Tetradentate N^N°N^N-type luminophores for Pt(II) complexes: Synthesis, photophysical and quantum-chemical investigation

Article abstract of DOI:10.1016/j.ica.2020.120090

Herein we report on dianionic tetradentate, pyridin-azole-based ligands for luminescent Pt(II) complexes. To improve their solubility in common organic solvents, a hexyl-chain was inserted in the periphery of the luminophoric ligand and different substituents were introduced at the 1H-pyrazole moieties including 4-hexylphenyl- (L1), adamantyl- (L2) and 3,5-dimethoxyphenyl (L3) substituents. For the new ligand precursors L1 and L2, the corresponding Pt(II) complexes Pt1 and Pt2 were synthesized and characterized by exact mass spectrometry as well as by ¹H NMR. L3 was also successfully synthesized and isolated, but due to the limited solubility of the resulting coordination compound, the purification and structural characterization of the corresponding Pt(II) complex Pt3 was not achieved. The absorption and steady-state as well as time-resolved photoluminescence spectra of Pt1 and Pt2 were investigated and interpreted employing TD–DFT. We found that the S₁ states for Pt1 and Pt2 can be described mainly as single electron HOMO→LUMO excitations with a ¹MP-ILCT character comprising the diazole units and the pyridine rings. At room temperature, Pt1 and Pt2 show phosphorescence in the green region of the electromagnetic spectrum peaking at 506 nm and 497 nm with photoluminescence quantum yields reaching 17% and 25%, respectively. DFT calculations show that the T₁ states of Pt1 and Pt2 can be mainly described as monoelectronic HOMO→LUMO excitations with predominant ³MP-ILCT character.

Full text of DOI:10.1016/j.ica.2020.120090

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Tetradentate N^N°N^N-type luminophores for Pt(II) complexes: Synthesis,
photophysical and quantum-chemical investigation
Marvin Cnudde, Dana Brünink, Nikos L. Doltsinis, Cristian A. Strassert
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Please cite this article as: M. Cnudde, D. Brünink, N.L. Doltsinis, C.A. Strassert, Tetradentate N^N°N^N-type
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Chimica Acta (2020), doi: https://doi.org/10.1016/j.ica.2020.120090
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Tetradentate N^N°N^N-type luminophores for Pt(II) complexes:
Synthesis, photophysical and quantum-chemical investigation
Marvin Cnuddea, Dana Brüninkb, Nikos L. Doltsinisb and Cristian A. Strassert*a
aInstitut für Anorganische und Analytische Chemie, Cells in Motion Interfaculty Centre, Center for Soft
Nanoscience, Center for Nanotechnology
- Westfälische Wilhelms-Universität Münster -
Heisenbergstraße 11, D-48149 Münster, Germany. eMail: ca.s@wwu.de
bInstitut für Festkörpertheorie, Center for Multiscale Theory and Computation - Westfälische
Wilhelms-Universität Münster - Wilhelm-Klemm-Straße 10, D-48149 Münster, Germany.
Abstract
Herein we report on dianionic tetradentate, pyridin-azole-based ligands for luminescent Pt(II)
complexes. To improve their solubility in common organic solvents, a hexyl-chain was inserted in the
periphery of the luminophoric ligand and different substituents were introduced at the 1H-pyrazole
moieties including 4-hexylphenyl- (L1), adamantyl- (L2) and 3,5-dimethoxyphenyl (L3) substituents.
For the new ligand precursors L1 and L2, the corresponding Pt(II) complexes Pt1 and Pt2 were
1
synthesized and characterized by exact mass spectrometry as well as by H-NMR. L3 was also
successfully synthesized and isolated, but due to the limited solubility of the resulting coordination
compound, the purification and structural characterization of the corresponding Pt(II) complex Pt3
was not achieved. The absorption and steady-state as well as time-resolved photoluminescence
spectra of Pt1 and Pt2 were investigated and interpreted employing TD-DFT. We found that the S1
states for Pt1 and Pt2 can be described mainly as single electron HOMO→LUMO excitations with a
1MP-ILCT character comprising the diazole units and the pyridine rings. At room temperature, Pt1 and
Pt2 show phosphorescence in the green region of the electromagnetic spectrum peaking at 506 nm
and 497 nm with photoluminescence quantum yields reaching 17 % and 25 %, respectively. DFT
calculations show that the T1 states of Pt1 and Pt2 can be mainly described as monoelectronic HOMO-
LUMO excitations with predominant 3MP-ILCT character.
Keywords: Pt(II) complex – tetradentate ligands – triplet emitter – steady state and time-resolved
spectroscopy – photophysics – NNNN – DFT
1

Introduction
Photoactive complexes involving the late transition metals (groups 8 – 10) constitute a highly
interesting category of compounds for applications in many areas, e.g. photocatalysis[1,2], bioimaging[3–
6], optoelectronic sensors[7–9] and organic light-emitting diodes (OLEDs)[10–16]. Metal-organic complexes
of Re(I)[13,17], Ru(II)[18,19], Os(II)[11,19,20], Ir(III)[15,21,22], Au(III)[23–26] and Pt(II)[22,27–29] have been intensively
investigated as triplet emitters. The late transition metals cause a strong spin-orbit-coupling (SOC),
due to the heavy-atom-effect, leading to an efficient intersystem crossing (ISC) and radiative decay
from excited triplet states, thus leading to higher external quantum yields in electroluminescent
devices.[30–33] Excited states mostly arise from electronic excitations involving the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) but also energetically
close (HOMO-n) and (LUMO+m) frontier orbitals, as well as combinations thereof. The chromophore,
more precisely the energy gap between the HOMO and the LUMO, can be conveniently tuned and the
photophysical properties can be set to desired performance.[34,35] The simplest luminophoric backbone
of the chelating chromophore typically includes at least one bidentate ligand with a delocalized π-
system. Enhanced metal chelate stability can be achieved using multidentate chromophores, such as
tri- or tetradentate ligands.[26,28,35–38] Square-planar cyclometalated complexes of Pt(II) are particularly
2
푑
푧
interesting, due to their doubly occupied -orbitals which offer the potential for Pt···Pt interactions,
which again leads to emerging photophysical properties that can be adjusted by proper modifications
to the ligand favouring or suppressing aggregation.[16,29,39,40] In this sense, the self-assembling
behaviour of square-planar transition metal complexes can be manipulated through the nature of the
]
luminophoric backbone.[41
Chang et al. reported N^N°N^N-chelating, azolate-functionalized type ligands for Os(II).[37] Inspired by
their results, we decided to perform studies of the analogous Pt(II) complexes. Initially, we tried to
obtain the corresponding species with trifluoromethyl-moieties at the 1H-pyrazoles but did not
succeed in isolating the desired coordination compound, due to its poor solubility precluding a proper
purification and characterization. In this regard, Liao et al. were able to attain enhanced solubilities
by introducing spiro-arranged moieties to reduce intermolecular π-π stacking.[42] However, we were
interested to investigate in detail the amino-bridged type of luminophores, as well as the
corresponding Pt(II) complexes, their solubilities in common organic solvents and aggregation
properties (see Fig. 1).
2

