Synthesis, photophysical characterization and DFT studies on fluorine-free deep-blue emitting Pt(II) complexes

Article abstract of DOI:10.1515/znb-2015-0229

Herein we show that cyclometalated, square planar Pt(II) complexes can be tuned to achieve deepblue phosphorescent emitters. For this purpose, the introduction of an electron-donating moiety on two different bidentate NN and NO fluorine-free luminophores,

Full text of DOI:10.1515/znb-2015-0229

Z. Naturforsch. 2016; 71(5)b: 463–473
Jan Sanning, Linda Stegemann, Marvin Nyenhuis, Constantin G. Daniliuc, Nikos L. Doltsinis
aSnyd CnritsthianeAs. iSstra,ssperht*otophysical characterization and
DFT studies on fluorine-free deep-blue emitting
Pt(II) complexes
DOI 10.1515/znb-2015-0229
Received December 21, 2015; accepted January 10, 2016
1 Introduction
Abstract: Herein we show that cyclometalated, square Triplet emitters have found application as dopants in
planar Pt(II) complexes can be tuned to achieve deep- optoelectronic devices, such as organic light-emitting
blue phosphorescent emitters. For this purpose, the diodes [1–3] (OLEDs) and light-emitting electrochemical
introduction of an electron-donating moiety on two dif- cells (LEECs) [4–10]. Besides Ir(III) [11–13], Rh(III) [14],
ferent bidentate NˆN and NˆO fluorine-free luminophores, Re(I) [15] and Cu(I) [16–20] complexes, coordination com-
namely 2-(1H-tetrazol-5-yl)pyridine and picolinic acid, pounds featuring Pt(II) [21–34] and Au(III) [35–40] cations
was carried out. The remaining two coordination sites of have been described. The latter possess a d8 electronic
the Pt(II) metal center were filled by a sterically demand- configuration and mostly a square-planar coordination
ing cyclometallating unit, namely a tertiary phosphite environment. Bidentate [41–52], tridentate [53–55] as well
CˆP ligand. This ancillary ligand avoids aggregation and as tetradentate [56–60] ligands have been employed,
provides high solubility in organic solvents. Based on this yielding highly luminescent coordination compounds. We
approach, we were able to blue-shift the emission of the have recently shown, that the frontier molecular orbitals
complexes down to 411 nm, and to achieve a maximal of neutral Pt(II) complexes bearing dianionic tridentate
photoluminescence quantum yield of 56% in the solid NˆNˆN ligands can be correlated with occupied and unoc-
state.
cupied states measured by a combination of scanning
tunneling microscopy (STM) and spectroscopy (STS) tech-
niques, and that they can also be independently tuned
by introducing electron donating and withdrawing moie-
ties. We found that the highest occupied molecular orbital
(HOMO) appears mainly associated with the triazolate
unit of the chelating luminophore, whereas the lowest
unoccupied molecular orbital (LUMO) is predominately
linked to the central pyridine ring. This behavior also cor-
relates with the photophysical properties, which showed
a structured emission band indicating metal-perturbed
ligand-centered triplet states (3MP-LC) [61–63]. However,
the search for stable, deep-blue emitting species with high
photoluminescence quantum yields (ΦL) is still a subject
of intensive research [50]. In order to achieve strongly
luminescent, blue emitting compounds, good S donors
with large ligand field splittings are required to destabilize
the otherwise thermally accessible, non-radiative metal-
centered states.
Keywords: deep-blue; density functional theory; phosphite;
photophysics; platinum.
Dedicated to: Professor Wolfgang Jeitschko on the occasion of his
80th birthday.
*Corresponding author: Cristian A. Strassert, Physikalisches
Institut and Center for Nanotechnology, Westfälische Wilhelms-
Universität Münster, Heisenbergstraße 11, D-48149 Münster,
Germany, e-mail: ca.s@wwu.de
Jan Sanning and Linda Stegemann: Physikalisches Institut and
Center for Nanotechnology, Westfälische Wilhelms-Universität
Münster, Heisenbergstraße 11, D-48149 Münster, Germany
Marvin Nyenhuis and Nikos L. Doltsinis: Institut für
Festkörpertheorie and Center for Multiscale Theory and
Computation, Westfälische Wilhelms-Universität Münster, Wilhelm-
Klemm-Straße 10, D-48149 Münster, Germany
Mydlak et al. have shown an interesting concept in
which tris(2,4-di-tert-butylphenyl) phosphite acted as a
bidentate ancillary ligand precursor, and either a NˆN pyr-
dine-triazole/pyrazole or a phenoxy-benzo(thi/ox)azole-
based chelators acted as the luminophoric unit (Fig. 1) [51].
Constantin G. Daniliuc: Organisch-Chemisches Institut,
Westfälische Wilhelms-Universität Münster, Corrensstraße 40,
D-48149 Münster, Germany
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢀꢀꢀꢁ
464ꢀ ꢀJ. Sanning et al.: Synthesis, photophysical characterization and DFT studies
The enhanced ligand field splitting provided by the ancil- can cause a fast radiationless deactivation to the ground
lary ligand, which coordinates to the metal ion with one state. In the case of blue triplet emitters with high-energy
electron-poor phosphorus on the one hand and a cyclo- excited states, thermally accessible metal-centered (MC)
metalating carbon atom on the other hand, yielded a set of states efficiently funnel the energy to the ground state by
emissive compounds with relatively high ΦL in poly(methyl vibronic coupling at conical intersections [64, 65], due to
metacrylate) films (PMMA) (λ ꢀ=ꢀ 444 nm, ΦL ꢀ=ꢀ 0.38). If com- the dissociative character associated with the population
pared with tridentate luminophores, bidentate ligands of unoccupied dx2–y2 orbitals overlapping with the ligands.
generally show a smaller π-conjugated system offering
Herein we present a straightforward strategy towards
a wider HOMO-LUMO gap that enables the fabrication square-planar Pt(II) complexes (C1–C4) which carry a
of deep-blue emitting species. However, deviation from bulky ancillary unit based on the ligand precursor tris(2,4-
the preferred square-planar geometry in the excited state di-tert-butylphenyl) phosphite (Lanc) and either picolinic
acid (L1), 4-methoxypicolinic acid (L2), 2-(1H-tetrazol-5-yl)
pyridine (L3) or 5-(3-methoxyphenyl)-1H-tetrazole (L4) as
luminophoric ligand precursors (Scheme 1). Lanc offers a
good solubility in a variety of organic solvents as the steri-
cal demand of the two remaining phenoxy moieties avoids
O
2
O
2
intermolecular aggregation and suppresses quenching
P
N
N
P
N
N
O
O
Pt
Pt
pathways. Cyclometallation provides a strong σ-donating
character, and the phosphite unit contributes with a strong
π-accepting capacity, which both enhance the ligand field
splitting as required to suppress the thermal population of
metal-centered excited states. The emission properties of
the complexes were tuned on the luminophore: To blue-
shift the luminescence by enhancing the gap between
N
N
N
CF3
Fig. 1:ꢀSelected structures of the Pt(II) complexes from Mydlak
et al. [51].
