Mixed-halide triphenyl methyl radicals for site-selective functionalization and polymerization

Article abstract of DOI:10.1039/d1ra04638a

Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage. However, poor reactivity of the chloride-moieties limits the yield of functionalization and thus the accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain mixed-bromide and chloride derivatives of TTM by simple Friedel-Crafts alkylation. The resulting radical compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the better leaving group character of the para-bromide. The mixed halide radicals give access to complex, and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building block for customized design and synthesis of stable luminescent radicals.

Full text of DOI:10.1039/d1ra04638a

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Mixed-halide triphenyl methyl radicals for site-
selective functionalization and polymerization†
Cite this: RSC Adv., 2021, 11, 27653
Lisa Chen,‡a Mona Arnold,‡a Remi Blinder,b Fedor Jelezkob
´
*
ac
and Alexander J. C. Kuehne
Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet
spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage.
However, poor reactivity of the chloride-moieties limits the yield of functionalization and thus the
accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain
mixed-bromide and chloride derivatives of TTM by simple Friedel–Crafts alkylation. The resulting radical
compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the
better leaving group character of the para-bromide. The mixed halide radicals give access to complex,
and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical
centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building
block for customized design and synthesis of stable luminescent radicals.
Received 15th June 2021
Accepted 9th August 2021
DOI: 10.1039/d1ra04638a
rsc.li/rsc-advances
such functionalization. Also, TTBrM is believed to be more
stable than the lighter halide homologues TTM and TFM, due to
Introduction
the larger size of the bromide groups and their associated steric
shielding.14 Functionalization of individual phenyl rings in all-
chloro TTM has also been reported, yielding highly emissive
products with signicantly enhanced stability.15,16 However, the
functionalization is not selective and the yield of these products
is low. By contrast, mixed-halide triphenyl methyl radicals
would enable site-selective functionalization or even polymeri-
zation, thus rendering the possibility to synthesize customized
open-shell molecules with unexplored properties.
Here, we report such mixed trichlorophenyl-tribromophenyl
methyl radicals. We compare their optical properties as well as
their stability to symmetric TTM and TTBrM systems. Further-
more, we show that our mixed halide precursors can be func-
tionalized selectively only on the para-bromo position with
much higher yields than in the previously pursued serendipi-
tous functionalization. Finally we show, that the bis(tri-
bromophenyl) (trichlorophenyl) methyl motif can be used to
produce polymers with the radical in the backbone.
Stable, carbon-centered p-conjugated radicals represent inter-
esting materials for redox-active systems in organic batteries, as
highly efficient electroluminescent SOMO emitters with effi-
ciencies beyond classical spin-statistics of closed-shell organic
semiconductors, and in organic spintronic applications.1–6
Halogenated triphenyl methyl radicals (or trityl radicals)
represent a prominent example of such stable, carbon-centered
radicals, which are easily accessible via Friedel–Cras reaction
of halogenated benzenes to chloroform, followed by oxidation
yielding the radical.7,8 This reaction provides facile access to one
of the few classes of luminescent open-shell molecules.9,10
While homo-halogenated tris(peruorophenyl) (TFM), tris(tri-
chlorophenyl) (TTM), and tris(tribromophenyl) methyl radicals
(TTBrM) have all been presented, mixed-halide radicals have
not been accessible via the Friedel–Cras route.11–13 Such
mixed-halide trityl methyl radicals would be of interest because
para-bromo sites of the phenyl rings can participate in transi-
tion metal-mediated cross-coupling reactions, such as Suzuki
coupling, while the halides in ortho-position to the central
methine carbon are sterically hindered and do not take part in
Results and discussion
Synthesis of mixed-halide triphenyl methyl radicals
aInstitute of Organic and Macromolecular Chemistry, Ulm University,
Albert-Einstein-Allee 11, 89081 Ulm, Germany. E-mail: alexander.kuehne@uni-ulm.de
bInstitute for Quantum Optics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm,
Germany
Typically, TTM and TTBrM are prepared in bulk in a single
Friedel–Cras reaction of chloroform with trichlorobenzene or
tribromobenzene followed by deprotonation and oxidation with
p-chloranil to form the respective radical.12,17 By contrast, our
open-shell mixed halide homologues are prepared by two
consecutive Friedel–Cras reactions (see Fig. 1). The radical is
produced by reaction with Bu4NOH and p-chloranil.
cDWI
– Leibniz-Institute for Interactive Materials, Forckenbeckstraße 50, 52074
Aachen, Germany
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d1ra04638a
‡ These authors contributed equally.
