Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals and Their Oxidation to Cationic High-Spin Molecules

Article abstract of DOI:10.1002/chem.201905734

Three 1 N-phenyl nitronyl nitroxide (NN) 4-substituted dithieno[3,2-b:2′,3′-d]pyrrole (DTP) derivatives with R1=4-phenyl-, 4H-, and 4-methylthiothiophenyl- (R¹₂DTP-Ph-NN, R¹=H, Ph and MeSTh) were designed, synthesized and

Full text of DOI:10.1002/chem.201905734

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Accepted Article
Title: Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals Offers
Their Oxidation to Cationic High-Spin Molecules
Authors: Martin - Baumgarten and Kubandiran Kolanji
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Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals
Offers Their Oxidation to Cationic High-Spin Molecules
Kubandiran Kolanji,[a], [b] and Martin Baumgarten*[a]
Abstract: Three 1N-phenyl nitronyl nitroxide (NN) 4-substituted
dithieno[3,2-b:2',3'-d]pyrrole (DTP) derivatives with R1 = 4-Phenyl-,
one electron oxidation. Especially, 1-phenyl NN 4-substituted-
2,5-di(thiophen-2-yl)-1H-pyrrole derivatives (TPT-Ph-NN),[12] NN‐
substituted conjugated oligomers of dithienyl‐N‐methylpyrrole
with methoxy substituents at the inner β‐position of thiophene
rings type of molecules (DTP‐P‐NN)[13] were focused on the
synthesis of cationic high-spin molecules. Since our interest is
synthesis, stable-radical species substituted with π-conjugated
electron donor systems and their radical cation formation for
high spin formation. Dithieno[3,2-b:2,3-d]-pyrrole (DTP)
derivatives are leading to better π-conjugation and lower
ionization potential by electron-donating nature of the molecules.
They also have two active positions at the thiophene, which
serve to modify the energy levels to substitute different donor
and or acceptor units which can assist to control the HOMO and
LUMO energy level of the molecules. In our molecular design,
two-phenyl (Ph) or -methylthiothiophene (MeSTh) groups were
introduced to tune the electronic properties of the molecules in
the DTP π-unit.[14]
4H-, and 4-methylthiothiophenyl- (R1 DTP-Ph-NN, R1 = H, Ph and
2
MeSTh) were designed, synthesized and characterized. The
electrochemical properties were studied by cyclic voltammetry (CV).
All the molecules exhibited two main oxidation peaks, first for radical
cation and next for dication formation. The cation and dication
formation were also confirmed by UV–vis absorption spectroscopy
for Ph2DTP-Ph-NN and MeSTh2DTP-Ph-NN titrated with tris(4-
bromophenyl)aminiumhexachloroantimonate (magic blue). In
addition, the cation and dication formation were verified by EPR
spectroscopy. Finally, the exchange interactions (J/kB) of NN and
radical cation were calculated by DFT studies.
Introduction
Organic high spin molecules are attractive due to their flexible
and controllable electronic properties and those were obtained
by different strategies.[1] High spin molecules have been used
for various applications such as spintronic device, and molecular
magnets.[1d, 2] The spin carrying units are very important in the
high spin molecules, because of the kinetic stability issues of
materials for further applications. To enhance the kinetic stability,
nitronylnitroxide (NN) iminonitroxide (IN) were the most
recognized spin units for the high spin organic molecules.[3]
Organic spin carrying unit linked with conjugated triarylaminium
radical cations are also of interest.[4] Their combination in mixed
stable radical and one electron oxidized cation–diradical
systems are more popular, because of their fair kinetic stability
and synthetic accessibility. The parent triphenylaminium radical
cation is not stable and quickly reacts via the para positions to
form benzidines. Thus, introduction of an electron donating para
substitutents eliminates this problem. Stable radical units linked
We report the design, synthesis, and structural characterization
of three, NN substituted DTP molecules with R1 = 4-Phenyl-, 4H-,
and
4-di(methylthiothiophenyl
dithieno[3,2-b:2',3'-d]pyrrole
derivatives (R1 DTP-Ph-NN R1 = H, Ph and MeSTh) together
2
with the formation of their radical cationic (R1 DTP-Ph-NN).+
2
forms. Furthermore, intra-molecular exchange interactions were
examined by DFT calculation.