previous work by
Chang et al.
Liao et al.
this work
R
N
R
R
N
N
N
N
N
N
N
N
NH HN
NH HN
NH HN
N
N
N
N
N
N
CF3
CF3
R
F3C
F3C
R
R = tBu
L1
L2
L3
: R = 4-hexylphenyl
: R = adamantyl
: R = 3,5-dimethoxyphenyl
Figure 1: Structural formulae of selected N^N°N^N-type ligand precursors
published by Chang et al.,[37] Liao et al.[42] and of the structures L1 – L3 presented
in this work.
Results and discussion
Synthesis and characterization
To keep the tertiary amine bridge while increasing the solubility, we decided to decorate the bridging
N-atom with a hexyl-phenyl substituent. Moreover, we tried different moieties at the 1H-pyrazole to
verify if any of them would lead to a reasonably soluble complex. Thus, adamantyl-, 3,5-
dimethoxyphenyl- and 4-hexylphenyl-moieties, were introduced.
The synthesis was carried out by variation of the route previously reported by Chang et al. for
N^N°N^N-type ligands.[37] Hence, the acetyl-group of 2-acetyl-6-bromopyridin was protected as
dioxolane by reaction with ethylene glycol, followed by a Buchwald-Hartwig-amination of 4-
hexylaniline with 2-bromo-6-(2-methyl-1,3-dioxolan-2-yl)pyridine (1) to form the precursor N-(4-
hexylphenyl)-N,N-bis-(6-(2-methyl-1,3-dioxolan-2-yl)pydid-2-yl)amine (2), which was deprotected
with HCl to obtain N,N-bis(acetylpyrid-6-yl)-N-(4-hexylphenyl)amine (3). In a one-pot synthesis
reported by Heller et al.,[43] 3 was at first allowed to react with lithium bis(trimethylsilyl)amide
(LiHMDS) to form the corresponding Li-enolate, which was then converted into the keto-species with
the desired acid chloride, followed by addition of hydrazine to facilitate the ring closure and resulting
in the formation of the desired bis(pyridyl-pyrazolate)-based ligand precursors L1 – L3 (Fig. 2). L1 – L3
were combined with Pt(dmso)2Cl2 in 2-methoxyethanol to give the corresponding platinum(II)
complexes Pt1 – Pt3, which displayed limited solubility in common organic solvents (such as DCM,
toluene, MeOH, THF, DMF) in correspondence with previous reports by Chang et al. and Liao et al.[37,42]
3

Br
Br
NaOtBu, Pd2(dba)3, dppf
Toluene, 100 °C, 24 h
N
O
Ethylene glycol, p-TsOH·H2O (cat.)
N
O
N
+
Benzene, reflux, 36 h
N
O
N
O
O
NH2
1
O
O
L1 Pt1
,
: R =
: R =
: R =
2
L2 Pt2
,
O
O
L3 Pt3
,
1) 0 °C, LiHMDS
N
N
2) 0 °C, acid chloride, 2 h
3) rt, acetic acid, pH 4-5
4) N2H4·H2O, 110 °C, 1 h
N
N
N
N
N
N
Pt(dmso)2Cl2
Pt
2-Methoxyethanol,
80 °C, 1 h
Toluene
N
O
N
O
N
N
NH HN
N
N
N
R
R
R
R
Pt1 Pt3
L1 L3
-
3
-
Figure 2: Synthetic route to platinum complexes Pt1 – Pt3.
We were not successful in purifying and characterizing the complex Pt3, as we could not find a proper
solvent mixture able to cope with its low solubility. In contrast, suitable purification processes were
elaborated for Pt1 and Pt2, and both were characterized. Pt2 shows an overall lower solubility in
common organic solvents than Pt1, and a 1H-NMR-spectrum of Pt2 was acquired in DMSO-d6 at 90 °C,
facilitated by its enhanced solubility at higher temperatures. Thus, the complex was dissolved in
DMSO-d6 at 90 °C and quickly pressed through a syringe filter to obtain a clear solution with the
highest possible concentration. This led to a useable 1H-NMR spectrum, even though the resolution of
the peaks is decreased because of the higher temperature. However, it was sufficient to proof the
formation of the complex in combination with exact mass spectrometry (EM-MS). A 13C-NMR
spectrum of Pt2 was also measured but was not suitable for unambiguous assignment, due to the
weak signal intensities caused by its low solubility. Apparently, similar properties were observed
before, due to the fact that not every complex reported by Liao et al. was characterized by 13C-NMR.[42]
1
In contrast to Pt2, Pt1 has a somewhat higher solubility. Beside EM-MS, a H-NMR spectrum of Pt1
was recorded in methylene chloride-d2 and chloroform-d at room temperature, respectively, but again
no 13C-NMR spectrum suitable for assignment was achievable. Single crystal X-ray diffraction could
not be obtained for any of the complexes: The low solubility of Pt2 precluded its successful
4

