Electrochemical and Spectroscopic Studies on Triarylamine-Polychlorotriphenylmethyl Dyads with Particularly Strong Triarylamine Donors

Article abstract of DOI:10.1002/ejoc.202100476

We present two new donor-acceptor dyads composed of a polychlorotriphenylmethyl radical (PTM^.) as the acceptor (A) and bis(4-dimethylaminophenyl)(phenyl)amine (TPAN) or 2,2’:6’,2’’:6’’,6-trioxytriphenylamine (TOTA) as particularly electron-rich triarylamine (TAA) donors (D). We assessed their electrochemical properties and electronic structures by cyclic voltammetry, UV/vis/NIR spectroscopy, EPR spectroscopy and quantum chemical calculations. By establishing the spectroscopic fingerprints of the oxidized and reduced forms, we probe for the possible coexistence of a zwitterionic TAA⁺-PTM^? valence tautomer (VT), besides neutral TAA-PTM^.. UV/vis/NIR and EPR spectroscopic studies at variable temperature and in various solvents however provide no indication for such equilibria. Quantitative spin counting experiments by EPR spectroscopy and quantum chemical calculations indicate that the one-electron oxidized forms of these dyads possess an open-shell singlet ground state which is energetically slightly below the triplet state.

Full text of DOI:10.1002/ejoc.202100476

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Electrochemical and Spectroscopic Studies on Triarylamine-
Polychlorotriphenylmethyl Dyads with Particularly Strong
Triarylamine Donors
Authors: Stefanie Breimaier and Rainer Friedrich Winter
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202100476
Link to VoR: https://doi.org/10.1002/ejoc.202100476
01/2020

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Electrochemical and Spectroscopic Studies on Triarylamine-
Polychlorotriphenylmethyl Dyads with Particularly Strong
Triarylamine Donors
Stefanie Breimaier[a] Rainer F. Winter* [a]
[a]
S. Breimaier, Prof. Dr. R. F. Winter
Department of Chemistry
University of Konstanz
Universitätsstraße 10, D-78457 Konstanz, Germany
E-mail: rainer.winter@uni-konstanz.de; stefanie.breimaier@uni-konstanz.de
Supporting information for this article is given via a link at the end of the document.
Abstract: We present two new donor-acceptor dyads composed of a
polychlorotriphenylmethyl radical (PTM) as the acceptor (A) and 4,4’-
molecule-based materials like molecular switches and
memories.[2,4,6,9]
bis(dimethylamino)triphenylamine
(TPAN)
or
2,2’:6’,2’’:6’’,6-
Some time ago, Veciana and co-workers introduced particularly
intriguing metal-organic valence tautomeric pairs based on
ferrocenyl-perchlorotriphenylmethyl radical dyads Fc-PTM
(Figure 1).[10,11,12,13] These dyads exhibited a characteristic, low-
energy electronic transition for IET between the Fc donor and the
PTM acceptor in the near infrared (NIR) region of the electronic
spectrum. The strong positive solvatochromism (max = 892 nm /
112190 cm-1 in n-hexane; 1003 nm / 9970 cm- 1 in DMSO) of this
band agrees with a less polar, neutral ground state Fc-PTM.[10]
While solution spectra contain only the characteristic absorption
bands of the neutral PTM radical, but none of the PTM-
anion,[10,11,14] Mößbauer spectroscopy on solid samples clearly
indicated that the zwitterionic Fc+-PTM- state is thermally
populated.[11,13,15] When the electron-richness of the Fc donor was
increased by introducing eight or nine methyl groups to the Cp
ligands, the zwitterionic form was also observed in polar solvents
like acetone or dimethylformamide (DMF).[16] Such coexistence of
neutral and zwitterionic species in solution was also reported for
trioxytriphenylamine (TOTA) as particularly electron-rich triarylamine
(TAA) donors (D). We assessed their electrochemical properties and
electronic structures by cyclic voltammetry, UV/vis/NIR spectroscopy,
EPR spectroscopy and quantum chemical calculations. By
establishing the spectroscopic fingerprints of the oxidized and
reduced forms, we probe for the possible coexistence of a zwitterionic
TAA+-PTM- valence tautomer (VT), besides neutral TAA-PTM.
UV/vis/NIR and EPR spectroscopic studies at variable temperature
and in various solvents however provide no indication for such
equilibria. Quantitative spin counting experiments by EPR
spectroscopy and quantum chemical calculations indicate that the
one-electron oxidized forms of these dyads possess an open-shell
singlet ground state which is energetically slightly below the triplet
state
Introduction
purely organic PTM-based D-A dyads featuring
a
tetrathiafulvalene (TTF) instead of a Fc donor and a TTF-
oxophenalenoxyl radical dyad.[17,18,19]
Valence tautomers (VTs) are different electronic isomers of a
compound composed of a donor and an acceptor unit. They differ
by the redox states adopted by the donor (D or D+) and the
acceptor (A or A-) and hence by the charge and spin density
distributions within the molecule. As individual VTs interconvert
via an intramolecular electron transfer (IET) process,[1] the
occurrence of valence tautomerism requires that the intrinsic
redox potentials of the D/D+ and the A/A- redox couples are not
too dissimilar. The phenomenon of valence tautomerism was
initially observed for transition metal complexes with redox active,
“non-innocent” ligands, particularly those of the ortho-
benzoquinone / semiquinonate / catecholate type and their many
isoelectronic imine or thio variations,[2,3,4] but was later expanded
to mixed-valent compounds with chemically inequivalent redox
sites.[5,6] Examples of electronic isomers with even more subtle
distinctions between two different electronic minima have also
appeared in the literature.[7] The fact that isomerization is
triggered by external stimuli, such as light irradiation or
temperature or pressure changes[8] and that VTs exhibit
individually different electronic and spectroscopic properties
render them stimuli-responsive building blocks for bistable
Figure 1. Equilibria between the neutral Fc-PTM and the zwitterionic Fc+-
PTM- states.
Other examples of purely organic donor-acceptor dyads
potentially capable of exhibiting valence tautomerism are
triarylamine-PTM dyads TAA-PTM. The latter constitute rare
examples of neutral, purely organic, redox-asymmetric mixed-
valence (MV) compounds with a low-energy electronic transition
to the TAA+-PTM- forms. Several such derivatives as well as a
diarylamine-appended PTM radical were scrutinized for solvent
effects on intramolecular charge transfer, taking advantage of the
good solubilities in nonpolar solvents and the lack of ion pairing
1
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
effects.[20–23,24] These studies disclosed, that the degree of
electronic coupling between the two dissimilar redox sites is
weaker than in mixed-valent bis(triarylamines) with similar -
conjugated linkers. This is due to an inherent redox asymmetry as
reflected by the different redox potentials of the donor and the
acceptor and the concomitant localization of the -HOSO on the
TAA and the -LUSO on the PTM entity, where HOSO and
LIUSO denote the energetically highest occupied / energetically
lowest unoccupied spin orbital.[20–23] Similar work was also
performed on various N-carbazole-polychlorotriphenlymethyl
radicals with a lesser degree of chlorination and hence lower
acceptor strengths.[25–30] One of these cases has provided hints
as to the presence of small quantities of a zwitterionic valence
tautomer in highly polar DMF.[29]
Synthesis. The required PTM precursors PTM-PPh3Br and PTM-
PO(OEt)2 were prepared according to established literature
procedures[35] (Scheme 1) via the so-called BMC chlorination
method of Ballester and co-workers.[36] TOTA was synthesized
according to the literature-known four-step sequence outlined in
Scheme 2.[34,37] It was then subjected to a Vilsmeier reaction,
which introduced the formyl group. Wittig reaction of TOTA-
CHO[38] with PTM-PO(OEt)2 afforded the corresponding
triarylmethane derivative TOTA-PTMH (Scheme 2) in modest
yield.
Scheme 1. Synthesis of PTM precursor PTM-PPh3Br and PTM-PO(OEt)2.
Figure 2. Illustration of the literature-known TTF- and Fc-PTM dyads (top) and
the new TAA-PTM dyads of the present study (bottom).
One important setscrew that governs the occurrence and
positioning of the valence tautomeric equilibrium is the intrinsic
difference between the half-wave potentials for donor oxidation
and reduction of the acceptor in such dyads. For all previously
studied TAA-PTM dyads, this potential separation E1/2 is larger
than 900 mV (> 86 kJ/mol, 5.4 eV). At the other end of the scale,
ferrocene-PTM dyads with the particularly electron-rich octa- and
nonamethylferrocene donors exhibit E1/2 values as low as
169 mV. It is these cases, where zwitterionic valence tautomers
could be observed in fluid solution.[6,16] Other work has described
valence tautomerism in conceptually related ferrocene-
diarylmethylium dyads with intrinsic half-wave potential
differences as large as 500 mV, albeit in these cases subsequent
dimerization of the ferrocenium-trityl isomers, which provides an
additional driving force, is entangled with the valence tautomeric
equilibria.[31] We therefore mused that TAA-PTM dyads might
also be capable of exhibiting valence tautomerism, if particularly
strong TAA donors are used. By screening the literature we
Scheme 2. Synthesis of TOTA-PTM.
identified
the
planar
2,2’:6’,2’’:6’’,6-trioxytriphenylamine
(TOTA)[32–34] and bis(4-dimethylaminophenyl)(phenyl)amine as
particular promising candidates (see Figure 2). Herein, we
present the synthesis as well as the electrochemical,
spectroscopic, and electronic properties of the corresponding
TAA-PTM dyads and their oxidized and reduced forms as well as
the results of solvent- and temperature-dependent UV/vis/NIR
and EPR studies as probes of possible valence tautomerism.
Scheme 3. Synthesis of TPAN-PTM.