Results and Discussion
Molecular design with DFT calculations
The computations were carried out to understand the electronic
structure of the molecules. All the DFT calculations were
performed using the Gaussian09 package.[15] The full geometry
optimizations were carried out by UB3LYP/6-31G(d) level for all
the neutral radical molecules. The optimized structures and spin
density distribution of the neutral radical molecules of DTP-Ph-
NN, Ph2DTP-Ph-NN, and MeSTh2DTP-Ph-NN are shown in
Figure 1.
with easily oxidizable aromatic amines are of particular interest
4b, 5]
for triplet ground state high spin molecules.[4a,
Thus, the
mixed stable radical with radical-cation molecules were provided
6]
for high spin triplet ground state molecules.[1d,
A series of
nitronyl nitroxide (NN) substituted triarylamine (TAA-NN)[7],
fused arylamine (FTAA-NN)[8], pyrazine (NNDPP)[9], thianthrene
(TA-NN)[10] phenothiazine (PTZ-NN)[11] and pyrrole-based[2b]
molecules and their radical-cationic forms were reported (Figure
S1), most of them afforded ground–state triplet diradicals upon
[a]
[b]
Dr. Kubandiran Kolnaji, Prof., Dr. Martin Baumgarten*
Max Planck Institute for Polymer Research, Ackermannweg 10,
55128 Mainz, Germany.
E-mail: kkubandiran@gmail.com, martin.baumgarten@mpip-
mainz.mpg.de
Current address for Dr. Kubandiran Kolanji,
Institute of Organic Chemistry,
Julius-Maximilians-Universität, Am Hubland, 97074, Würzburg,
Deutschland. Email:kubandiran.kolanji@uni-wuerzburg.de
Supporting information for this article is given via a link at the end of
the document.
Figure 1: Optimized structures (a), (b), and (c), spin density distributions (d),
(e) and (f) for DTP-Ph-NN, Ph2DTP-Ph-NN, and MeSTh2DTP-Ph-NN),
respectively, calculated by DFT using ub3lyp/6-31g(d) basis set.
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In order to get triplet ground state high spin molecules, one
electron could be oxidized from HOMO of the neutral molecules.
The proposed one electron oxidation mechanism is described in
carried out between 6 and bromobenzene, or 2-bromo-5-
(methylthio)thiophene[21] yielding 7a and 7b, respectively.
Further 7a or 7b were reacted with tetrabutylammoniumfluoride
(TBAF) to yield Ph2DTP-Ph-NN and MeSTh2DTP-Ph-NN.[20] All
the diamagnetic precursors were characterized by NMR
paramagnetic neutral radical molecules by Uv–vis EPR
spectroscopy and HRMS mass spectrometry.
Figure S14 for spin polarized donor radicals.
A similar
mechanism was also reported using molecular orbital theory to
analyses one electron oxidation of the amine-based spin-
polarized donors radical and pyrrole derivatives molecules.[3b]
Therefore, the energy level of the neutral molecules were
analyzed using DFT calculations. The energy levels of the
HOMO, LUMO and SOMO were summarized in the Figure 2 and
table S1. The HOMO of the DTP-Ph-NN (–5.18 eV) is higher
energy than HOMO (–5.19 eV) of the Ph2DTP-PhNN and
MeSTh2DTP-Ph-NN (–5.26 eV). The energy level of the SOMO
for DTP-Ph-NN (–5.06 eV) is lower than for Ph2DTP-PhNN
SOMO (–4.85 eV) and MeSTh2DTP-Ph-NN (–4.22 eV). The
energy difference between HOMO and SOMO are gradually
increased for DTP-Ph-NN, Ph2DTP-PhNN and MeSTh2DTP-Ph-
NN, respectively. The results clearly indicate that the
substitutions on their terminal sites in the core DTP π-unit with
two-Ph or -MeSTh groups were changed the electronic
properties of the molecules.
Scheme 1. Synthesis of NN substituted DTP molecules with R1 = 4-Phenyl-,
4H-, and 4-methylthiothiophenyl dithieno[3,2-b:2',3'-d]pyrrole derivatives of
R12DTP-Ph-NN (R = H, Ph and MeSTh).
Reaction conditions: (a) Pd2(dba)3, t-Bu3ONa, t-Bu3P, toluene,125 °C, 46%,
(b) BHA, DMF, 65 C, 52%, (c) NaIO4, DCM, H2O, 0 °C, 62%, (d) t-BuMe2SiCl,
imidazole, 55 °C, DMF, 83%, (e) n-BuLi, THF, -20 °C, Me3SnCl, THF, 91%, (f)
bromobenzene, Pd2dba3, P(o-tolyl)3, toluene, 90 °C, (f) TBAF, THF.