crystallization, whereas the three hexyl chains of Pt1, on the other hand, seem to prevent the
formation of crystalline solids for diffractometric analysis.
Photophysical properties and frontier orbitals
Selected photophysical data are summarized in Table 1. Absorption spectra were measured in diluted
dichloromethane solutions at room temperature and are shown in Fig. 3 along with the calculated
spectra obtained via time dependent density functional theory (TD-DFT). The alkyl chains of the
complexes were replaced by hydrogen atoms in order to reduce the computational cost, since they
were shown to have a negligible effect on the spectral properties. The computed absorption and
emission spectra are found in the electronic supporting information (ESI, Fig. S34 and S35). Also,
isosurface plots of the molecular orbitals that are relevant for the description of the excited states can
be found in the ESI (Fig. S36). The S1 states for Pt1 and Pt2 can be mainly described as a
monoelectronic HOMO→LUMO excitation, while the states at higher energy (Sn) are composed of
(multiple) HOMO-n→LUMO+m excitations (vide infra). The orbital isosurfaces of Pt1 and Pt2 for the
optimized geometry in the electronic ground state show that the LUMOs are largely localized at the
pyridine units, whereas the HOMOs are mainly related to the 1H-pyrazoles with a sizeable contribution
of the metal centre. Therefore, the lowest excited singlet states of Pt1 and Pt2 can mostly be described
as monoelectronic excitations with a metal-perturbed intra-ligand charge-transfer (1MP-ILCT)
character (vide infra). For Pt1 also the peripheral phenyl-moieties participate on the HOMO, HOMO-
1, and HOMO-5.
Table. 1: Selected photophysical data for Pt(II)-complexes Pt1 and Pt2.
77K
77K
Air
Ar
77K
λabs
[nm] [nm] [nm]
λexc
λexc
λem
[nm] [nm]
λem
τAir
[μs]
τAr
[μs]
τ77K
[μs]
kr
knr
Φ
L
Φ
L
Φ
L
[104 s-1]
[104 s-1]
Pt1
Pt2
278,
351
363
350
347
339
506,
537
494,
520
2.08 ± 0.03
(1 %),
0.66 ± 0.01
(6 %),
0.155 ± 0.001
(93 %)
[0.20 ± 0.03]
9.64 ± 0.06
(42 %),
3.50 ± 0.07
(58 %)
97.3 ± 0.9
(19 %),
40.3 ± 0.4
(81 %)
< 0.02
< 0.02
0.17
± 0.02
0.92
± 0.04
Ar:
2.8 ± 0.4
Ar:
13.6 ± 0.6
77K:
1.8 ± 0.1
77K:
0.16 ± 0.08
[6.1 ± 0.3]
[51 ± 1]
246
278,
342
497,
515
488,
516
0.506 ± 0.001
(52 %),
0.398 ± 0.002
(48 %)
20.2 ± 0.2
(69 %),
7.5 ± 0.5
(31 %)
131 ± 1
(40 %),
49 ± 1
(60 %)
[81 ± 2]
0.25
± 0.02
0.91
± 0.04
Ar:
1.5 ± 0.2
Ar:
4.6 ± 0.3
77K:
1.12 ± 0.08
77K:
0.11 ± 0.05
[0.454 ± 0.002]
[16.2 ± 0.6]
Excitation and emission spectra were measured for c = 10-5 M solutions in dichloromethane at room temperature. Air: measured in air-
equilibrated c = 10-5 M solutions in dichloromethane. Ar: measured in deaerated c = 10-5 M solutions in dichloromethane by bubbling the
sample with argon. 77K: measured in frozen glassy matrices of dichloromethane/methanol (V:V = 1:1, c = 10-5 M) at 77 K. Lifetimes were
obtained from the bluest emission maximum, the fitted components are reported with the corresponding relative amplitudes in parentheses.
Amplitude-weighted average lifetimes are given in square brackets; average rate constants (kr and knr) based on photoluminescence quantum
yields and amplitude-weighted average lifetimes.
5

The experimental absorption spectrum of Pt1 shows two sets of bands peaking at 278 nm
(ε = 56510 M-1 cm-1) and 351 nm (ε = 32878 M-1 cm-1). Additionally, shoulders at 238 nm and 363 nm,
respectively, and a weak absorption tail at λ > 380 nm are observed. According to DFT calculations,
the band centred at 278 nm can be ascribed to a S0→S17 transition, where S17 corresponds
predominantly to a HOMO-3→LUMO+2 electronic configuration.
Figure 3: Normalized TD-DFT-calculated absorption spectra for a solution in dichloromethane (black lines) and experimental
spectra (red lines; validity range: c = 10-6 M in dichloromethane, see supporting information Fig. S33 for more details) for Pt1
and Pt2.
The absorption band of Pt1 peaking at 351 nm is primarily assigned to two main contributions: a S0→S5
and a S0→S6 transition, where the S5 state mainly has an excited HOMO-2→LUMO configuration and
the S6 state mainly corresponds to a HOMO-2→LUMO+1 monoelectronic excitation. The HOMO-1,
HOMO-2, and HOMO-3 of Pt1 exhibit contributions of the metal centre, whereas the LUMO+1 and the
LUMO+2 do not show noticeable contributions of the platinum atom. The shoulder at 363 nm
corresponds to a S0→S3 transition and consists predominantly of HOMO→LUMO+1 and HOMO-
1→LUMO excitations. The absorption tail at 380 nm mainly arises from a S0→S1 transition. Therefore,
1
the excited singlet states of Pt1 can be described as monoelectronic excitations with MP-ILCT
character. Pt2 shows three absorption bands peaking at 246 (ε = 12844 M-1cm-1), 278 (ε = 12411 M-
1cm-1), and 342 nm (ε = 11301 M-1cm-1), respectively. An additional intense shoulder is located at 367
nm. By DFT calculations, the absorption band peaking at 246 nm can be ascribed to a S0→S34
transition, where the excited state corresponds to a HOMO→LUMO+5 configuration. The absorption
band peaking at 278 is ascribed to a S0→S16 transition where the excited state corresponds to a
HOMO-3→LUMO+2 configuration. The absorption band peaking at 342 nm can be primarily
attributed to multiple contributions: S0→S3, S0→S4, S0→S5, and S0→S6 transitions, where the excited
singlet states S3 – S6 have mainly HOMO→LUMO+1 (S3), HOMO-2→LUMO (S4), HOMO-2→LUMO+1
6

(S5), and HOMO-1→LUMO+1 (S6) monoelectronic excitation character. The shoulder at 367 nm
represents the S0→S7 transition which can be described as a mixture of HOMO-1 → LUMO and HOMO
→ LUMO+1 excitations. Since the orbital pictures show a noticeable participation of the platinum
centre in the HOMO, HOMO-2 and HOMO-3 as well as a small contribution in the LUMO+1, the excited
1
singlet states of Pt2 can also be mostly described as monoelectronic excitations with MP-ILCT
character.
a)
b)
Exc
Em
Exc
Em
Pt1
Pt2
Pt1
Pt2
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
250
300
350
400
450
500
550
600
650
700
250
300
350
400
450
500
550
600
650
700
 [nm]
 [nm]
Figure 4: a) Normalized excitation spectra (dashed lines, λEm = 500 nm) and emission spectra (solid lines,
λExc = 350 nm) at room temperature in deaerated dichloromethane (c = 10-5 M); b) normalized excitation spectra
(dashed lines, λEm = 520 nm for Pt1 and λEm = 500 nm for Pt2) and emission spectra (solid lines, λExc = 350 nm) in glassy
matrices of DCM/MeOH (V:V = 1:1, c = 10-5 M) at 77 K.
Photoluminescence spectra were recorded in dilute fluid solutions (c = 10-5 M) of deaerated
dichloromethane at room temperature and in frozen glassy matrices corresponding to a 1:1 (V:V)
mixture of dichloromethane/methanol at 77 K and are shown in Fig. 4 along with the corresponding
excitation spectra. The emission spectrum of Pt1 in fluid dichloromethane at room temperature shows
a clear vibrational progression peaking at 506 nm and 537 nm. Pt2 shows a less pronounced
vibrational progression peaking at 497 nm and 515 nm. Both emission spectra show an emission
shoulder at ca. 475 nm - 480 nm, which is more pronounced in the case of Pt2. The excited state
lifetimes of both complexes in solution are longer in the absence of oxygen (see Table 1). Together
with the increased quantum yields of 0.17 and 0.25 for deaerated solutions, respectively, if compared
to ΦL < 0.02 (i.e. below the detection limit for both complexes) in the presence of oxygen, the triplet
state nature of the emissive states can be confirmed. The ligand centred nature of these states is
indicated by the absence of significant blue-shifts and the pronounced vibrational progressions in the
emission spectra at 77 K, if compared to those at room temperature. DFT-calculated isosurface plots
of the HOMO and the LUMO at the optimized T1 geometry are shown in Fig. 5. According to our TD-
DFT calculations the T1 states of both complexes can be mainly described as HOMO→LUMO
excitations accounting for 70% (Pt1) and 76% (Pt2) of all single electron contributions, respectively.
As the MOs depicted in Fig. 5 clearly illustrate, the excited triplet states T1 of Pt1 and Pt2 can be
7

