Reductive Coupling of Diynes at Rhodium Gives Fluorescent Rhodacyclopentadienes or Phosphorescent Rhodium 2,2’-Biphenyl Complexes

Article abstract of DOI:10.1002/chem.201601912

Reactions of [Rh(κ²-O,O-acac)(PMe₃)₂] (acac=acetylacetonato) and α,ω-bis(arylbutadiynyl)alkanes afford two isomeric types of MC₄metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5-bis(arylethynyl)rhodacyclopentadienes (A) are formed, which display intense fluorescence (Φ=0.07–0.54, τ=0.2–2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes (B), which show exceptionally long-lived (hundreds of μs) phosphorescence (Φ=0.01–0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent β-H-shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T₁state in the biphenyl complexes B, allowing for more efficient intersystem crossing S₁→T_nand T₁→S₀. Control of the isomer distribution is achieved by modification of the bis- (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds.

Full text of DOI:10.1002/chem.201601912

DOI: 10.1002/chem.201601912
Full Paper
&
Rhodium Complexes
Reductive Coupling of Diynes at Rhodium Gives Fluorescent
Rhodacyclopentadienes or Phosphorescent Rhodium 2,2’-Biphenyl
Complexes
Carolin Sieck,[a] Meng Guan Tay,[b, c] Marie-HØl›ne Thibault,[b] Robert M. Edkins,[a]
Karine Costuas,[d] Jean-FranÅois Halet,[d] Andrei S. Batsanov,[b] Martin Haehnel,[a]
Katharina Edkins,[e] Andreas Lorbach,[a] Andreas Steffen,[a, b] and Todd B. Marder*[a, b]
Abstract: Reactions of [Rh(k2-O,O-acac)(PMe3)2] (acac=
acetylacetonato) and a,w-bis(arylbutadiynyl)alkanes afford
two isomeric types of MC4 metallacycles with very different
photophysical properties. As a result of a [2+2] reductive
coupling at Rh, 2,5-bis(arylethynyl)rhodacyclopentadienes
(A) are formed, which display intense fluorescence (F=
0.07–0.54, t=0.2–2.5 ns) despite the presence of the heavy
metal atom. Rhodium biphenyl complexes (B), which show
exceptionally long-lived (hundreds of ms) phosphorescence
(F=0.01–0.33) at room temperature in solution, have been
isolated as a second isomer originating from an unusual
[4+2] cycloaddition reaction and a subsequent b-H-shift. We
attribute the different photophysical properties of isomers A
and B to a higher excited state density and a less stabilized
T1 state in the biphenyl complexes B, allowing for more effi-
cient intersystem crossing S1!Tn and T1!S0. Control of the
isomer distribution is achieved by modification of the bis-
(diyne) linker length, providing a fundamentally new route
to access photoactive metal biphenyl compounds.
lines the importance and potential of such compounds.[2] How-
ever, it is worth noting that our knowledge of the optical prop-
erties of metallacyclopentadienes, that is, MC4ÀnNn (n=0–2)
compounds, is mainly limited to {M(k2-N,N’-C2N2)}- and {M(k2-
N,C-C3N)}-type complexes.
Introduction
Transition metal complexes of 2,2’-bipyridine (bpy) and 2-phe-
nylpyridine (ppy), or derivatives thereof, usually exhibit triplet
excited states with lifetimes of a few ms, which can be exploit-
ed in photocatalysis, light-emitting devices, and biological
imaging.[1] The great attention that the prototypical com-
pounds [Ru(bpy)3]2+ and [Ir(ppy)3] have received for their em-
ployment in solar energy conversion and OLEDs, respectively,
and the resulting progress in those areas impressively under-
Synthesis of M(2,2’-bph) complexes (bph=biphenyl) as MC4
analogues can be achieved, for example, by insertion of a low-
valent, electron-rich transition metal fragment into a CÀC bond
of biphenylene or via reaction of a 2,2’-dilithiated biphenyl
with a metal dihalide (Scheme 1).[3] These methods clearly limit
the range of accessible substituted 2,2’-bph complexes, and
hence photophysical studies have been performed on only
[a] C. Sieck, Dr. R. M. Edkins, Dr. M. Haehnel, Dr. A. Lorbach, Dr. A. Steffen,
Prof. Dr. T. B. Marder
Institut für Anorganische Chemie
Julius-Maximilians-Universität Würzburg
Am Hubland, 97074 Würzburg (Germany)
E-mail: todd.marder@uni-wuerzburg.de
[b] Dr. M. G. Tay, Dr. M.-H. Thibault, Dr. A. S. Batsanov, Dr. A. Steffen,
Prof. Dr. T. B. Marder
Department of Chemistry, Durham University
South Road, Durham DH1 3LE (UK)
[c] Dr. M. G. Tay
Faculty of Resource Science and Technology
Universiti Malaysia Sarawak, 94300 Kota Samarahan (Malaysia)
[d] Dr. K. Costuas, Prof. Dr. J.-F. Halet
Institut des Sciences Chimiques de Rennes
UMR 6226 CNRS UniversitØ de Rennes 1 35042 Rennes Cedex (France)
[e] Dr. K. Edkins
School of Medicine, Pharmacy and Health, Durham University
University Boulevard, Stockton-on-Tees, TS17 6BH (UK)
Scheme 1. General synthetic access to transition metal biphenyl complexes
(top) and synthesis of luminescent 2,5-bis(arylethynyl)rhodacyclopenta-2,4-
dienes established by Marder et al. (bottom).[6]
Supporting information and ORCIDs for this article can be found under
http://dx.doi.org/10.1002/chem.201601912.
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a small number of transition metal biphenyl compounds of Pd,
Pt, Ir, and Au.[4] These few examples exhibit phosphorescence
with quantum yields of 0.01–0.16, but attempts to improve
their performance have not been reported. In contrast, metal-
lacyclopentadienes derived from the reductive coupling of al-
kynes are well known intermediates in cyclotrimerization reac-
tions of alkynes and alkyne/nitrile combinations,[5] and are thus
much more readily accessible. However, apart from our recent
reports,[6] nothing is known about their photophysical proper-
ties.