X‐ray crystallographic studies
The crystal structure analysis is important to understand
magnetic interactions in the solid state. Single crystals suitable
for X-ray diffraction analysis were obtained by slow evaporation
of DCM solution for MeSTh2DTP-Ph-NN and mixtures of DCM
and PhCN solution for Ph2DTP-Ph-NN.
Figure 2: Relative energy levels of the HOMO green line, LUMO blue line and
SOMO redline diagram of the DTP-Ph-NN, Ph2DTP-Ph-NN, and MeSTh2DTP-
Ph-NN), respectively.
The bond distance between NN and Ph unit is 1.461 Å and Ph
and DTP-backbone is 1.412, these values are same for all the
derivatives. The torsion between NN and its attached phenyl is
slightly varies for different derivatives such as 7.2°, 1.4°, and
1.7°, similarly between phenyl and DTP-backbone also varies as
39.9, 48.9 and 41.1 for
DTP-Ph-NN, Ph2DTP-Ph-NN, and
MeSTh2DTP-Ph-NN, respectively.
Synthesis
The syntheses of R2DTP-Ph-NNs are demonstrated in scheme 1.
Compound 1[16] and 2[17] were prepared by literature procedure
and 3 obtained by modified procedure with improved yield.[18]
Ullman condensation of
3 with 2,3-bis(hydroxylamino)-2,3-
dimethylbutane (BHA) yielded 4.[19] Oxidation of 4 by NaIO4
offered DTP-Ph-NN. Then N−OH groups were protected for 4
Figure 3. X–ray crystal structure of (a) Ph2DTP-Ph-NN, (b) molecular packing
(c) and (d) MeSTh2DTP-Ph-NN of the conformers, hydrogen atoms and PhCN
for Ph2DTP-Ph-NN are omitted for clarity.
with
tert-butyldimethylsilyl
(TBDMS)
through
tert-
butyldimethylsilyl chloride (t-BuMe2SiCl) in the presence of
imidazole in DMF as solvent to afford 5.[20] Further compound 5
was reacted with n-butyllithium solution followed by
trimethyltinchloride (Me3SnCl) yielding 6. Stille coupling was
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The blue plate Ph2DTP-PhNN was crystallized with PhCN
solvent molecule in orthorhombic, Pbcn space group. The
structure of the molecules is given in the Figure 3a. The torsions
between the radical NN and phenyl are 14.0°. The torsions
between the central phenyl and π-unit is 48.5°. Further, the
molecular packing is displayed in Figure 3b, providing a short
intermolecular distance (3.24 Å) between two oxygen atoms, in
addition short π–π intermolecular distances are found as 3.45 Å
for S11…C5 and 3.48 Å for S11…C4.
The green block MeSTh2DTP-Ph-NN was crystallized in dimeric
triclinic form with P–1 space group (Figure S3a). The two
structures of the unit cell are given in the Figures 3c and d. The
two independent molecules differ mainly in the orientation of the
thiophene unit and the torsion angles. In MeSTh2DTP-PhNN-A,
the sulfur atoms are arranged as S5 and S13 in syn–orientations,
S8 and S20 in anti–orientations while in molecule MeSTh2DTP-
Ph-NN-B, both S5 and S13, then S8 and S20 are arranged in
anti–orientations. The torsions between the radical NN and Ph
are also different in both molecules 34.0° and 15.1° for
MeSTh2DTP-Ph-NN-A, and MeSTh2DTP-PhNN-B, respectively.
Similarly slightly different torsion angles were found between the
center Ph and DTP core as 30.2° and 27.6° for MeSTh2DTP-Ph-
NN-A, and MeSTh2DTP-Ph-NN-B, correspondingly. These
variations are due to intermolecular interaction present between
the molecules in the molecular packing.
Table 1. Oxidation potentials of half-wave potentials for R2DTP-Ph-NN
ox1
ox2
ox3
E1/2
E1/2
E1/2
DTP-Ph-NN
+0.38
+0.33
+0.23
+0.78
+0.48
+0.41
+1.14
+1.00
+1.11
Ph2DTP-Ph-NN
MeSTh2DTP-Ph-NN
Oxidative process with half-wave potentials versus Fc/Fc+ in V with (±
0.02 V).
molecules showed two reversible and one irreversible oxidation
waves. The second and third oxidation waves probably
correspond to the oxidation process of the NN groups and/or the
oxidation process of the DTP core which allotted for the dication
formation. The DTP-Ph-NN was polymerized and/or some other
side reaction occurred at 0.8 V and 1.1 V (Figure S4b). The
extension of the π–bridge is also benefits for better donor ability
to the π-core. These two molecules exhibited both the first and
second oxidation potentials lower than those of the NN radical. It
means that first and second steps were radical cation and
dication formations in the oligomer moieties (scheme 2).