3
described as having MP-ILCT character. A more detailed numerical analysis of the contributions of
the different subsystems performed using the TheoDORE software[52] confirms that Pt1 has a
somewhat more pronounced ligand-to-ligand charge-transfer (LLCT) character and reduced metal-to-
ligand charge-transfer (MLCT) contributions (Fig. 6). The partitioning of the complexes used for this
analysis is shown in Fig. 7.
8

Figure 5: Selected molecular orbital isosurface plots with an isovalue of 0.03 at the
optimized T1 geometry in dichloromethane. Shown are the MOs involved in the most
significant monoelectronic excitations contributing to the description of the emissive T1
state (percentages of the contributions are given for each complex).
9

Figure 6: Numerical analysis of subsystem contributions to the T1 excited state for Pt1
(black) and Pt2 (red) using TheoDORE.[52]
Figure 7: Partitioning of Pt1 (left) and Pt2 (right) into subsystems for the numerical
analysis shown in Fig. 6.
In glassy matrices at 77 K, the emission spectrum of Pt2 appears with a clearly structured vibrational
progression and is blue-shifted if compared with measurements at room temperature, which can be
attributed to a reduced charge-transfer character in frozen matrices. The emission spectrum of Pt1 at
77 K also shows a significant blue-shift with respect to room temperature, if referring to the bluest
local emission maximum at 494 nm. Nonetheless, the emission spectrum at 77 K of Pt1 has a less
defined vibrational progression than Pt2, probably due to the phenyl moieties at the pyrazoles: In fact,
since the phenyl rings have a significant contribution to the HOMO, HOMO-1, and HOMO-5 and can
adopt different conformations around the connecting σ-bonds, various degrees of conjugation are
available for Pt1 at 77 K that globally lead to a featureless vibrational progression and a red-shift for
Pt1. The observed red shift of Pt1 in comparison to Pt2 can also be seen in the calculated vibrationally
resolved emission spectra using the PBE0 functional (Fig. 8, right). However, this shift is absent when
10

the long-range corrected CAM-B3LYP functional is employed (Fig. 8, left), hinting at the fact that it is
overestimated by PBE0 due to the increased charge-transfer character of the T1 state in Pt1.
Interestingly, no trace of excimeric emission pointing towards Pt-Pt interactions were detectable,
despite their low solubility.
Figure 8: Normalized calculated vibrationally resolved emission spectra of Pt1 and Pt2
in dichloromethane at 300 K obtained with the PBE0 and CAM-B3LYP functionals,
respectively, together with the corresponding experimental spectra.
Conclusions
In agreement with previously reported azole-functionalized structures, the investigated complexes
Pt1 – Pt3 show rather low solubilities. However, two out of three new platinum(II) complexes (Pt1 and
Pt2) were successfully characterized by EM-MS and 1H-NMR and their photophysical properties were
investigated, while a purification and characterization of Pt3 has not been achieved so far. DFT
calculations along with experimental absorption spectra indicate a ligand-centred nature of the
transitions for both complexes, which is confirmed by the absence of significant hypsochromic shifts
when going from room temperature to frozen matrices as well as by observed enhanced structural
vibrational progression in the excitation- and emission-spectra monitored at 77 K. Furthermore, DFT-
investigations show that the excited S1 and T1 states can be mainly described as monoelectronic
1
3
HOMO→LUMO excitations with MP-ILCT and MP-ILCT character, respectively, where the charge-
transfer character arises from the diazole-related HOMOs with contribution from the metal and the
pyridine-based LUMOs. The platinum(II) complexes Pt1 and Pt2 show green luminescence at 506 nm
and 497 nm and quantum yields at room temperature rising from 17 % to 25 % upon replacement of
phenyl moieties by adamantly groups. Despite their rather low solubilities, no excimeric emission
pointing towards intermetallic interactions were detected, which can be attributed to the bulk of the
peripheral substituents.
11

Acknowledgments
The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft
(DFG: TRR 61, GA 2430/1-1, DO 768/3-1, STR 1186/3-1; SFB 858; Priority Programme 2102 “Light-
controlled Reactivity of Metal Complexes” DO 768/5-1, STR 1186/6-1). CAS would like to acknowledge
the Cluster of Excellence Cells in Motion (DFG EXC 1003) for financial support. Computation time at
the HPC cluster PALMA II of the University of Münster is gratefully acknowledged. We wish to dedicate
this paper to Prof. Luisa De Cola on the occasion of her 60th birthday.
Experimental
Experimental procedures
Commercially available reagents were used without further purification. Silica gel 60 (0.063 –
0.200 mm) for column chromatography from Merck (mentioned as silica) and aluminium oxide 90
standardized for column chromatography adsorption analysis acc. to Brockmann from Merck
(mentioned as alox) were used for column chromatography if not otherwise stated.
MS-ESI-EM were determined at the Organisch-Chemisches Institut - WWU Münster, using a LTQ
Orbitap LTQ XL (Thermo-Fisher Scientific, Bremen) with nanospray-injection. Relative intensities are
given for single isotopic patterns each.
NMR-spectra were obtained from the Organisch-Chemisches Institut – WWU Münster, using with an
Agilent DD2 500/ Agilent DD2 600 or a Bruker Avance II 300/ Bruker Avance II 400. All measurements
were obtained at room temperature if not otherwise mentioned.
Absorption spectra were measured on a Varian Cary 5000 double-beam UV-Vis-NIR spectrometer and
baseline-corrected. Steady-state excitation and emission spectra were recorded on a FluoTime300
spectrometer from PicoQuant equipped with a 300 W ozone-free Xe lamp (250-900 nm), a 10 W Xe
flash-lamp (250-900 nm, pulse width < 10 µs) with repetition rates of 0.1 – 300 Hz, an excitation
monochromator (Czerny-Turner 2.7 nm/mm dispersion, 1200 grooves/mm, blazed at 300 nm), diode
lasers (pulse width < 80 ps) operated by a computer-controlled laser driver PDL-820 (repetition rate
up to 80 MHz, burst mode for slow and weak decays), two emission monochromators (Czerny-Turner,
selectable gratings blazed at 500 nm with 2.7 nm/mm dispersion and 1200 grooves/mm, or blazed at
1250 nm with 5.4 nm/mm dispersion and 600 grooves/mm), Glan-Thompson polarizers for excitation
(Xe-lamps) and emission, a Peltier-thermostatized sample holder from Quantum Northwest (-40 °C –
105 °C), and two detectors, namely a PMA Hybrid 40 (transit time spread FWHM < 120 ps, 300 –
720 nm) and a R5509-42 NIR-photomultiplier tube (transit time spread FWHM 1.5 ns, 300-1400 nm)
12