We have recently achieved the regioselective, quantitative
formation of rod-like, conjugated 2,5-bis(arylethynyl)-rhodacy-
clopentadienes, and one iridium analogue, by reductive cou-
pling of 1,4-diarylbuta-1,3-diynes or linked bis(diynes) Ar-CꢀCÀ
CꢀC-(CH2)4-CꢀC-CꢀC-Ar (Scheme 1).[6] A ruthenium analogue
has been reported in a purely synthetic study by Hill et al.[7]
Such MC4 metallacycles are structurally related to 2,5-bis(aryl-
ethynyl)-substituted main group heterocycles, such as siloles,[8]
phospholes,[9] or thiophenes,[10] which display interesting linear
and non-linear optical properties. Surprisingly, our rhodacyclo-
pentadienes exhibit highly efficient fluorescence with quantum
yields of up to FPL =0.69,[6b,c] despite the presence of the
heavy metal atom that would be expected to facilitate rapid
S1!Tn intersystem crossing (ISC) and thus to quench the fluo-
rescence.[1c,h] This finding motivated us to prepare new MC4
metallacycles and to investigate their photophysical properties.
Scheme 2. Synthesis of rhodacyclopentadienes (A) and rhodium biphenyl
complexes (B).
actions shown in Scheme 2 occur with complete conversion of
the starting materials to the two isomers A and B in 100%
total yield, with no byproducts observed by in situ solution
NMR spectroscopy (Figure 1).
Isomers A and B were separated by column chromatogra-
phy, crystallization and washing with hot hexane, giving analyt-
ically pure samples that were used to grow single crystals suit-
Results and Discussion
Synthesis of rhodium 2,2’-biphenyl complexes and 2,5-bis-
(arylethynyl)rhodacyclopenta-2,4-dienes
We decided to examine the influence of the ligand sphere
around the rhodium center on the ISC processes in the above-
mentioned fluorescent rhodacyclopentadienes by introduction
of p-electron-donating groups, such as acetylacetonato. Inter-
estingly, the reaction of [Rh(k2-O,O-acac)(PMe3)2][11] (1) with
either a,w-bis(arylbutadiynyl)alkane 2a or 2b in a 1:1 ratio in
homogeneous solution at room temperature leads to the for-
mation of two isomers, that is, 2,5-bis(arylethynyl)rhodacyclo-
pentadienes A (3a,b) and rhodium biphenyl complexes B
(4a,b) (Scheme 2). The product ratio depends on the tempera-
ture and on the aryl substituents, with the acceptor-substitut-
ed (CO2Me) substrate favoring isomer B, and the donor-substi-
tuted (SMe) substrate leading to an excess of A.
In contrast, simple modification of the a,w-bis(arylbuta-
diynyl)alkane, that is, changing the linker length from four CH2
groups in 2a,b to three CH2 groups in 5a and 5b, dramatically
favors the formation of the rhodium biphenyl isomer B for en-
tropic reasons, leading to an A:B ratio of 1:20 at room temper-
ature. For these shorter chain substrates the para-substituents
of the aryl rings have no influence on the isomer distribution
although they do affect the reaction rate, with the acceptor-
substituted (CO2Me) a,w-bis(arylbutadiynyl)alkanes 2a and 5a
reacting the fastest. Also remarkable is that the shorter chain
substrates react much faster (complete in 3 days) than the
longer ones (several weeks). It is important to note that all re-
1
Figure 1. In situ 31P{1H} and H NMR spectra of the reactions of
[Rh(acac)(PMe3)2] (1) with 2a at 293 K (top) and with 5a at 333 K (bottom)
giving A:B isomer ratios of 1:2.6 and 1:25, respectively.
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able for X-ray diffraction, and which were used for lumines-
cence spectroscopy (see below). The molecular structures of
3a and 4a in the solid state (Figure 2) confirm the identity of
these two fundamentally different classes of MC4 metallacycles
containing highly conjugated organic p-systems.
Scheme 3. Synthesis of rhodacyclopentadiene 11 and rhodium biphenyl
complexes 9 and 10.
Figure 2. Molecular structures of 3a (top) and 4a (bottom) in the solid state
determined by single-crystal X-ray diffraction, and their respective toluene
solutions under UV (365 nm) irradiation. H atoms are omitted for clarity.
Due to the fact that the para-substituents of the aryl moiet-
ies influence the reaction rate (see above), we were interested
in the selectivity of the reaction of unsymmetrical donor/ac-
Figure 3. Molecular structure of 9 in the solid state determined by single-
crystal X-ray diffraction; H atoms are omitted for clarity.
ceptor-substituted a,w-bis(arylbutadiynyl)alkanes
8
with
[Rh(k2-O,O-acac)(PMe3)2] (1), as we were seeking hints on the
reaction pathway that discriminates the formation of the bi-
phenyl complexes from the [2+2+M] cycloaddition that gives
the 2,5-substituted rhodacyclopentadienes. In addition, use of
8 was expected to lead to different isomers with increased
charge-transfer character in their excited states in comparison
to 3, 4, 6, and 7, potentially leading to materials with interest-
ing non-linear optical properties.
nucleophiles[12] or be stabilized by, for example, AgI or other
Lewis acids.[13] The latter allows for a Friedel–Crafts-type elec-
trophilic aromatic substitution to occur, leading to a hydroaryla-
tion forming biaryls. We cannot exclude that, related to the
HDDA reaction, a Rh benzyne p-complex is formed as an inter-
mediate, undergoing subsequent CÀH activation of the pend-
ent p-(CO2Me)C6H4 ring to give the RhIII biphenyl complexes B
instead of the rhodacyclopentadienes A. However, we note
that HDDA reactions usually require elevated temperatures,
even in the presence of a metal complex, while formation of B
is observed at or even below room temperature. We have not
yet been able to clarify the kinetics (i.e., the reaction order in
M and bis(diyne)) via in situ NMR spectroscopic investigations
due to the limited solubility range of the starting materials,
but further synthetic and mechanistic studies are currently
being performed to gain more insight into the mechanism of
this exciting and very unusual reaction.
The reaction of 1 with the a,w-bis(arylbutadiynyl)alkane 8 at
333 K gave the biphenyl complex 9 as the major product
(83%), while its isomer 10 and rhodacyclopentadiene 11 are
formed in 12% and 5% yield, respectively (Scheme 3). We
were able to isolate pure 9 and 11, and the identity of the rho-
1
dium biphenyl complex 10 was confirmed by H and 31P{1H}
NMR spectroscopic studies of the reaction mixture. The molec-
ular structure of 9 obtained from single-crystal X-ray diffraction
is shown in Figure 3, unambiguously identifying that isomer.