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Fig. 1 Synthetic route towards mixed-halide trityl radicals using a two-step Friedel–Crafts alkylation, followed by deprotonation and subsequent
oxidation. The colour code of the four different radicals in continued in the other figures.
In our synthetic strategy we rst produce the homo- conrmed by the clear electron paramagnetic resonance (EPR)
biphenylated product before coupling of the respective third signals (see Fig. 2a).
and opposite trihalobenzene. To obtain TBr3Cl6M, chloroform
is added stoichiometrically because once the monophenylated
Characterization of mixed-halide triphenyl methyl radicals
intermediate a,a0,2,4,6-pentachlorotoluene forms, the reactive
To characterize the nonahalo-triphenyl methyl radicals we rst
conduct DFT studies on the U-B3LYP(6-31+G(d)) level and the
energy diagram for the electronic ground state of TTM and
mixed halide radicals is obtained (see Fig. 2b). The unrestricted
treatment shows a large energy separation for a- and b-spin in
the SOMO while the HDMO and the LUMO are almost identical
for a- and b-spin. A comparison of these SOMO levels obtained
by DFT with the empirically determined absorption energies
obtained from UV-Vis spectroscopy suggests that the SOMO
might be best described by averaging the energies of the a-state
(occupied) and the and b-state (unoccupied) in the spin-
unrestricted theoretical treatment (cf. dashed line in Fig. 2b
and absorption spectra in Fig. 2c). According to the DFT
calculations for the different molecules, there is no signicant
difference in the symmetry of the Frontier orbitals (see Fig. 2b
for TBr3Cl6M and Fig. S3† for related radicals). Substitution of
chlorine by bromine leads to a systematic bathochromic shi in
the photoluminescence spectra of our nonahalo-trityl radicals.
This shi can be explained by a decreasing HDMO-SOMO gap,
evoked by increasing HDMO energies when substituting Cl by
Br from TTM to TTBrM (from blue to red in Fig. 2b). To gain
deeper insight into the emission behaviour of our radicals, we
perform TD-DFT geometry optimization for the D1 states, since
the emission of TTM is supposed to arise from the vertical D1 /
D0 transition (rst excited doublet state D1 to doublet ground
state D0).15,19 This transition corresponds to the SOMO to
HDMO relaxation (cf. Fig. 2b). TD-DFT correctly predicts the red-
planar benzyl carbocation immediately adds to the second tri-
chlorobenzene, producing the desired intermediate product.18
By contrast, to obtain the bisphenyl precursor to TBr6Cl3M, the
larger bromo-substituents entail a higher rotation barrier in
1,3,5-tribromo-2-(dichloromeꢀthyl)benzene. It is important to
perform this synthesis at 60 C, below the melting point of tri-
bromobenzene to avoid the formation of halide-exchanged
byproducts.19 Therefore, an excess of chloroform is required
to obtain a liquid reaction mixture, yielding a considerable
fraction of stable monophenylated side-product.19 We obtain
the bisphenylated products without coupling of a third phenyl
ring by adjusting the ratio of tribromobenzene to chloroform
(see Fig. 1). To obtain the respective mixed halide trityl
compound, the bisphenyl precursors are puried and the third
opposite trihalobenzene is added in excess to give the desired
product aer Friedel–Cras alkylation.
