI-MS: m/z 1532.5. Anal. Calc.
C−). PNMR (121.53 MHz, CDCl ): δ = 29.21 (s, PPh ) ppm. ESI-
3
3
3
3
for C H Cu I N P S : C, 55.40; H, 3.27; N, 1.75%; found: C, 55.53;
MS: m/z 1525.30. Anal. Calc. for C H Cu I N O P S : C, 53.44; H,
74
52
2 2
2
2
6
68 48 2 2 2 4 2 4
H, 3.33; N, 1.78%.
(L4) (CuI) (PPh ) ], 4. This compound was synthesized by
3.17; N, 1.83%; found: C, 53.33; H, 3.13; N, 1.88%.
[(CuI) (L3) (R2) ], 9. This compound was synthesized by following
[
2
2
3 2
2
2
2
following a procedure similar to that described above for 1 using
L4 (0.10g, 0.41 mmol), CuI (78 mg), and triphenylphosphine (108
mg), yielding 4 as a pale yellow solid (0.20 g, 69%) IR (ATR,
a procedure similar to that described above for 1 using L3 (90 mg,
0.28 mmol), CuI (53 mg), and 4-(diphenylphosphino)benzoic acid
(73 mg), yielding 9 as a light yellow solid (0.16 g, 67%). IR (ATR,
diamond): ν/cm− 2196 (−CC−). H NMR (700 MHz, CDCl3):
1
1
diamond): ν/cm 2198 (−CC−), 1701(-CO(OH)). H NMR
−1
1
δ/ppm 7.90 (m, 4H, H ), 7.67−7.49 (m, 34H, PPh , H ), 7.36
dd, J = 4.55 Hz, 2.9 Hz, 2H), 7.23 (d, J = 7.0 Hz, 4H). C NMR
700 MHz, CDCl ):δ/ppm149.93, 145.87, 145.87, 139.50, 134.11,
(700 MHz, CDCl ): δ/ppm 9.23 (s, 2H of COOH), 8.60−8.57 (m,
α‑pyr
3
β‑pyr
3
1
3
(
(
4H,H ), 7.92−7.40 (m,26H, PPh ), 7.67 (dd, J = 4.9 Hz, 1.2 Hz,
α‑pyr
3
4H, Hβ‑pyr), 7.41−7.35 (m, 4H), 7.22−7.26 (m, 4H), 7.15 (d, J = 4.2
3
13
1
1
1
34.03, 132.86, 132.68, 132.22, 132.13, 132.96, 131.96, 131.94,
31.11, 129.76, 129.17, 128.55, 128.48, 125.96, 125.22, 124.22,
Hz, 4H), 7.10 (d, J = 3.8 Hz, 2H), 6.99 (d, J = 2.9 Hz, 2H). C NMR
(700 MHz, CDCl ): δ/ppm 169.72 (C of COOH), 149.80, 138.50,
3
3
1
20.02 (Aromatic C), 90.68, 88.11 (−CC−). P NMR (121.53
137.91, 136.61, 136.44, 135.87, 134.74, 132.90, 131.82, 130.84,
130.48, 128.62, 128.01, 127.91, 126.43, 125.82, 124.51, 124.10,
MHz, CDCl ): δ = 29.09 (s, PPh ) ppm. ESI-MS: m/z 1385.27. Anal.
3
3
3
1
Calc. for C H Cu I N P S : C, 53.64; H, 3.19; N, 2.02%; found: C,
123.54, 122.10 (Aromatic C), 97.33, 94.68(−CC−). PNMR
62
44
2 2
2 2 4
5
3.54; H, 3.23; N, 2.0%.
(L5) (CuI) (PPh ) ], 5. This compound was synthesized by
(121.53 MHz, CDCl ): δ = 29.15 (s, PPh ) ppm. ESI-MS: m/z
3
3
[
1690.5. Anal. Calc. for C H Cu I N O P S : C, 53.93; H, 3.10; N,
2
2
3 2
76 52 2 2 2 4 2 6
following a procedure similar to that described above for 1 using
L3 (100 mg, 0.43 mmol), CuI (83 mg), and triphenylphosphine (113
mg), yielding a pale yellow solid (0.19 g, 65%). IR (ATR, diamond):
1.66%; found: C, 53.79; H, 3.13; N, 1.68%.