The synthesis of the second target compound TPAN-PTM is
illustrated in Scheme 3. First, the phosphonium salt PTM-PPh3Br
was reacted with 4-iodobenzaldehyde 7. The obtained Wittig
product 8[35] was then subjected to a Pd-catalyzed Buchwald-
Results and Discussion
2
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Hartwig amination with bis(4-dimethylaminophenyl)amine to
afford TPAN-PTMH. Both TAA-substituted triphenylamines
1
provided well-resolved H and 13C NMR spectra which attest to
their spectroscopic purities (see Figures S1 to S4 of the
Supporting Information). The target radical dyads were then
prepared via the usual two-step sequence involving deprotonation
of the triarylmethyl constituent with potassium tert-butoxide and
subsequent oxidation of the ensuing anions with p-chloranil
(Schemes 2, 3).
Figure 3. Cyclic voltammograms of the oxidation (left) and reduction (right) of
TPAN-PTM in CH2Cl2/NBu4PF6 (0.1 M) at room temperature and ν = 0.1 Vs-1.
Electrochemistry. The redox properties of TOTA-PTM and
TPAN-PTM were probed by cyclic voltammetry in 0.1 M
NBu4PF6/CH2Cl2 and NBu4PF6/DMF at r. t. Representative
voltammograms (CVs) in CH2Cl2 are shown in Figure 3 and in
Figures S7 and S8 of the SI, while the associated data are
collected in Table 1. Both radicals exhibit a one-electron wave for
the reduction of the PTM radical to the corresponding carbanion.
Increasing the donor strength of the TAA from TOTA to TPAN
shifts the half-wave potential E1/2/- of this process only slightly
cathodic, from -708 mV to = -729 mV. This agrees with previous
findings of Lambert on other TAA-PTM donor-acceptor dyads.[19]
Owing to the presence of very electron-rich TAA donors, the CVs
of both dyads also show two consecutive one-electron oxidation
waves. Reverse-to-forward peak current ratios r of near unity
attest to the high degree of chemical reversibility. This also seems
to hold for the second oxidation of the TOTA dyad, where the
proximity of this wave to the anodic discharge limit prevents us
from obtaining meaningful values of r. The half-wave potential of
the first oxidation of the TOTA derivative of 119 mV is already by
ca. 120 mV lower than that of Lambert´s most electron-rich di(4-
anisyl)phenylamine TAA-PTM derivative. TPAN-PTM oxidizes
at an even lower potential of - 205 mV vs. the
ferrocene/ferrocenium standard, which brings E1/2 down to
524 mV (Table 1). Changing the solvent to more polar DMF
causes a sizable anodic shift of the half-wave potential for PTM
reduction by 300 mV, while causing only smaller (TPAN-PTM) or
negligible effects (TOTA-PTM) on those for triarylamine oxidation.
This reduces the energy differences between the neutral and the
zwitterionic forms considerably.
Comparison of the redox potentials for the first oxidation and
reduction with those of Veciana´s PTM radical HOC-Sty-PTM on
the one hand and those of pristine TOTA and TPANH on the other
provides us with a glimpse of how the TAA donor and the PTM
acceptor affect each other. Thus, on replacing the formyl acceptor
by the (4-MeOC6H4)2N(C6H4) donor, E1/2/- shifts cathodically by a
rather moderate margin of ca. 80 mV. For the TOTA-derived dyad
this shift is even down to 60 mV.[40] Quite surprisingly, attaching
the nominal –CH=CH-PTM acceptor to the TOTA and the
TPANH[32,41] donors also introduces a cathodic shift of 9 to 145
mV with respect to their unsubstituted parents. Obviously, the
effect of enlarging the -conjugated system overrides the
inductive influence of the remote acceptor. Both these findings
indicate that the TAA donor and the PTM acceptor are largely
decoupled from each other in the electronic ground states of these
dyads, which is a necessary prerequisite for observing valence
tautomerism.
Table 1. Cyclic voltammetry data of TOTA-PTM, TPAN-PTM and reference
compounds.[a]
0/+//0
E1/20/+(ΔEp)
E1/2+/2+(ΔEp)
E1/20/-(ΔEp)
E1/2
CH2Cl2 DMF
CH2Cl2 DMF
CH2Cl2 DMF CH2Cl2 DMF
TOTA-
PTM
119
(65)
124
(59)
932
-
-708
(115) (60)
-391 827 515
(86)
The origin of the second oxidation wave in these dyads cannot be
assigned unambiguously on the basis of CV data alone. While no
second oxidations seem to have been reported for TOTA and
TPAN, similar, electron rich triaryl- or N,N-diaryl-N-methylamines
were found to undergo further oxidation at ca. 300 – 400 mV more
positive E1/2 as the first oxidation and to yield robust, quinoid
dications.[39] Similar triarylmethyl-based oxidations were also
observed for carbazole-triarylmethyl dyads with only partially
chlorinated aryl substituents.[25–30] Lambert and coworkers did
nevertheless not observe the oxidation of the PTM radical entity
within their TAA-PTM dyads up to potentials of 1000 mV.[20,22] On
the other hand, the 4-formylstyryl-appended PTM radical
(C6Cl5)2C(2,3,5,6-C6Cl4-CH=CH-C6H4-4-CHO) (HOC-Sty-PTM)
was found to oxidize at ca. 590 mV.[40] As we will discuss later,
this issue can however be resolved by the spectroscopic
characterization of the doubly oxidized forms.
TPAN-
PTM
-205
(66)
- 119
(79)
187
(66)
106
(59)
-729
(94)
-426 524 307
(60)
OHC-
Sty-
PTM [c]
590 (-)
-
-
-
-
-
-
-650(-)
-
-
-
-
-
-
TOTA-
Br [d]
215
(91)
-
TOTA[e]
110 (-)
-60 (-)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
TPANH[f]
[a] All data in millivolts versus Cp2Fe0/+ in CH2Cl2/NBu4PF6 (0.1 M) at r. t. and at
ν = 0.1 Vs-1. [b] Reversibility coefficient r = ip,rev/ip,fw; n. p. = not provided in the
cited references. [c] From ref. [40]. [d] See Figure 8 in the Supporting
Information. [e] From ref. [33]. [f] From ref. [41].
UV/vis/NIR spectroscopy of the neutral, the reduced and the
oxidized forms of the dyads. TOTA-PTM and TPAN-PTM are
red-colored in the solid state and in solution and exhibit an intense,
structured absorption band with two distinct peaks at 389 nm and
at 408 nm or 414 nm, respectively, in CH2Cl2 (Figure 4, Table 2).
The 389 nm band is the characteristic fingerprint of the PTM
radical and was observed at an identical wavelength in several
3
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
other oligophenylenevinylene- (OPV-) appended mono- or OPV-
bridged bis(PTM) diradicals[40] and in other previously reported
donor-PTM acceptor dyads.[10,18,42,43,44]
induced partial decomposition on continued electrolysis.
Otherwise, the original spectra of the neutral compounds were
fully recovered on reoxidation of the TAA-PTM- anions or
rereduction of the oxidized forms.
Reduction of the present TAA-PTM dyads induces similar
spectroscopic changes as those observed for the previous
congeners.[22] Thus, the intensity of the PTM absorption at
389 nm decreases with a concomitant shift of the remaining
absorption to lower energies, while the CT band in the NIR
vanishes (see left panel of Figure 5). At the same time, two
likewise intense bands at ca. 520 nm and at 562 nm or 581 nm
grow in. According to our TD-DFT calculations, these transitions
involve CT from mainly the reduced methanide center to either
the electron poor C6Cl5 entities or the C6Cl4-CH=CH linker (see
Figures S14 to S18 and Tables S3 and S4 of the Supporting
Information) with some admixture of CT from the TAA-based
donor to the linker-based LUMO+1.
The first oxidation the dyads induces even more significant
changes of the electronic spectra. We first note a slight
intensification of the characteristic PTM absorption band.
Secondly, the originally poorly resolved CT transitions at ca. 510-
530 nm shift slightly hypsochromically and evolve into clear bands.
The most remarkable alterations are the appearance of two new
low-energy absorption bands. The most prominent of these is a
vibrationally structured, intense band peaking at 716 nm or
1082 nm, which corresponds to the oxidized TAA donor.[47] We
also note a close resemblance of the low-energy band of the
TOTA+ chromophore to that reported for other salts of this
cation.[32,48] The second feature is a less intense, unstructured
band which is either disposed to lower (TOTA+-PTM) or higher
(TPAN+-PTM) energies compared to the TAA+ band.
Figure 4. UV/vis/NIR spectrum of TPAN-PTM in toluene (red), CH2Cl2 (orange),
acetone (green) and nitromethane (blue).
The results of time dependent (TD)-DFT calculations at the pbe1-
pbe-DFT level of theory also agree with this assignment.
Comparisons between experimental and computed spectra, the
compositions of the relevant MOs and the corresponding electron
density difference maps (EDDMs) can be found as Figures S9 to
S13 and Tables S1 and S2 in the Supporting Information.
According to these calculations, all other electronic bands at lower
excitation energies involve, to various degrees, charge transfer
(CT) from the TAA donor to the PTM acceptor, similar to what
has been reported for other OPV- and donor-appended PTM
radicals.[10,40,42,44] This is particularly true for the most red-shifted
absorption band, which is adequately described as the β-
HOSOβ-LUSO transition and hence corresponds to an
intramolecular electron transfer.[10,13,18,42,45] In agreement with the
ca. 300 mV lower half-wave potential difference E1/2 between
TAA oxidation and PTM reduction, the underlying transition is
red-shifted from 819 nm for the TOTA- to 973 nm for the TPAN-
derivative and its intensity is increased by a factor of 2. In further
support of its CT character, this band also proved to be
solvatochromic (Figure 4 and Figure S30 in the Supporting
Information).
Table 2. UV/vis/NIR spectroscopic data for TOTA-PTMn+ and TPAN-PTMn+ in
their neutral, anionic, monocationic and dicationic states.[a]
n
0
λmax (ε[103M-1cm-1])
TOTA-PTM
TPAN-PTM
389 (24.7). 408 (20.6), 532 (3.4), 819 (1.6)
412 (13.5), 517 (18.9), 581 (18.6)
-1
+1
389 (24.8), 475 (15.6), 671 (10.4), 716 (17.1), 793
(3.6), 968 (2.9)
0
389 (27.4), 414 (22.4), 512 (7.7), 973 (3.2)
397 (16.7), 527 (18.5), 562 (18.0)
-1
+1
389 (27.5). 412 (23.2), 506 (8.9), 729 (7.3), 1082
(27.5)
+2
386 (20.0), 420 (14.4), 630 (14.8), 786 (40.3)
In order to obtain additional insights into the electronic
characteristics of the corresponding oxidized and reduced forms
of these dyads, which mirror the individual TAA+ or PTM- sites of
the CT excited state or of a possible zwitterionic TAA+-PTM-
valence tautomer, we monitored the concomitant changes of the
[a] Data are reported in nm. Measurements were carried out in
1,2-C2H4Cl2/NBu4PF6 at room temperature.