O
O
O
N
P Pt
C
N
P Pt
C
O
O
C
P
C
=
O
C1
C2
X
Pt precursor, NaOMe
N
P
DCM-MeOH, 50°C, 12 h
O
O
L1−L4
N
N
2
N
P Pt
C
N
P Pt
C
N
N
N
N
N
N
C3
C4
Ligand precursors
Pt precursor
O
O
O
N
N
OH
OH
O
2
L1
L2
=
P
X
N
Cl
Cl
O
Pt
Pt
O
O
L1−L4
P
O
N
N
N
N
N
N
HN
HN
N
N
2
L3
L4
Scheme 1:ꢀSynthetic route towards complexes C1–C4.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢁꢀꢀꢀ
J. Sanning et al.: Synthesis, photophysical characterization and DFT studiesꢂ
ꢂ465
the frontier orbitals, two strategies were pursued. On the
one hand, the introduction of a π electron-donating OCH3
2.2 Molecular structures in the crystal
substituent on the central pyridine should destabilize the To verify the structure of the two classes of complexes,
LUMO of the corresponding complex (C1 vs. C2, C3 vs. C4). the coordination geometries were studied by X-ray dif-
On the other hand, substituting the five-membered tetra- fraction. C2 and C3 were dissolved in dichloromethane-
zole ring of the chromphoric ligand by an electron-poor methanol (1:1) and the solvent was slowly evaporated
and less delocalized carboxylic group (C3 vs. C1, C4 vs. at –18°C, yielding crystals suitable for X-ray diffracto-
C2) should stabilize the HOMO and further shift the emis- metric analysis. The relevant crystal data can be found
sion to shorter wavelengths, while keeping the basicity of in Table 1. Figures 2 and 3 clearly indicate that the nitro-
the anionic coordination site unaffected.
gen atom of the pyridine from the luminophore [N1 (C2)
or N5 (C3)] is coordinated trans to the cyclometallating
carbon (C36) of the ancillary ligand, whereas the anionic
moiety of the luminophore [O4 (C2); N1 (C3)] is coordi-
nated trans to the phosphorus of the ancillary ligand (P1).
The bite angle of the bidentate luminophoric and ancil-
lary ligands cause a distorted square-planar coordina-
tion geometry for the structures of both complexes [C2:
2 Results and discussion
2.1 Synthesis and characterization
The ligand precursors L1, L2 and L3 are commercially O4–Pt1–N1 78.8(1)°, C36–Pt1–P1 80.7(1)°; C3: N1–Pt1–N5
available; the synthesis of L4 and of the intermedi- 77.6(2)°, C36–Pt1–P1 81.2(2)°]. The Pt–C bond lengths [C2:
ate E1 were carried out by adapting known procedures 2.003(4) Å; C3: 2.015(7) Å] are significantly shorter than
(Schemes 1 and 2) [66–68]. Compound L4 was prepared the Pt–N bonds [C2: 2.102(3) Å; C3: 2.134(6) Å], indicat-
by heating 4-methoxypyridine-2-carbonitrile and sodium ing a strong trans effect of the cyclometallating, in-plane
azide in a mixture of n-butyl alcohol and acetic acid. After coordinated phenyl ring due to its strong σ donor char-
addition of water, the product precipitated as a white acter. The same is valid for the second pair of coordina-
powder and no further purification was necessary.
tive bonds trans to each other. The carboxylic acid oxygen
The binuclear Pt(II) complex E1 was synthesized atom as well as the nitrogen atom of the tetrazole are
by refluxing tris(2,4-di-tert-butylphenyl) phosphite and much closer to the metallic center [C2: 2.070(3) Å; C3:
potassium tetrachloroplatinate (II) in 2-methoxyethanol, 2.084(6) Å] than the phosphorus atom [C2: 2.142(1) Å; C3:
followed by a two-step purification procedure. Compound 2.165(2) Å]. The observed metal-ligand bonds and angles
E1 is a mixture of cis and trans isomers (only the trans are in good agreement with those described for related
isomer is shown in Scheme 2 for clarity). The general syn- complexes [51].
thesis of the complexes C1–C4 is described in Scheme 1.
The corresponding chromophoric ligand precursors L1–
L4 were reacted overnight with the binuclear complex 2.3 Photophysical characterization
E1 at 50°C in a 1:1 mixture of dichloromethane (DCM) and
methanol. The crude product was then purified by column The absorption spectra of C1–C4 are shown in Fig. 4. Each
chromatography on silica gel with dichloromethane- complex shows two absorption bands, one centered at
methanol as eluent to give the desired pure compound.
225 nm and another band in the range between 320 and
Scheme 2:ꢀPreparation of the binuclear Pt(II) complex E1.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢀꢀꢀꢁ
466ꢀ ꢀJ. Sanning et al.: Synthesis, photophysical characterization and DFT studies
Table 1:ꢀCrystal structure data for C2 and C3.
ꢁ
C2
ꢁ C3
Formula
ꢃ
C49H68NO6PPt · 2 CH3OHꢃ C48H66N5O3PPt
Formula weight Mr ꢃ 1057.19
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
987.12
Crystal size, mm3
Temperature, K
Wavelength/λ, Å
Crystal system
Space group
a, Å
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
0.22 ꢃ×ꢃ 0.16 ꢃ×ꢃ 0.10
223(2)
MoKα/0.71073
monoclinic
P21/n
12.8655(1)
25.1730(3)
16.4476(2)
90
92.542(1)
90
5321.5(1)
4
1.32
2.7
2184
35383
10436/0.044
16, –29:31, 20
0.15 ꢃ×ꢃ 0.15 ꢃ×ꢃ 0.04
223(2)
MoK /0.71073
tricliαnic
̅
P1
13.3179(2)
15.2625(2)
15.2754(2)
65.387(1)
69.850(1)
75.049(1)
2626.1(1)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
Volume, Å3
Z
D
calcd., g cm−3
1.25
2.7
1012
24211
μ(MoKα), mm−1
F(000), e
Refl. collected
Refl. unique/Rint
hkl range
R1 / wR2 [I ꢃ>ꢃ 2 σ(I)]ꢃ 0.0351/0.0739
R1/wR2 (all data) 0.0441/0.0793
Goodness of fit (F2) ꢃ 1.067
Δρmax/min, e Å−3
0.80/–0.72
9058/0.053
–14:15, –16:18, +18
0.0524/0.1213
0.0609/0.1266
1.038
Fig. 3:ꢀMolecular structure of compound C3 in the crystal. Displace-
ment ellipsoids are drawn at the 30% probability level, H atoms
were omitted for clarity.