In both synthetic routes towards the mixed halide
compounds, the yield is limited by the Friedel–Cras alkylation
of tribromobenzene, giving overall yields for the closed-shell
compounds of 42% for bis(tribromophenyl)trichlorophenyl
methane (HBr3Cl6M) and 18% for tribromophenyl-
bis(trichlorophenyl)methane (HBr6Cl3M). For comparison, we
have also conducted the synthesis of the pure halides HTTM
and HTTBrM following previously reported protocols, which
gave yields of 81% and 21% in a single step.12,17 Deprotonation
and oxidation yield the respective open shell radicals, as
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Fig. 2 (a) X-band EPR spectra of the TTM (blue), TBr3Cl6M (green), TBr6Cl3M (orange) and TTBrM (red) in toluene solution, indicating an increase
of the g-factor with increasing number of bromine atoms. (b) Energy diagram for the electronic ground state of TTM, TBr3Cl6M, TBr6Cl3M and
TTBrM radicals obtained by DFT calculations using U-B3LYP/6-31+G(d). The SOMO energies of all molecules (dashed line) are estimated by
ESOMO ¼ 1/2(Ea + Eb). The Frontier orbitals are shown for the case of TBr3Cl6M. (c) Absorption (dashed line) and photoluminescence (solid line)
spectra of TTXM radicals. The emission is bathochromically shifted from yellow to red with increasing number of bromine atoms. The inset shows
a photograph of solutions of TTM, TBr3Cl6M, TBr6Cl3M and TTBrM (from left to right) in toluene under irradiation at 365 nm. (d) Fluorescence
decay of TTXM in degassed toluene solutions (1 mM) under irradiation using a 355 nm pulsed laser (pulse width: 7 ns, frequency: 10 Hz, energy
density: 2.87 ꢁ 105 mJ cmꢂ2). The lines are a guide to the eye. (e) Photoluminescence quantum yield (f) (squares) and fluorescence lifetimes (s)
(circles) of TTXM radicals in dichloromethane solution obtained from measurements using an integrating sphere and applying transient PL
measurements, respectively. The connecting lines are a guide to the eye. Both values decrease with increasing number of bromine atoms.
shi observed in our empirical photoluminescence experiment TTBrM – again, the mixed halide radicals exhibit uorescence
(see Table S1†). Furthermore, we observe increasing g-factors of lifetimes inside of this interval (see Fig. 2e and S4†). The rate
the unpaired electron in our EPR experiment for increasing constants of radiative (kr) and non-radiative decay (knr), can be
degrees of bromo-functionalization, indicating stronger spin– estimated from f and s using the following equations:
orbit interactions of the heavier bromine atoms (see Fig. 2a).20
The introduction of brominated phenyl rings also increases the
stability of the radicals against photo-bleaching (see Fig. 2d).
kr
f ¼
kr þ knr
The improved fastness derives presumably from enhanced
spin–orbit coupling together with the enhanced steric
hindrance with increasing bromine-functionalization, thus
preventing rotation and offering better protection of the radical
centre from oxidation and intramolecular ring-closing reac-
tions. However, advancing substitution of chlorides by
bromides leads to decreasing photoluminescence quantum
yields (f) from 3.1% for TTM to 0.8% for TTBrM – f of the mixed
halide radicals are between these values. In addition, the uo-
rescence lifetime (s) is reduced from 5.9 ns for TTM to 2.9 ns for
1
s ¼
kr þ knr
knr rises with an increasing number of bromine atoms, while kr
decreases (see Table 1). Previously, this phenomenon has been
explained by a more planar conformation of the phenyl rings
and stronger electron delocalization for lighter halo-atoms. The
enhanced p-conjugation facilitates uorescence by signicantly
suppressing vibrational relaxation.14 Conversely, the heavier
Table 1 Photophysical and EPR properties of mixed halide TTMs
Compound
g-Factora [ꢂ]
Fb [%]
sc [ns]
krd [106 sꢂ1
]
knrd [106 sꢂ1
]
t1/2e [103 s]
E1/2e [kJ cm2]
TTM
2.0037
2.0045
2.0056
2.0066
3.1
1.8
1.2
0.8
5.92
3.77
3.29
2.91
5.24
4.77
3.64
2.75
163.68
260.48
300.30
340.89
0.01
2.40
2.31
1.70
0.03
7.08
6.51
4.71
TBr3Cl6M
TBr6Cl3M
TTBrM
a
In toluene solution at 25 ꢀC. b f in DCM solution. c In oxygen-free DCM at 25 ꢀC. d Rate constants calculated using f ¼ kr/(kr + knr) and s ¼ 1/(kr +
knr). In 1 mM oxygen-free toluene irradiated at 355 nm (energy density: 2.87 ꢁ 105 mJ cmꢂ2, pulse width: 7 ns, frequency: 10 Hz).