Accompanying (TD)-DFT calculations place the triplet state
52 kJ/mol (TOTA+-PTM) or 44 kJ/mol (TPAN+-PTM) below the
closed-shell singlet state, but slightly above the open-shell singlet
(see below). We also note that the TD-DFT computed spectra of
the diradical forms show an overall better agreement with the
experimental spectra than those computed for the closed-shell
singlet states (see Figures S19 and S20 and Tables S5 to S8 of
the Supporting Information), for which only one or two transitions
UV/vis/NIR
spectra
by
in
situ
electrolysis
in
a
spectroelectrochemical (SEC) setup, employing an optically
transparent thin-layer electrolysis (OTTLE) cell.[46] Figure 5
provides graphical accounts of the spectral changes on reduction
as well as on the first and on the second oxidation. Experimental
data are collected in Table 2. All redox processes except for the
second oxidation of the TOTA-PTM dyad proceeded smoothly
with clear isosbestic points. For TOTA-PTM, the required high
voltages prevented full conversion to the dioxidized form and
4
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Figure 5. UV/vis/NIR spectroelectrochemistry of TPAN-PTM (top panels) and TOTA-PTM (bottom panels) during the reduction (left) as well as the first (middle)
and the second oxidation (right) in an OTTLE cell (1,2-C2H4Cl2/NBu4PF6 (0.1 M), at r. t.). The asterisk marks an artefact caused by our instrumentation.
with relevant oscillator strengths are predicted. The results of our
TD-DFT analysis confirm the assignment of the most intense, low-
energy band as a ππ* transition within the oxidized TAA+
chromophore subunit, augmented with some CT from the PTM
moiety for TOTA+-PTM. The broad band of TPAN+-PTM at
729 nm, is caused by a β-HOSO-1  β-LUSO transition and
represents CT from the -C6Cl4-CH=CH- linker to the TPAN+
moiety, in agreement with other oxidized TAA-PTM
derivatives.[22,23] The 968 nm band of TOTA+-PTM is likely of
similar origin although our computations failed to produce such a
transition.
PTM dyad as the relevant electron transfer site of also the second
oxidation step.
After having identified the double band at ca. 520 nm and at 560
or 580 nm as the spectroscopic fingerprints of the reduced PTM-
and the transition near 800 nm or 1100 nm to the aminium-
centred absorption of the oxidized TAA+ constituents of our dyads,
we recorded UV/vis/NIR spectra of the neutral compounds in
several solvents of different polarity in order to probe for the
possible presence of a second, zwitterionic valence tautomer (see
Figure 4 and Figure S30 in the Supporting Information).
Electronic spectra of both dyads however provided no
conspicuous features that would point to the existence of such a
species. One should note here that the band structuring in some
solvents is likely due to a vibrational progression, as it was
observed on earlier occasions for similar systems.[22] This is also
As was already mentioned, we could only achieve partial
conversion of TOTA+-PTM to the corresponding dication before
the onset of decomposition, which is indicated by the gradual loss
of the initial isosbestic points and the lack of reversibility on back
electrolysis. No such problems were encountered for TPAN-PTM. supported by the lack of spectral changes for the TPAN-PTM
During the second oxidation, the prominent band at 1082 nm
vanishes and is replaced by an even more intense absorption with
a similar vibrational structuring at 786 nm. According to our TD-
DFT calculations, this band originates from two close-lying
transitions, which correspond to CT from the styryl-PTM moiety
to the doubly oxidized N(C6H4-4-NMe2) group and a ππ* transition
confined to the oxidized TAA2+ chromophore itself (see Figures
S25 and S29 and Tables S9 and S10 of the Supporting
Information). This finally confirms the TPAN donor of the TPAN-
dyad on varying the temperature from -70 °C up to 40 °C in CH2Cl2
in or N,N-dimethylformamide as shown in Figure S31 of the
Supporting Information. All things considered, the electronic
spectra of the two new TAA-PTM dyads provide no hints to the
presence of a second, zwitterionic isomer in solution.
EPR spectroscopy on the parent radicals and their oxidized
and reduced forms. Their unpaired spin renders TOTA-PTM
and TPAN-PTM EPR active. In the presence of valence
tautomerism, one would expect an additional EPR resonance for
5
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
the second isomer with the unpaired spin density on the aminium
instead of the PTM site and with slightly different g values and
hyperfine splitting (hfs) patterns. EPR spectroscopy of the
radicals was initially performed in CH2Cl2 and the individual hfs
constants were determined by digital simulations (see Figure 6
and Table 3).
Figure 7. Calculated spin density maps of TOTA-PTM (left) and TPAN-PTM
(right).
Samples of the monocations for EPR studies were prepared by
chemical oxidation of the neutral compounds, using
acetylferrocenium hexafluoroantimonate (TOTA-PTM) or
ferrocenium hexafluorophosphate (TPAN-PTM) as the oxidant.
The purity of these samples was verified by comparing their
Figure 6. Experimental (black) and simulated (blue) EPR spectra of
TOTA-PTM (left) and TPAN-PTM (right) in CH2Cl2 at room temperature.
UV/vis/NIR
spectra
to
those
collected
in
our
spectroelectrochemical measurements. Likewise, dioxidized
TPAN2+-PTM was prepared by chemical oxidation of the neutral
compound
with
2.1
equiv.
of
acetylferrocenium
Table 3. EPR data of the target compound TOTA-PTM and TPAN-PTM in their
neutral, monocationic and dicationic states.[a]
hexafluoroantimonate. The corresponding data are displayed in
Figure S34-S36 of the SI. EPR spectroscopy confirms the
presence of paramagnetic species by virtue of strong resonance
signals. Cation TOTA+-PTM does not show separate signal sets
for the two different kinds of EPR active subunits, which suggests
that their g values are basically identical. While broad and ill-
resolved at r. t., the signal gradually evolves into a well-defined,
non-binomial triplet resonance on cooling with a 14N hyperfine
splitting of 11.1 G and additional, partially resolved hyperfine
splittings A(1H) = 3.8 G and A(1H) = 2.4 G. Cation TPAN+-PTM
shows an even poorer resolution, but apparently consists of two
giso
A(1H)
A(13C)
A(14N)
TOTA-PTM
TOTA+-PTM
TPAN-PTM
TPAN+-PTM
1.9949
1.9936
1.9945
1.9938
1.9938
1.9942
2.7
13.9 (2 C), 13.0 (4C)
-
3.8, 2.4
-
11.1
-
-
13.9 (2 C), 12.0 (4 C)
-
8.2
-
-
2.2
-
TPAN2+-PTM
2.7, 0.7
16.8 (2 C), 13.5 (4 C)
-
different subspectra, one showing
a
hyperfine splitting
[a] All hyperfine coupling constants are reported in Gauss. The monocation of
TPAN-PTM was generated with ferrocenium hexafluorophosphate, while the
other mono- and dications are generated with acetylferrocenium
hexafluoroantimonate as the oxidant.
A(14N) = 8.2 G, and one with a hyperfine splitting A(1H) = 2.2 G,
both with a g value of 1.9938. These results match with our DFT
calculations, which indicate almost uniform spin distributions over
the entire molecule with equal spin densities at the TAA+ and the
PTM subunits (see Figure 8). In no case we could observe a half-
field signal for the nominally forbidden ms = 2 transition, which
indicates that the coupling constant J is small (i. e. the unpaired
spins in these diradicaloid species behave essentially
independently). This is consistent with the rather large distance of
>12 Å between the nominal spin-bearing centers as derived from
the geometry-optimized structures.[50] DFT calculations indicate
that the open-shell singlet and triplet states are nearly
isoenergetic with a very slight preference (ca. 0.6 kJ/mol) for the
former. Quantitative spin counting experiments on TPAN+-PTM
with stable DPPH as the calibrant indicated, that the open-shell
singlet is indeed the ground state and that, at r. t., the triplet state
is thermally populated and accounts for ca. 40% of the sample
with a further decrease as T is lowered, e. g. to 32% at -50 °C.
The TPAN2+-PTM dication shows a resolved doublet resonance
at a g value of 1.9942 and hyperfine coupling constants A(1H) of
2.7 G and 0.7 G to one proton each, and A(13C) of 16.8 G two and
of 13.5 G to four equivalent C atoms. The close resemblance to
the spectrum of neutral TPAN-PTM confirms double oxidation at
the TAA site. This annihilates the TPAN-based spin, but leaves
that of the PTM radical unaltered.
The EPR spectrum of TOTA-PTM consists of a doublet
resonance with a g-value of 1.9949 and coupling constants of
A(1H) = 2.7 G, A(13C) = 13.9 G (2 C atoms) and A(13C) = 13.0 G
(4 C atoms), while the EPR signal of TPAN-PTM only reveals as
a single resonance line with coupling constants of A(13C) = 12.0 G
(2 C atoms) and A(13C) = 13.9 G (4 C atoms) as derived from the
small, additional features on either side of the main peak.[29,49] [47]
This matches with our DFT calculations, which indicated a PTM
centered spin (see Figure 7). We next recorded T-dependent EPR
spectra of TOTA-PTM and TPAN-PTM in a solvent of lower
(toluene) and higher polarity (DMF) than dichloromethane. No
conspicuous changes of the signal could be observed in either
toluene or DMF over a temperature range from -60 °C to 100 °C
or 120 °C, apart from the expected increase/decrease of the
signal intensity upon cooling/warming according to the Boltzmann
distributions between the ground and the excited states (see
Figures S32 and S33 of the SI).