ꢃ
ꢃ
0.85/–0.95
C1
C2
9000
40000
20000
0
C3
C4
6000
3000
0
300
350
400
250
300
Wavelength (nm)
350
400
Fig. 4:ꢀAbsorption spectra of complexes C1–C4 in dichloromethane
at r. t.
350 nm. Additionally, all complexes show a shoulder
around 275 nm.
The bands at high energies and the shoulder at
275 nm can be attributed to ligand-centered (LC) π-π*
transitions of the phosphite ligand, whereas the band at
320–350 nm can be assigned to π-π* transitions arising
from the chromophoric ligand. The latter is significantly
red-shifted upon replacement of the carboxylic moiety
Fig. 2:ꢀMolecular structure of compound C2 in the crystal. Displace-
ment ellipsoids are drawn at the 30% probability level, H atoms
were omitted for clarity.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢁꢀꢀꢀ
J. Sanning et al.: Synthesis, photophysical characterization and DFT studiesꢂ
ꢂ467
by a tetrazole, as the size of the chromophoric system is substituent to C3 yielding C4, leads to the bluest emis-
increased. Notably, introduction of a OCH3 substituent sion of all complexes, with a maximum peaking at 411 nm.
on the chromophoric ligand does not significantly This shows again that the influence of the OCH3 groups is
change the absorption spectrum of C2 as compared to solely found in complexes with extended luminophores.
C1 which lets us assume that the OCH3 group does not On the other hand, the introduction of the OCH3 substitu-
significantly affect the frontier orbital gaps for the NˆO ent decreases ΦL, which can be related to the blue-shift
luminophore. In contrast, the absorption of C4 com- that brings the emissive state energetically closer to dark
pared to C3 is significantly blue shifted, which points to metal-centered states, which in turn become thermally
a shift in the HOMO-LUMO gap upon introduction of the more accessible.
OCH3 moiety.
All the complexes are weakly emissive in doped
Emission at room temperature in degassed dichlo- PMMA, as neat films and as powders, with the notable
romethane was not measureable for the complexes, point- exception of C3 which shows an impressively high ΦL in
ing towards fast radiationless deactivation processes the amorphous solid state (CIE coordinates: 0.196, 0.251;
such as coupling with solvent molecules or thermal popu- Fig. 6). It is clear that the luminophore needs to have a
lation of dark states. Emission spectra of C1–C4 in frozen significant delocalization, as provided by the tetrazolate
glassy matrices of dichloromethane-methanol (1:1) at 77 K unit, and that shorter emission wavelengths are associ-
are shown in Fig. 5 along with the calculated vibration- ated with highly energetic excited states that favor the
ally resolved emission spectra. In Table 2, the key pho- thermal population of dark metal-centered states.
tophysical properties of all complexes are shown. The
measured spectra show broad, unstructured emission
profiles, which can be attributed to excited states with 2.4 Density functional theory studies
charge-transfer character, whereas the microsecond-
range lifetimes are indicative of a clear 3MP-LC character. We have determined the character of the vertical
The emission band of C1, which possesses an electron- T1 → S0 transition by analyzing the eigenvector of the T1
poor carboxylate group on the small pyridine-based de-excitation at the TDDFT optimized T1 geometry. For
chromophoric ligand, appears blue-shifted as compared all complexes, the transition has an almost pure HOMO–
to that of C3 carrying a tetrazolate ring with extended LUMO character, with a weight of at least 81% in all cases,
delocalization. However, upon introduction of the OCH3 independently of the different ligands and their substitu-
substituent on C1 to yield C2, no significant shift is ent. Figure 7 also shows that the shape of the HOMO and
observed (Table 2). In contrast, introduction of the OCH3 LUMO orbitals is practically invariant for C1–C4.
Fig. 5:ꢀNormalized emission spectra at 77 K (solid line) and vibrationally resolved calculated emission spectra of complexes C1–C4 at 77 K
(dashed line).
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢀꢀꢀꢁ
468ꢀ ꢀJ. Sanning et al.: Synthesis, photophysical characterization and DFT studies
Table 2:ꢀPhotophysical data of C1–C4.
The HOMO is associated with the cyclometallating
phenyl group and the Pt(II) center, whereas the LUMO is
mainly related to the luminophoric ligand. These find-
ings are in agreement with the spectroscopically observed
charge-transfer character of the emissive state (vide supra),
which can now be confidently ascribed to an inter-ligand
charge-transfer excitation mixed with a metal-to-ligand
charge-transfer portion that explains the observed phos-
phorescence. Moreover, the calculations also show that the
HOMO energy is only marginally affected by the changes
on the luminophoric ligand, whereas the LUMO is destabi-
lized upon replacement of tetrazolate moieties by carboxy-
late donors and upon insertion of OCH3 groups, which in
turn widens the HOMO-LUMO gap. The calculated blue-
shift is larger for tetrazolate-bearing ligands, as already
observed in the absorption and emission spectra (vide
supra). Actually, no spectroscopic shift is experimentally
observed when OCH3 units are inserted on picolinate che-
lators, which points toward the fact that the emissive states
cannot be simply described as monoelectronic excitations,
even though the calculated trends are in good agreement
with the experimental results. Finally, the lack of vibra-
tional progression in the emission spectra at 77 K can be
ascribed to the frozen solvent matrix, as opposed to the
calculated spectra showing defined vibrational shoulders.
ꢁ
C1ꢁ
C2ꢁ
C3ꢁ
C4
λabs, nm
ꢃ
ꢃ
227, 323ꢃ
427ꢃ
226, 321ꢃ
427ꢃ
226, 353ꢃ
441ꢃ
227, 335
411
λem, 77K, nm
a
τ77K 0.5, μs ꢃ
15.2ꢃ
15.1ꢃ
13.1ꢃ
11.8
ΦL,neat 0.02
ꢃ
ꢃ<ꢃ0.01ꢃ
ꢃ<ꢃ0.01ꢃ
0.03ꢃ
ꢃ<ꢃ0.01ꢃ
ꢃ<ꢃ0.01ꢃ
ꢃ<ꢃ0.01ꢃ
0.04ꢃ
0.01
ΦL,PMMA 0.02 ꢃ
ΦL,powder 0.02ꢃ
0.10ꢃ
0.03
0.56ꢃ
0.03
aIntensity-weighted average lifetimes.