with external cooling (-80 °C) from Hamamatsu. Steady-state and fluorescence lifetimes 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 inspection of the weighted residuals and
their autocorrelation. Luminescence quantum yields were measured with a Hamamatsu Photonics
absolute PL quantum yield measurement system (C9920-02) equipped with a L9799-01 CW Xenon
light source (150 W), monochromator, C7473 photonic multi-channel analyzer, integrating sphere
(± 0.02 for ΦL is estimated) and employing U6039-05 PLQY measurement software (Hamamatsu
Photonics, Ltd., Shizuoka, Japan). All solvents used were of spectrometric grade.
DFT calculations
All density functional theory (DFT) calculations of gas phase complexes were carried out using the
quantum chemistry package Gaussian 09 Rev. D.01[44] employing the hybrid functional PBE0[45] and
the SDD basis set, which applies an effective core potential for the Pt atoms[46] and the D95 basis set
for H, C, N and O atoms[47]
.
Absorption spectra of the gas phase monomers were obtained from time-dependent density
functional linear response theory (TDDFT) calculations of the 40 lowest excited singlet states. A
Lorentzian broadening with a half width at half maximum (HWHM) of 10 nm was used for each
transition.
Vibrational Franck-Condon spectra were calculated according the method of Barone et al.[48,49] with
Kohn-Sham DFT-based geometry optimizations in the S0 and T1 states followed by frequency analysis
calculations. The energies were corrected by zero-point vibrational energies and thermal free energy
contributions. In order to calculate the overlap integrals for the vibronic spectra, the transitions are
divided into classes Cn where n is the number of the excited normal modes in the final electronic state.
The maximum number of quanta per mode was set to 100, the maximum number of quanta for
combinations of two modes to 65. The number of integrals calculated was limited to 1.5 × 108. A
maximum of 20 classes were computed. The line spectrum was broadened by Gaussian functions with
a half-width at half-maximum of 135 cm-1. The solvent dichloromethane (DCM) was taken into account
by the polarizable continuum model (PCM) in an integral equation formalism framework[50] with
atomic radii from the universal force field model (UFF)[51]. The character of the emissive T1 state in
terms of single orbital excitations was determined by TDDFT calculations at the T1 geometry optimized
with unrestricted Kohn-Sham DFT. A subsequent numerical analysis of the contributions of different
subsystems to the T1 excitation was performed using the TheoDORE software.[52] As a first step this
13

requires partitioning the molecule into different fragments (see Fig. 7 for our choice). The numbers
given in Fig. 6 are charge transfer numbers obtained by integrating the square modulus of the one-
electron density matrix over two different fragments using a population analysis scheme.
Preparation of 1
The reaction procedure reported by Hatanaka et al.[53] was varied, using 2-acetyl-6-bromopyridine
(8.00 g, 40.0 mmol, 1 eq), ethylene glycol (3.36 mL, 60.0 mmol, 1.5 eq) and p-TsOH·H2O (0.38 g,
2.00 mmol, 0.05 eq) in benzene (50 mL). The crude product was purified via column chromatography
on silica, eluting with a mixture of n-hexane/ethyl acetate (2:1, V:V) to obtain the desired product as
a colourless oil, which was recrystallized from n-hexane/ethyl acetate to obtain a white solid (8.59 g,
35.2 mmol, 88 %).
MS-ESI-EM (MeOH/CHCl3, M = C9H10N1O2Br1):
m/z (%) calcd.: [M+H]+ = 243.9968 (100), 244.9999 (10), 245.9948 (98), 246.9979 (10);
[M+Na]+ = 265.9787 (100), 266.9819 (10), 267.9767 (98), 268.9799 (10); [2M+H]+ = 486.9863 (51),
487.9894 (10), 488.9843 (100), 489.9874 (20), 490.9826 (51); [2M+Na]+ = 508.9682 (51),
509.9714 (10), 510.9663 (100), 511.9694 (20), 512.9645 (51), 513.9675 (10), 514.9700 (1).
m/z (%) found: [M+H]+ = 243.9967 (100), 245.0002 (9), 245.9946 (99), 246.9979 (9);
[M+Na]+ = 265.9786 (100), 266.9820 (10), 267.9765 (99), 268.9798 (10); [2M+H]+ = 486.9859 (42),
487.9920 (1), 488.9842 (100), 489.9633 (4), 490.9813 (24); [2M+Na]+ = 508.9682 (49),
509.9717 (10), 510.9660 (100), 511.9692 (19), 512.9638 (49), 513.9672 (9), 514.9692 (1).
1H-NMR (400 MHz, methylene chloride-d2): δ (ppm) = 7.56 (td, J = 7.6, 3.5 Hz, 1H), 7.50 (dd, J = 7.3,
2.7 Hz, 1H), 7.41 (dd, J = 7.6, 2.5 Hz, 1H), 4.27 – 3.61 (m, 4H), 1.66 (d, J = 3.5 Hz, 3H).
13C-NMR (101 MHz, methylene chloride-d2): δ (ppm) = 163.01, 142.17, 139.52, 127.87, 118.93,
108.43, 65.65, 25.31.
Preparation of 2
Under argon atmosphere, 1 (7.32 g, 30.0 mmol, 2 eq), 4-hexylaniline (2.66 g, 15.0 mmol, 1 eq),
1,1′-ferrocenediyl-bis(diphenylphosphine) (dppf, 1.39 g, 2.50 mmol, 0.08 eq), Pd2(dba)3 (0.92 g,
1.00 mmol, 0.03 eq) and NaOtBu (3.75 g, 39.0 mmol, 2.5 eq) were dissolved in toluene (50 mL) and
refluxed at 100 °C for 25 h. After reaching room temperature, the reaction mixture was neutralized
with 1 N HCl (aq.) and extracted with dichloromethane (3x30 mL). The combined organic phases were
dried over Na2SO4 and the solvents removed under reduced pressure. After purification via column
14