6
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
pseudoreference electrode. A platinum electrode (ø = 1.1 mm, BASi) was
used as working electrode and polished with diamond pastes from Buehler
and Wirtz with successively decreasing particle sizes of 1.5 µm and 1 µm
prior to the experiment. CH2Cl2/NBu4PF6 (0.1 M) was used as supporting
electrolyte and the cell was connected to an argon gas bottle. The
voltammograms were recorded by a computer-controlled BASi EPSILON
potentiostat. Referencing was performed by adding appropriate quantities
-
of cobaltocenium hexafluorophosphate (Cp2Co+ PF6 ) as the internal
standard after all scans of interest had been carried out. All potentials are
reported against ferrocene/ferrocenium (Cp2Fe0/+) reference couple with
E1/2 (Cp2Co+) PF6- = -1330 mV vs. Cp2Fe0/+ under our conditions. Redox
potentials are subject to an error of 3 mV.
Figure 8. Calculated spin density maps of the monocations TOTA+-PTM (left)
and TPAN+-PTM (right).
UV/vis/NIR spectroelectrochemistry was carried out in a custom-built
OTTLE cell[46] featuring two CaF2 windows of a conventional liquid IR cell
with a Pt-mesh working and counter electrode and a thin silver foil as
reference electrode sandwiched in between. 1,2-C2H4Cl2/NBu4PF6 (0.1 M)
was used as the supporting electrolyte. The UV/vis/NIR measurements
were performed on a diode-array TIDAS spectrometer by J&M ANALYTIK
AG with a spectroscopic window of 250-2100 nm. The applied voltage was
adjusted with the potentiostat Wenking Pos2 from Bank Electronics –
Intelligent Controls GmBH.
Conclusions
We report on two new donor-acceptor dyads that comprise of a
2,2’:6’,2’’:6’’,6-trioxytriphenylamine
(TOTA)
or
4,4’-
bis(dimethylaminophenyl)(phenyl)amine (TPAN) donor and a
polychlorotriphenylmethyl (PTM) acceptor unit. Cyclic
voltammetry revealed a PTM-based one-electron reduction and
two consecutive TAA-based one-electron oxidations, whose half
wave potentials shift cathodically as the electron-releasing
capability of the TAA donor increases (TOTA < TPAN). Half-wave
potential differences between the first oxidation and the reduction
are notably lowered by ca. 300 mV as the solvent polarity is
increased from CH2Cl2 to DMF, attesting to a lower energy gap
between the neutral TAA-PTM ground state and the excited
zwitterionic TAA+-PTM- state. The UV/vis/NIR spectra of TOTA-
PTM and TPAN-PTM exhibit the characteristic absorption band
of the PTM chromophore, as well as a broad, solvatochromic NIR
band that can be assigned to an intramolecular electron transfer
between the respective TAA donor and the PTM acceptor.
UV/vis/NIR spectroelectrochemistry confirmed the identity of the
individual redox sites and established the spectroscopic
fingerprints of the PTM- and the TAA+ chromophores. None of
these features was observed in solutions of the neutral dyads.
EPR spectra of the native radicals also failed to identify a possible
zwitterionic isomer. Quantitative spin counting EPR spectroscopy
and DFT calculations indicate that the open-shell singlet and
triplet states of the one-electron oxidized forms are nearly
degenerate. UV/Vis/NIR and EPR spectroscopy also allow us to
safely identify the TPAN-donor as the site of the second oxidation.
EPR spectroscopy was performed on a MINISCOPE400MS X-band
benchtop spectrometer by Magnettech GmbH with
a temperature
controller from the same manufacturer as thermostat. Low-temperature
measurements were performed by cooling with liquid nitrogen. For cooling
the magnet, a Thermo Fischer Scientific Inc. HAAKE A10 cooling unit was
used. The compounds were chemically oxidized with ferrocenium
hexafluorophosphate or acetylferrocenium hexafluoroantimonate and
dissolved in CH2Cl2 at room temperature prior to measuring. Simulations
of the experimental EPR spectra were performed using MATLAB Easyspin
program.[51] Quantitative spin counting experiments employed the DPPH
radical standard as the calibrant. Its purity was checked by titration with
hydroquinone using a UV/Vis/NIR probe prior to measurements.[52] Further
details as to the employed procedures are provided in the Supporting
Information. Experimental settings were adjusted as follows to avoid any
overmodulation and saturation effects: microwave frequency of 9.4 GHz,
microwave attenuation of 36 dB (corresponds to 0.05 mW of microwave
power), modulation amplitude of 3 G, sweep width of 6000 G, and a
number of 8192 data points.
DFT calculations were carried out using the Gaussian 16 program
package.[53] Geometry optimization was followed by vibrational analysis
with the polarizable continuum model (PCM) performed in 1,2-
dichloroethane as solvent.[54] Using the TD-DFT method the electronic
spectra were calculated at the optimized ground-state structures.
Polarized douple-ζ basis sets [6-31G(D), geometry optimization] were
employed together with the pbe1pbe functional.[55] In TD-DFT calculations
the solvation effects were modelled by the polarizable continuum model.[54]
The GaussSum,[56] Avogadro, GNU Parallel, and vmd program packages
were used in combination with POV-Ray[57] for data processing and
graphical representations.[57,58]
Experimental Section
General procedures. All syntheses were performed under nitrogen at-
mosphere using standard Schlenk techniques. The solvents for synthesis
and characterization were dried over the appropriate drying agent, dis-
tilled, stored under nitrogen atmosphere prior to use. All reagents were
purchased from commercial suppliers and were used without additional
purification. 1H, 13C NMR spectra were recorded on a Bruker AVANCE III
400 and a Bruker AVANCE III 600 spectrometer at room temperature. The
residual signal of the protonated solvents was used as the reference and
coupling constants are given in Hertz. Mass spectra were recorded on a
LTQ Orbitrap Velos (Thermo Scientific) with ESI capable of a resolution at
least 60000. The spectrometer was calibrated with the Pierce LTQ Velos
ESI Positive Calibration Solution (Thermo Fisher Scientific) prior to every
measurement. Detection was done in the positive-ion mode.
Synthesis and Characterization.
Diphenyl(p-tolyl)methanol.[59] To a suspension of 3.10 g (127 mmol,
1.25 eq.) of magnesium turnings in 20 mL of dry diethyl ether, 0.43 mL
(0.94 g, 5 mmol, 0.05 eq.) of 1,2-dibromoethane were added. 13.33 mL of
bromobenzene (20.00 g, 127 mmol, 1.25 eq.), dissolved in 35 mL of dry
diethyl ether, were slowly added and the brownish reaction mixture was
stirred for further 30 min after addition was complete. 20.00 g (102 mmol,
1.00 eq.) of 4-methylbenzophenone were dissolved in 45 mL of dry
diethyl ether and were slowly added. The mixture was stirred for 3 h at
60 °C. After the mixture was cooled in an ice bath, 100 mL of 3 M
hydrochloric acid were added, and the organic phase was washed with
H2O (3 x 300 mL) and brine (1 x 300 mL). The organic phase was dried
over MgSO4 and the solvent was evaporated. The resulting yellow oil was
Cyclic voltammetry was performed in a custom-made one-compartment
cell with
a platinum wire counter electrode and a Ag/AgCl wire
7
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
recrystallized from n-hexane to obtain a white solid (yield: 5.18 g, 19%).
1H NMR (400 MHz, CDCl3): δ [ppm] = 7.36-7.28 (m, 10H, Hphenyl), 7.18,
7.14 (each d, 3JH-H = 8.3 Hz, 2H, Htolyl), 2.79 (s, 1H, OH), 2.37 (s, 3H, CH3).
13C NMR (151 MHz, CD2Cl2): δ [ppm] = 147.2 (s), 144.1 (s), 137.0 (s),
128.7 (s), 128.0 (s), 128.0 (s), 128.0 (s), 127.3 (s), 82.0 (s), 21.2 (s).
for further 40 min. After cooling to room temperature, the solution was
extracted with CHCl3 (3 x 40 mL). The combined organic phases were
dried over MgSO4 and the solvent was evaporated. Purification was
achieved by silica gel column chromatography (n-pentane, yield: 0.98 g,
46%). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.00 (s, 1H, Ar3CH), 4.09 (td,
3
3
2
4H, JH-H = 7.1 Hz, JH-P = 7.3 Hz, POCH2), 3.77 (d, JH-P = 22.6 Hz, 2H,
4-Methylbenzophenone 1.[59] 4.327 g (15.8 mmol, 1.0 eq.) of diphenyl(p-
tolyl)methanol were dispersed in 100 mL of 98% formic acid and the
mixture was stirred at 99 °C for 3 d. 40 mL of H2O were added, and the
solution was neutralized with K2CO3 while being cooled in an ice bath. The
phases were separated, and the organic phase was washed with H2O
(3 x 500 mL) and dried over MgSO4. The solvent was removed to provide
a viscous oil (yield: 3.40 g, 83%). 1H NMR (400 MHz, CDCl3): δ [ppm] =
7.37-7.33 (m, 4H, Hmeta-phenyl), 7.29-7.28 (m, 2H, Hpara-phenyl), 7.21-7.16 (m,
6H, Hortho-tolyl, Hortho-phenyl), 7.10-7.08 (m, 2H, Hmeta-tolyl), 5.60 (s, 1H, Ar3CH),
2.40 (s, 3H, CH3). 13C NMR (151 MHz, CD2Cl2): δ [ppm] = 196.4 (s), 143.2,
137.8 (s), 134.9 (s), 132.1 (s), 130.2 (s), 129.9 (s), 128.8 (s), 128.2 (s),
21.6 (s)..
PhCH2), 1.27 (t, JH-H = 7.1 Hz, 6H, POCH2CH3). 13C NMR (151 MHz,
3
CD2Cl2): δ [ppm] = 136.6 (s), 136.5 (d, JPC = 3 Hz), 135.1 (s), 134.9 (d, JPC
= 8 Hz), 134.0 (d, JPC = 4 Hz), 133.9 (d, JPC = 4 Hz), 133.7 (s), 133.0 (s),
132.9 (s), 132.6 (s), 62.7 (d, 2JCP = 6.8 Hz, POCH2), 56.7 (s, CH2P), 32.8
(JCP = 139 Hz, CH2P) 16.5 (d, 3JCP = 6.4 Hz, CH3).