Whereas the rhodacyclopentadienes of type A are the result
of a “normal” [2+2] cycloaddition reaction, and thus structural-
ly related to well established intermediates in metal-mediated
alkyne cyclotrimerization,[5] the mechanism of formation of the
biphenyl complexes (B) is more complicated. Formally, a [4+2]
diyne–alkyne cyclization occurs with a subsequent ortho CÀH
activation and b-H-shift (Scheme 2). Recently, it has been dem-
onstrated that the hexadehydro Diels–Alder (HDDA) reaction
gives an aryne species, which can either be trapped directly by
Photophysical and DFT/TD-DFT studies
Isomers A exhibit intense visible fluorescence with FPL =0.01-
0.54 and emission lifetimes of a few nanoseconds in toluene
and 2-MeTHF solutions, as well as in the solid state and in
PMMA films at room temperature (Figure 4 and Table 1, and
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The other derivatives show only marginal changes of the
photophysical properties upon changing the solvent or in
PMMA. Interestingly, the radiative rate constants kr of 3a,b,
6a,b and 11 are very similar, but the non-radiative rate con-
stants knr of donor-substituted 3b and 6b as well as of the
donor-acceptor compound 11 are greatly enhanced in compar-
ison to the acceptor-substituted 3a and 6a. No additional
phosphorescence at 77 K is observed, and dioxygen has no
effect on the luminescence properties of the rhodacyclopenta-
dienes. We recently showed[6b,14] that SOC mediated by the
heavy metal atom in 2,5-bis(arylethynyl)rhoda- and iridacyclo-
pentadienes is negligible. Below 233 K, a temperature-inde-
pendent ISC process occurs inefficiently via pure SOC. At room
temperature, a second thermally activated ISC process is the
major pathway for triplet state population. However, fluores-
cence remains a competitive process, and those triplet states
that are formed do not phosphoresce due to efficient non-radi-
ative decay channels.
Figure 4. Emission spectra of rhodacyclopentadienes 6a (black), 6b (blue),
and 11 (red) in degassed toluene solution at room temperature.
The origin of this fluorescence, despite the presence of
a heavy metal atom, lies in the pure intra-ligand (IL) nature of
the excited states S1 and T1. The HOMO and the LUMO are
nearly pure p and p* ligand orbitals, respectively, and the
HOMO is energetically well separated by more than 1 eV from
the filled Rh d orbitals (Figure 5, 6 and S32). This inhibits low-
energy MLCT transitions, which could contribute to the nature
of the emissive state and facilitate spin-orbit coupling (SOC),
leading to a much lower triplet state density around S1 than in
B (vide infra), and hampering the ISC process. The absence of
phosphorescence in transition metal complexes due to mainly
IL character of the excited states is not unusual, even for
metals heavier than Rh with more SOC, occasionally resulting
in residual S1 emission despite ISC S1!Tn being sufficiently fast
for population of T1.[1c,e,h,6b,14,15] However, there are very few
complexes which exhibit fluorescence with the efficiency dis-
Supporting Information). The CO2Me-substituted compounds
3a and 6a show significantly higher FPL and a bathochromic
shift in the absorption and emission spectra in comparison to
their SMe-substituted congeners 3b and 6b, due to a more
pronounced charge-transfer from the RhC4 core to the phenyl
moieties. The NMe2/CO2Me-substituted rhodacyclopentadiene
11 experiences a strong intra-ligand charge-transfer, resulting
in an emission with lmax =576 nm, lmax =600 nm and lmax
=
651 nm in toluene, PMMA and 2-MeTHF, respectively. Interest-
ingly, at 77 K in 2-MeTHF, the bathochromic shift of the emis-
sion in comparison to toluene solutions at 297 K is negligible,
which suggests that the CT in more polar environments at
room temperature is accompanied by a significant geometrical
reorganization in the excited state, which is hampered at low
temperatures in the glassy matrix.
Table 1. Selected photophysical data of compounds 3, 4, 6, 7 (all a/b), 9 and 11 recorded under oxygen-free conditions.
Toluene 2-MeTHF/297 K
2-MeTHF/77 K
Cpd.
labs
lem
FPL
t
kr
[sÀ1
knr
[sÀ1
lem
FPL
t
lem
t
[nm]
[nm]
]
]
[nm]
[nm]
3a
3b
514
481
579
534
0.50
0.13
2.5 ns
2.0”108
2.0”108
579
544
0.24
0.09
0.5 ns
0.4 ns
581
532
2.8 ns
2.0 ns (25%),
0.5 ns (75%)
162 ms
43 ms (40%),
119 ms (60%)
1.7 ns
1.5”108[a]
9.9”108[a]
0.9 ns (57%),
2.4 ns (43%)
537 ms
2750 ms (80%),
3950 ms (20%)
2.1 ns (90%),
3.1 ns (10%)
2.2 ns
4a
4b
410
390
545
542
0.12
0.01
740
110[a]
5430
11200
544
577
0.33
0.02
372 ms
81 ms
540
530
6a
6b
7a
7b
9
535
503
377
382
371
498
563
522
540
535
536
576
0.54
0.07
0.14
0.02
0.29
0.22
3.2”108
2.8”108[a]
770
2.7”108
3.7”109[a]
4750
570
522
541
534
535
651
0.57
0.08
0.16
0.10
0.21
0.13
1.7 ns
0.2 ns
338 ms
646 ms
569
515
537
527
534
582
0.3 ns (77%),
0.1 ns(23%)
181 ms
374 ms (97%),
1340 ms (3%)
1920 ms (73%),
2770 ms (27%)
680 ms (66%),
1100 ms (34%)
2.2 ns (98%),
4.5 ns (2%)
61 ms (98%),
163 ms (2%)
164 ms (12%),
496 ms (88%)
0.8 ns
330[a]
16000[a]
1560[a]
640[a]
45 ms (34%),
210 ms (66%)
0.5 ns
11
2.8”108
9.8”108
[a] Calculated from weighted average lifetimes.
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Figure 7. Emission (solid) and excitation (dashed) spectra of rhodium bi-
phenyl complexes 3a (red) and 4a (blue) in degassed toluene solution at
room temperature.
complexes (Figure 7),[1c,h,17] with quantum yields of up to 0.29
for 9 in toluene and up to 0.33 for 4a in 2-MeTHF, and emis-
sion lifetimes on the timescale of tens to hundreds of micro-
seconds (Table 1 and S2) at room temperature. We note that
the PLQYs and lifetimes in PMMA differ for some of the iso-
mers B from the data obtained in solution. We exclude aggre-
gation from being responsible for this phenomenological ob-
servation due to the superimposition of the emission spectra
(see the Supporting Information). Apparently, the interaction
of B with the surrounding matrix leads to changes in the
Franck–Condon factors for the vertical transition T1!S0, in-
creasing or decreasing the rate constants for radiative and
non-radiative decay.
Figure 5. Selected molecular orbitals of rhodacyclopentadiene 3a (left) and
rhodium biphenyl complex 4a (right). Contour values: Æ0.035 [e/bohr3]1/2
.