Fig. 6:ꢀNormalized emission spectrum of compound C3 (powder, at
room temperature).
Complex
1
2
3
4
–2.66 eV
–2.44 eV
–2.61 eV
–2.32 eV
LUMO
∆(LUMO-
HOMO)
2.88 eV
3.04 eV
3.03 eV
3.26 eV
HOMO
–5.54 eV
–5.48 eV
–5.64 eV
–5.58 eV
Fig. 7:ꢀVisualization of the calculated HOMO and LUMO orbitals of complexes C1–C4 together with the respective orbital energies and
HOMO-LUMO gaps.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢁꢀꢀꢀ
J. Sanning et al.: Synthesis, photophysical characterization and DFT studiesꢂ
ꢂ469
NMR chemical shifts are referenced to Na2PtCl6, whereas
3 Conclusion
31
the P NMR chemical shifts are referenced to phosphoric
We have reported the synthesis, structural and photo- acid as an external standard. The signal multiplicities are
physical characterization of Pt(II) complexes bearing flu- abbreviated as follows: s, singlet; d, doublet; t, triplet; q,
orine-free bidentate luminophores and cyclometallating quartet; m, multiplet. All coupling constants (J) are given
ancillary ligands. The complexes exhibit deep-blue phos- in Hertz. High resolution mass spectrometry (HRMS) was
3
phorescence, which can be assigned to mixed LC/3MLCT performed via electrospray ionization (ESI) on a Bruker
states. We found that the electronic molecular set-screws Daltonics MicroTof spectrometer with loop injection.
that enable the tuning of the excited state energies are
located on different submolecular units: Variations in the
substitution pattern of the luminophoric ligand mainly 4.2 Synthesis of 4-methoxy-2-(1H-tetrazol-
affect the LUMO, whereas the HOMO could be further
adjusted if the ancillary ligand is varied. For instance,
5-yl)pyridine (L4)
introduction of electron withdrawing moieties could sta- 4-Methoxypicolinonitrile (776 mg, 5.79 mmol) and NaN3
bilize the HOMO, shifting the emission into the near UV. (526 mg, 8.11 mmol) were suspended in n-butanol (14 mL)
However, further blue-shifts would be associated with fast and acetic acid (1.37 mL, 23.15 mmol) was added drop-
radiationless deactivation processes that diminish the wise. The mixture was stirred for 2 h at 80°C. After the
quantum yields, due to thermal population of dark metal- mixture had cooled down, the same amount of acetic acid
centered states. Our findings provide useful criteria for was added, followed by stirring at 80°C overnight. After
the design and realization of fluorine-free phosphorescent cooling down, water was added and a white precipitate
dopants for electroluminescent devices with improved was formed, which was filtered off, washed with water and
stability, and could also be relevant for photocatalysis and dried. The compound was again dissolved in ethyl acetate
light-harvesting units in general.
and absorbed onto silica gel by removing the solvent under
reduced pressure. This was loaded onto a column packed
with silica gel to perform a column chromatography sepa-
ration with hexane-ethyl acetate as eluent to get the pure
4 Experimental section
1
compound L4 as a white solid (748 mg, 73%). – H NMR
(400 MHz, [D6]DMSO6): δ ꢀ=ꢀ 8.59 (d, J ꢀ=ꢀ 5.8 Hz, 1H), 7.73 (d,
J ꢀ=ꢀ 1.8 Hz, 1H), 7.21 (dd, J ꢀ=ꢀ 5.9, 1.6 Hz, 1H), 3.96 (s, 3H).
– 13C NMR (101 MHz, [D6]DMSO): δ ꢀ=ꢀ 166.58, 154.79, 151.08,
4.1 Synthesis and characterization
As starting materials tris(2,4-di-tert-butylphenyl) phos- 145.21, 112.21, 108.42, 55.99. – HRMS ((+)-ESI; MeOH):
+
phite (98%; Sigma-Aldrich, Munich, Germany), K2PtCl4 m/z ꢀ=ꢀ 178.07185 (calcd. 178.07234 for C7H8N5O, [M+H] ),
+
(99.95%; ChemPur, Karlsruhe, Germany), and 4-meth- 201.05717 (calcd. 201.05644 for C7H7N5ONa, [M+Na] ).
oxypyridine-2-carbonitrile (98%; abcr, Karlsruhe,
Germany) were used as received. The luminophoric
ligand precursors L1 (2-picolinic acid, 99%; Sigma- 4.3 Synthesis of [{Pt-(μ-Cl){κ2-P,C-P(OC6H2-
2,4-tBu2)(OC6H3-2,4-tBu2)2}}2] (E1)
Aldrich, Munich, Germany), L2 (4-methoxy-pyridine-
2-carboxylic acid Sigma-Aldrich, Munich, Germany) and
L3 (5-(2-pyridyl)-1H-tetrazole, 98%; Alfa Aesar, Karlsruhe, Tris(2,4-di-tert-butylphenyl) phosphite (934 mg, 1.44
Germany), were commercially available. Column chroma- mmol) and K2PtCl4 (600 mg, 1.44 mmol) were combined
tography was performed with silica gel 60 (particle size in 2-methoxyethanol (48 mL) and heated to 140°C under
35–70 μm, 230–400 mesh, Merck). NMR and mass spectra nitrogen overnight. The clear solution was cooled to room
were measured at the Department of Organic Chemistry, temperature and the solvent was removed under reduced
University of Münster. NMR spectra were recorded on pressure. The off-white residue was dissolved in dichlo-
an Avance 400 Spectrometer from Bruker Analytische romethane and filtered through a pad of celite. The filtered
Messtechnik (Karlsruhe, Germany) for ligand precur- solution was then concentrated under reduced pressure
sor L4 and on an DD2 600 spectrometer from Agilent for and the product was precipitated from dichlorometh-
1
the Pt(II) complexes. The H NMR chemical shifts (δ) of ane with ethanol to yield a white solid. The supernatant
the signals are given in parts per million (ppm) and ref- was removed and the solid dried under vacuum (1.27 g
erenced to residual protons in the deuterated solvents 50%). – HRMS ((+)-ESI; MeOH): m/z ꢀ=ꢀ 1791.72042 (calcd.
+
[D6]DMSO (2.50 ppm) and [D2]DCM (5.32 ppm). The 195Pt 1791.72005 for C84H126Cl2KO6P2Pt2, [M+K] ).