Bis(3-methoxyphenyl)ether.[37] 11.82 g (0.11 mol, 1.00 eq.) of KOtBu were
suspended in 20 mL of dry DMF and 11.34 mL (12.82 g, 0.10 mol,
0.98 eq.) of 3-methoxyphenol 3 in 10 mL of dry DMF were added slowly.
The dark solution was heated to reflux for 1 h and 13.24 mL (19.71 g,
0.11 mol, 1.00 eq.) of 3-bromoanisole, 4, and 15.12 g (0.11 mol, 1.00 eq.)
of CuBr were added. After heating to reflux for 4 h the solvent was
removed, and the solid residue was dissolved in diethyl ether. The organic
phase was washed with 0.5 M HCl (1 x 100 mL), 0.5 M NaOH (5 x 100 mL)
and brine (1 x 100 mL), dried over Na2SO4 and the solvent was removed
under vacuum. Purification followed by silica gel column chromatography
using n-pentane as eluent (yield: 3.73 g, 15%). H NMR (400 MHz, CDCl3):
δ [ppm] = 7.26-7.18 (m, 2H, H1), 6.70-6.55 (m, 6H, H4-6), 3.78 (s, 6H,
CH3). 13C NMR (151 MHz, CD2Cl2): δ [ppm] = 161.1 (s), 158.3 (s), 130.2
(s), 111.2 (s), 109.1 (s), 105.1 (s), 55.4 (s).
6,6’-((2,3,5,6-Tetrachloro-4-methylphenyl)methylene)bis(1,2,3,4,5-
pentachlorobenzene) 2.[36] 0.68 g (5.1 mmol, 0.38 eq.) of AlCl3 and
0.80 mL (1.36 g, 10.1 mmol, 0.76 eq.) dicholordisulfane were dissolved in
110 mL of sulfuryl chloride. The mixture was heated to 70 °C under
protection from light and a solution of 3.25 g (12.6 mmol, 1.00 eq.) of 4-
methylbenzophenone (1) in 260 mL of sulfuryl chloride was slowly added.
Refluxing was continued for 22 h. During that time another 200 mL of
sulfuryl chloride were added in portions so as to keep the volume of the
reaction mixture constant. The solvent was removed and 15.00 g of
NaHCO3 in 500 mL of H2O were added. The mixture was stirred at 120 °C
for 1 h. The solution was acidified with conc. HCl and heated to 120 °C for
1 h. After cooling to r. t. the aqueous phase was removed and the residue
was suspended in diethyl ether. The white precipitate was filtered off and
washed several times with diethyl ether to give a white powder (yield:
Bis(2-iodo-3-methoxyphenyl)ether 5.[34] 1.00 g (4.34 mmol, 1.00 eq.) of
bis(3-methoxyphenyl)ether were dissolved in 10 mL of dry THF and cooled
in an ice/water bath. 6.16 mL (9.86 mmol, 2.27 eq.) of a 1.6 M n-hexane
solution of n-butyllithium was slowly added. After the mixture was stirred
at r. t. for 1 h it was cooled with an ice/water bath. To the yellow solution
2.69 g (9.55 mmol, 2.2 eq.) of 1,2-diiodoethane were slowly added and the
solution was stirred at r t. overnight. The mixture was poured into 40 mL of
a 10% aqueous solution of sodium bisulfite and the mixture was extracted
with CH2Cl2 (3 x50 mL). The organic layer was washed with H2O (70 mL)
and brine (70 mL). The organic layer was dried over Na2SO4 and the
solvent was evaporated in vacuum. The resulting crystals were washed
with EtOH and cold n-hexane to afford a pale yellow solid (yield: 1.45 g,
1
3.50 g, 34%). H NMR (400 MHz, CDCl3): δ [ppm] = 6.99 (s, 1H, Ar3CH),
2.63 (s, 3H, CH3). 13C NMR (151 MHz, CD2Cl2): δ [ppm] = 137.6 (s), 136.8
(s), 136.8 (s), 135.3 (s), 135.1 (s), 134.5 (s), 134.4 (s), 134.1 (s), 134.1 (s),
133.7 (s), 133.7 (s), 133.6 (s), 133.4 (s), 132.6 (s), 132.5 (s), 56.6 (s), 20.8
(s).
3
6,6’-((4-(Bromomethyl)-2,3,5,6-tetrachlorophenyl)methylene)bis-
(1,2,3,4,5-pentachlorobenzene) PTM-Br.[60] 2.000 g (2.70 mmol, 1.00 eq.)
of compound 2, 0.445 g (1.47 mmol, 0.54 eq.) of activated benzoyl
peroxide and 0.651 g (3.66 mmol, 1.35 eq.) of N-bromosuccinimide were
dissolved in 60 mL of tetrachloromethane and stirred for 4 d at 85 °C. The
suspension was filtered off and the solution was concentrated under
vacuum. The solid was washed with n-hexane and acetone to obtain the
product as a beige solid (yield: 1.83 g, 83%). 1H NMR (400 MHz, CDCl3):
δ [ppm] = 7.00 (s, 1H, Ar3CH), 4.82 (s, 2H, CBrH2). 13C NMR (151 MHz,
CD2Cl2): δ [ppm] = 138.1 (s), 136.5 (s), 136.4 (s), 135.2 (s), 135.1 (s),
134.8 (s), 134.1 (s), 133.9 (s), 133.7 (s), 133.7 (s), 132.7 (s), 132.7(s), 56.7
(s), 29.0 (s).
69%). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.22 (t, JH-H = 8.2 Hz, 2H),
3
4
3
6.62 (dd, JH-H = 8.2 Hz, JH-H = 1.0 Hz, 2H), 6.42 (dd, JH-H = 8.2 Hz,
4JH-H = 1.0 Hz, 2H), 3.93 (s, 3H). 13C NMR (151 MHz, CD2Cl2): δ [ppm] =
160.2 (s), 157.5 (s), 130.0 (s), 111.6 (s), 106.3 (s), 81.0 (s), 56.8 (s).
10-(2’,6’-Difluorophenyl)-1,9-dimethoxy-10H-phenoxazine.[34]
2.00 g
(4,15 mmol, 1.01 eq.) of compound 5, 0.53 g (4.11 mmol 1.00 eq.) of 2,6-
difluoroaniline, 1.19 g (12.40 mmol, 1.00 eq.) of NaOtBu, 0.21 g
(0.21 mmol, 0.05 eq.) of [Pd(dba)3]·CHCl3 and 1.8 mL (0.622 mmol,
0.15 eq.) of a 10% n-hexane solution of PtBu3 were dissolved in 10 mL of
dry toluene and heated under reflux for 16 h. After cooling to room
temperature, the mixture was filtered through a pad of Celite and
concentrated under vacuum until the solid product precipitated. The
supernatant was filtered off and the remaining solid was washed with n-
pentane (yield: 1.11 g, 75%). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.15
4-[Bis(perchlorophenyl)methyl]-2,3,5,6-tetrachlorobenzyl)-triphenylphos-
phonium bromide PTM-PPh3Br.[35] 1.00 g (1.22 mmol, 1.00 eq.) of PTM-
Br and 0.50 g (1.90 mmol, 1.56 eq.) of triphenylphosphine were dissolved
in 50 mL of dry benzene and stirred for 20 h at 80 °C. The resulting solid
was filtered off and washed with benzene to give the product as a white
solid (yield: 1.10 g, 83%). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.86-7.66
(tt, 3JH-H = 8.3 Hz, 4JH-F = 6.0 Hz, 1H), 6.94-6.82 (m, 4H), 6.56 (dd, 3JH-H
8.2 Hz, JH-H = 1.1 Hz, 2H), 6.43 (dd, JH-H = 8.2 Hz, JH-H = 1.1 Hz, 2H),
=
4
3
3.64 (s, 6H).
2
(m, 15H, P(C6H5)3), 6.90 (d, JH-H = 1.6 Hz, Ar3CH), 5.89 (d, 2H,
10-(2’,6’-Difluorophenyl)-1,9-hydroxy-10H-phenoxazine.[34]
1.081 g
2JH-H = 14.4 Hz, CH2PPh3Br). 13C NMR (151 MHz, CD2Cl2): δ [ppm] =
138.6 (d, 4JCP = 3 Hz, Cp, P+Ph3), 136.0 (d, JPC = 3 Hz), 135.6 (s), 135.4 (d,
JPC = 7 Hz), 135.0 (s), 134.9 (d, JPC = 4 Hz), 134.5 (s), 134.3 (d, JPC = 4
(3.042 mmol, 1.0 eq.) of 10-(2’,6’-difluorophenyl)-1,9-dimethoxy-10H-
phenoxazine were dissolved in 80 mL of dry DCM and cooled to -78°C.
1.53 mL (4.035 g, 16.123 mmol, 5.3 eq.) of BBr3 were slowly added
whereupon the solution turned violet. After stirring at r. t. overnight the
mixture was poured into 100 mL water and extracted with CH2Cl2
(3 x 50 mL). The organic phase was washed with H2O (50 mL) and brine
(2 x 50 mL), dried over Na2SO4 and the solvent was evaporated. The
crude product was used without further purification.
2
Hz), 134.1 (d, JPC = 5 Hz), 133.8 (s), 133.6 (d, JCP = 11 Hz, Co, P+Ph3),
132.8 (s), 130.4 (d, 3JCP = 13 Hz, Cm, P+Ph3), 128.4 (s), 117.9 (d, JCP = 88
Hz, Cipso, P+Ph3), 56.7 (s), 33.0 (d, JCP = 56 Hz, CH2-P+Ph3).