[(CuI) (L3) (R3) ], 10. This compound was synthesized by following
2
2
2
a procedure similar to that described above for 1 using L3 (100 mg,
0.29 mmol), CuI (55 mg), and 2-(diphenylphosphino)-
benzenesulfonic acid (99 mg), yielding 12 as a light yellow solid
−
1
1
ν/cm 2220 (−CC−). H NMR (700 MHz, CDCl ): δ/ppm 7.86
3
(
d, J = 1.1 Hz, 4H, H ), 7.76−7.46 (m, 34H, PPh , H ), 7.20−
α‑pyr
3
β‑pyr
1
3
−1
7
1
1
1
.10 (m, 12H, Aromatic H). C NMR (700 MHz, CDCl ): δ/ppm
(0.15 g, 59%). IR (ATR, diamond): ν/cm 2200 (−CC−), 1481,
3
1
51.16, 150.08, 147.92, 134.25, 134.13, 134.05, 132.83, 132.24,
32.14, 132.09, 131.96, 131.94, 131.50, 131.42, 131.22, 129.76,
28.95, 128.55, 128.53, 128.48, 126.19, 125.69, 122.05, 119.99
1168 (-SO(O)(OH)). H NMR (700 MHz, CDCl ): δ/ppm9.59
3
(s, 2H of SO H), 8.45 (dd,J = 5.1 Hz, 1.3 Hz, 2H, H ), 8.21 (d, J =
3
α‑pyr
6.1 Hz, 2H, Hα‑pyr), 7.73−7.50 (m, 32H,PPh , H ), 7.40−7.36 (m,
3
β‑pyr
3
1
(
Aromatic C), 91.86, 90.94 (−CC−). PNMR (121.53 MHz,
4H), 7.17 (d, J = 5.2 Hz, 4H), 7.12−7.09 (m, 4H), 6.99 (d, J = 4.1
1
3
CDCl ): δ = 29.14 (s, PPh ) ppm. ESI-MS: m/z 1321.30. Anal. Calc.
Hz, 2H). C NMR (700 MHz, CDCl ): δ/ppm 145.6 (C of (-S
3
3
3
for C H Cu I N P : C, 59.79; H, 3.69; N, 4.10%; found: C, 59.73;
O(O)(OH)), 149.8, 138.5, 137.9, 136.6, 136.4, 135.8, 134.7, 132.9,
131.8, 130.8, 130.4, 128.6, 128.0, 127.9, 126.4, 125.8, 124.5, 124.1,
68
50
2 2
4 2
H, 3.63; N, 4.18%.
(L6) (CuI) (PPh ) ] , 6. This compound was synthesized by
3
1
[
123.5, 122.1(Cs of Aromatics), 96.39, 94.08 (−CC−). PNMR
2
2
3 2 ∞
following a procedure similar to that described above for 1 using
L3 (90 mg, 0.38 mmol), CuI (78 mg), and triphenylphosphine (125
mg), yielding a pale yellow solid (0.16 g, 61%). IR (ATR, diamond):
(121.53 MHz, CDCl ): δ = 29.14 (s, PPh ) ppm. ESI-MS: m/z
3
3
1766.7. Anal. Calc. for C H Cu I N O P S : C, 50.37; H, 2.97; N,
7
4
52
2 2
2
6 2 8
1.59%;found: C, 50.39; H, 3.03; N, 1.61%.
−
1
1
ν/cm 2216 (−CC−). H NMR (700 MHz, CDCl ): δ/
X-ray Crystallography. Single-crystal X-ray structure determi-
nations were performed on 1, 2, 4, and 5, at 150 K, and 6 at 120 K on
a Rigaku Oxford Diffraction Xcalibur CCD diffractometer, for 1, 4
and 5, and on a Stoe IPS II diffractometer for 6, using monochromatic
Mo−Kα radiation (λ = 0.71073 Å), and on an Rigaku Oxford
Diffraction SuperNova CCD diffractometer, with Cu Kα radiation (λ
= 1.54178 Å) for 2. The sample temperature was controlled using an
Oxford Diffraction Cryojet apparatus. A multiscan absorption
correction was applied in all cases.
3
ppm8.66−8.75 (m, 2H, H ), 8.20−8.29 (m, 1H, H ), 7.99−
α‑pyr
α‑pyr
8
.04 (m, 1H, H ), 7.66−7.38 (m, 34H, PPh , H ), 7.17−7.08
α‑pyr β‑pyr
13
3
(
m, 2H), 7.42−7.45 (m, 4H). C NMR (700 MHz, CDCl ): δ/
3
ppm154.61, 154.49, 150.29, 134.29, 134.21, 129.83, 128.62, 128.56,
3
1
1
25.91, 121.85 (Aromatic C), 93.13, 89.65 (−CC−). PNMR
(
121.53 MHz, CDCl ): δ = 29.14 (s, PPh ) ppm. ESI-MS: m/z
3
3
1
6
376.2.Anal. Calc. for (C H Cu I N P S ) :C, 53.96; H, 3.21; N,
62 44 2 2 6 2 2 ∞
.09%; found: C, 54.03; H, 3.23; N, 6.12%.
(CuI) (L1) (R2) ], 7. This compound was synthesized by following
[
The data reduction, including an empirical absorption correction
using spherical harmonics, implemented in SCALE3 ABSPACK
2
2
2
a procedure similar to that described above for 1 using L1 (130 mg,
J
DOI: 10.1021/acs.inorgchem.8b01684
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
5
scaling algorithm, was performed using the CrysAlisPro software
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01684.