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢀꢀꢀꢁ
470ꢀ ꢀJ. Sanning et al.: Synthesis, photophysical characterization and DFT studies
(td, J ꢀ=ꢀ 7.8, 1.5 Hz, 1H), 7.64 (dd, J ꢀ=ꢀ 8.6, 1.7 Hz, 2H), 7.43–
7.40 (m, 2H), 7.39 (ddd, J ꢀ=ꢀ 7.1, 5.6, 1.4 Hz, 1H), 7.19 (t, J ꢀ=ꢀ 2.1
Hz, 1H), 7.02 (dd, J ꢀ=ꢀ 8.6, 2.5 Hz, 2H), 1.55 (s, 18H), 1.46 (d,
4.4 General synthetic procedure for the
preparation of complexes C1–C4
The corresponding ligand precursors L1–L4 (0.228 mmol) J ꢀ=ꢀ 0.5 Hz, 9H), 1.22 (d, J ꢀ=ꢀ 0.6 Hz, 19H), 1.12 (s, 9H). – 31P
and NaOMe (0.228 mmol) were dissolved in dichlorometh- NMR (243 MHz, [D2]DCM): δ ꢀ=ꢀ 96.88 (d, J ꢀ=ꢀ 6581.5 Hz). –
ane-methanol (1:1, 25 mL) and stirred for 30 min. Next, 195Pt NMR (128 MHz, [D2]DCM): δ ꢀ=ꢀ –4270.80 (d, J ꢀ=ꢀ 6570.1
the reaction mixture was degassed intensely before the Pt Hz). – HRMS ((+)-ESI; MeOH): m/z ꢀ=ꢀ 987.46676 (calcd.
+
precursor E1 (0.114 mmol) was added. After the reaction 987.46275 for C48H67N5O3PPt, [M+H] ), 1009.44891 (calcd.
+
mixture was stirred at 50°C for 12 h in a nitrogen atmos- 1009.44470 for C48H66N5O3PPtNa, [M+Na] ).
phere, it was cooled down. A small amount of silica gel
was added into the reaction vessel and the crude product
was absorbed onto silica gel by removing the solvent under
4.4.4 C4
reduced pressure. This was loaded onto a column packed
with silica gel, and a column chromatographic separation
was performed using dichloromethane-methanol as the
1H), 8.73 (d, J ꢀ=ꢀ 6.4 Hz, 1H), 7.82 (d, J ꢀ=ꢀ 2.8 Hz, 1H), 7.64
eluent to give the final product C1–C4 as white solid.
(dd, J ꢀ=ꢀ 8.6, 1.8 Hz, 2H), 7.41 (dd, J ꢀ=ꢀ 2.4, 1.3 Hz, 2H), 7.17
1
Yield: 28%. – H NMR (600 MHz, [D2]DCM): δ ꢀ=ꢀ 9.01 (t,
(t, J ꢀ=ꢀ 2.2 Hz, 1H), 7.02 (dd, J ꢀ=ꢀ 8.6, 2.5 Hz, 2H), 6.83 (dd,
J ꢀ=ꢀ 6.5, 2.9 Hz, 1H), 4.00 (s, 3H), 1.54 (s, 18H), 1.46 (s,
4.4.1 C1
31
9H), 1.22 (s, 18H), 1.12 (s, 9H). – P NMR (243 MHz, [D2]
DCM): δ ꢀ=ꢀ 97.02 (d, J ꢀ=ꢀ 6600.3 Hz). – 195Pt NMR (128
1
Yield: 31%. – H NMR (600 MHz, [D2]DCM): δ ꢀ=ꢀ 8.68 (d,
MHz, [D2]DCM): δ ꢀ=ꢀ –4278.58 (d, J ꢀ=ꢀ 6607.6 Hz). – HRMS
J ꢀ=ꢀ 5.3 Hz, 1H), 8.16–8.12 (m, 1H), 8.07 (td, J ꢀ=ꢀ 7.7, 1.5 Hz,
((+)-ESI; MeOH): m/z ꢀ=ꢀ 1017.47675 (calcd. 1017.47333 for
1H), 7.77 (t, J ꢀ=ꢀ 2.3 Hz, 1H), 7.60 (dd, J ꢀ=ꢀ 8.6, 1.6 Hz, 2H),
+
C49H69N5O4PPt, [M+H] ), 1039.45838 (calcd. 1039.45527 for
7.48 (ddd, J ꢀ=ꢀ 7.5, 5.4, 1.5 Hz, 1H), 7.44–7.39 (m, 2H), 7.14 (t,
+
C49H68N5O4PPtNa, [M+Na] ).
J ꢀ=ꢀ 2.2 Hz, 1H), 7.04 (dd, J ꢀ=ꢀ 8.6, 2.5 Hz, 2H), 1.53 (s, 18H),
1.39 (s, 9H), 1.23 (s, 18H), 1.11 (s, 9H). – 31P NMR (243 MHz,
[D2]DCM): δ ꢀ=ꢀ 90.24 (d, J ꢀ=ꢀ 6926.8 Hz). – 195Pt NMR (128
MHz, [D2]DCM): δ ꢀ=ꢀ –4152.40 (d, J ꢀ=ꢀ 6937.4 Hz). – HRMS 4.5 X-ray diffractometry
((+)-ESI; MeOH): m/z ꢀ=ꢀ 963.44227 (calcd. 963.44034 for
+
C48H67NO5PPt, [M+H] ), 985.42408 (calcd. 985.42228 for The crystallographic data of C2 and C3 (Table 1) were col-
+
C48H66NO5PPtNa, [M+Na] ).
lected on a rotating anode Nonius κ-CCD diffractometer
with Montel mirror-monochromatized MoKα radiation (λ ꢀ=ꢀ
0.71073 Å) by using an ω-ϕ scan method at 223(2) K. Pro-
grams used: data collection Collect [69]; data reduction
Denzo-smn [70]; absorption corrections were applied
4.4.2 C2
Yield: 35%. – 1H NMR (600 MHz, [D2]DCM): δ ꢀ=ꢀ 8.45 (d, J ꢀ=ꢀ using multi-scan techniques, Denzo [71]; the structures
6.3 Hz, 1H), 7.77 (t, J ꢀ=ꢀ 2.1 Hz, 1H), 7.65 (d, J ꢀ=ꢀ 2.9 Hz, 1H), 7.61 were solved by Direct Methods and refined by full-matrix
(dd, J ꢀ=ꢀ 8.6, 1.3 Hz, 2H), 7.42 (s, 2H), 7.14 (t, J ꢀ=ꢀ 2.0 Hz, 1H), least-squares techniques using the program Shelxl-97
7.06 (dd, J ꢀ=ꢀ 8.6, 2.4 Hz, 2H), 6.93 (dd, J ꢀ=ꢀ 6.2, 2.9 Hz, 1H), [72]; graphics were done with Xp [73]. The non-hydrogen
3.96 (s, 3H), 1.54 (s, 18H), 1.40 (s, 9H), 1.25 (s, 18H), 1.12 (s, atoms of the compounds were refined anisotropically. The
9H). – 31P NMR (243 MHz, [D2]DCM): δ ꢀ=ꢀ 90.16 (d, J ꢀ=ꢀ 6963.3 hydrogen atoms attached to carbon atoms were generated
Hz). – 195Pt NMR (128 MHz, [D2]DCM): δ ꢀ=ꢀ –4167.59 (d, J ꢀ=ꢀ geometrically.