Unlike in the solid state, the biphenyl complexes B are
chemically sensitive to dioxygen in solution, thus we ensured
rigorous exclusion of O2. In contrast to rhodacyclopentadienes
A, the para-substituents of the phenyl rings barely influence
the absorption and emission spectra (Figure 8). However, we
Figure 6. a) MO diagrams of the frontier orbital region of 3a and 4a. b) Cal-
culated vertical excitations of 3a and 4a (blue: singlet states, red: triplet
states).
played by our rhodacyclopentadienes,[16] which involves excep-
tionally slow S1!Tn ISC on the timescale of nanoseconds
rather than in a few picoseconds or faster.
In stark contrast, the unusual biphenyl complexes B display
purely phosphorescence, as expected of second-row metal
Figure 8. Emission spectra of rhodacyclopentadienes 7a (black), 7b (blue)
and 9 (red) in degassed toluene solution at room temperature.
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found that, again, the acceptor-substituted compounds show
higher FPL. Interestingly, the NMe2/CO2Me- and the CO2Me-
substituted biphenyl complexes 9 and 4a are, to the best of
our knowledge, among the most efficient phosphorescing Rh
complexes as well as among the most efficient metal biphenyl
triplet emitters to date,[4l] being even more efficient than
known Ir– and Pt–biphenyl complexes.[4,18]
then mainly determines the color of the OLED, whereas at low
voltages the low-energy emitter is dominant. Also, long-lived
excited states are of interest for photocatalysis, energy up-con-
version and non-linear optics, as has been shown recently, for
example, for PdII porphyrin and AuIII 2,6-diphenylpyridine com-
plexes.[19b,c]
The fundamentally different photophysical properties of B in
comparison with A may arise from the energetic proximity of
the filled frontier molecular orbitals in B, which are mixtures of
ligand p and metal d orbitals (Figure 5, 6, and S33). As a result,
a number of triplet excited states with some MLCT contribu-
tion can efficiently connect the S1 state with the emitting T1
state (see Figure 6 and TD-DFT results in the Supporting Infor-
mation).[1c,h] Indeed, as no fluorescence is detected even at low
temperature, it can be assumed that S1!Tn ISC must be faster
than both fluorescence and non-radiative decay from S1 and,
therefore, FISC =1 (vide infra). This contrasts with the behavior
of the isomeric rhodacyclopentadienes (e.g., 3, 6, 11) for which
we have previously shown that the unusually slow ISC occurs
on a timescale that is competitive with fluorescence (vide
supra).
Conclusion
In conclusion, we report a very unusual reaction which produ-
ces two isomeric metallacycles with fundamentally different
photophysical properties. Whereas unusual fluorescent 2,5-bis-
(arylethynyl)rhodacyclopentadienes
are
obtained
from
a known type of reductive coupling of two alkyne moieties,
a highly unusual [4+2] coupling reaction with subsequent b-H-
shift leads to a novel class of highly phosphorescent Rh(2,2’-
bph) complexes. The exceptional luminescence performance of
the latter compounds, that is, lifetimes in solution of up to
646 ms and, for biphenyl complexes, unusually high quantum
yields of up to 0.33,[4,18,19] clearly demonstrates the potential of
this class of materials. We also show that control over the
isomer distribution is possible by simple modification of the
a,w-bis(arylbutadiynyl)alkane linker length, providing a new
synthetic methodology to access a range of dibenzo-metallacy-
clopentadienes. We are currently carrying out experimental
and theoretical studies of the reaction mechanism in order to
understand the factors leading to isomers A and B, and explor-
ing applications of the new long-lived triplet states of the di-
benzometallacyclopentadienes.
However, the very small values of the radiative rate con-
stants kr =110–770 sÀ1 of 4, 7, and 9 in toluene indicate that
3
the nature of the T1 state is purely IL with weak SOC mediated
by the Rh atom. This was further confirmed by luminescence
measurements on those compounds in 2-MeTHF (Table 1). For
example, compound 9 shows lifetimes of tav =154 ms and tav =
823 ms at room temperature and at 77 K, respectively. The in-
crease in emission lifetime upon cooling from 298 K, at which
temperature the quantum yield has been determined to be
FPL =0.21, to 77 K by a factor of five indicates a phosphores-
cence quantum yield of unity and thus supports 100% ISC
with FISC =1. Thus, their phosphorescence efficiency in solu-
tion at room temperature is even more impressive, as non-radi-
ative coupling of the excited state with the ground state with
energy loss to the environment on a sub-ms timescale typically
precludes phosphorescence. Instead, the rigidity of the organic
p-system allows the ligand-based triplet excited state to exist
in solution for up to about 500 ms for 9 in toluene, and even
up to 646 ms for 7b in 2-MeTHF, and to emit with exceptional
quantum yields for biphenyl complexes of 0.29 and 0.33 for 9
and 4a, respectively.
Experimental Section
General considerations: The syntheses of a,w-bis(arylbutadiynyl)-
alkanes and 1 are described in the Supporting Information. All
other starting materials were purchased from commercial sources
and used without further purification. Inhibitor-free anhydrous 2-
MeTHF was purchased from Sigma Aldrich. All other solvents for
synthetic reactions and for photophysical measurements were of
HPLC grade, further treated to remove trace water using an Inno-
vative Technology Inc. Pure-Solv Solvent Purification System and
deoxygenated using the freeze-pump-thaw method. All reactions
were performed under an argon atmosphere in an Innovative Tech-
nology Inc. glovebox or using standard Schlenk techniques. 1H,
13C{1H} and 31P{1H} NMR spectra were measured on a Varian
VNMRS-700 (1H, 700 MHz; 13C{1H}, 176 MHz; 31P{1H}, 283 MHz),
Bruker Avance-500 (1H, 500 MHz; 13C{1H}, 126 MHz; 31P{1H},
202 MHz), Bruker Avance-400 (1H, 400 MHz; 13C{1H}, 101 MHz) or
Bruker Avance III 300 (1H, 300 MHz; 13C{1H}, 75 MHz; 31P{1H},
121 MHz) NMR spectrometer. Mass spectra were recorded on
a Bruker Daltonics autoflex II LRF mass spectrometer operating in
the MALDI mode, unless stated otherwise. The mass spectra of 2a
and 2b were obtained by using an Applied Biosystem Voyager-DE
STR MALDI ToF mass spectrometer. The mass spectra of 3a and 3b
were obtained in ESI mode using a Thermo-Finnigan LTQ FT mass
spectrometer operating in positive-ion mode. Elemental analyses
were performed on a Leco CHNS-932 Elemental Analyzer. The ele-
mental analysis for compounds 2a, 2b, 3a, and 3b were per-
formed on an Exeter Analytical CE-440 analyzer.