4-[Bis(perchlorophenyl)methyl]-2,3,5,6-tetrachlorobenzyl-phosphonate
PTM-PO(OEt)2.[35] 2.000 g (2.44 mmol, 1.00 eq.) of PTM-Br and 2.50 mL
(2.420 g, 14.57 mmol, 5.97 eq.) of P(OEt)3 were heated to reflux at 155 °C
for 130 min. 17 mL of H2O were added and heating to reflux was continued
2,2’:6’,2’’:6’’,6-Trioxytriphenylamine 6 (TOTA).[34] The crude 10-(2’,6’-
difluorophenyl)-1,9-hydroxy-10H-phenoxazine and 2.144 g of K2CO3
8
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
(15.514 mmol, 5.1 eq.) were dissolved in 50 mL of dry DMF and stirred at
100 °C for 17 h. The mixture was poured into 100 mL of H2O and a yellow
solid precipitated. The precipitate was filtered off and washed with 150 mL
of H2O and 15 mL of n-pentane (yield: 0.77 g, 88%).
1H NMR (400 MHz, C6D6): δ [ppm] = 6.30-6.23 (m, 9H). 13C NMR
(151 MHz, CD2Cl2): δ [ppm] = 142.7 (s), 123.7 (s), 117.3 (s), 111.5 (s).
Na2SO4 and the solvent was evaporated. Purification was achieved by
silica gel column chromatography with n-hexane as the eluent (yield:
1.103 g, 62%). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.74 (d,
3
3JH-H = 8.3 Hz, 2H, H5), 7.27 (d, JH-H = 8.3 Hz, 2H, H4), 7.06 (d,
3JH-H = 16.6 Hz, 1H, H2), 7.02 (s, 1H, H1), 6.99 (d, 3JH-H = 16.6 Hz, 1H, H3).
13C NMR (151 MHz, CD2Cl2): δ [ppm] = 138.1 (s), 137.8 (s), 137.5 (s),
137.3 (s), 136.7 (s), 136.6 (s), 136.4 (s), 135.6 (s), 135.2 (s), 135.2 (s),
135.0 (s), 134.1 (s), 133.8 (s), 133.9 (s), 133.7 (s), 133.7 (s), 133.5 (s),
133.4 (s), 132.6 (s), 132.4 (s), 129.8 (s), 128.7 (s), 125.2 (s), 123.9 (s),
94.7 (s), 94.3 (s), 56.8 (s).
4-Formyl-2,2’:6’,2’’:6’’,6-trioxytriphenylamine (TOTA-CHO).[38] 0.300 g
(1.044 mmol, 1.0 eq.) of TOTA were dissolved in 21 mL of dry 1,4-dioxane
and 8.04 mL (7.649 g, 104.504 mmol, 100.1 eq.) of dry DMF. POCl3
(9.75 mL, 16.376 g, 106.801 mmol, 102 eq.) was added. The mixture was
stirred under reflux conditions for 2 h. After cooling to r. t., the solution was
poured into 100 mL of a 10% aqueous NaOH solution and extracted with
CH2Cl2 (3 x 80 mL). The combined organic phases were washed with
100 mL of brine, dried over Na2SO4 and the solvent was evaporated under
reduced pressure. The residue was subjected to silica gel column
chromatography using toluene as the eluent to afford the product as an
orange solid (yield: 0.18 g, 55%). 1H NMR (400 MHz, CDCl3): δ [ppm] =
9.35 (s, 1H, CHO), 6.75 (s, 2H, H1), 6.38-6.20 (m, 6H, H2-4). 13C NMR
(151 MHz, CD2Cl2): δ [ppm] = 189.3 (s), 142.2 (s), 142.1 (s), 124.8 (s),
114.9 (s), 113.1 (s), 112.0 (s), 111.6 (s), 29.9 (s).
TPAN-PTMH. 0.790 g (0.828 mmol, 1.00 eq.) of compound 8 and 0.232 g
(0.910 mmol, 1.10 eq.) of bis(dimethylaminophenyl)amine were dissolved
in 30 mL of dry toluene and 0.043 g (0.041 mmol, 0.05 eq.)
[Pd2(dba)3]·CHCl3, 0.1 mL (0.033 mmol, 0.04 eq.) of a 10% n-hexane
solution of PtBu3 and 0.199 g (2.069 mmol, 2.5 eq.) of K2CO3 were added.
The mixture was heated under reflux for 22 h and the solvent was removed.
The residue was dissolved in 100 mL of CH2Cl2, washed with H2O
(3 x 80 mL), dried over Na2SO4 and the solvent was removed. Column
chromatography over silica gel (n-pentane/EtOAc/NEt3 10:1:0.1) yielded
0.295 g, 33%) of the product. 1H NMR (600 MHz, CD2Cl2): δ [ppm] = 7.31
3
(d, JH-H = 8.8 Hz, 2H, H5), 7.08-6.95 (m, 6H, H1, H3, H9), 6.87 (d,
3
TOTA-PTMH. A solution of 0.202 g (0.231 mmol, 1.0 eq.) of PTM-
PO(OEt)2. in 35 mL of dry THF was cooled to -78 °C and 0.064 g
(0.554 mmol, 2.4 eq.) KOtBu were added. The resulting mixture was
stirred for 20 min. and then allowed to warm to 0 °C. Then, 0.080 g
(0.254 mmol, 1.1 eq.) of TOTA-CHO in 120 mL of dry THF were added.
The solution was allowed to slowly warm to r. t. and stirred for 2 d. 90 mL
of 2N HCl were added, the phases were separated, and the aqueous
phase was extracted with CHCl3 (3 x 100 mL). The combined organic
phases were washed with H2O (1 x 100 mL), dried over Na2SO4 and the
solvent was removed under reduced pressure. Purification was performed
by silica gel column chromatography (n-pentane/EtOAc 10:1) to yield
50 mg (21%) of the product. 1H NMR (600 MHz, CD2Cl2): δ [ppm] = 7.01
(s, 1H, H1), 6.87 (d, 3JH-H = 16.5 Hz, 1H, H3), 6.83 (d, 3JH-H = 16.5 Hz, 1H,
H2), 6.70 (t, 3JH-H = 8.3 Hz, 2H, H11), 6.64 (s, 2H, H5), 6.48-6.44 (m, 4H,
H10, H12). 13C NMR (151 MHz, CD2Cl2): δ [ppm] = 142.5 (s, C8), 142.5 (s,
C7), 142.3 (s, C13), 137.2 (s), 137.2 (s, C3), 136.7 (s), 136.7 (s), 136.1 (s),
135.3 (s), 135.2 (s), 135.0 (s), 134.1 (s), 134.1 (s), 134.1 (s), 133.8 (s),
133.8 (s), 133.7 (s), 133.6 (s), 133.4 (s), 132.6 (s), 132.6 (s), 132.3 (s),
132.0 (s, C4), 124.1 (s, C11), 122.3 (s, C2), 117.4 (s, C6), 116.32 (s, C9),
111.7 (s, C10/C12), 111.6 (s, C10/C12), 110.1 (s, C5), 56.75 (s, C1). FTIR:
2921 (w), 2851 (w), 1593 (w), 1504 (m), 1321 (w), 1259 (m), 1178 (w),
1159 (w), 1063 (w), 1033 (w), 946 (w), 861 (w), 809 (w), 759 (w), 704 (w),
676 (w). MALDI HRMS (DCTB, positive mode) calcd. for C39H11Cl14NO3
1036.6290 [M]+, found 1036.6282. Anal. Calcd. for C39H11Cl14NO3: C,
45.14; H, 1.07; N, 1.35; Found: C, 45.38; H, 1.91; N, 1.36.
3JH-H = 16.5 Hz, 1H, H2), 6.82 (d, JH-H = 8.8 Hz, 2H, H6), 6.70 (d,
3JH-H = 8.9 Hz, 4H, H10), 2.93 (s, 12H, N(CH3)2. 13C NMR (151 MHz,
CD2Cl2): δ [ppm] = 150.7 (s, C7), 148.4 (s, C11), 138.8 (s, C3) 138.6 (s),
137.2 (s), 137.2 (s), 136.9 (s, C8), 135.6 (s), 135.5 (s), 135.4 (s), 135.0 (s),
134.5 (s), 134.4 (s), 134.2 (s), 133.9 (s), 133.9 (s), 133.8 (s), 133.8 (s),
133.6 (s), 132.8 (s), 132.8 (s), 132.5 (s), 128.0 (s, C5), 127.6 (s, C9), 126.5
(s, C4), 119.3 (s, C2), 118.3 (s, C6), 113.8 (s, C10), 57.0 (s, C1), 41.0 (s,
C12). FT-IR: 3661 (w), 2980 (m), 2890 (w), 1595 (w), 1505 (m), 1381 (w),
1323 (w), 1290 (w), 1259 (w), 1159 (m), 1071 (w), 948 (w), 808 (m), 704
(w).
MALDI HRMS (DCTB, positive mode) calcd. for C43H27Cl14N3 1080.7756
[M]+, found: 1080.7750. Anal. Calcd. for C43H27Cl14N3C7H8 (as detected
by NMR): C, 51.15; H, 3.00; N, 3.58; Found: C, 51.52; H, 3.35; N, 3.85.
TPAN-PTM·. To a suspension of 100 mg (0.092 mmol, 1 eq.) of TPAN-
PTMH in 20 mL of dry DMSO, 21 mg (0.185 mmol, 2 eq.) of KOtBu were
added and stirred at room temperature for 1.5 h in the dark. 23 mg
(0.092 mmol, 1 eq.) of tetrachloro-1,4-benzoquinone were added and the
solution was stirred for 1.5 h and the solvent was evaporated. The residue
was subjected to silica gel column chromatography using DCM as eluent.
Further purification was achieved by adding a concentrated CH2Cl2
solution of the crude product dropwise to methanol (2 times) to yield 58 mg,
53% of the target compound. FT-IR: 2923 (w), 2852 (w), 1592 (w), 1502
(m), 1442 (w), 1322 (w), 1259 (w), 1227 (w), 1178 (w), 1159 (w), 1061 (w),
946 (w), 811 (w), 768 (w), 713 (w). MALDI HRMS (DCTB, positive mode)
calcd. for C43H26Cl14N3 1079.7678 [M]+, found: 1079.7672. Anal. Calcd. for
C43H27Cl14N3C7H8: C, 51.19; H, 2.92; N, 3.58; Found: C, 51.83; H, 3.94;
N, 3.53.