6973.4 Hz). – HRMS ((+)-ESI; MeOH): m/z ꢀ=ꢀ 993.45150
Exceptions and special features: Compound C2 con-
+
(calcd. 993.45091 for C49H69NO6PPt, [M+H] ), 1015.43322 tains in the asymmetric unit tree tert-butyl groups and
+
(calcd. 1015.4330 for C49H68NO5PPtNa, [M+Na] ).
two methanol molecules disordered over two positions.
For compound C3 four tert-butyl groups were found to be
disordered over two positions. Several restraints (SADI,
SAME, ISOR and SIMU) were used in order to improve
refinement stability. A badly disordered (probably) meth-
4.4.3 C3
Yield: 29%. – 1H NMR (600 MHz, [D2]DCM): δ ꢀ=ꢀ 9.03 (t, J ꢀ=ꢀ anol molecule was found in the asymmetrical unit and
1.8 Hz, 1H), 8.99 (d, J ꢀ=ꢀ 5.5 Hz, 1H), 8.36–8.32 (m, 1H), 8.11 could not be satisfactorily refined. The routine SQUEEZE
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢁꢀꢀꢀ
J. Sanning et al.: Synthesis, photophysical characterization and DFT studiesꢂ
ꢂ471
in Platon [74] was therefore used to remove mathemati-
cally the effect of the solvent. The quoted formula and
derived parameters do not include the squeezed solvent The DFT calculations were performed with the Gaussian
molecule. 09 package [75] using the PBE0 hybrid exchange-correla-
4.7 Density functional theory
CCDC 1435528 (C2) and 1435529 (C3) contain the sup- tion functional [76]. The SDD basis set [77] was employed
plementary crystallographic data for this paper. These for all elements with the exception of phosphorus, which
data can be obtained free of charge from the Cambridge was described by the 6-31G* basis set. Vibrationally
Crystallographic Data Centre via www.ccdc.cam.ac.uk/ resolved emission spectra at 77 K were calculated with
data_request/cif.
the Franck-Condon method [78]. For this purpose, the S0
ground state and T1 excited state geometries were opti-
mized using standard Kohn-Sham DFT with multiplic-
ity 0 and 1, respectively. To plot the emission spectrum,
each vibronic line was represented by a Gaussian with
4.6 Photophysical characterization
Absorption spectra were measured on a Varian Cary half width at half maximum of 300 cm−1. To determine the
5000 double-beam UV/Vis-NIR spectrometer and base- character of the T1 → S0 transition, TDDFT calculations
line-corrected. Steady-state excitation and emission were carried out at the TDDFT-optimized T1 geometry.
spectra were recorded on a FluoTime300 spectrometer The molecular orbitals at the T1 geometry were visualized
from PicoQuant equipped with a 300 W ozone-free Xe using the VMD program [79]
lamp (250–900 nm), a 10 W Xe flash lamp (250–900
nm, pulse width ꢀ<ꢀ 10 μs) with repetition rates of 0.1– Acknowledgments: J.S. wrote the original manuscript,
300 Hz, an excitation monochromator (Czerny-Turner synthesized and characterized the ligand precursors and
−1
2.7 nm mm dispersion, 1200 grooves mm−1, blazed at complexes; L.S. carried out the photophysical characteri-
300 nm), diode lasers (pulse width ꢀ<ꢀ 80 ps) operated zation of the complexes; C.G.D. performed the X-ray dif-
by a computer-controlled laser driver PDL-820 (repeti- fractometric analysis; M.N. and N.L.D. carried out the DFT
tion rate up to 80 MHz, burst mode for slow and weak calculations; C.A.S. conceived the experiments, discussed
decays), two emission monochromators (Czerny-Turner, the results and wrote the original manuscript. Financial
selectable gratings blazed at 500 nm with 2.7 nm mm1 support from the DFG (SFB-TRR 61, projects B13 and C07)
dispersion and 1200 grooves mm−1, or blazed at 1250 nm is gratefully acknowledged.
with 5.4 nm mm−1 dispersion and 600 grooves mm−1),
Glan-Thompson polarizers for excitation (Xe lamps) and
emission, a Peltier-thermostatized sample holder from
Quantum Northwest (–40 to 105°C), and two detectors,
References
namely a PMA Hybrid 40 (transit time spread FWHM ꢀ<ꢀ
120 ps, 300–720 nm). Steady-state and fluorescence life-
times were recorded in TCSPC mode by a PicoHarp 300
(minimum base resolution 4 ps). Emission and excitation
spectra were corrected for source intensity (lamp and
grating) by standard correction curves. Lifetime analysis
was performed using the commercial FluoFit software.
The quality of the fit was assessed by minimizing the
reduced chi squared function (χ2) and visual inspec-
tion of the weighted residuals and their autocorrelation.
Luminescence quantum yields were measured with a
Hamamatsu Photonics absolute PL quantum yield meas-
urement system (C9920-02) equipped with a L9799-01
CW Xenon light source (150 W), monochromator, C7473
photonic multi-channel analyzer, integrating sphere and
employing U6039-05 ΦL measurement software (Hama-
matsu Photonics, Ltd., Shizuoka, Japan). All solvents
used were of spectrometric grade.
[1] M. A. Baldo, D. O’Brien, Y. You, A. Shoustikov, S. Sibley,
M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151.
[2] K. Müllen, U. Scherf (Eds.), Organic Light-Emitting Devices,
Wiley-VCH, Weinheim, 2006.
[3] H. Yersin (Ed.), Highly Efficient OLEDs with Phosphorescent
Materials, Wiley-VCH, Weinheim, 2008.
[4] Q. Pei, G. Yu, C. Zhang, Y. Yang, A. J. Heeger, Science 1995, 269,
1086.