chromatography on silica, eluting with a mixture of n-hexane/ethyl acetate (2:1, V:V) the product was
obtained as an orange oil (4.31 g, 8.55 mmol, 57 %).
MS-ESI-EM (MeOH, M = C30H37N3O4):
m/z (%) calcd.: [M+H]+ = 504.2857 (100), 505.2889 (34), 506.2918 (6); [M+Li]+ = 509.2930 (8),
510.2939 (100), 511.2971 (34), 512.3000 (6); [M+Na]+ = 526.2676 (100), 527.2708 (34), 528.2737 (6);
[2M+Na]+ = 1029.5460 (100), 1030.5492 (68), 1031.5523 (25), 1032.5552 (6).
m/z (%) found: [M+H]+ = 504.2856 (100), 505.2890 (32), 506.2923 (5); [M+Li]+ = 509.2929 (8),
510.2937 (100), 511.2972 (32), 512.3005 (6); [M+Na]+ = 526.2672 (100), 527.2706 (33), 528.2739 (6);
[2M+Na]+ = 1029.5465 (100), 1030.5498 (70), 1031.5532 (24), 1032.5563 (6).
1H-NMR (300 MHz, methylene chloride-d2): δ (ppm) = 7.53 (td, 7.9, 0.8 Hz, 2H), 7.19 (dt, J = 8.5,
2.1 Hz, 2H), 7.13 (dd, J = 7.5, 0.8 Hz, 2H), 7.07 (dt, J = 8.4, 2.4 Hz, 2H), 6.93 (dd, J = 8.3, 0.8 Hz, 2H),
4.04 – 3.81 (m, 8H), 2.63 (t, 2H), 1.70 – 1.58 (m, 2H), 1.54 (s, 6H), 1.42 – 1.27 (m, 6H), 0.96 – 0.82 (m,
3H).
13C-NMR (75 MHz, methylene chloride-d2): δ (ppm) = 159.80, 157.92, 142.89, 141.01, 137.96, 129.76,
127.95, 116.17, 113.61, 108.97, 65.56, 36.00, 32.30, 32.02, 29.55, 24.95, 23.20, 14.43.
Preparation of 3
2 (4.28 g, 8.50 mmol, 1 eq) was heated to 80 °C for 12 h in 1 M HCl (aq., 25 mL). After reaching room
temperature, the mixture was neutralized with aqueous 1 M NaHCO3 and extracted with
dichloromethane (3x30 mL). The combined organic phases were dried over Na2SO4 and the solvent
was removed under reduced pressure. After purification via column chromatography on silica, eluting
with a mixture of n-hexane/ethyl acetate (2:1, V:V) the product was obtained as a pale-brownish solid
(2.75 g, 6.63 mmol, 78 %).
MS-ESI-EM (MeOH, M = C26H29N3O2):
m/z (%) calcd.: [M+H]+ = 416.2333 (100), 417.2364 (30), 418.2394 (5); [M+Na]+ = 438.2152 (100),
439.2184 (30 %), 440.2213 (5).
m/z (%) found: [M+H]+ = 416.2328 (100), 417.2364 (27), 418.2400 (4); [M+Na]+ = 438.2146 (100),
439.2181 (27), 440.2216 (4).
1H-NMR (400 MHz, methylene chloride-d2): δ (ppm) = 7.71 (td, J = 7.9, 7.8, 0.8 Hz, 2H), 7.62 (dd,
J = 7.4, 0.9 Hz, 2H), 7.32 (dd, J = 8.3, 0.9 Hz, 2H), 7.28 (dt, J = 8.4, 2.1 Hz, 2H), 7.18 (dt, J = 8.4, 2.5,
15

1.9 Hz, 2H), 2.67 (t, J = 7.4 Hz, 2H), 2.37 (s, 6H), 1.75 – 1.56 (m, 2H), 1.48 – 1.20 (m, 6H), 0.96 – 0.81
(m, 3H).
13C-NMR (101 MHz, methylene chloride-d2): δ (ppm) = 200.29, 157.19, 152.27, 142.22, 141.92,
138.45, 130.25, 128.76, 120.17, 115.79, 54.00, 36.02, 32.29, 31.98, 29.40, 25.87, 23.20, 14.43, 1.34.
Preparation of L1
Under argon atmosphere, 3 (1.00 g, 2.41 mmol, 1 eq) was dissolved in dry toluene (20 mL), at 0 °C
LiHMDS (5.06 mL, 1.0 M solution in THF, 5.06 mmol, 2.1 eq) was added and the solution stirred for
15 min at 0 °C. At 0 °C, 4-hexylbenzoyl chloride (1.14 g, 5.06 mmol, 2.1 eq) was added and the reaction
mixture was stirred for 2 h to reach room temperature. Acetic acid (glacial, 100 %) was added first,
until pH = 4 - 5 was reached, followed by addition of ethanol (20 mL) to form a suspension. Afterwards
hydrazine-monohydrate (4.72 mL, 96.3 mmol, 40 eq) was added and the mixture was heated to 110 °C
for 1 h. After reaching room temperature, water (40 mL) was added and the mixture was extracted
with dichloromethane (3x30 mL). The combined organic phases were dried over Na2SO4 and the
solvents were removed under reduced pressure. The crude product was purified via column
chromatography on silica, eluting with a mixture of cyclohexane/ethyl acetate (2:1, V:V) to obtain the
desired product as a white solid (0.32 g, 0.41 mmol, 17 %).
MS-ESI-MS (MeOH/CHCl3, M = C52H61N7):
m/z (%) calcd.: [M+H]+ = 784.5061 (100), 785.5092 (60), 786.5124 (17), 787.5155 (3);
[M+Na]+ = 806.4881 (100), 807.4912 (60), 808.4943 (17), 809.4974 (3); [2M+Na]+ = 1589.9869 (84),
1590.9900 (100), 1591.9931 (59), 1592.9963 (23), 1593.9994 (7), 1595.0025 (2).
m/z (%) found: [M+H]+ = 784.5068 (100), 785.5100 (57), 786.5134 (16), 787.5167 (3);
[M+Na]+ = 806.4886 (100), 807.4918 (59), 808.4952 (17), 809.4985 (2); [2M+Na]+ = 1589.9884 (84),
1590.9917 (100), 1591.9954 (57), 1592.9987 (22), 1594.0012 (7), 1595.0293 (1).
1H-NMR (400 MHz, methylene chloride-d2): δ (ppm) = 10.86 (s, 2H), 7.71 (d, J = 7.7 Hz, 4H), 7.62 (t,
J = 7.9 Hz, 2H), 7.33 (d, J = 7.5 Hz, 2H), 7.27 – 7.19 (m, 8H), 6.99 (d, J = 8.3 Hz, 2H), 6.95 (s, 2H),
2.69 – 2.61 (m, 6H), 1.81 – 1.51 (m, 6H), 1.49 – 1.24 (m, 18H), 0.99 – 0.83 (m, 9H).
1H-NMR (500 MHz, chloroform-d): δ (ppm) = 7.72 (d, J = 7.9 Hz, 4H), 7.59 (t, J = 8.0 Hz, 2H), 7.29 (d,
J = 7.5 Hz, 2H), 7.25 – 7.18 (m, 8H), 6.98 (d, J = 8.3 Hz, 2H), 6.92 (s, 2H), 2.67 (t, J = 7.7 Hz, 2H), 2.63 (t,
J = 7.7 Hz, 4H), 1.78 – 1.52 (m, 6H), 1.40 – 1.21 (m, 18H), 0.96 – 0.83 (m, 9H).
16