TOTA-PTM·. To a suspension of 100 mg (0.092 mmol, 1 eq.) TOTA-
PTMH in 20 mL of dry DMSO 21 mg (0.185 mmol, 2 eq.) of KOtBu were
added. The purple solution was stirred in the dark for 1.5 h and then 23 mg
(0.092, 1 eq.) of chloranil were added. After further stirring for 1.5 h in the
dark the solvent was evaporated. Purification followed by silica gel column
chromatography using DCM as eluent and the crude product was
precipitated twice by dissolving it in DCM and adding it dropwise to
methanol (yield: 53 mg, 53%). FTIR: 2981 (w), 2932 (w), 1593 (w), 1502
(m), 1322 (w), 1259 (m), 1178 (w), 1259 (w), 1063 (w), 946 (w), 809 (m),
705 (w). MALDI HRMS (DCTB, positive mode) calcd. for C39H10Cl14NO3
1035.6212 [M]+, found 1035.6210. Anal. Calcd. for C39H10Cl14NO3: C,
45.18; H, 0.97; N, 1.35; Found: C, 45.78; H, 1.68; N, 1.40.
Acknowledgements
We gratefully acknowledge financial support of this work by the
Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) – SFB 767 – Project-ID 32152442 (project C14) and
grant number INST 40/467-1 FUGG (JUSTUS cluster). We also
wish to thank the reviewers for their insightful comments and
suggestions.
1-[Bis(2,3,4,5,6-pentachlorophenyl)methyl]-4-[2-(4-iodophenyl)ethenyl]-
2,3,5,6-tetrachlorobenzene 8.[35] To a suspension of 2.000 g (1.849 mmol,
1.00 eq.) of PTM-PPh3Br in 55 mL of dry THF 0.207 g (1.849 mmol,
1.00 eq.) of KOtBu were added. After stirring for 1 h at r. t. 0.349 g
(1.885 mmol, 1.02 eq.) of 4-iodobenzaldehyde 7 were added and stirring
was continued overnight. The mixture was quenched with 15 mL of 1 M
HCl and the suspension was stirred for 1 h. The phases were separated,
and the aqueous phase was extracted with CHCl3 (3 x 80 mL). The
combined organic phase was washed with H2O (3 x 80 mL), dried over
Keywords: donor-acceptor dyads • EPR spectroscopy • PTM
radical • spectroelectrochemistry • TOTA
9
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Chem. Solids 2004, 65, 753; d) C. Sporer, I. Ratera, D. Ruiz-
Molina, Y. Zhao, J. Vidal-Gancedo, K. Wurst, P. Jaitner, K. Clays,
A. Persoons, C. Rovira, J. Veciana Angew. Chem. Int. Ed. 2004,
43, 5266.
References
[1]
[2]
O. Kahn, J. P. Launay, Chemtronics 1988, 3, 140.
C. Roux, D. M. Adams, J. P. Itié, A. Polian, D. N. Hendrickson, M.
Verdaguer, Inorg. Chem. 1996, 35, 2846.
[15] G. D'Avino, L. Grisanti, A. Painelli, J. Guasch, I. Ratera, J. Veciana,
CrystEngComm 2009, 11, 2040.
[16] J. Guasch, L. Grisanti, S. Jung, D. Morales, G. D’Avino, M. Souto,
X. Fontrodona, A. Painelli, F. Renz, I. Ratera, J. Veciana, Chem.
Mater. 2013, 25, 808.
[17] a) J. Guasch, N. Crivillers, M. Souto, I. Ratera, C. Rovira, P.
Samorì, J. Veciana, J. Appl. Phys. 2019, 125, 142909; b) S.
Nishida, Y. Morita, K. Fukui, K. Sato, D. Shiomi, T. Takui, K.
Nakasuji, Angew. Chem. Int. Ed. 2005, 44, 7277.
[18] J. Guasch, L. Grisanti, V. Lloveras, J. Vidal-Gancedo, M. Souto, D.
C. Morales, M. Vilaseca, C. Sissa, A. Painelli, I. Ratera, C. Rovira,
J. Veciana, Angew. Chem. Int. Ed. 2012, 51, 11024.
[19] M. Souto, D. C. Morales, J. Guasch, I. Ratera, C. Rovira, A.
Painelli, J. Veciana, J. Phys. Org. Chem. 2014, 27, 465.
[20] A. Heckmann, C. Lambert, M. Goebel, R. Wortmann, Angew.
Chem. Int. Ed. 2004, 43, 5851.
[21] S. Dümmler, W. Roth, I. Fischer, A. Heckmann, C. Lambert, Chem.
Phys. Lett. 2005, 408, 264.
[22] A. Heckmann, C. Lambert, J. Am. Chem. Soc. 2007, 129, 5515.
[23] D. Reitzenstein, T. Quast, F. Kanal, M. Kullmann, S. Ruetzel, M. S.
Hammer, C. Deibel, V. Dyakonov, T. Brixner, C. Lambert, Chem.
Mater. 2010, 22, 6641.
[24] a) S. F. Nelsen, R. F. Ismagilov, J. Phys. Chem. A 1999, 103,
5373; b) R. L. Blackbourn, J. T. Hupp, J. Phys. Chem. 1990, 94,
1788.
[25] V. Gamero, D. Velasco, S. Latorre, F. López-Calahorra, E. Brillas,
L. Juliá, Tetrahedron Lett. 2006, 47, 2305.
[26] D. Velasco, S. Castellanos, M. López, F. López-Calahorra, E.
Brillas, L. Julia, J. Org. Chem. 2007, 72, 7523.
[27] S. Castellanos, D. Velasco, F. López-Calahorra, E. Brillas, L. Julia,
J. Org. Chem. 2008, 73, 3759.
[28] L. Fajarí, R. Papoular, M. Reig, E. Brillas, J. L. Jorda, O. Vallcorba,
J. Rius, D. Velasco, L. Juliá, J. Org. Chem. 2014, 79, 1771.
[29] A. Gilabert, L. Fajarí, I. Sirés, M. Reig, E. Brillas, D. Velasco, J. M.
Anglada, L. Juliá, New J. Chem. 2017, 41, 8422.
[30] P. Ballesteros, A. Cuadrado, A. Gilabert, L. Fajarí, I. Sirés, E.
Brillas, M. P. Almajano, D. Velasco, J. M. Anglada, L. Juliá, Phys.
Chem. Chem. Phys. 2019, 21, 20225.
[31] R. F. Winter, L. A. Casper, M. Linseis, S. Demeshko, M. Azarkh, M.
Drescher, Chem. Eur. J. 2021, doi.org/10.1002/chem.202101032.
[32] M. Kuratsu, M. Kozaki, K. Okada, Angew. Chem. Int. Ed. 2005, 44,
4056.
[33] M. Kuratsu, S. Suzuki, M. Kozaki, D. Shiomi, K. Sato, T. Takui, K.
Okada, Inorg. Chem. 2007, 46, 10153.
[3]
a) A. Caneschi, A. Cornia, A. Dei, Inorg. Chem. 1998, 37, 3419; b)
D. Ruiz, J. Yoo, D. N. Hendrickson, I. A. Guzei, A. L. Rheingold,
Chem. Commun. 1998, 2089; c) D. Ruiz-Molina, J. Veciana, K.
Wurst, D. N. Hendrickson, C. Rovira, Inorg. Chem. 2000, 39, 617;
d) G. Speier, Z. Tyeklár, P. Tóth, E. Speier, S. Tisza, A.
Rockenbauer, A. M. Whalen, N. Alkire, C. G. Pierpont, Inorg.
Chem. 2001, 40, 5653; e) S. H. Bodnar, A. Caneschi, A. Dei, D. A.
Shultz, L. Sorace, Chem. Commun. 2001, 2150; f) W. Kaim, B.
Schwederski, Coord. Chem. Rev. 2010, 254, 1580; g) D.
Schweinfurth, F. Weisser, B. Sarkar, Nachr. Chem. 2009, 57, 862;
h) W. Kaim, Eur. J. Inorg. Chem. 2012, 2012, 343; i) W. Kaim,
Inorg. Chem. 2011, 50, 9752; j) A. Dei, L. Sorace, Appl. Magn.
Reson. 2010, 38, 139; k) M. Mitsumi, Y. Komatsu, M. Hashimoto,
K. Toriumi, Y. Kitagawa, Y. Miyazaki, H. Akutsu, H. Akashi, Chem.
Eur. J. 2021, 27, 3074.
[4]
[5]
C. G. Pierpont, Coord. Chem. Rev. 2001, 216-217, 99.
a) T. Ito, N. Imai, T. Yamaguchi, T. Hamaguchi, C. H. Londergan,
C. P. Kubiak, Angew. Chem. Int. Ed. 2004, 43, 1376; b) M. Lohan,
F. Justaud, T. Roisnel, P. Ecorchard, H. Lang, C. Lapinte,
Organometallics 2010, 29, 4804; c) M. Lohan, F. Justaud, H. Lang,
C. Lapinte, Organometallics 2012, 31, 3565; d) R. Sakamoto, K. P.
Rao, H. Nishihara, Chem. Lett. 2011, 40, 1316; e) E. C. Fitzgerald,
A. Ladjarafi, N. J. Brown, D. Collison, K. Costuas, R. Edge, J.-F.
Halet, F. Justaud, P. J. Low, H. Meghezzi, T. Roisnel, M. W.
Whiteley, C. Lapinte, Organometallics 2011, 30, 4180; f) J. Chen,
E. Wuttke, W. Polit, T. Exner, R. F. Winter, J. Am. Chem. Soc.
2013, 135, 3391; g) C. Hassenrück, P. Mücke, J. Scheck, S.
Demeshko, R. F. Winter, Eur. J. Inorg. Chem. 2017, 2017, 401; h)
C. Hassenrück, M. Azarkh, M. Drescher, M. Linseis, S. Demeshko,
F. Meyer, R. F. Winter, Organometallics 2020, 39, 153; i) G. K.
Lahiri, A. Singh, S. Panda, S. Dey, Angew. Chem. Int. Ed. Engl.