e
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bromine atoms in our mixed halide radicals prevent a co-planar stable and exhibit EPR signals aer weeks of storage despite the
conformation of the molecules, thus assisting non-radiative dehalogenation (see Fig. S6d†). To date, almost exclusively
vibrational relaxation, causing the reduction in
increasing bromine content.
f
with electron donor groups have been coupled to TTM. Coupling of
an acceptor unit to the TTM radical moiety would endow this
open-shell molecule with new electronic and emissive proper-
ties.2 The pyrimidine-functionalization of the TBr3Cl6M repre-
sents such an acceptor-coupled radical, emphasizing the huge
potential of our synthetic approach for the design of organic
luminescent radicals of novel electronic structure (see Fig. 3a).2
Cross-coupling reactions of mixed-halide triphenyl methanes
as radical precursors for small molecules
To showcase the usefulness of our mixed halide radicals, we
perform transition metal catalysed cross-coupling reactions,
which preferentially involve the para-bromide-functionality due
to their better leaving-group character versus the chloride-
sites.21 This will give access to radicals of anisotropic and
Radical polymers obtained by cross-coupling reactions of
mixed-halide triphenyl methanes
complex structure that have been inaccessible to date. We test To highlight the full potential of our selectively addressable
our mixed-halide compounds in a variety of transition metal trityl units, we also employ HBr6Cl3M in Stille-, Sonogashira-,
medicated C–C cross-coupling reactions (see Table S3†). While and Suzuki-polymerizations. Successful coupling is conrmed
cross-coupling under typical Heck-, direct arylation-, and by 1H-NMR, size exclusion chromatography (SEC), and MALDI-
Yamamoto-reaction conditions are challenging, the mixed- ToF (the latter only for the Sonogashira coupled polyradical).
halide molecules successfully undergo Suzuki-, Sonogashira- MALDI-ToF clearly shows the repeating unit of the polyradical
and Stille-type coupling reactions. Coupling to HBr3Cl6M fol- (see ESI for NMR spectra and Fig. S2†). The resulting polymers
lowed by deprotonation and oxidation yields monofunctional exhibit Mw of 14–17 kDa as determined by SEC. The polymers
radicals or bridged biradicals (see Fig. 3a and S5a,c†). By can be converted into the open-shell species by deprotonation
coupling two phenylacetylene molecules to HBr6Cl3M and and subsequent oxidation, yielding linear polymers with the
subsequent conversion to the radical, a bi-functionalized open- radical moieties as part of the backbone, as conrmed by EPR
shell molecule is obtained (see Fig. S5b†). Single peaks in the spectroscopy (see Fig. S6e†). The synthesis of such conjugated
EPR spectra indicate successful conversion and that the polymers with radical electrons in their backbone is unprece-
unpaired electron of these species is localized at the central dented. However, spin-density measurements indicate that the
methine atom (see Fig. S6†). UV-Vis absorption spectroscopy conversion to the open-shell trityl radical is incomplete at 2–3%
reveals a strong band for all radical species at ꢃ400 nm, which (and up to 25% for poly(uorene-co-TBr6Cl3M) obtained by
is absent in the respective closed-shell precursors (cf. red and Suzuki coupling) when applying standard reaction conditions.
grey dashed lines in Fig. 3a and S5†). Concomitantly, the This low yield in conversion to the radical species could origi-
emission of the open-shell molecules exhibits a bathochromic nate either from (i) inefficient deprotonation and oxidation or
shi to the red spectrum around 600 nm, compared to the (ii) radical electron combination aer oxidation, producing
corresponding closed-shell molecules (see Fig. 3a and S5a–c†). quinodal p-conjugation along the backbone. Since radicals as
Note that we observe partial substitution of the ortho-bromines well as quinodal structures are NMR silent, we turn to IR- and
with hydrogens during Suzuki-coupling (see 1H-NMR spectra in Raman-spectroscopy but we do not detect a difference between
ESI†). We hypothesize that aer successful coupling of the the precursor and the polymer converted to the radical (see
boronic acid compound to the bromine atoms in para-position, Fig. S7†). However, when we employ higher temperature and
the bromides in ortho-position to the central methine group are larger concentrations of base, we observe higher degrees of
attacked by the palladium catalyst. Due to steric hindrance, conversion up to 40% (see Table S4†). The absorption spectra of
coupling with another boronic acid compound is prevented, the radical polymers resemble those of the closed-shell
leading to dehalogenation via b-hydride elimination as a side precursor polymers; however, with an additional absorption
reaction.22 However, the resulting radicals appear relatively band at lower energies, originating from the HDMO–SOMO
Fig. 3 Normalized absorption (dashed lines) and photoluminescence spectra (solid lines) of (a) a pyrimidine-functionalized radical and (b)
a polymer radical (red) in dichloromethane. The spectra of their precursors (grey) in the same solvent are shown for comparison. The photo-
luminescence spectra of the radicals result from excitation at the wavelength of the HDMO to SOMO transition.