13C-NMR (126 MHz, chloroform-d): δ (ppm) = 157.15, 142.97, 141.73, 141.54, 138.31, 129.84, 128.87,
128.38, 125.63, 115.46, 113.79, 99.78, 77.17, 35.89, 35.77, 31.88, 31.87, 31.53, 31.46, 29.33, 29.13,
22.77, 22.75, 14.25.
Preparation of L2
Following the same procedure as for L1, using 3 (0.50 g, 1.20 mmol, 1 eq), dry toluene (10 mL), LiHMDS
(2.52 mL, 1.0 M solution in THF, 2.52 mmol, 2.1 eq), 1-adamantanecarbonyl chloride (0.50 g,
2.52 mmol, 2.1 eq), acetic acid (glacial, 100 %), ethanol (10 mL) and hydrazine-monohydrate (2.34 mL,
48 mmol, 40 eq). The crude product was purified via column chromatography on silica, eluting with a
mixture of n-hexane/ethyl acetate/triethylamine (1:3:1, V:V:V) to obtain the desired product as a pale
green solid (0.38 g, 0.51 mmol, 42 %).
MS-ESI-EM (MeOH/CHCl3, M = C48H57N7):
m/z (%) calcd.: [M+H]+ = 732.4748 (100), 733.4779 (55), 734.4810 (15), 735.4841 (3);
[M+Na]+ = 754.4568 (100), 755.4599 (55), 756.46230 (15), 757.4660 (3); [2M+H]+ = 1463.9424 (91),
1464.9455 (100), 1465.9486 (55), 1466.9516 (20); [2M+Na]+ = 1485.9243 (91), 1486.9274 (100),
1487.9305 (55), 1488.9336 (20), 1489.9367 (5).
m/z (%) found: [M+H]+ = 732.4753 (100), 733.4785 (54), 734.4821 (13), 735.4855 (2);
[M+Na]+ = 754.4573 (100), 755.4606 (53), 756.4641 (14), 757.4676 (2); [2M+H]+ = 1463.9449 (90),
1464.9477 (100), 1465.9513 (56), 1466.9541 (17); [2M+Na]+ = 1485.9263 (92), 1486.9291 (100),
1487.9330 (54), 1488.9363 (19), 1489.9390 (5).
1H-NMR (300 MHz, methylene chloride-d2): δ (ppm) = 7.58 (td, J = 7.8, 0.7 Hz, 2H), 7.31 (d, J = 7.3 Hz,
2H), 7.24 (dt, J = 8.4, 2.1 Hz, 2H), 7.17 (dt, J = 8.4, 2.1 Hz, 2H), 6.92 (dd, J = 8.3, 0.8 Hz, 2H), 6.47 (s, 2H),
2.66 (t, J = 8.1, 7.5 Hz, 2H), 2.04 (m, 6H), 1.94 (m, 12H), 1.85 – 1.71 (m, 12H), 1.66 (m, 2H), 1.43 – 1.28
(m, 6H), 0.94 – 0.84 (m, 3H).
13C-NMR (75 MHz, methylene chloride-d2): δ (ppm) = 138.56, 130.05, 128.47, 115.58, 113.99, 99.19,
43.07, 37.26, 34.21, 32.31, 32.02, 29.68, 29.26, 23.20.
Preparation of L3
Following the same procedure as for L1, using 3 (1.73 g, 4.15 mmol, 1 eq), dry toluene (30 mL), LiHMDS
(8.72 mL, 1.0 M solution in THF, 8.72 mmol, 2.1 eq), 3,5-dimethoxybenzoyl chloride (1.75 g,
8.72 mmol, 2.1 eq), acetic acid (glacial, 100 %), ethanol (20 mL) and hydrazine-monohydrate (8.13 mL,
166 mmol, 40.0 eq). The crude product was purified via column chromatography on silica, eluting with
17

a mixture of dichloromethane/acetone/cyclohexane (0:0:100 → 4:3:7, V:V:V) to obtain the desired
product as a white solid (0.34 g, 0.47 mmol, 11 %).
MS-ESI-EM (MeOH/CHCl3, M = C44H45N7O4):
m/z (%) calcd.: [M+H]+ = 736.3606 (100), 737.3636 (51), 738.3666 (13), 739.3695 (2);
[M+Na]+ = 758.3425 (100), 759.3456 (51), 760.3485 (13), 761.3514 (2); [2M+H]+ = 1471.7139
(98), 1472.7170 (100), 1473.7200 (52), 1474.7229 (18); [2M+Na]+ = 1493.6958 (98), 1494.6989 (100),
1495.7019 (52), 1496.7049 (18), 1497.7078 (5).
m/z (%) found: [M+H]+ = 736.3609 (100), 737.3642 (49), 738.3675 (12), 739.3707 (2);
[M+Na]+ = 758.3431 (100), 759.3465 (48), 760.3496 (12), 761.3527 (2); [2M+H]+ = 1471.7165 (100),
1472.7196 (99), 1473.7227 (49), 1474.7259 (14); [2M+Na]+ = 1493.6986 (100), 1494.7017 (99),
1495.7049 (50), 1496.7075 (17), 1497.7109 (3).
1H-NMR (300 MHz, methylene-chloride-d2): δ (ppm) = 10.87 (s, 1H), 7.63 (t, J = 8.0 Hz, 2H), 7.32 (d,
J = 7.5 Hz, 2H), 7.26 (d, J = 8.4 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H), 7.02 – 6.94 (m, 8H), 6.43 (t, J = 2.3 Hz,
2H), 3.82 (s, 12H), 2.66 (t, J = 7.6 Hz, 2H), 1.67 (p, J = 7.4 Hz, 2H), 1.41 – 1.28 (m, 6H), 0.95 – 0.81 (m,
3H).
1H-NMR (600 MHz, methylene chloride-d2): δ (ppm) = 7.63 (t, J = 7.9 Hz, 2H), 7.33 (d, J = 7.5 Hz, 2H),
7.27 (d, J = 8.2 Hz, 2H), 7.20 (d, J = 8.3 Hz, 2H), 6.99 (d, J = 8.2 Hz, 2H), 6.98 (d, J = 2.3 Hz, 4H), 6.97 (s,
2H), 6.44 (t, J = 2.3 Hz, 2H), 3.83 (s, 12H), 2.67 (t, J = 7.9 Hz, 2H), 1.72 – 1.63 (m, 2H), 1.42 – 1.32 (m,
6H), 1.04 – 0.75 (m, 3H).
13C-NMR (151 MHz, methylene chloride-d2): δ (ppm) = 161.74, 157.83, 142.16, 142.14, 138.95,
130.24, 128.56, 116.28, 114.34, 104.05, 100.67, 100.48, 55.95, 36.12, 32.32, 31.95, 29.70, 27.50,
23.21, 14.45.
Preparation of platinum(II) complex Pt1
L1 (0.14 g, 0.18 mmol, 1 eq) and Pt(dmso)2Cl2 (0.08 g, 0.18 mmol, 1 eq) were dissolved in
2-methoxyethanol (5 mL) and stirred at 80 °C for 1 h. After reaching room temperature, water (5 mL)
was added to give a yellow precipitate, which was filtered and washed with water (5 mL). The crude
product was purified via column chromatography on neutral alox, eluting with chloroform to obtain
the desired product as yellow solid (0.10 g, 0.10 mmol, 56 %).
MS-ESI-EM (MeOH/CHCl3, M = C52H59N7Pt):
m/z (%) calcd.: [M+H]+ = 974.4515 (1), 976.4532 (62), 977.4556 (100), 978.4570 (96), 979.4595 (41),
980.4601 (24), 981.4622 (10), 982.4650 (3); [M+Na]+ = 998.4351 (62), 999.4376 (100), 1000.4390 (96),
18