2021; j) K. P. Rao, T. Kusamoto, F. Toshimitsu, K. Inayoshi, S.
Kume, R. Sakamoto, H. Nishihara, J. Am. Chem. Soc. 2010, 132,
12472; k) A. Neidlinger, C. Förster, K. Heinze, Eur. J. Org. Chem.
2016, 2016, 4852.
[6]
[7]
T. Tezgerevska, K. G. Alley, C. Boskovic, Coord. Chem. Rev.
2014, 268, 23.
a) T. Bally, Nat. Chem. 2010, 2, 165; b) B. Müller, T. Bally, F.
Gerson, A. de Meijere, M. von Seebach, J. Am. Chem. Soc. 2003,
125, 13776; c) F. F. Puschmann, J. Harmer, D. Stein, H. Rüegger,
B. de Bruin, H. Grützmacher, Angew. Chem. Int. Ed. Engl. 2010,
49, 385.
[8]
[9]
a) J. S. Miller, M. Drillon, Shultz, D. A. In:. Magnetoscience-From
Molecules to Materials, Wiley-VCH, New York, 2000; b) P. Gütlich,
A. Dei, Angew. Chem. Int. Ed. 1997, 36, 2734.
[34] S. Suzuki, N. Tanaka, M. Kozaki, D. Shiomi, K. Sato, T. Takui, K.
Okada, Chem. Eur. J. 2017, 23, 16014.
[35] C. Rovira, D. Ruiz-Molina, O. Elsner, J. Vidal-Gancedo, J.
Bonvoisin, J.-P. Launay, J. Veciana, Chem. Eur. J. 2001, 7, 240.
[36] M. Ballester, J. Castañer, J. Riera, A. Ibanez, J. Pujadas, J. Org.
Chem. 1982, 47, 259.
[37] F. Yang, J. Zhao, Y. Li, S. Zhang, Y. Shao, H. Shao, T. Ma, C.
Gong, Eur. Polym. J. 2009, 45, 2053.
[38] M. Kuratsu, S. Suzuki, M. Kozaki, D. Shiomi, K. Sato, T. Takui, T.
Kanzawa, Y. Hosokoshi, X.-Z. Lan, Y. Miyazaki, A. Inaba, K.
Okada, Chem. As. J. 2012, 7, 1604.
a) O. Sato, J. Tao, Y.-Z. Zhang, Angew. Chem. Int. Ed. 2007, 46,
2152; b) O. Sato, S. Hayami, Z.-z. Gu, K. Takahashi, R. Nakajima,
A. Fujishima, Chem. Phys. Lett. 2002, 355, 169; c) H. W. Liu, K.
Matsuda, Z. Z. Gu, K. Takahashi, A. L. Cui, R. Nakajima, A.
Fujishima, O. Sato, Phys. Rev. Lett. 2003, 90, 167403; d) A.
Hauser, J. Jeftić, H. Romstedt, R. Hinek, H. Spiering, Coord.
Chem. Rev. 1999, 190-192, 471; e) P. Gütlich, Coord. Chem. Rev.
2001, 219-221, 839; f) A. Ghosh, T. Wondimagegn, E. Gonzalez, I.
Halvorsen, J. Inorg. Biochem. 2000, 78, 79; g) A. Dei, Angew.
Chem. Int. Ed. 2005, 44, 1160; h) N. A. Vázquez-Mera, F. Novio,
C. Roscini, C. Bellacanzone, M. Guardingo, J. Hernando, D. Ruiz-
Molina, J. Mater. Chem. C 2016, 4, 5879.
[39] V. Dvořák, I. Němec, J. Zýka, Microchem. J. 1967, 12, 350.
[40] V. Lloveras, J. Vidal-Gancedo, T. M. Figueira-Duarte, J.-F.
Nierengarten, J. J. Novoa, F. Mota, N. Ventosa, C. Rovira, J.
Veciana, J. Am. Chem. Soc. 2011, 133, 5818.
[10] I. Ratera, C. Sporer, D. Ruiz-Molina, N. Ventosa, J. Baggerman, A.
M. Brouwer, C. Rovira, J. Veciana, J. Am. Chem. Soc. 2007, 129,
6117.
[41] F. Pragst, R. Ziebig, E. Boche, J. Lumin. 1979, 21, 21.
[42] M. Souto, J. Calbo, I. Ratera, E. Ortí, J. Veciana, Chem. Eur. J.
2017, 23, 11067.
[11] I. Ratera, D. Ruiz-Molina, F. Renz, J. Ensling, K. Wurst, C. Rovira,
P. Gütlich, J. Veciana, J. Am. Chem. Soc. 2003, 125, 1462.
[12] a) O. Elsner, D. Ruiz-Molina, I. Ratera, J. Vidal-Gancedo, C.
Rovira, J. Veciana, J. Organomet. Chem. 2001, 637-639, 251; b)
O. Elsner, D. Ruiz-Molina, J. Vidal-Gancedo, C. Rovira, J. Veciana,
Chem. Commun. 1999, 579.
[43] a) M. Ballester, J. Riera-Figueras, J. Castaner, C. Badfa, J. M.
Monso, J. Am. Chem. Soc. 1971, 93, 2215; b) M. Ballester, J.
Castaner, J. Riera, A. Ibanez, J. Pujadas, J. Org. Chem. 1982, 47,
259.
[44] M. Souto, M. V. Solano, M. Jensen, D. Bendixen, F. Delchiaro, A.
Girlando, A. Painelli, J. O. Jeppesen, C. Rovira, I. Ratera, J.
Veciana, Chem. Eur. J. 2015, 21, 8816.
[45] L. Grisanti, G. D'Avino, A. Painelli, J. Guasch, I. Ratera, J. Veciana,
J. Phys. Chem. B 2009, 113, 4718.
[46] M. Krejčik, M. Daněk, F. Hartl, J. Electroanal. Chem. 1991, 317,
[13] G. D'Avino, L. Grisanti, J. Guasch, I. Ratera, J. Veciana, A. Painelli,
J. Am. Chem. Soc. 2008, 130, 12064.
[14] a) M. Ballester, J. Riera, J. Castañer, C. Badía, J. M. Monsó, J.
Am. Chem. Soc. 1971, 93, 2215; b) V. Lloveras, J. Vidal-Gancedo,
D. Ruiz-Molina, T. M. Figueira-Duarte, J.-F. Nierengarten, J.
Veciana, C. Rovira, Faraday Discuss. 2006, 131, 291-305;
discussion 307-24; c) C. Sporer, I. Ratera, D. Ruiz-Molina, J. Vidal
Gancedo, K. Wurst, P. Jaitner, C. Rovira, J. Veciana, J. Phys.
179.
[47] a) S. Amthor, B. Noller, C. Lambert, Chem. Phys. 2005, 316, 141;
b) S. Dapperheld, E. Steckhan, K.-H. G. Brinkhaus, T. Esch, Chem.
Ber. 1991, 124, 2557; c) C. Quinton, V. Alain-Rizzo, C. Dumas-
10
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Verdes, F. Miomandre, G. Clavier, P. Audebert, RSC Adv. 2014, 4,
34332.
[48] a) M. Dibrelle, R. Hoekstra, M. N. Weaver, K. Okada, S. F. Nelsen,
J. I. Zink, J. Phys. Org. Chem. 2012, 25, 578; b) Y. Nakano, H.
Yamochi, G. Saito, M. Kuratsu, K. Okada, J. Phys.: Conf. Ser.
2008, 132, 12024.
[49] A. Bobet, A. Cuadrado, L. Fajarí, I. Sirés, E. Brillas, M. P.
Almajano, V. Jankauskas, D. Velasco, L. Juliá, J. Phys. Org.
Chem. 2019, 32, e3974.
[50] M. Abe, Chemical reviews 2013, 113, 7011.
[51] S. Stoll, A. Schweiger, J. Magn. Reson. 2006, 178, 42.
[52] O. Chen, J. Zhuang, F. Guzzetta, J. Lynch, A. Angerhofer, Y. C.
Cao, J. Am. Chem. Soc. 2009, 131, 12542.
[53] M. J. Frisch, G. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheesman, G. Scalmani, V. Barone, B. Mennucci, G. A. Pe-
tersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izma-
ylov, J. Blonio, 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, F.
Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,K. N. Kudin, V. N.
Staroverov, T. Keith, 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. Stratmann, 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. Dannenberg, S.
Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J.
Cioslowski, D. J. Fox, Gaussian 09, Revision B.01, Gaussian Inc.:
Wallingford, CT 2010.
[54] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem.
2003, 24, 669.
[55] Perdew, Burke, Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865.
[56] N. M. O'Boyle, A. L. Tenderholt, K. M. Langner, J. Comput. Chem.
2008, 29, 839.
[57] M. D. Hanwell, D. E. Curtis, D. C. Lonie, T. Vandermeersch, E.
Zurek, Hutchison, G. R. Avogadro: an advanced semantic
chemicaleditor, visualization, and analysis platform, J. Cheminf.
2012, 4, 1.
[58] O. Tange, USENIX Magazine 2011, 36, 42.
[59] J.-L. Muñoz-Gómez, I. Marín-Montesinos, V. Lloveras, M. Pons, J.
Vidal-Gancedo, J. Veciana, Org. Lett. 2014, 16, 5402.
[60] M. Ballester, J. Veciana, J. Riera, J. Castaner, C. Rovira, O. Armet,
J. Org. Chem. 1986, 51, 2472.
11
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100476
European Journal of Organic Chemistry
FULL PAPER
Entry for the Table of Contents
Graphic for Table of Contents
Text for graphical abstract:
Two new donor-acceptor dyads with a particular electron-rich triarylamine (TAA) donor and the perchlorotriphenylmethyl radical
acceptor (PCT) are probed for their propensity to equilibrate with their zwitterionic valence tautomers TAA+-PCT-. The UV/vis/NIR
and EPR spectroscopic profiles of their oxidized and reduced forms were recorded, but failed to identify such isomers in the neutral
state. The cations have an open-shell singlet ground state, situated slightly below the triplet state.
12
This article is protected by copyright. All rights reserved.