Cyclic voltammetry studies
Scheme 2. Oxidation and reduction of the R2DTP-Ph-NN and oxidation of
(R2DTP-Ph-NN)+. molecules.
A prerequisite for generating a radical cationic molecule is that
the arylamine of DPT moiety has a lower oxidation potential than
those of the NN radical. Hence, the electrochemical properties of
all the molecules were investigated by the cyclic voltammetry in
UV–vis absorption studies
acetonitrile for R1 DTP-Ph-NN, (R1
= H, and Th), and
The optical properties were studied for R1 DTP-Ph-NN (R1 = H,
2
2
benzonitrile for Ph2DTP-PhNN at room temperature. The cyclic
voltammograms are given in Figure 4 for Ph2DTP-Ph-NN, and
Ph and MeSTh) by UV–vis spectroscopy. The absorption
spectra are displayed in Figure S5. Two main absorption bands
appeared, one around 280–450 nm for π–π* transitions of the
donor π-unit and another about 500-750 nm for n–π* transitions
of NN radical units which is similar to typically reported
nitronylnitroxide molecules.[20]
for R1 DTP-Ph-NN, (R1 = H, and Th in Figure S4). The oxidative
2
process with half-wave potentials are summarized versus
+
ferrocene/ferrocenium (Fc/Fc ) in Table 1.
Figure 4. Cyclic voltammograms in PhCN solution of Ph2DTP-Ph-NN at a 0.1
V/s scan rate, with 0.1M (n-C4H9)4NBF4 as supporting electrolyte, versus
ferrocene/ferrocenium (Fc/Fc+).
Figure 5. UV–vis absorption spectra of Ph2DTP-Ph-NN in toluene (~10–4 M)
solution (solid green line) and its oxidation by addition of magic blue in CH2Cl2
at room temperature. Note: (broken lines) are formation of intermediates, solid
blue line) monoradical cation, and (solid red line) dication.
The first oxidation wave occurs at +0.23, and +0.33, (±0.02) V vs
+
Fc/Fc , for Th2DTP-Ph-NN and Ph2DTP-Ph-NN respectively.
The chemical oxidation reactions were conducted by tris(4-
The first oxidation potentials were apparently lower than those of
the NN unit,[2b, 12] and similar compounds of DTP-Ph, Ph2DTP-
Ph, and MeSTh2DTP-Ph reported in the literature.[14d-f] All the
bromophenyl)aminiumhexachloroantimonate
(magic
blue,
–
(BrC6H4)3N•+SbCl6 ) as the oxidant at room temperature in air,
and these reactions were monitored by UV–vis absorption
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spectroscopy. During first oxidation two new peaks were formed
at 521 and 805 nm for Ph2DTP-Ph-NN (Figure 5) and at 539 and
945 nm for MeSTh2DTP-Ph-NN (Figure S6) due to production of
radical cation, at the mean time the absorption band at 380 for
Ph2DTP-Ph-NN and 425 for MeSTh2DTP-Ph-NN for the neutral
compounds were superseded. The absorption in the longer
wavelength regions was assigned as the HOMO−SOMO and
shorter for SOMO−LUMO transition, respectively. For second
oxidation, another new peak appeared at 730 nm for Ph2DTP-
Ph-NN and 887 nm for MeSTh2DTP-Ph-NN and former peaks
decreased.
The blue solution of Ph2DTP-Ph-NN in DCM become brown
during addition of the AgSbF6, in which the EPR spectra was
recorded, there is a clear change in the spectrum where the
center is shifted upfield and the total width narrowed as given in
Figure S8b and Figure 4. After addition of one equivalent oxidant,
30 line EPR spectra were obtained (Figure 4), once the neutral
precursor was consumed. The solution was cooled to 160 K to
minimize decomposition of the biradical cations and (Figure
S10b). The one very week signal was found at 160 K, this is due
to dimerization occurred at lower temperature. Therefore, no
zero field splitting could be observed. Then warmed and the
variable temperature EPR spectra’s of the oxidized specie of the
EPR studies
.