1001.4415 (41), 1002.4421 (24); [2M+H]+ = 1951.8994 (18), 1952.9016 (52), 1953.9034 (91),
1954.9054 (100), 1955.9071 (84), 1956.9089 (57), 1957.9104 (35), 1958.9123 (18), 1959.9142 (8),
1960.9160 (3); [2M+Na]+ = 1973.8813 (18), 1974.8835 (52), 1975.8854 (91), 1976.8873 (100),
1977.8891 (84), 1978.8908 (57), 1979.8924 (35), 1980.8943 (18).
m/z (%) found: [M+H]+ = 974.4570 (1) 976.4575 (62), 977.4599 (100), 978.4607 (94), 979.4639 (39),
980.4647 (22), 981.4670 (9), 982.4690 (2); [M+Na]+ = 998.4393 (69), 999.4423 (100), 1000.4439 (96),
1001.4456 (37), 1002.4444 (12); [2M+H]+ = 1951.9070 (16), 1952.9099 (49), 1953.9114 (85),
1954.9134 (100), 1955.9157 (81), 1956.9164 (54), 1957.9180 (35), 1958.9198 (19), 1959.9199 (11),
1960.9207 (6); [2M+Na]+ = 1973.8923 (25), 1974.8927 (54), 1975.8943 (90), 1976.8957 (100),
1977.8976 (76), 1978.8982 (54), 1979.9010 (29), 1980.9049 (9).
1H-NMR (300 MHz, methylene chloride-d2): δ (ppm) = 7.93 (d, J = 7.7 Hz, 2H), 7.88 (d, J = 8.1 Hz, 4H),
7.43 (d, J = 8.0 Hz, 2H), 7.26 (d, J = 7.9 Hz, 4H), 7.20 (t, J = 8.1 Hz, 2H), 6.99 (d, J = 7.4 Hz, 2H), 6.61 (s,
2H), 5.74 (d, J = 8.7 Hz, 2H), 2.81 – 2.57 (m, 6H), 1.74 – 1.62 (m, 6H), 1.54 – 1.30 (m, 18H), 1.03 – 0.89
(m, 12H).
1H-NMR (599 MHz, chloroform-d): δ (ppm) = 7.93 (s, 2H), 7.86 (d, J = 7.5 Hz, 4H), 7.37 (d, J = 7.9 Hz,
2H), 7.21 (d, J = 7.6 Hz, 4H), 7.13 (t, J = 7.8 Hz, 2H), 6.95 (d, J = 7.0 Hz, 2H), 6.57 (s, 2H), 5.67 (d,
J = 8.7 Hz, 2H), 2.71 – 2.62 (m, 6H), 1.76 – 1.61 (m, 6H), 1.45 – 1.34 (m, 18H), 0.99 – 0.95 (m, 3H),
0.95 – 0.92 (m, 6H).
13C-NMR (151 MHz, chloroform-d): δ (ppm) = 146.82, 144.76, 136.89, 131.26, 128.37, 125.48, 36.06,
31.98, 31.96, 31.72, 31.65, 29.49, 29.42, 22.85, 22.84, 14.30, 14.29, 1.16.
Preparation of platinum(II) complex Pt2
L2 (0.24 g, 0.33 mmol, 1 eq) and Pt(dmso)2Cl2 (0.14 g, 0.33 mmol, 1 eq) were dissolved in
2-methoxyethanol (10 mL) and stirred at 80 °C for 1 h. After reaching room temperature, water was
added for precipitation. The precipitate was washed with ethanol and acetone to give the product as
yellow solid (0.21 g, 0.22 mmol, 67 %).
MS-ESI-MS (MeOH/CHCl3, M = C48H55N7Pt):
m/z (%) calcd.: [M+H]+ = 922.4202 (2), 924.4219 (64), 925.4243 (100), 926.4256 (94), 927.4281 (38),
928.4286 (23), 929.4308 (9), 930.4336 (2); [2M+H]+ = 1847.8367 (19), 1848.8390 (55), 1849.8407 (93),
1850.8427 (100), 1851.8443 (82), 1852.8461 (54), 1853.8476 (33), 1854.8495 (17), 1855.8513 (7).
19

m/z (%) found: [M+H]+ = 922.4246 (2), 924.4258 (63 , 925.4280 (100), 926.4287 (94), 927.4316 (37),
928.4324 (22), 929.4348 (8), 930.4377 (2); [2M+H]+ = 1847.8437 (18), 1848.8459 (54), 1849.8576 (91),
1850.8501 (100), 1851.8514 (81), 1852.8540 (52), 1853.8552 (31), 1854.8570 (15), 1855.8599 (6).
1H-NMR (600 MHz, dimethylsulfoxide-d6, 90 °C): δ (ppm) = 8.27 (t, J = 8.4 Hz, 2H), 8.13 (s, 2H), 7.67 (d,
J = 7.8 Hz, 2H), 7.60 (d, J = 7.8 Hz, 2H), 7.29 (s, 2H), 6.76 (s, 2H), 2.82 (t, J = 8.0 Hz, 2H), 2.23 (s, 12H),
2.14 (s, 6H), 1.89 – 1.80 (m, 12H), 1.80 – 1.70 (m, 2H), 1.48 – 1.42 (m, 2H), 1.41 – 1.33 (m, 4H),
0.95 – 0.89 (m, 3H).
20

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25

Dear Ladies and Gentlemen,
we kindly acknowledge the exhaustive and in-depth review report from our colleagues. We have
addressed all their questions and issues and modified the manuscript accordingly (all changes have
been highlighted in yellow). A revised version of the main manuscript and of the supporting
information file has been uploaded accordingly, along with a response letter addressing all the
questions and suggestions from the Referees.
We are strongly convinced that our manuscript has improved in quality and readability and are
looking forward to seeing our paper published in this exciting special issue!
With kindest regards from Münster,
Prof. Cristian A. Strassert
L1 Pt1
,
: R =
: R =
: R =
N
N
L2 Pt2
,
N
N
N
N
N
N
Pt(dmso)2Cl2
2-Methoxyethanol,
80 °C, 1 h
O
Pt
NH HN
L3 Pt3
,
N
N
N
N
R
R
R
R
Pt1 Pt3
-
L1 L3
-
26