The exceptionally long lifetimes and small radiative rate con-
stants of the rhodium biphenyl complexes in comparison to
3
other IL emitters of, for example, PtII or AuIII[19] presumably are
a result of the long conjugation of the organic ligand p-
system. According to our TD-DFT studies, the T1 state involves
charge-transfer from the biphenyl ligand into the arylethynyl
moiety away from the rhodium atom, which reduces SOC of
the metal center that would be necessary for fast phosphores-
cence.
Such long-lived triplet excited states can be very useful for
application in color-tunable OLEDs,[19a] in which at high voltag-
es the emissive excited state of a low-energy emitter must
have a long lifetime in order to become saturated by energy
transfer from a short-lived high-energy luminophore. The latter
Chem. Eur. J. 2016, 22, 10523 – 10532
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10528
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Full Paper
General procedure for the synthesis of rhodium biphenyl com-
plexes (4a, 4b, 7a, 7b, 9, 10) and rhodacyclopentadienes (3a,
3b, 6a, 6b, 11): One equivalent of 1 and one equivalent of the
corresponding bis(diyne) (2a for 3a, 4a), (2b for 3b, 4b), (5a for
6a, 7a), (5b for 6b, 7b), (8 for 9, 10, 11), were suspended in THF
(10 mL) and the reaction mixture was stirred. For specific reaction
temperatures and reaction times, see below. Then, the volatiles
were removed in vacuo to give isomers A and B in 100% total
yield as demonstrated in Figure 1. The product mixture was dis-
solved in THF and separation was achieved by column chromato-
graphy (Al2O3), eluting with hexane and THF (2:1). The rhodium bi-
phenyl complexes 4a, 4b, 7a, 7b, 9, and 10 were recrystallized
from THF and washed with hot hexane, both steps several times,
to obtain spectroscopically pure samples, and to ensure that trace
impurities are not present which might influence the photophysi-
cal characterization. The yields given below are of the isolated
single crystalline samples, after several purification steps, used for
luminescence spectroscopy.
quat. carbon atom could not be determined; 31P{1H} NMR
(121 MHz, C6D6, r.t.): d=À2.0 ppm; (d, JRh-P =113 Hz, 2 P); elemental
analysis calcd (%) for C38H45O6P2Rh: C 59.85, H 5.95; found: C 59.81,
H 6.12. MS (MALDI-TOF): m/z: 761 [MÀH]+, 662 [MÀacac]+.
7b: Stirring at 608C for 5 days. Yellow solid. Isolated yield: 0.15 g
1
(7%). H NMR (500 MHz, C6D6, r.t.): d=9.42 (d, J=8 Hz, 1H, CHarom),
8.28 (m, 1H, CHarom), 8.20 (m, 1H, CHarom), 7.56 (d, J=8 Hz, 2H,
CHarom), 7.32 (d, J=8 Hz, 1H), 6.99 (d, J=8 Hz, 2H, CHarom), 5.12 (s,
1H, CH), 3.34 (m, 2H, CH2), 3.05 (m, 2H, CH2), 2.34 (s, 3H, CH3), 2.03
(m, 2H, CH2), 1.89 (s, 3H, CH3), 1.88 (s, 3H, CH3) 1.84 (s, 3H, CH3),
0.60 ppm (vt, JP-H =3 Hz, 18H, PMe3); 13C{1H} NMR (126 MHz, C6D6,
r.t.): d=187.9, 187.7, 166.4 (dt, 1JRh-C =10 Hz, 2JP-C =31 Hz), 162.9 (dt,
1JRh-C =11 Hz, 2JP-C =31 Hz), 151.1, 149.6, 142.6, 139.2, 139.1, 134.2,
131.9, 130.4, 129.1, 126.5, 124.1, 121.6, 120.6, 112.6, 99.1, 97.0, 91.2,
33.9, 33.5, 30.0, 28.7, 28.6, 25.1, 16.1, 15.0, 10.6 ppm (vt, JC-P
14 Hz); 31P{1H} NMR (121 MHz, C6D6, r.t.): d=À2.26 ppm (d, JRh-P
=
=
114 Hz, 2 P); elemental analysis calcd (%) for C36H45O2P2RhS2: C
58.53, H 6.14, S 8.68; found: C 58.85, H 6.16, S 8.47. MS (MALDI-
TOF): m/z: 738 [M+].
4a: Stirring at room temperature for 14 days. Yellow solid. Isolated
yield: 0.09 g (4.1%). 1H NMR (500 MHz, C6D6, r.t.): d=9.52 (d, J=
8 Hz, 1H, CHarom), 9.10 (s, 1H, CHarom), 8.37 (d, J=8 Hz, 1H, CHarom),
8.05 (d, J=8 Hz, 2H, CHarom), 8.04 (s, 1H, CHarom), 7.57 (d, J=8 Hz,
2H, CHarom), 5.13 (s, 1H, CH), 3.62 (s, 3H, CH3), 3.62 (s, 3H, CH3),
3.48 (m, 2H, CH2), 3.24 (m, 2H, CH2), 2.91 (m, 2H, CH2), 1.89 (s, 3H,
CH3), 1.88 (s, 3H, CH3) 1.70 (m, 2H, CH2), 0.57 ppm (vt, JP-H =3 Hz,
18H, PMe3); 13C{1H} NMR (126 MHz, C6D6, r.t.): d=188.4, 187.7,
168.2, 166.3, 166.0, 163.1 (dt, 1JRh-C =10 Hz, 2JP-C =31 Hz), 158.7,
149.9, 134.7, 134.5, 134.2, 133.3, 131.4, 130.1, 129.7, 129.5, 128.4,
126.6, 124.5, 123.5, 116.5, 99.3, 99.2, 93.8, 51.6, 51.3, 30.9, 28.8,
28.7, 24.3, 23.7, 10.6 ppm (vt, JC-P =14 Hz). Due to the low intensity,
9: Stirring at 608C for 5 days. Yellow solid. Isolated yield: 0.26 g
(8%); 1H NMR (500 MHz, C6D6): d=9.74 (d, J=8 Hz, 1H, CHarom),
9.09 (m, 1H, CHarom), 8.43 (m, 1H, CHarom), 8.20 (d, J=8 Hz, 2H,
CHarom), 7.73 (d, J=8 Hz, 1H), 6.44 (d, J=8 Hz, 2H, CHarom), 5.12 (s,
1H, CH), 3.39 (m, 2H, CH2), 3.62 (s, 3H, CH3), 3.04 (m, 2H, CH2), 2.41
(s, 6H, CH3), 2.02 (m, 2H, CH2), 1.89 (s, 3H, acac-CH3), 1.88 (s, 3H,
CH3), 0.58 ppm (vt, JP-H =3 Hz, 18H, PMe3); 13C{1H} NMR (126 MHz,
1
2
C6D6): d=188.3, 187.6, 168.3, 164.9 (dt, JRh-C =11 Hz, JPÀC =31 Hz),
159.2, 159.1, 150.2, 142.5, 140.5, 133.2, 132.8, 128.4, 126.2, 124.6,
123.2, 115.2, 112.6, 112.4, 99.2, 88.7, 67.8, 51.2, 39.8, 34.0, 33.6, 28.7,
28.6, 25.8, 25.1, 10.6 ppm (vt, JC-P =14 Hz); due to the low intensity,
1
2
1
2
the JRh-C and JP-C coupling of the second quaternary carbon atom
could not be determined. 31P{1H} NMR (121 MHz, C6D6, r.t., ): d=
À2.2 ppm (d, JRh-P =113 Hz, 2 P); elemental analysis calcd (%) for
C38H47O6P2Rh: C 60.31, H 6.10; found: C 60.42, H 6.17. MS (MALDI-
TOF): m/z: 776 [M+], 677 [MÀacac]+.