(Ph2DTP-Ph-NN) + were measured (Figure S10b). While
decreasing the temperature, the intensity of the EPR line also
decreased until at 200 K, It is just above the melting point
(176.5 K) of CH2Cl2. For MeSTh2DTP-Ph-NN in DCM the light
blue/green solution became dark green during addition of the
AgSbF6, and formed dark green precipitate. The poor soluble
materials might be dimerized radical cations. The new EPR line
appeared during addition of AgSbF6 along with MeSTh2DTP-Ph-
NN (5 line) but the spectra are not resolved as demonstrated in
Figure S8d. The π-dimerization of dithienylpyrrole radical cation
molecules is known from the literature.[13, 22] Further addition of
one more equivalent of the AgSbF6, kept at –10 °C for 6 hours,
five lines EPR spectra was retained for Ph2DTP-Ph-NN and
MeSTh2DTP-Ph-NN, the spectra are given the Figures S8e-f.
These results indicate the dication formation on the DTP core
without decomposition of the NN radical.
The EPR spectra of neutral radicals of DTP-Ph-NN, Ph2DTP-
Ph-NN and MeSTh2DTP-Ph-NN in toluene (10−4 M) in argon-
saturated solutions were measured at room temperature and in
frozen solution at 130 K. The experiment spectra’s with
simulated are displayed in Figure S7a-c. All the molecules
showed equally separated five lines at room temperature
assigned to hyperfine coupling of two equivalent nitrogen nuclei
of the NN unit. The g values (g = 2.0070, ± 0.02) are nearly
same for the all three neutral radicals. The variable temperature
EPR spectra’s of the Ph2DTP-Ph-NN and Th2DTP-Ph-NN are
displayed in Figure S9. Moreover, frozen solution spectra’s are
asymmetric with an anisotropic component in the spectra, which
gives the different number of the shoulders in both the side of
the outermost region (Figure S7d-f). Initially, we tried to oxidize
using magic blue as an oxidant in the oxidation process, but the
reaction could not be monitored clearly by EPR spectroscopy. It
might be the unreacted magic blue affected resolutions of the
spectra. Further, the chemical oxidation reaction was carried out
for all the neutral radicals by the silver hexafluoroantimonate
(AgSbF6) and the reaction was monitored with EPR
spectroscopy. DTP-Ph-NN in DCM (blue solution) was titrated
with AgSbF6 as an oxidant and the spectra are given in Figure
S8a. During addition of the oxidant, the blue solution of DTP-Ph-
NN turned to green and the intensity of the five line spectra
decreased. Finally, all the EPR lines disappeared, this is due to
decomposition of the NN, and polymerisation of the molecules or
some other side reaction occurred.
Magnetic interaction calculations using DFT calculations
The intra molecular interaction (Jintra calc) of NN and radical-cation
,
.
was calculated for (R1 DTP-Ph-NN) + for all the molecules with
2
density functional theory (DFT) and hybrid function BLYP, and
basis set 6-31G(d) in the gas phase using Gaussian 09
package.[15] The X-ray structure geometry of Ph2DTP-Ph-NN,
MeSTh2DTP-Ph-NN and optimized geometry for DTP-Ph-NN
with positive charge were used for the calculationa. The Jintra calc
,
values are –3580 K, +5000 K, +965 K for DTP-Ph-NN, Ph2DTP-
Ph-NN MeSTh2DTP-Ph-NN respectively. The interaction
between NN and radical-cation is positive and ferromagnetic-
interaction with high-spin molecules for Ph2DTP-Ph-NN and
MeSTh2DTP-Ph-NN whereas for DTP-Ph-NN is negative
indicating antiferromagnetic-interaction. The spin densities were
6.0x105
3.0x105
0.0
also calculated for both the neutral R1 DTP-Ph-NN and charged
2
.
(R2DTP-Ph-NN) + molecules. The spin density is mostly localized
on Ph-NN for the neutral molecules while delocalized over the
extended π–unit for charged molecules in Figure 5 for Ph2DTP–
.
Ph-NN (Ph2DTP-Ph-NN) + and see in Figure S11-12 for R2DTP-
.
PhNN, R1 DTP-Ph-NN and (R1 DTP-Ph-NN) + (R = H, and Th).
-3.0x105
-6.0x105
2
2
.
The Jintra calc
,
is nearly five time higher for (Ph2DTP-Ph-NN) + than
for (MeSTh2DTP-Ph-NN) + because the positive charges are
.
distributed equally over the entire molecule for (Ph2DTP-Ph-
.
NN) + whereas in MeSTh2DTP-Ph-NN the positive charge and
331.5
332.0
332.5
333.0
the spin are better delocalized over the extended π–unit and
less spin is on the central phenyl.