16
■
*
package. The crystal structures were solved by direct methods using
the online version of AutoChem 2.0 in conjunction with OLEX2 suite
of programs implemented in the CrysAlis software, and then refined
by full-matrix least-squares (SHELXL2014) on F . The non-
hydrogen atoms were refined anisotropically. All of the hydrogen
atoms were positioned geometrically in idealized positions and refined
with the riding model approximation, with U (H) = 1.2 or 1.5
U (C). For the structure of 4, only poor-quality crystals could be
obtained, and a low resolution structure is reported. In this structure,
the geometry is clearly defined, although there are larger errors on the
bond parameters than in the other structures reported. For the
molecular graphics the program MERCURY from the CSD package
S
17
2
18
Table of crystal data information, data collection, and
refinement parameters for compounds 1, 2, 4, 5, and 6
iso
eq
(PDF)
Accession Codes
CCDC 1834959−1834963 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
19
was used.
Voltammetry. Electrochemical experiments were carried out with
an Autolab potentiostat type III using software GPES. Cyclic
voltammetry (CV) and differential pulse voltammetry (DPV)
experiments were conducted in a three-electrode cell using glassy
carbon (GC, 3 mm diameter, BASi) and Pt-wire electrodes as working
and counter electrode, respectively. An Ag wire electrode was used as
a quasi-reference electrode. The samples were dissolved in dry
acetonitrile containing 0.1 M tetrabutylammonium hexafluorophos-
phate (Bu NPF ) as supporting electrolyte. The electrolytic solution
was purged with Ar gas for 15 min before performing CV or DPV
analysis in order to remove any dissolved oxygen. All experiments
were carried out under an inert Ar atmosphere at 298 K. Any presence
of air bubbles inside the glass assembly was removed by gently
tapping the electrode body.
AUTHOR INFORMATION
Corresponding Authors
E-mail: msk@squ.edu.om.
E-mail: mshahidi@uic.edu.
E-mail: wai-yeung.wong@polyu.edu.hk.
E-mail: f.marken@bath.ac.uk.
E-mail: p.r.raithby@bath.ac.uk.
■
*
*
*
*
*
4
6
ORCID
Computational Modeling. All the electronic structure calcu-
lations were carried out with Gaussian09. The structural optimization
of Cu-complexes has been carried out at the B3LYP level of theory
with the 6-31G(d) basis set. The calculated values of the HOMO−
LUMO energy gap are presented in Table 1. UV−vis spectra of the
Cu-complexes were calculated with TD-DFT calculations using the
B3LYP level of theory with the 6-31G(d) basis set in the gas phase,
CH Cl , toluene, and water solvent systems with the polarizable
continuum model (PCM) as implemented in Gaussian09. By default,
the PCM model builds up the cavity using the united atom (UA0)
model, i.e., putting a sphere around each solute heavy atom; hydrogen
atoms are enclosed in the sphere of the atom to which they are
bonded.
Ashanul Haque: 0000-0002-6780-632X
Wenjun Wu: 0000-0003-0044-1917
Wai-Yeung Wong: 0000-0002-9949-7525
Frank Marken: 0000-0003-3177-4562
Paul R. Raithby: 0000-0002-2944-0662
Notes
2
2
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.S.K. thanks The Research Council (TRC), Oman (Grant
No. ORG/EI/SQU/13/015) and His Majesty’s Trust Fund
for Strategic Research (Grant No. SR/SQU/SCI/CHEM/16/
Solar Cell. Fabrication of the DSSCs. The working electrode was
composed of a 16 μm thick TiO film, including a 12 μm transparent
2
0
2) for funding. M.J. acknowledges the TRC, Oman for a
layer with 18 NRT and 4 μm scattering layer with 18NR-AO. The dye
solutions were 0.3 mM in dichloromethane and the photoanodes
underwent dipping for 12 h to complete the loading with sensitizers.
The DSSCs were assembled a sandwich structure with dyed TiO2
films and Pt-counter electrode, finally sealed with thermal adhesive
films of 30 μm Surlyn 1702(DuPont) by hot pressing technique. The
volatile liquid electrolyte was composed of 0.6 M BMII (1-butyl-3-
methylimidazoliumiodide), 0.1 M DMPII (1, 2-dimethyl-3-propyli-
Ph.D. scholarship, and R.A.A. acknowledges Sultan Qaboos
University, Oman for a Ph.D. scholarship. W.-Y.W. acknowl-
edges the financial support from the Areas of Excellence
Scheme of the University Grants Committee of HKSAR
(AoE/P-03/08), Hong Kong Research Grants Council (PolyU
153051/17P), the Hong Kong Polytechnic University (1-
ZE1C) and Ms. Clarea Au for the Endowed Professorship
(847S). P.R.R. and F.M. are grateful to the Engineering and
Physical Sciences Research Council, U.K., for funding through
an EPSRC Programme Grant (Grant EP/K004956/1).
midazolium iodide), 0.05 M I , 0.1 M LiI, 0.1 M GuSCN
2
(
guanidinium thiocyanate) and 0.5 M 4-tert-butylpyridine (TBP) in
a mixture of acetonitrile(AN) and valeronitrile(volume ratio, 85:15).
The platinum counter electrodes were obtained by spin-coating
H PtCl6 isopropanol solution (0.02 M) on the FTO glass with
2
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■
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−
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power of the simulated light was calibrated to 100 mW cm by using
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Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b01684
Inorg. Chem. XXXX, XXX, XXX−XXX