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transition as in the case of the small molecular radicals. When FL6500 within a wavelength range of 350–800 nm. Quantum
exciting the polymers into this absorption band, we observe yields of the radicals in dichloromethane are measured with the
deep red emission of low intensity (cf. grey and red curves in same spectrometer equipped with an integrating sphere. Fluo-
Fig. 3b and S5d, e†).
rescence spectra of the radicals are recorded on a custom build
laser reection spectrometer from AIQTEC that is described in
detail below.
Conclusions
EPR spectroscopy. Electron Paramagnetic Resonance spectra
are recorded using a X-band EPR system (Bruker ELEXSYS E580)
with an ER 4122 SHQE cavity, using the soware xEPR for data
acquisition. Measurements are performed at microwave
frequency fX z 9.84 GHz, with a resonance quality factor Q ¼
8000, a power 0.15 mW (30 dB attenuation in xEPR). Modulation
amplitude and frequencies are 1 G/100 kHz. Prior to the
measurement, samples are inserted into 4 mm quartz EPR
tubes (Wilmad 707-SQ-100M) and dissolved into toluene. The
acquisition time for each spectrum is 40 s. For better illustra-
tion the magnetic eld of all four compounds is normalized
considering the microwave frequency used for the measure-
ment on TBr3Cl6M. Determination of the radical concentration
was performed using the built-in spin-counting module, avail-
able in xEPR.
Infrared spectroscopy. The infrared spectra are either
collected on a PerkinElmer Spectrum two spectrometer or on
a Bruker Alpha II spectrometer, both equipped with a diamond
ATR-crystal.
Gel permeation chromatography (GPC). The molecular
weight of the polymer is determined by gel permeation chro-
matography (GPC) on a 1260 Innity II GPC/SEC System from
Agilent Technologies with polystyrene as a standard and THF as
The simple functionalization of our mixed-halide compounds
gives access to ne-tuning and tailoring of the properties of
TTM-type radicals and the paradigm of more complex open-
shell molecules. Especially the successful synthesis of poly-
mers with radical centres in the backbone, as a rst of its kind,
showcases the manifold possibilities of designing future
unprecedented open-shell molecules. This facile functionaliza-
tion of open-shell molecules provides great potential for new
applications of radical emitters. Such novel open-shell
compounds will nd application as luminophores in optoelec-
tronics, as spin-sensitive sensors in the eld of spintronics, or
as active electrode material.
Experimental section
Materials
All reagents and solvents are purchased from Sigma-Aldrich,
TCI chemicals or Alfa Aesar and are used without further puri-
cation. All reactions are performed under argon atmosphere.
General methods
NMR spectroscopy. The H and 13C NMR spectra are recor- the eluent.
1
ded on a 400 MHz Bruker Avance DRX 400 spectrometer. The
Photostability measurement. Photostability experiments are
chemical shis (d) in the 1H-NMR spectra are reported in parts performed on an AIQTEC Microscopic Imaging Spectrometer
per million (ppm) versus the residual proton content of the (MIS1000). Prior to measurement the sample is dissolved in
deuterated solvent at ambient temperature, coupling constants toluene (2 mM) and purged with argon in a sealable 1 cm quartz
are given in Hertz (Hz). The spin multiplicities are designated as glass cuvette. The cuvette is placed on an inverted microscope
follows: s ¼ singlet, d ¼ doublet, t ¼ triplet and m ¼ multiplet. equipped with a 40ꢁ objective. The laser source is a frequency-
The obtained data are evaluated with the MestReNova program tripled Nd:YAG laser with a pulse duration of 7 ns at a repetition
from Mestrelab Research.