the JRh-C and JP-C coupling of the second quat. carbon atom could
not be determined; 31P{1H} NMR (121 MHz, C6D6): d=À2.23 ppm
(d,
J
Rh-P =113 Hz,
2
P); elemental analysis calcd (%) for
C38H48NO4P2Rh: C 61.05, H 6.47, N 1.87; found: C 61.30, H 6.76, N
1.67. MS (MALDI-TOF): m/z: 747 [M+], 648 [MÀacac]+. Compound
1
10 was identified by H and 31P{1H} NMR spectroscopy in the prod-
4b: Stirring at room temperature for 14 days. Yellow solid. Isolated
yield: 0.02 g (3.5%). 1H NMR (500 MHz, C6D6, r.t.): d=9.47 (d, J=
8 Hz, 1H, CHarom), 8.29 (m, 1H, CHarom), 7.98 (s, 1H, CHarom), 7.56 (d,
J=8 Hz, 2H, CHarom), 7.56 (s, 1H, CHarom), 7.32 (d, J=8 Hz, 1H,
CHarom) 7.00 (d, J=8 Hz, 2H, CHarom), 5.12 (s, 1H, CH), 3.34 (m, 2H,
CH2), 2.94 (m, 2H, CH2), 2.32 (s, 3H, CH3), 1.90 (s, 3H, CH3), 1.89 (s,
1
uct mixture. H NMR (300 MHz, C6D6, r.t.): d=9.29 (d, J=8 Hz, 1H,
CHarom), 8.23 (s, 1H, CHarom), 8.05 (m, 2H, CHarom), 7.73 (d, J=8 Hz,
2H, CHarom), 7.64 (d, J=8 Hz, 2H), 5.17 (s, 1H, CH), 3.45 (s, 3H, CH3),
3.33 (m, 2H, CH2), 3.09 (m, 2H, CH2), 2.90 (s, 6H, CH3), 2.75 (m, 2H,
CH2), 1.92 (s, 3H, CH3), 1.91 (s, 3H, CH3), 0.67 ppm (vt, JP-H =3 Hz,
18H, PMe3); 31P{1H} NMR (121 MHz, C6D6, r.t.): d=À2.13 ppm (d, JRh-
P =115 Hz, 2 P).
3H, CH3) 1.84 (s, 3H, CH3), 1.74 (m, 2H, CH2), 0.60 ppm (vt, JP-H
=
3 Hz, 18H, PMe3); 13C{1H} NMR (176 MHz, C6D6, r.t.): d=187.9, 187.7,
1
2
1
2
167.0 (dt, JRh-C =10 Hz, JP-C =31 Hz), 160.7 (dt, JRh-C =10 Hz, JP-C
=
For ease of isolation of spectroscopically pure rhodacyclopenta-
dienes (3a, 3b, 6a, 6b, 11), a different reaction procedure was de-
veloped: one equivalent of [Rh(acac)(P(p-tolyl)3)2], which was pre-
pared via a modification of the synthesis for compound 1, and one
equivalent of the corresponding bis(diyne) (2a for 3a), (2b for 3b),
(5a for 6a), (5b for 6b), (8 for 11), were suspended in THF (10 mL)
at 608C and stirred for 5 days. Once the reaction was complete,
PMe3 (excess) was added in situ to the reaction mixture, which was
stirred at 608C for 2 days. Then, the volatiles were removed in
vacuo and the product was recrystallized from THF and washed
with hot hexane to give 3a, 3b, 6a, 6b, and 11, respectively. The
yields given below are those of single-crystalline material used for
spectroscopic investigations obtained after several purification
steps to ensure the absence of any trace impurities, such as free
phosphine, which might influence the photophysical measure-
ments.
31 Hz), 151.2, 150.5, 139.1, 134.3, 133.9, 132.8, 131.9, 130.3, 128.4,
127.9, 126.6, 124.5, 121.7, 120.5, 115.8, 99.4, 99.1, 91.2, 30.9, 28.8,
28.7, 28.6, 24.4, 23.9, 16.1, 15.0, 10.7 ppm (vt, JC-P =14 Hz); 31P{1H}
NMR (202 MHz, C6D6, r.t.): d=À2.26 ppm (d, JRh-P =114 Hz, 2 P); ele-
mental analysis calcd (%) for C37H47O2P2RhS2: C 59.04, H 6.29, S
8.52; found: C 59.44, H 6.42, S, 8.56. MS (MALDI-TOF): m/z: 676
[MÀPMe3]+.
7a: Stirring at 608C for 2 days. Yellow solid. Isolated yield: 0.24 g
1
(9%); H NMR (300 MHz, C6D6, r.t.): d=9.46 (d, J=8 Hz, 1H, CHarom),
9.10 (m, 1H, CHarom), 8.38 (d, J=8 Hz, 1H, CHarom), 8.25 (s, 1H,
CHarom), 8.04 (d, J=8 Hz, 2H, CHarom), 7.57 (d, J=8 Hz, 2H, CHarom),
5.13 (s, 1H, CH), 3.62 (s, 3H, CH3), 3.48 (s, 3H, CH3), 3.25 (m, 2H,
CH2), 3.01 (m, 2H, CH2), 1.99 (m, 2H, CH2), 1.89 (s, 3H, CH3), 1.88 (s,
3H, CH3) 0.57 ppm (vt,
J
P-H =3 Hz, 18H, PMe3); 13C{1H} NMR
1
(126 MHz, C6D6, r.t.): d=188.4, 187.7, 168.2, 166.3, 165.4 (dt, JRh-C
=
2
1
10 Hz, JP-C =31 Hz), 158.5, 148.9, 143.3, 140.6, 133.4, 131.5, 129.8,
129.8, 129.4, 128.4, 126.6, 124.6, 123.1, 113.4, 99.3, 96.9, 93.8, 67.8,
51.6, 51.3, 33.9, 33.4, 30.1, 28.7, 25.0, 10.6 ppm (vt, JC-P =14 Hz).