[5] J.-K. Lee, D. S. Yoo, E. S. Handy, M. F. Rubner, Appl. Phys. Lett.
1996, 69, 1686.
[6] J. C. de Mello, N. Tessler, S. C. Graham, X. Li, A. B. Holmes,
R. H. Friend, Synth. Met. 1997, 85, 1277.
[7] C. H. Lyons, E. D. Abbas, J. K. Lee, M. F. Rubner, J. Am. Chem.
Soc. 1998, 20, 12100.
[8] S. Welter, K. Brunner, J. W. Hofstraat, L. De Cola, Nature 2003,
421, 54.
[9] J. D. Slinker, J. A. De Franco, M. J. Jaquith, W. R. Silveira,
Y.-W. Zhong, J. M. Moran-Mirabal, H. G. Craighead, H. D. Abruna,
J. A. Marohn, G. G. Malliaras, Nat. Mater. 2007, 6, 894.
[10] M. Mydlak, C. Bizzarri, D. Hartmann, W. Sarfert, G. Schmid,
L. De Cola, Adv. Funct. Mater. 2010, 20, 1812.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢀꢀꢀꢁ
472ꢀ ꢀJ. Sanning et al.: Synthesis, photophysical characterization and DFT studies
[11] C. Adachi, M. A. Baldo, S. R. Forrest, M. E. Thompson, Appl.
Phys. Lett. 2000, 77, 904.
[41] M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah,
D. Lipa, R. J. Lachicotte, R. Eisenberg, Inorg. Chem. 2000, 39,
447.
[42] C. E. Whittle, J. A. Weinstein, M. W. George, K. S. Schanze,
Inorg. Chem. 2001, 40, 4053.
[43] F. Hua, S. Kinayyigit, J. R. Cable, F. N. Castellano, Inorg. Chem.
2005, 44, 471.
[44] F. Castellano, I. E. Pomestchenko, E. Shikhova, F. Hua,
M. L. Muro, N. Rajapakse, Coord. Chem. Rev. 2006, 250, 1819.
[45] F. Hua, S. Kinayyigit, J. R. Cable, F. N. Castellano, Inorg. Chem.
2006, 45, 4304.
[46] F. Hua, S. Kinayyigit, A. A. Rachford, E. R. Shikhova, S. Goeb,
J. R. Cable, C. J. Adams, K. Kirschbaum, A. A. Pinkerton,
F. N. Castellano, Inorg. Chem. 2007, 46, 8771.
[47] C. Bronner, S. Baudron, M. W. Hosseini, C. A. Strassert,
A. Guenet, L. De Cola, Dalton Trans. 2010, 39, 180.
[48] I. Stengel, C. A. Strassert, E. A. Plummer, C.-H. Chien,
L. De Cola, P. Bäuerle, Eur. J. Inorg. Chem. 2012, 1795.
[49] I. Stengel, C. A. Strassert, L. De Cola, P. Bäuerle,
Organometallics 2014, 33, 1345.
[12] L. Flamigni, A. Barbieri, C. Sabatini, B. Ventura, F. Barigelletti,
Top. Curr. Chem. 2007, 281, 143.
[13] C. Ulbricht, B. Beyer, C. Friebe, A. Winter, U. S. Schubert, Adv.
Mater. 2009, 21, 4418.
[14] A. Steffen, M. G. Tay, A. S. Batsanov, J. A. K. Howard, A. Beeby,
K. Q. Vuong, X.-Z. Sun, M. W. George, T. B. Marder, Angew.
Chem. Int. Ed. 2010, 49, 2349.
[15] M. Mauro, E. Q. Procopio, Y. Sun, C.-H. Chien, D. Donghi,
M. Panigati, P. Mercandelli, P. Mussini, G. D’Alfonso, L. De Cola,
Adv. Funct. Mater. 2009, 19, 2607.
[16] V. A. Krylova, P. I. Djurovich, M. T. Whited, M. E. Thompson,
Chem. Commun. 2010, 46, 6696.
[17] V. A. Krylova, P. I. Djurovich, J. W. Aronson, R. Haiges,
M. T. Whited, M. E. Thompson, Organometallics 2012, 31, 7983.
[18] H. Yersin, R. Czerwieniec, A. Hupfer, Proc. SPIE 2012, 8435,
843508.
[19] J. Nitsch, C. Kleeberg, R. Fröhlich, A. Steffen, Dalton Trans.
2015, 44, 6944.
[20] D. M. Zink, M. Bächle, T. Bauman, M. Nieger, M. Kühn, C. Wang,
W. Klopper, U. Monkowius, T. Hofbeck, H. Yersin, S. Bräse,
Inorg. Chem. 2013, 52, 2292.
[21] V. Adamovich, J. Brooks, A. Tamayo, A. M. Alexander,
P. I. Djurovich, B. W. D’Andrade, C. Adachi, S. R. Forrest,
M. E. Thompson, New J. Chem. 2002, 26, 1171.
[22] J. A. G. Williams, A. Beeby, E. S. Davies, J. A. Weinstein,
C. Wilson, Inorg. Chem. 2003, 42, 8609.
[23] W. Lu, B.-X. Mi, M. C. W. Chan, Z. Hui, C.-M. Che, N. Zhu,
S.-T. Lee, J. Am. Chem. Soc. 2004, 126, 4958.
[24] S.-W. Lai, C.-M. Che, Top. Curr. Chem. 2004, 24, 127.
[25] H.-F. Xiang, S.-C. Chan, K. K.-Y. Wu, C.-M. Che, P. T. Lai, Chem.
Commun. 2005, 1408.
[26] S. C. F. Kui, I. H. T. Sham, C. C. C. Cheung, C.-W. Ma, B. Yan,
N. Zhu, C.-M. Che, W.-F. Fu, Chem. Eur. J. 2007, 13, 417.
[27] A. F. Rausch, H. H. H. Homeier, H. Yersin, Top. Organomet.
Chem. 2010, 193.
[28] C.-M. Che, C.-C. Kwok, S.-W. Lai, A. F. Rausch, W. J. Finkenzeller,
N. Zhu, H. Yersin Chem. Eur. J. 2010, 16, 233.
[29] K. M.-C. Wong, V. W.-W. Yam, Acc. Chem. Res. 2011, 44, 424.
[30] A. Y.-Y. Tam, D. P.-K. Tsang, M.-Y. Chan, N. Zhu, V. W.-W. Yam,
Chem. Commun. 2011, 47, 3383.
[31] M. C.-L. Yeung, V. W.-W. Yam, Chem. Eur. J. 2011, 17, 11987.