rate of 10 Hz. For the photostability studies the sample is
MALDI-ToF mass spectrometry. MALDI-FTICR spectra of the exposed to the pulsed laser with an energy density of 2.87 ꢁ 105
small organic molecules are recorded on a solariX mass spec- mJ cmꢂ2 over a certain time period. Photoluminescence and
trometer (Bruker Daltonics) using trans-2-[3-(4-t-butyl-phenyl)-2- reected light are collected through the same former
methyl-2-propenylidene]malononitrile (DCTB) as matrix. The mentioned objective and sent through a spectral edgepass lter
polymer samples are analyzed by MALDI-ToF mass spectrom- (cut-on wavelength 400 nm) to lter out the excitation signal.
etry using a solvent-free sample preparation method. The The ltered signal is then sent through a spectrograph with an
matrix (DCTB) and the polymer are mixed with a Retsch MM400 ICCD sensor to collect the emission spectra aer each laser
ball mill for 30 min (frequency: 30 Hz) and the resulting powder pulse. The intensity proles in the studies are obtained by
is applied on the MALDI target plate. The spectra are recorded integration of the emission spectra and evaluation over time.
on a Bruker rapieX mass spectrometer in the linear mode.
Time-correlated single-photon counting (TCPSC). The uo-
UV-Vis spectroscopy. UV-Vis measurements are performed rescence lifetime measurements are also conducted on the MIS
using a Lambda 365 spectrophotometer by Perkin Elmer with 1000, which is also equipped with a fs-pulsed laser diode with
UV WinLab as standard soware. The measurements are an emission wavelength at 375 nm and a repetition rate of 80
carried out within the wavelength range of 250–800 nm with MHz. The samples are measured under argon atmosphere in
a scan speed of 600 nm minꢂ1. The samples are diluted in a sealed cuvette, which is placed on top of the objective with
toluene as standard solvent and measured in 1 cm quartz glass 40ꢁ magnication. The signal is detected by a TCSPC photo-
cuvettes.
diode attached to the spectrometer. The grating of the spec-
Photoluminescence spectroscopy. The uorescence spectra trometer is centered at the wanted detection wavelength and the
of the precursor components are recorded with a PerkinElmer slit of the spectrometer is set at 100 mm.
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6 M. Mas-Torrent, N. Crivillers, V. Mugnaini, I. Ratera,
C. Rovira and J. Veciana, J. Mater. Chem., 2009, 19, 1691–
1695.
DFT/TD-DFT. DFT and TD-DFT calculations are performed
on the TTXM radicals with Gaussian g16.C.01.23 The exchange-
correlation functional UB3LYP of Becke, Lee, Yang and Parr is
applied with the 6-31+G(d) basis set.24–28 Diffuse functions and
additional polarization functions are important for the heavy
atoms, while both functions on hydrogen atoms do not lead to
signicant changes. The structures of the radicals are optimized
geometrically in vacuo. Molecular orbitals are visualized with
Gaussview 6.1.29 The electronic self-consistent eld (SCF)
procedure is considered to be converged when the total energy
difference is less than 10ꢂ4 eV, and all forces are at least smaller
´
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.
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Author contributions
AJCK devised the project. AJCK, LC, and MA designed the study,
and MA and LC synthesized and characterized the compounds.
LC performed transient spectroscopy, MA performed quantum
chemical calculations. RB and FJ provided support for the EPR
experiments. AJCK, LC, and MA wrote the paper, all authors
discussed and commented on the manuscript.
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Conflicts of interest
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There are no conicts to declare.
´
17 P. Mayorga-burrezo, V. G. Jimenez, D. Blasi, T. Parella,
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I. Ratera, A. G. Campana and J. Veciana, Chem.–Eur. J.,
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The authors gratefully acknowledge fruitful discussions with F.
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Joachim Rader from the Max-Planck-Institute for Polymer
Research for performing MALDI-ToF measurements of the
polymers and Dr Markus Lamla at Uni Ulm for performing
MALDI-FTICR measurements of the small organic molecules.
The German research foundation is acknowledged for funding
within the priority program SPP 2248 Polymer-Based Batteries.
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27658 | RSC Adv., 2021, 11, 27653–27658
© 2021 The Author(s). Published by the Royal Society of Chemistry