3a: Red solid. Isolated yield: 0.07 g (3.5%); H NMR (700 MHz, C6D6,
r.t., ppm): d=8.13 (d, J=8 Hz, 4H, CHarom), 7.68 (d, J=8 Hz, 4H,
CHarom), 5.13 (s, 1H, CH), 3.47 (s, 6H, CH3), 2.91 (m, 4H, CH2), 1.91 (s,
6H, CH3), 1.66 (m, 4H, CH2), 0.88 ppm (vt, J=4 Hz, 18H, PMe3);
1
2
Due to the low intensity, the JRh-C and JP-C coupling of the second
Chem. Eur. J. 2016, 22, 10523 – 10532
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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13C{1H} NMR (126 MHz, C6D6, r.t.): d=187.1, 166.5, 158.4, 140.3 (dt,
1JRh-C =10 Hz, 2JP-C =31 Hz), 132.2, 131.0, 130.0, 128.3, 110.0, 99.0,
98.0, 51.5, 30.7, 28.5, 24.9, 10.9 ppm (vt, JC-P =14 Hz); 31P{1H} NMR
(161 MHz, C6D6, r.t.): d=À0.50 ppm (d, JRh-P =113 Hz, 2 P); elemen-
tal analysis calcd (%) for C39H47O6 P2Rh: C 60.31, H 6.10; found: C
60.15, H 6.10. MS (ES+): m/z: 776 [M+], 700 [MÀPMe3]+, 677
[MÀacac]+.
608C to give the isomers 3a and 4a in a ratio of 1:1.5, 1:0.2 for
3b, 4b; 1:25 for 6a, 7a and 6b, 7b.
Single-crystal X-ray diffraction: Single-crystals suitable for X-ray
diffraction were selected, coated in perfluoropolyether oil, and
mounted on MiTeGen sample holders. Diffraction data were col-
lected on Bruker 3-circle diffractometers with CCD area detectors,
SMART 1000 (3a, 3b, 4a), SMART APEX (6b, 9), and 4-circle diffrac-
tometers with CCD area detectors, Apex II (2b, 4a, 6a, 7b, 11),
and D8 QUEST with CMOS area detector PHOTON 100 (7a), using
Mo-Ka radiation monochromated by graphite (3a, 3b, 4a, 6b, 9)
or multi-layer focusing mirrors (6a, 7a, 7b, 11). The crystals were
cooled using Cryostream open-flow N2 gas cryostats. The structures
were solved using direct methods (SHELXS, for 3a, 3b, 4a),[20] or
the intrinsic phasing method (ShelXT)[21] and Fourier expansion
technique, or by using the olex2.solve algorithm.[22] All non-H
atoms were refined anisotropically, with the exception of highly
3b: Red solid. Isolated yield: 0.01 g (2.2%); 1H NMR (400 MHz,
C6D6, r.t.): d=7.62 (d, J=8 Hz, 4H, CHarom), 7.08 (d, J=8 Hz, 4H,
CHarom), 5.17 (s, 1H, CH), 2.96 (m, 4H, CH2), 1.97 (s, 6H, CH3), 1.93 (s,
6H, CH3), 1.69 (m, 4H, CH2), 0.96 ppm (vt, JP-H =4 Hz, 18H, PMe3);
13C{1H} NMR (126 MHz, C6D6, r.t.): d=186.8, 156.5, 137.1, 131.4,
126.8, 124.4, 109.7, 98.8, 94.7, 30.9, 28.6, 25.1, 15.4, 10.9 ppm (vt, JC-
1
2
P =14 Hz). Due to the low intensity, the JRh-C and JP-C coupling
could not be determined. 31P{1H} NMR (161 MHz, C6D6, r.t.): d=
À0.41 ppm (d, JRh-P =114 Hz, 2 P); elemental analysis calcd (%) for
C37H47O2 P2RhS2: C 59.04, H 6.29; found: C 59.60, H 6.08. MS (ES+):
m/z: 752 [M+], 676 [MÀPMe3]+, 653 [MÀacac]+.
disordered groups.
H atoms were refined isotropically using
a riding model. All structures were refined by full-matrix least
squares against F2 of all data using the programs SHELXL[20] and
OLEX2.refine.[23] The program DIAMOND was used for graphical
representation.[24] General color code: carbon (white), sulfur
(yellow), oxygen (red), phosphorus (purple), rhodium (dark green),
nitrogen (blue). Crystal data and experimental details are listed in
Table S1; CCDC 1419146, 1419147, 1419148, 1419149, 1419150,
1419151, 1419152, 1419153, 1419154, 1419155 and 1419156 con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre.
1
6a: Red solid. Isolated yield: 0.03 g (9%); H NMR (300 MHz, C6D6,
r.t.): d=7.58 (d, J=8 Hz, 4H, CHarom), 7.18 (br. s, 4H, CHarom), 5.07 (s,
1H, CH), 2.71 (m, 4H, CH2), 2.27 (s, 6H, CH3), 2.10 (m, 2H, CH2), 1.76
(s, 6H, CH3), 0.95 ppm (vt, JP-H =3 Hz, 18H, PMe3); 13C{1H} NMR
(126 MHz, C6D6, r.t.): d=186.4, 156.5, 144.6, 132.9, 129.6, 128.4,
98.2, 30.9, 30.5, 28.3, 21.4, 12.5 ppm (vt, JC-P =14 Hz); due to the
1
2
low intensity, the JRh-C and JP-C coupling could not be determined.
Two carbon signals were not observed. 31P{1H} NMR (121 MHz,
C6D6, r.t.): d=À3.0 ppm (d, JRh-P =113 Hz, 2 P); elemental analysis
calcd (%) for C38H45O6P2Rh: C 59.85, H 5.95; found: C 59.55, H 5.97.
MS (MALDI-TOF): m/z: 762 [M+], 663 [MÀacac]+.
General photophysical measurements: UV-visible absorption
spectra were obtained on an Agilent 1100 Series Diode Array spec-
trophotometer using standard 1 cm path length quartz cells. Emis-
sion spectra were recorded on an Edinburgh Instruments FLSP920
spectrometer, equipped with a 450 W Xenon arc lamp, double
monochromators for the excitation and emission pathways, and
a red-sensitive photomultiplier tube (R928-P PMT) as the detector.