[32] S. C. F. Kui, P. K. Chow, G. Cheng, C.-C. Kwok, C. L. Kwong,
K.-H. Low, C.-M. Che, Chem. Commun. 2013, 49, 1497.
[33] A. Tronnier, T. Strassner, Dalton Trans. 2013, 42, 9847.
[34] A. Jackel, M. Linseis, C. Häge, R. F. Winter, Inorganics 2015,
3, 55.
[35] V. K.-M. Au, K. M.-C. Wong, N. Zhu, V. W.-W. Yam, Chem. Eur. J.
2011, 17, 130.
[36] V. K.-M. Au, W. H. Lam, W.-T. Wong, V. W.-W. Yam, Inorg. Chem.
2012, 51, 7537.
[37] W.-P. To, G. S.-M. Tong, W. Lu, C. Ma, J. Liu, A. L.-F. Chow,
C.-M. Che, Angew. Chem. Int. Ed. 2012, 51, 2654.
[38] W. Lu, K.T. Chan, S.-X. Wu, Y. Chen, C.-M. Che, Chem. Sci. 2012,
3, 752.
[39] M.-C. Tang, D. P.-K. Tsang, M. M.-Y. Chan, K. M.-C. Wong,
V. W.-W. Yam, Angew. Chem. Int. Ed. 2013, 52, 446.
[40] W.-P. To, K. T. Chan, G. S. M. Tong, C. Ma, W.-M. Kwok, X. Guan,
K.-H. Low, C.-M. Che, Angew. Chem. Int. Ed. 2013,52, 6648.
[50] Y. Unger, D. Meyer, O. Molt, C. Schildknecht, I. Münster,
G. Wagenblast, T. Strassner, Angew. Chem. Int. Ed. 2010, 49,
10214.
[51] M. Mydlak, C.-H. Yang, F. Polo, A. Galstyan, C. G. Daniliuc,
M. Felicetti, J. Leonhardt, C. A. Strassert, L. De Cola, Chem. Eur.
J. 2015, 21, 5161.
[52] A. R. Naziruddin, A. Galstyan, A. Iordache, C. G. Daniliuc,
C. A. Strassert, L. De Cola, Dalton Trans 2015, 44, 8467.
[53] J. A. G. Williams, Top. Curr. Chem. 2007, 281, 205.
[54] L. Murphy, J. A. G. Williams, Top. Organomet. Chem. 2010,
28, 75.
[55] C. Bronner, M. Veiga, A. Guenet, L. De Cola, M. W. Hosseini,
C. A. Strassert, S. A. Baudron, Chem. Eur. J. 2012, 18, 4041.
[56] G. Cheng, P.-K. Chow, S. C. F. Kui, C.-C. Kwok, C.-M. Che, Adv.
Mater. 2013, 25, 6765.
[57] E. Turner, N. Bakken, J. Li, Inorg. Chem. 2013, 52, 7344.
[58] D. A. K. Vezzu, J. C. Deaton, J. S. Jones, L. Bartolotti, C. F. Harris,
A. P. Marchetti, M. Kondakova, R. D. Pike, S. Huo, Inorg. Chem.
2010, 49, 5107.
[59] X.-C. Hang, T. Fleetham, E. Turner, J. Brooks, J. Li, Angew.
Chem. Int. Ed. 2013, 52, 6753.
[60] P.-K. Chow, G. Cheng, G. S. M. Tong, W.-P. To, W.-L. Kwong,
K.-H. Low, C.-C. Kwok, C. Ma, C.-M. Che, Angew. Chem. Int. Ed.
2015, 54, 2084.
[61] P. Ewen, J. Sanning, N. L. Doltsinis, M. Mauro, C. A. Strassert,
D. Wegner, Phys. Rev. Lett. 2013, 111, 267401.
[62] P. Ewen, J. Sanning, T. Koch, N. L. Doltsinis, C. A. Strassert,
D. Wegner, Beilstein J. Nanotechn. 2014, 5, 2248.
[63] J. Sanning, P. R. Ewen, L. Stegemann, J. Schmidt, C. G. Daniliuc,
T. Koch, N. L. Doltsinis, D. Wegner, C. A. Strassert, Angew.
Chem. Int. Ed. 2015, 54, 786.
[64] V. Prusakova, C. E. McCusker, F. N. Castellano, Inorg. Chem.
2012, 51, 8589.
[65] Z. M. Hudson, C. Sun, M. G. Helander, Y.-L. Chang, Z.-H. Lu,
S. Wang, J. Am. Chem. Soc. 2012, 134, 13930.
[66] J. Li, M. A. Siegler, M. Lutz, A. L. Spek, R. J. M. Klein Gebbink,
G. van Koten, Organometallics 2009, 28, 5323.
[67] R. B. Bedford, S. L. Hazelwood, D. A. Albisson, Organometallics
2002, 21, 2599.
[68] H.-S. Lee, Y. Ha, Mol. Cryst. Liq. Cryst. 2009, 504, 67.
Unauthenticated
Download Date | 5/5/16 12:03 PM

ꢁꢀꢀꢀ
J. Sanning et al.: Synthesis, photophysical characterization and DFT studiesꢂ
ꢂ473
[69] R. Hooft, Collect, Bruker Analytical X-ray Instruments, Delft
(The Netherlands) 2008.
[70] Z. Otwinowski, W. Minor in Methods in Enzymology, Macro-
molecular Crystallography, Part A, Vol. 276 (Eds.: C. W. Carter Jr,
R. M. Sweet), Academic Press, New York, 1997, p. 307.
[71] Z. Otwinowski, D. Borek, W. Majewski, W. Minor, Acta Crystallogr.
2003, A59, 228.
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Strat- mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich,
A. D. Daniels, Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
D. J. Fox, Gaussian 09 (revision D.01), Gaussian Inc.
Wallingford CT (USA) 2009.
[72] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112.
[73] G. M. Sheldrick, Xp, Bruker Analytical X-ray Instruments Inc.,
Madison, Wisconsin (USA) 2000.
[74] A. L. Spek, J. Appl. Cryst. 2003, 36, 7.
[75] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
[76] C. Adamo, V. Barone, J. Chem. Phys. 1999, 110, 6158.
[77] D. Andrae, U. Häußermann, M. Dolg, H. Stoll, H. Preuß, Theor.
Chim. Acta 1990, 77, 123.
[78] V. Barone, J. Bloino, M. Biczysko, F. Santoro, J. Chem. Theory
Comput. 2009, 5, 540.
[79] W. Humphrey, A. Dalke, K. Schulten, J. Mol. Graphics 1996,
14, 33.
Unauthenticated
Download Date | 5/5/16 12:03 PM