Magnetic filed (mT)
.
+
Figure 6. EPR spectra of the (Ph2DTP-Ph-NN) biradical cation monomer
obtained by chemical oxidation titrated with AgSbF6 as an oxidant in DCM at
room temperature.
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cation. Further charged molecules will be isolated and analyzed
for magnetic properties by magnetic susceptibility. Syntheses of
similar radical cationic molecules are under way. The Ph2DTP-
Ph-NN and MeSTh2DTP-Ph-NN type molecules are suitable for
spintronic and molecular based magnetic materials application.
Experimental Section
The experimental details are given in the supporting information.
Acknowledgements
Dieter Schollmeyer for the X-ray structure analysis and we
acknowledge the SFB-TR49 for financial support.
Figure 7. Spin density distributions of the (a) Ph2DTP–PhNN and (b)
.
+
(Ph2DTP–PhNN)
.
Keywords: • dithienopyrrole (DTP) • stable radical • nitronyl
nitroxide • radical cation • high spin molecules.
The Jintra calc
,
is antiferromagnetic interaction for (DTP–PhNN).+
while ferromagnetic interaction for (Ph2DTP–PhNN).+ and
.
(MeSTh2DTP–PhNN) +. To investigate this variation, vertical
References:
ionization potential (IPver = Ecation - Eneutral) calculation was used.
These (IPver) calculations were performed by the DFT with BLYP,
6-31G(d) basis set in the gas phase using Gaussian 09 package
(Figure S15-16). The NN was deleted from the X-ray structures
for Ph2-DTP-Ph and MeSTh2-DTP-Ph whereas for DTP-Ph and
Ph-NN optimised structure were used for calculation. The
calculated IPver were 5.54 eV and 4.98 eV for Ph2-DTP and
MeSTh2-DTP-Ph respectively. These are much lower than 6.24
eV of NN-Ph (Figure S15). Therefore, neutral molecules of
Ph2DTP-Ph-NN, MeSTh2DTP-Ph-NN are easily oxidized and
form high spin ground state molecules. In case of DTP-Ph the
vertical ionization potential is IPver = 6.37 eV which is higher than
the IPver = 6.24 eV for phenyl nitronyl nitroxide radical (Ph-NN,
.
Figure S13). Consequently, in DTP-Ph-NN + nitroxide is charged
with a low spin ground state and the triplet is much higher in
energy.
In another aspect from DFT, as we mention before to generate a
radical cation is that the arylamine of DPT moiety has a lower
oxidation potential than those of the NN radical. The important
factor now is the energy difference between HOMO and SOMO
must be high enough. In case of the DTP-Ph-NN, the energy
level of the SOMO is –5.18 eV and HOMO is –5.06 eV. Then,
the energy difference between HOMO and SOMO is only (0.12
eV) while the HOMO of the phenyl nitronyl nitroxide (Ph-NN) is –
5.17 eV. It is very closer with the SOMO of the DTP-Ph-NN (–
5.18 eV). Therefore, we cannot determine very clearly that the
removal of the first electron is either from the SOMO or HOMO
for DTP-Ph-NN during oxidation. In case of another two
molecules the energy difference between HOMO and SOMO
were –0.39 and –1.04 for Ph2DTP-PhNN and MeSTh2DTP-Ph-
NN, respectively which are better enough to generate the
cationic molecules.
Thus, three Ph-NN substituted donor π–core of (DTP)
derivatives (R2DTP-Ph-NN) molecules were prepared and
characterized. The molecular structures and packing of Ph2DTP-
Ph-NN and Th2DTP-Ph-NN were examined by single crystal x–
ray structure analysis. The Th2DTP-Ph-NN is crystalized in the
dimeric form with shorter intermolecular distance of N–O…C–Ph
(3.31 Å), while Ph2DTP-Ph-NN crystalized in monomeric
structure with smaller intermolecular distance found between
two oxygen atoms for N–O…N–O (3.24 Å) in molecular packing.
Upon one electron oxidation, the (R1 DTP-Ph-NN, R1 = Ph and
2
.
MeSTh) + offered triplet ground state radical-cationic high spin
molecules. Although for (DTP-Ph-NN) + the calculated magnetic
.
interaction is antiferromagnetic between the NN and radical-
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10.1002/chem.201905734
Chemistry - A European Journal
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TOC graphics
Dithienopyrrole Derivatives with phenyl and methylthiothiophenyl
connected with phenylnitronylnitroxides were oxidized to their
cations forming high spin S=1 molecules.
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