All spectra were fully corrected for the spectral response of the in-
strument. Unless otherwise mentioned, the longest-wavelength ab-
sorption maximum of the compound in the respective solvent was
chosen as the excitation wavelength for the solution-state emis-
sion spectra. The emission spectra are independent of the excita-
tion wavelength, and the absorption and excitation spectra are
comparable across the measured range. All solutions used in pho-
tophysical measurements had a concentration lower than 6”
10À6 m to minimize inner filter effects during photoluminescence
measurements. Films of poly(methylmethacrylate) (PMMA) were
produced by drop-casting from chloroform solutions with a concen-
tration of 0.1 wt%.
1
6b: Red solid. Isolated yield: 0.06 g (16%); H NMR (300 MHz, C6D6,
r.t.): d=7.60 (d, J=8 Hz, 4H, CHarom), 7.05 (br. s, 4H, CHarom), 5.15 (s,
1H, CH), 2.74 (m, 4H, CH2), 2.19 (m, 2H, CH2), 1.96 (s, 6H, CH3), 1.92
(s, 6H, CH3), 1.03 ppm (vt, JP-H =3 Hz, 18H, PMe3); 13C{1H} NMR
(126 MHz, C6D6, r.t.): d=186.3, 165.9, 136.8, 131.0, 126.4, 124.0,
107.0, 98.5, 94.9, 30.1, 29.9, 28.2, 15.0, 10.7 ppm (vt, JC-P =14 Hz);
1
2
due to the low intensity, the JRh-C and JP-C coupling could not be
determined. 31P{1H} NMR (121 MHz, C6D6, r.t.): d=À1.14 ppm (d, JRh-
P =114 Hz, 2 P); elemental analysis calcd (%) for C36H45O2P2RhS2: C
58.53, H 6.14, S 8.68; found: C 58.92, H 6.19, S 8.23. MS (MALDI-
TOF): m/z: 738 [M+].
1
11: Red solid. Isolated yield: 0.19 g (21%); H NMR (300 MHz, C6D6,
r.t.): d=8.11 (d, J=8 Hz, 2H, CHarom.), 7.72 (d, J=8 Hz, 2H, CHarom.),
7.67 (d, J=8 Hz, 2H, CHarom.), 6.52 (d, J=8 Hz, 2H, CHarom.), 5.16 (s,
1H, acac-CH), 3.47 (s, 3H, CH3), 2.75 (m, 4H, CH2), 2.42 (s, 6H, CH3),
2.20 (m, 2H, CH2), 2.20 (s, 3H, CH3), 1.93 (s, 3H, CH3), 1.03 ppm (vt,
J
Rh-P =3 Hz, 18H, 2 PMe3); 13C{1H} NMR (126 MHz, C6D6, r.t.): d=
186.7, 186.6, 168.6, 166.6, 164.1 (dt, 1JRh-C =11 Hz, 2JP-C =31 Hz),
149.5, 132.6, 132.3, 130.7, 129.9, 128.4, 127.7, 115.4, 112.6, 110.1,
106.6, 99.6, 98.9, 92.4, 51.4, 39.9, 30.6, 30.4, 30.3, 30.1, 28.6, 28.5,
Fluorescence quantum yield measurements: The emission quan-
tum yields were measured using a calibrated integrating sphere
from Edinburgh Instruments combined with the FLSP920 spec-
trometer described above.[25]
1
2
11.1 ppm (vt, JC-P =14 Hz); due to the low intensity, JRh-C and JP-C
coupling could not be determined. 31P{1H} NMR (121 MHz, C6D6,
r.t.): d=À1.18 ppm (d, JRh-P =114 Hz, 2 P); elemental analysis calcd
(%) for C38H48NO4P2Rh: C 61.05, H 6.47, N 1.87; found: C 61.78, H
6.34, N 1.84. MS (MALDI-TOF): m/z: 747 [M+].
Lifetime measurements: The luminescence lifetimes were mea-
sured on the FLSP920 spectrometer using either a mF900 pulsed
60 W Xenon microsecond flashlamp, with a repetition rate of
100 Hz, and a multichannel scaling module, or with a picosecond
pulsed laser diode (lex =420 or 376 nm) and a time-correlated
single-photon counting (TCSPC) unit. The emission was collected
at right angles to the excitation source with the emission wave-
length selected using a double grated monochromator and detect-
ed by a R928-P PMT. Very short lifetimes for compounds 6a, 6b,
and 11 were recorded using an Edinburgh Instruments FLS980
spectrometer equipped with a high speed photomultiplier tube
positioned after a single emission monochromator. Data were col-
In order to determine an accurate isomer ratio, NMR experiments
were conducted. One equivalent of 1 and one equivalent of the
corresponding bis(diyne) were dissolved in toluene (20 mL) and
1
the reaction mixture was stirred at room temperature. For H and
31P{1H} NMR, 0.6 mL of the reaction solution was transferred to
a Young’s NMR tube and the solvent was removed in vacuo, then
C6D6 (0.6 mL) was added. Isomer ratios of 1:2.6 for compounds 3a
and 4a, 1:0.3 for 3b, 4b; 1:20 for 6a, 7a and 6b, 7b were ob-
served. The same procedure was performed for the reaction at
Chem. Eur. J. 2016, 22, 10523 – 10532
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10530
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
145–153; k) A. Hagfeldt, M. Grätzel, Acc. Chem. Res. 2000, 33, 269–277;
l) K. Kalyanasundaram, M. Grätzel, Coord. Chem. Rev. 1998, 177, 347–
414.
lected to 10000 counts in the peak channel and were fitted over
>1000 channels. The instrument response function (IRF) was mea-
sured using a scattering sample (LUDOX) and setting the emission
monochromator at the wavelength of the excitation beam. The re-
sulting intensity decay is a convolution of the luminescence decay
with the IRF, and iterative reconvolution of the IRF with one or two
decay function(s) and non-linear least squares analysis was used to
analyze the convoluted data. A bi-exponential decay fit was
chosen only when the fit was significantly better than with a single
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Acknowledgements
We thank the DFG for support. A.S. thanks the DAAD and the
EU (Marie-Curie FP7), M.-H.T. thanks the FQRNT Quebec,
Canada, and R.M.E. and A.L. thank the Alexander von Hum-
boldt Foundation for postdoctoral fellowships. M.G.T. thanks
Universiti Malaysia Sarawak, Malaysia, for a Ph.D. scholarship.
Part of this work was conducted within the scope of the CNRS
Associated European Laboratory “Molecular Materials and Cat-
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Durham University and the Institut des Sciences Chimiques de
Rennes of the University of Rennes 1, and within the Collabora-
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Received: April 24, 2016
Published online on June 29, 2016
Chem. Eur. J. 2016, 22, 10523 – 10532
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10532
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim