Vibrational dynamics in dendridic oligoarylamines by raman spectroscopy and incoherent inelastic neutron scattering

Article abstract of DOI:10.1021/jp502735s

Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C-H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C-C and C-N deformation modes with those of C-H nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation. ? 2014 American Chemical Society.

Full text of DOI:10.1021/jp502735s

Article
pubs.acs.org/JPCB
Vibrational Dynamics in Dendridic Oligoarylamines by Raman
Spectroscopy and Incoherent Inelastic Neutron Scattering
Irena Kulszewicz-Bajer,*,† Guy Louarn,*,‡ David Djurado,§ Lukasz Skorka,† Marek Szymanski,§,⊥
Jean Yves Mevellec,‡ Stephane Rols,∥ and Adam Pron†
†Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
‡Insitut des Materiaux Jean Rouxel, CNRS-University of Nantes, 2 rue de la Houssinier, 44322 Nantes, France
§University Grenoble Alpes, INAC-SPrAM; CNRS, INAC-SPrAM; CEA, INAC-SPrAM, F-38000 Grenoble, France
∥Institut Laue Langevin, 6 rue J. Horovitz, 38042 Grenoble, France
S
* Supporting Information
ABSTRACT: Vibrational dynamics in triarylamine dendrimers was studied in a
complementary way by Raman and infrared (IR) spectroscopies and incoherent
inelastic neutron scattering (IINS). Three molecules were investigated, namely,
unsubstituted triarylamine dendrimer of the first generation and two dendrimers of
the first and second generation, substituted in the crown with butyl groups. To
facilitate the assignment of the observed IR and Raman modes as well as the IINS
peaks, vibrational models, based on the general valence force field method (GVFF),
were calculated for all three compounds studied. A perfect consistency between the
calculated and experimental results was found. Moreover, an important
complementarity of the vibrational spectroscopies and IINS was established for
the investigated dendrimers. The IINS peaks originating mainly from the C−H
motions were not restricted by particular selection rules and only dependent on the
IINS cross section. To the contrary, Raman and IR bands were imposed by the
selection rules and the local geometry of the dendrimers yielding mainly C−C and C−N deformation modes with those of C−H
nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their
cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different
levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In
particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral
information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous
monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of
oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved
one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found
in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some
inhomogeneity of the oxidation.
light emitting diodes (OLEDs),16−21 including the first
INTRODUCTION
■
reported multilayer OLED.29
The triarylamine moiety is a widely used building block for a
Dendridic oligoarylamines constitute a special class of this
variety of functional materials used in organic and hybrid
family of organic conductors. They have been studied for nearly
(organic/inorganic) electronics,1−6 optoelectronics,7−22 and
25 years30−33 due to the peculiar topology of their macro-
electrochemical devices.23−27 Linear and branched triarylamine
molecules and the capability of forming spin-delocalized, stable
multicationic states.34−37
homooligomers as well as their polymeric analogues are
frequently used as active materials in p-channel organic field
effect transistors (OFETs), since they combine reasonably high
Molecular dynamics of neutral and polycationic triarylamine
dendrons deposited as thin films is of fundamental interest,
hole mobilities with amorphous structure, the latter facilitating
the formation of structurally homogeneous films by solution
processing.3,5 Cyclic triarylamines, in turn, readily crystallize to
yield anisotropic layers of columnar-type supramolecular
organization.28 Besides their use as active layers in OFETs,
both low and high molecular weight triarylamine derivatives
serve as hole injection and hole transporting layers in organic
since it is closely related to their redox, magnetic, and electrical
transport properties. Raman spectroscopy and incoherent
inelastic neutron scattering (IINS) are convenient and
Received: March 19, 2014
Revised: April 25, 2014
Published: April 25, 2014
© 2014 American Chemical Society
5278
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
Scheme 1. Structural Formulae of the First and Second Generation Triarylamine Dendrimers Studied
complementary tools for studying vibrational properties of such
molecules. Raman spectroscopy gives a high energy resolution
and is very sensitive to electronic and optical properties of
molecules under study. IINS by contrast has a lower energy
resolution, but it is not sensitive to the presence of electrons
and gives access to all vibrational modes of the system without
any selection rule.38 Raman studies of thin layers of triarylamine
dendrimers, reported to date, are scarce and limited to the
studies of the effect of annealing of thin arylamine films on their
spectra obtained with one excitation line.39−41 To the best of
our knowledge, incoherent inelastic neutron scattering
investigations have never been reported for this class of organic
semiconductors. In this paper, we present a theoretically
calculated vibrational model for first and second generation
triarylamine dendrons and confront it with experimental data
derived from Raman and neutron scattering studies.
not be discussed here. Readers interested in the details of the
synthesis are referred to ref 42.
Raman spectra of low and high molecular weight aromatic
amines, both in their neutral and oxidized (cationic) states, are
very sensitive toward the energy of the excitation line which is
caused by resonance effects, frequently interfering in the
measurements.43,44 Therefore, registration of the spectra
obtained with excitation lines of different energy, λexc, is highly
desirable. In Figures 1 and 2, Raman spectra of 1 and 2,
registered for λexc of decreasing energy, are compared.
In the UV−vis spectra of neutral 1 and 2, no band giving rise
to a significant value of absorbance above 400 nm can be
distinguished (vide infra). This means that the resonance effect
is expected for none of the applied excitation line. Although the
positions of the observed Raman bands do not vary with the
energy of the excitation line, the quality of the spectrum,
determined by the signal-to-noise ratio, is strongly dependent
on λexc. It increases with decreasing energy of the excitation
line, being the best for λexc = 647 nm (red line). For the IR
excitation line (λexc = 1064 nm), the spectrum quality worsens
again. Only a low resolution spectrum of the neutral form has
been registered for 3 (Figure 3); see also Table 1.
RESULTS AND DISCUSSION
■
Neutral Dendrimers. The studied dendridic triarylamines
are depicted in Scheme 1.
1 has already been reported,33 and 2 and 3 were also
described, however, with different alkyl or alkoxy substitu-
ents.33,37,42 For this reason, the applied synthetic pathways will
5279
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
Figure 1. Raman spectra of neutral arylamine dendrimer 1 registered
using different excitation lines: (a) blue line 458 nm; (b) green line
514 nm; (c) red line 647 nm; d) Fourier transform Raman spectrum,
infrared line 1064 nm.
Figure 3. Raman spectra of neutral arylamine dendrimers registered
using different excitation lines: (a) dendrimer 1 (647 nm); (b)
dendrimer 2 (647 nm); (c) dendrimer 3 (1064 nm, Fourier transform
Raman spectrum).
lines can be found which are absent in the spectrum of 2, at
1027, 1000, and 745 cm−1. They are characteristic of C−H
deformations in monosubstituted benzene rings,46,47 and their
presence confirms the coexistence of monosubstituted and
para-substituted rings in 1. In the spectrum of 2, a very weak
band can be noticed at 1448 cm−1, i.e., in the spectral range
characteristic of CH2/CH3 deformations of the aliphatic
groups. In aromatic amines or conjugated molecules (macro-
molecules), the aliphatic bands are very weak, especially under
resonance conditions. Therefore, we tend to ascribe this band
to the CH2/CH3 in the butyl substituent. There are two
additional findings which further support this attribution: (i)
this band is absent in the spectrum of 1 (unsubstituted
analogue of 2); (ii) it remains unchanged upon oxidation of the
molecule being clearly detectable in the spectra of the oxidized
forms of 2 (vide infra).
Close inspection of the spectra of 1 and 2 reveals the
presence of additional bands of low intensity which cannot be
assigned to the vibrations of neutral arylamine molecules, in
their reduced state. A weak band in the vicinity of 1480−1500
cm−1 can tentatively be ascribed to CN stretching.48 This
attribution is reasonable, since both 1 and 2 are very sensitive
to oxidation; thus, minute amounts of these compounds could
be partially oxidized upon their dissolution and film casting. A
weak peak at 1333 cm−1 should in turn be ascribed to the
presence of very small amounts of radical cations characteristic
of the first oxidation step of 1 and 2.48 One should not attempt
to perform any type of quantitative estimation of the fraction of
the oxidized forms of 1 and 2 in the studied samples, since
bands originating from the vibrations of the oxidized parts of
the molecule are resonantly enhanced when λexc = 647 nm (red
line) is used. This resonance enhancement is even more
pronounced in the spectrum of 1 obtained with the IR
excitation line (λexc = 1064 nm) where the intensity of lines
assigned to the oxidized form relatively increases (see Figure
1d). This problem will be discussed in detail in a subsequent
part of the paper.
Figure 2. Raman spectra of neutral arylamine dendrimer 2 registered
using different excitation lines: (a) blue line 458 nm; (b) green line
514 nm; (c) red line 647 nm; (d) Fourier transform Raman spectrum,
infrared line 1064 nm.
We will focus here on a comparative discussion of the spectra
of 1 and 2 registered with λexc = 647 nm. There are some
common Raman lines in both spectra. In particular, two
strongly overlapping, sharp peaks at 1595 and 1610 cm−1 can
unambiguously be assigned to the C−C stretching deforma-
tions in the benzenoid type of ring, consistent with the reduced
neutral state of 1 and 2 in which all aromatic rings are quasi-
equivalent and benzenoid in nature. A clear band at 1289 cm−1,
which is usually attributed to the C−N stretching in aromatic
amines,40,45,46 is also characteristic of the neutral state of 1 and
2. A weak band at ca. 1175 cm−1 together with a strong band at
ca. 1162 cm−1 are characteristic of the C−H in-plane bending
deformations in the aromatic ring. Finally, a weak intensity peak
at ca. 820−825 cm−1 should be attributed to the deformations
of the amine group; i.e., its presence corroborates the neutral
state of both molecules. In the spectrum of 1, three additional
To confront the obtained experimental spectra of the studied
dendrimers with theoretical predictions, we have elaborated
their vibrational models. The applied calculation methodology
5280
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
Table 1. Calculated and Experimentally Measured Frequencies (in cm−1) of the Main Vibrational Modes of 1, 2, and 3 in Their
Neutral Form
dendrimer 1
exptl bands
dendrimer 2
exptl bands
Raman
dendrimer 3
exptl bands
Raman
benzene
Wilson notation54
47,55
IINS
1600
Raman
FTIR
calcd modes
IINS
FTIR
assignments
ring stretch
ring stretch
1596 (8a)
1596 (8b)
1486 (19a)
butyl gr.
1610
1595
1493
1616
1624
1489
1616
1605
1510
1439
1333
1616
1587
1488
1607
1496
1465
1487
1499
1344
ring stretch + deformation
methyl and methylene H−C−H def.
radical cation (residual)
1455
1300
doping
1333
butyl gr.
1310
1305
1263
1178
1113
1015
in-plane methylene twisting−rocking
ring stretch
1326 (3)
1300
1165
1022
1310
1287
1163
1310
1310
1280
1166
1102
1020
996
1286
1165
1105
1015
1280
1165
C−N stretch + ring stretch
ring C−H deformation
aromatic C−H bend
C−H deformation
ring deformation
1178 (9a)
1038 (18b)
1038 (18a)
1010 (12)
975 (17a)
849 (10a)
673 (11)
703 (4)
1178
1108
1010
1028
1000
968
832
752
700
617
411
966-
829
942
822
733
C−H deformation (out of plane)
C−H deformation (out of plane)
C−H deformation (out of plane)
ring deformation (out of plane)
ring deformation
835
747
820
750
691
811
751
821
747
693
606 (6b)
410 (16a)
644
648
625
415
643
418
423
ring deformation (out of plane)
Figure 4. Vibrational spectra of dendrimer 1 (left) and dendrimer 2 (right): (a and d) Raman scattering (red excitation); (b and e) IR absorption; (c
and f) inelastic incoherent neutron scattering.
has previously been tested with success in elaborating
vibrational models of electroactive molecules and macro-
molecules,46,49 including aromatic amines.50 Its detailed
description can be found in ref 51; here, we only briefly
outline it. The force field and frequencies are determined using
the Fourier dynamic matrix. The calculations require the
knowledge of bond lengths, bond angles, and force constants.
To obtain the former, it is necessary to optimize the molecule
geometry, which is usually done by applying semiempirical or
ab initio quantum chemistry methods depending on the
complexity of the studied molecules. In our case, it is carried
out with the Hyperchem 75 software (semiempirical method:
PM3). An internal coordinate system is used to compute the
fundamental vibrations of the studied molecules. Local
redundancies can be handled by suitable symmetry coordinates.
The calculations start from a minimal set of force constants,
expressed in terms of internal coordinates. It is necessary to
assume that certain force constants must be fairly local, i.e., only
dependent on the nearest chemical environment. For this
reason, they can be transferred from model compounds of
simpler topology. Using this procedure, the number of force
constants used in the calculations can be minimized, which
leads to a significant reduction of the number of independent
parameters. These parameters are finally adjusted from the
experimental and calculated frequencies with a least-squares
method. The calculated bond lengths and angles between
bonds, derived from the optimized geometry, as well as the
obtained main force constants (FG matrix) and modeling
Cartesian displacements of the main experimental modes are
listed in the Supporting Information (Chart S1). The measured
and calculated modes, together with their assignment, are listed
in Table 1.
5281
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
On the basis of our semiempirical modeling, the three
studied dendrimers have at least a C3 symmetry. The phenyl
rings are assumed to be flat and identical to each other, with
fixed C−C (1.409 Å) and C−H (1.078 Å) distances and
∠CCC angles and ∠CCH angles of exactly 120°. The values for
the bond lengths are the averaged values as obtained from our
modeling, and from spectroscopic and X-ray crystallographic
studies of TPA (triphenylamine) in the solid state.52,53 Then
there are only three other parameters left that are allowed to
vary, i.e., the C−N distance (taken as 1.421 Å), the φ angle by
which the phenyl groups are rotated around the C−N bonds,
and the ∠CNC angle. The angles are defined in such a manner
that a fully planar geometry of TPA means φ = 0 and ∠CNC =
120°. If ∠CNC is exactly120°, an additional C2 symmetry axis
exists, passing through each of the three phenyl rings, yielding a
D3 symmetry for the molecule. Our modeling gives a φ angle
somewhere between 40 and 60° and a ∠CNC angle between
119 and 120°, the values similar to those previously obtained
for triaryl amine derivatives.52,53 This φ angle likely changes
during the oxidation process. Since we cannot exclude the
impact of this torsion on the position and the intensity of some
vibrational modes, we assume that this evolution only concerns
modes with very low frequencies (<600 cm−1). Above this
frequency, modes are mainly due to valence bond stretchings or
bendings and the contribution of the torsion or twist is
negligible. In addition, it should be stressed here that all
nitrogen atoms in the dendrimer structures are located in the
same plane. More details can be found in the Supporting
Information.
These considerations concerning the symmetries of the
dendrimers are very important in regard to the selection rules
and the relative intensities of IINS, IR, and Raman bands. In
Figure 4, where the vibrational data of 1 and 2 are presented on
the same graph, the complementarity of these spectroscopies
can easily be noticed. For instance, the Raman and IR spectra
present mainly two lines in the 1400−1700 cm−1 range,
assigned to C−C stretching deformations and pointed in 1 at
1610 and 1493 cm−1. These peaks can be ascribed without
ambiguities to 8a and 19a modes in Wilson notation. These
modes are weakly active in the IINS spectra, due to the low
contribution of the CH motions. On the contrary, the in-plane
and out-of-plane CH-bending modes, well-known as modes 9a
and 10a in Wilson notation, can be observed with a high
intensity in the IINS spectra at 1165 and 832 cm−1 (144 and
103 meV). The intense peaks pointed at 968 and 942 cm−1 in
the IINS of 1 and 2, respectively, fully absent in Raman and IR
spectra, deserve some discussion. As already written above, in
contrast to the Raman and IR spectroscopies, IINS gives access
to all vibrational modes without any selection rules. Therefore,
we have assigned this peak to the out-of-plane CH mode arising
from mode 17a (Wilson notation). Indeed, this mode is almost
never observed by Raman or IR spectoscopies, especially in the
case of para-substituted aromatic compounds. In our study, the
inactivity of this mode may be surprising if one takes into
account the symmetry of the dendrimers, and their point group
as either C3 or D3. Indeed, the nonexclusion of Raman and IR
active modes due to the lack of inversion point, for instance,
should lead to a larger number of bands in both spectra.
However, it can be assumed that the local environment of the
para-substituted benzene ring retains a pseudosymmetry D2h.
Thus, it can be postulated that, in the studied dendrimers, the
E2u mode (17a) in the benzene ring becomes locally Au, again
Raman and IR inactive. Another point, which merits attention,
concerns the difference between the IINS data of 1 and 2.
Logically, these differences are due to the modes originating
from the butyl substituent on the crown. Thus, the new intense
bands which appear on IINS spectra of 2 at 1300 and 1444
cm−1 are assigned, respectively, to the overlapping of the CH3
antisymmetric deformation (methyl out-of-plane HCH defor-
mation) and the CH2 scissors, and the in-plane methylene
twisting-rocking mode.
All other assignments can be found in Table 1, with the
associated number in Wilson notation.
Oxidized Dendrimers. The studied dendrimers are
electron-rich molecules characterized by a high lying HOMO
level (with respect to the vacuum level) and a low value of the
ionization potential (IP). As a consequence, they are readily
oxidized, forming stable radical cations and consecutively
higher cationic states.42,56−58 This is clearly manifested in
their cyclic voltammograms.42,56,58−60 Dendrons of the first
generation with alkoxy substituents give rise to three reversible
redox couples in the potential range from ca. −0.2 to +0.6 V vs
Fc/Fc+, associated with three consecutive one-electron
oxidations from a neutral molecule to a three cation.54,56 We
observe qualitatively the same behavior for 2 in cyclic
voltammetry and differential scanning voltammetry, however,
with the potential of each redox couple systematically shifted to
slightly higher values by 0.15−0.20 V. This difference between
2 and its methoxy-substituted analogue is obviously related to
higher electron donating properties of the alkoxy substituents
as compared to the alkyl ones.
As evidenced by cyclic voltammetry, neutral dendrons of the
second generation can be oxidized to hexacations through three
consecutive one-electron oxidations, followed by a three-
electron oxidation. For the methoxy-substituted counterpart
of 3, these four oxidations occur in the potential range from ca.
−0.30 V to ca. +0.20 V vs Fc/Fc+.54,56 The voltammetric
behavior of 3 is qualitatively very similar; again, the
corresponding peaks are shifted to higher potentials by 0.15−
0.20 V, as expected.
UV−vis spectra of neutral dendrimers are characterized by
two strongly overlapping peaks in the vicinity of 310 and 340
nm. In Figure 5, the spectrum of 2 is shown as a representative
example.
It has been previously demonstrated by the correlation of
cyclic voltammetry, UV−vis/NIR spectroelectrochemistry, and
EPR data that the oxidation of a given dendrimer to a radical
cation results in a sharp decrease of the band at ca. 350 nm and
a smaller decrease of the 310 nm band; however, this band
overlaps with that originating from the reduced form of the
oxidant. Concomitantly, two new bands appear: a narrow one
at ca. 440 nm in the case of 2 and a broad one with a clear
maximum in the near-infrared part of the spectrum (at 1158
nm for 2). Oxidation to higher cationic states induces a
hypsochromic shift of the lower energetic (infrared) peak to
1130 nm with a simultaneous decrease in the intensity of the
higher energetic band (440 nm in the case of 2).42 These
changes are clearly reproduced in the spectra presented in
Figure 5. For 2 oxidized with 1 equiv of the oxidant, the
spectrum is characteristic of the radical cation state, and for the
dendrimer oxidized with 3 equiv of the oxidant, it corresponds
to the tricationic state. Note also that there is very little
difference between the spectra of the dendrimer oxidized with 3
and 4 equiv of the oxidant, indicating the stability of the
tricationic state.
5282
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
In principle, one could expect a resonance enhancement of
the spectral lines for λexc = 458 nm, since it matches in energy
the oxidation-induced small absorption band at 440 nm.
However, this absorption band does not yield any resonance,
since using the blue excitation yields spectra of poor quality
with two dominant lines characteristic of neutral amines (at
1611 and 1170 cm−1). This means that vibrations from these
parts of the dendrimer which do not bear positive charge are
preferentially detected. Peaks originating from the charged
(cationic) parts are present as broad, poorly resolved features in
the spectral range between 1200 and 1600 cm−1. Thus, the blue
excitation line is of little use for investigating either neutral or
oxidized (charged) forms of the discussed dendrimers.
With increasing wavelength of the excitation line from blue
(λexc = 458 nm) to green (λexc = 514 nm) to red (λexc = 647
nm) to infrared (λexc = 1064 nm), the quality of the spectrum
increases and the bands originating from the oxidized (charged)
parts of 2 grow in intensity. For the infrared excitation line,
they dominate the spectrum. This indicates that the lower
energetic, oxidation-induced NIR band contributes to the
resonance effect, since its maximum at 1110 nm closely
matches the energy of the excitation line (1064 nm).
Figure 5. UV−vis spectra of thin films of 2 in its neutral state and
oxidized with 1, 2, 3, and 4 equiv of tris(4-bromophenyl)ammonium
hexachloroantimonate [(BrC6H4)3NSbCl6].
In Figure 7, Raman spectra of neutral, partially oxidized, and
fully oxidized 2 are compared. The corresponding spectra of 1
can be found in the Supporting Information (Figures S2−S4).
These profound changes in the UV−vis/NIR spectra of the
studied dendrimers have an important impact on the registered
Raman spectra, since the resonance conditions are completely
different for neutral molecules and for the oxidized (cationic)
ones. In order to verify this effect, we have registered Raman
spectra of thin films of 1 and 2 oxidized with either 1 or 3 equiv
of the oxidant, yielding the lowest and highest cationic states,
respectively. For 3, we used 1 and 6 equiv of the oxidant. In the
subsequent text, the corresponding samples will be termed
“partially” and “fully” oxidized.
The effect of the excitation line energy on the resulting
Raman spectra is demonstrated in Figure 6, where the case of
fully oxidized 2 is used as an instructive example. For partially
oxidized 2 and partially and fully oxidized 1, the observed
changes are very similar and the corresponding spectra can be
found in the Supporting Information (Figures S1−S4).
Figure 7. Raman spectra of (a) neutral 2 and 2 oxidized with (b) 1
and (c) 3 equiv of the oxidant (“partially oxidized” and “fully oxidized”,
respectively). λexc = 647 nm.
Before analyzing the spectra, it is instructive to discuss
possible charge and spin configurations in the oxidized
(charged) dendrimers. The use of 1 equiv of the oxidant
imposes the presence of one radical cation per molecule of
“partially” oxidized 2, provided that the oxidation process
occurs in a perfectly homogeneous way. Thus, semiquinone
radical cation structure is expected in this case (Scheme 2). In
“fully” oxidized 2, three charges are introduced per molecule for
a perfectly homogeneous oxidation. These three charges can be
present as three radical cations of semiquinone structure or as
one radical cation and one spinless dication, whose presence
imposes the formation of a quinone-type ring (Scheme 2).
Figure 6. Raman spectra of 2 oxidized with 3 equiv of the oxidant
(“fully oxidized”) registered using different excitation lines: (a) blue
line 458 nm; (b) green line 514 nm; (c) red line 647 nm; (d) Fourier
transform Raman spectrum, infrared line 1064 nm.
5283
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
Scheme 2. Chemical Structures of Triarylamine Dendrimer Oxidized to Radical Cation, Tri(radical cation), and Dication +
Radical Cation
Table 2. Raman Frequencies (in cm−1) of the Main Vibrational Modes of 1, 2, and 3 in Their Neutral and Highest Oxidation
State
dendrimer 1
exptl bands
dendrimer 2
exptl bands
dendrimer 3
exptl bands
neutral
Ox
neutral
Ox
neutral
Ox
assignments
1610
1611
1584
1569
1487
1455
1357
1331
1299
1278
1173
sh
1616
1615
1596
1573
1495
1427
1355
1332
1302
1283
1175
sh
1616
1611
1582
aromatic ring CC stretch
semiquinonoid CC stretch
quinonoid ring, CC stretch (dication)
1499
1493
1427
1348
1332
1303
1279
1176
sh
CN°+ stretch (spinless dication)
CN°+ stretch (radical cation)
CN°+ stretch (radical cation)
C−N stretch (dication)
1333
1310
1287
1333
1286
1165
1344
1280
1165
C−N stretch
C−H deformation (semiquinonoid ring)
C−H deformation (neutral and quinonoid ring)
quinonoid ring deformation
1163
801
804
801
Oxidation of 2 to the tricationic state involves profound
spectral changes as revealed for the spectra obtained with either
red or infrared excitation lines. First, the line at 1612 cm−1,
characteristic of the benzenoid ring in the neutral form of the
molecule, diminishes in intensity on the expense of two lines at
1595 and 1571 cm−1, which are usually attributed to CC
stretching in quinone or semiquinone rings. Concomitantly, the
band originating from the CN stretching at 1494 cm−1,
which is very weak in the spectrum of neutral 2 and indicates
minute amounts of oxidation products, grows in intensity.
Second, a new peak ascribed to the formation of radical cations
in the oxidized form of the molecule appears at 1358 cm−1 and
is accompanied by a second “radical cation” peak at 1333 cm−1,
already detected in the spectrum of the neutral form of 2.
Consistent with these changes, the band at 1289 cm−1,
attributed to the CN stretching and clearly resolved in the
spectrum of the neutral molecule, diminishes in intensity and in
the case of the use of λexc = 1064 nm is present as a weak
5284
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
shoulder of the 1333 cm−1 band. Third, the peak attributed to
the deformations of the amine group at 821 cm−1 in the
spectrum of neutral 2 is shifted to 794 cm−1, confirming the
oxidation of the amine moiety. Finally, the band at 1171 cm−1
(CH in-plane bending deformations in the aromatic ring)
remains relatively unchanged with respect to the corresponding
band in the spectrum of neutral 2.
From this analysis, it appears clear that in the fully oxidized
molecule both radical cations and quinone-type dications are
present. This is perfectly consistent with the above outlined
picture of the charge and spin storage configurations. However,
the spectra of “partially” oxidized 2 also show the presence of a
quinone-type dication, which should be absent if the oxidation
was totally homogeneous. This finding may imply some
nonhomogeneity in the oxidation process. However, the
bands originating from quinone-type vibrations are strongly
resonantly enhanced; therefore, the content of dications in the
“partially” oxidized samples may be very low. Anyhow, resonant
effects exclude in this case any quantitative estimation.
chemistry methods, assignments of the main incoherent
inelastic neutron scattering (IINS) bands in the 60−240 meV
range were proposed in relation to the experimentally observed
Raman and IR bands. To support these interpretations,
numerical vibrational models of the studied compounds,
based on the general valence force field method (GVFF),
were established which additionally corroborated the proposed
assignments. Moreover, the activity/inactivity of particular
modes in different spectroscopies (IINS, Raman, IR) could be
explained through symmetry considerations and taking into
account the IINS cross section.
Raman spectroscopy was also applied to the investigations of
the vibrational properties of cationic (oxidized) forms of these
dendrimers. The obtained results allowed us to formulate the
following conclusions. First, Raman spectra registered at
different oxidation levels of the dendrimers strongly depended
on the position of the excitation line with respect to their
electronic spectrum. In particular: (1) the blue (458 nm)
excitation line turned out to be insensitive toward the radical
cationic and cationic forms of these compounds and revealed
only the presence of unoxidized segments or unmodified
aromatic rings from the crown. (2) The use of the red (647
nm) and infrared (1064 nm) excitation lines allowed for an
unambiguous monitoring of the oxidation reaction, showing at
the same time the formation of semiquinoid and quinoid
segments in the cationic forms of the molecules. Finally, from
these experimental observations, and based on the assignments
of the Raman bands established for neutral molecules, it was
possible to propose a mechanism of their oxidation to cationic
forms, consistent with the experimental findings.
Our attempts to register Raman spectra of “fully” oxidized 3
were unsuccessful, independently of the excitation line used.
The spectra of “partially” oxidized samples were very similar to
those obtained for “partially” oxidized 1 and 2. In Figure 8, its
EXPERIMENTAL SECTION
■
1
Characterization Techniques. H and 13C NMR spectra
were recorded on a Varian Mercury (400 and 100 MHz)
spectrometer and referenced with respect to TMS and solvents.
IR spectra were monitored on a Bio-RAD FTS-165
spectrometer using KBr pellets. UV−vis/NIR spectra were
registered using a Cary 5000 (Varian) spectrometer. Mass
spectra were measured by the EI method on an AMD 604 mass
spectrometer. All synthesized compounds studied were subject
to C, H, N, and Br elemental combustion analysis.
Reagents. Tris(4-bromophenyl)amine, 4-butylaniline, 4-
butylbromobenzene, diphenylamine, palladium acetate, Pd-
(OAc)2, tris-tert-butylphosphine, t-Bu3P, 2,2′-bis-
(diphenylphosphino)-1,1′-binaphtyl, BINAP, sodium tert-but-
oxide, t-BuONa, di-tert-butyl dicarbonate, trifluoroacetic acid,
tris(4-bromophenyl)amminium hexachloroantimonate, TBA·
SbCl6 anhydrous toluene, anhydrous dichloromethane, and
anhydrous acetonitrile were purchased from Aldrich.
Di-(4-butylphenyl)amine was prepared according to ref 61.
All glassware was oven-dried, assembled hot, and cooled
under a dry argon stream before use. All reactions were
performed under dry argon.
Figure 8. Raman spectra of 3 oxidized with 1 equiv of the oxidant
(“partially oxidized”), registered using different excitation lines: (a)
blue line 458 nm; (b) green line 514 nm; (c) red line 647 nm; (d)
Fourier transform Raman spectrum, infrared line 1064 nm.
representative spectra, obtained for different λexc values, are
presented. They can be interpreted in the same manner as the
spectra of 2. One should however note that the bands
attributed to the presence of radical cations, in the spectral
range 1330−1350 cm−1, are relatively more intensive than in
other cases. This may imply more homogeneous oxidation.
However, the resonance effects exclude any quantitative
approach.
The dendrimers were prepared according to the procedure
described by Ito et al.42 Below, we give the detailed description
of the preparation of dendrimer 2 as an example.
Dendrimer 1. 1H NMR (400 MHz, C6D6) δ, 7.12 (d, J = 8.4
Hz, 12H), 7.06−7.02 (m, 18H), 6.95 (d, J = 9.2 Hz, 6H), 6.82
(t, J = 7.4 Hz, 6H). 13C NMR (100 MHz, C6D6) δ, 148.4,
143.5, 143.0, 129.5, 126.0, 125.1, 124.1, 122.7. IR (cm−1): 3033,
2953, 2924, 2871, 1589, 1502, 1493, 1308, 1270, 1172, 1074,
820, 752, 695. Anal. Calcd for C54H42N4: C, 86.86; H, 5.63; N,
7.51. Found: C, 86.54; H, 5.56; N, 7.27.
CONCLUSIONS
■
To conclude, two families of dendrimers based on triphenyl-
amine units were synthesized with two different crowns. On the
basis of the geometries and the symmetry point groups of these
compounds, obtained by applying semiempirical quantum
5285
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
Dendrimer 2. Di-(4-butylphenyl)amine, 0.927 g (3.3 mmol);
tris(4-bromophenyl)amine, 0.482 g (1 mmol); sodium tert-
butoxide, 0.346 g (3.6 mmol); palladium acetate, 20.2 mg (0.09
mmol); and t-Bu3P, 54.6 mg (0.27 mmol) were dissolved in 15
mL of dry toluene under an argon atmosphere. The reaction
mixture was stirred and heated at 110 °C for 12 h. The reaction
mixture was then cooled to room temperature and washed with
30 mL of distilled water. The aqueous phase was extracted with
three 5 mL portions of diethyl ether. The organic layers were
combined and dried over MgSO4. Removal of the solvents
followed by chromatography on silica gel with hexanes/CH2Cl2
(2:1) resulted in a yellow solid. The resulting solid was
recrystallized from THF/ethanol to give 0.95 g of 2 as a slightly
yellow powder (yield 88%).
ASSOCIATED CONTENT
* Supporting Information
■
S
A brief description of the neutron scattering theory; calculated
bond lengths and angles, main force constants, and modeling
Cartesian displacements (Chart S1a, b, and c); and Raman
spectra of 2 (partially oxidized) and 1 (partially and fully
oxidized). This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: ikulsz@ch.pw.edu.pl.
*E-mail: Guy.Louarn@cnrs-imn.fr.
■
Present Address
⊥Institute of Computational Physics, Zurich University of
Applied Sciences, Wildbachstrasse 21, CH-8401 Winterthur,
Switzerland.
1H NMR (400 MHz, C6D6) δ, 7.18 (d, J = 8.4 Hz, 12H),
7.06 (d, J = 2.8 Hz, 12H), 6.95 (d, J = 8.4 Hz, 12H), 2.43 (t, J =
7.6 Hz, 12H), 1.52−1.44 (m, 12H), 1.29−1.20 (m, 12H), 0.84
(t, J = 7.4 Hz, 18H). 13C NMR (100 MHz, C6D6) δ, 146.5,
143.5, 143.1, 137.1, 129.6, 125.2, 125.1, 124.4, 35.1, 33.9, 22.4,
13.9. IR (cm−1): 3027, 2956, 2927, 2871, 1505, 1466, 1306,
1267, 1114, 1016, 827. Anal. Calcd for C78H92N4: C, 86.51; H,
8.32; N, 5.17. Found: C, 86.34; H, 8.19; N, 5.23. m/z = 1082.8.
Dendrimer 3. 1H NMR (400 MHz, C6D6) δ, 7.18 (d, J = 8.4
Hz, 24H), 7.07 (s, 36H), 6.95 (d, J = 8.4 Hz, 24H), 2.42 (t, J =
7.6 Hz, 24H), 1.52−1.44 (m, 24H), 1.28−1.20 (m, 24H), 0.84
(t, J = 7.2 Hz, 36H). IR (cm−1): 3027, 2956, 2927, 2871, 1505,
1466, 1306, 1267, 1114, 1016, 827. Anal. Calcd for
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
I.K.-B., A.P., and L.S. wish to acknowledge financial support
from National Centre of Science in Poland (NCN, Grant No.
UMO-2011/01/B/ST5/03903). ILL is acknowledged for
neutron beam time allocated for this work. Alexandre Ivanov
is acknowledged for his assistance for measurements on IN1 at
ILL. M.S. wishes to acknowledge CEA for a Ph.D. scholarship.
L. Monestier and M. Bailo Diallo are thanked for their
contributions during their Master trainings in CEA-Grenoble.
C174H192N10: C, 86.28; H, 7.93; N, 5.79. Found: C, 85.91; H,
8.06; N, 5.80.
REFERENCES
Oxidation Procedure. The chemical oxidation of the
dendrimers was carried out in an argon atmosphere. In a typical
procedure, 6.5 × 10−5 mol of the dendrimer was dissolved in
2.2 mL of THF and then oxidized with the appropriate amount
of tris(4-bromophenyl)amminium hexachloroantimonate, TBA·
SbCl6, in acetonitrile solution. The solution of the oxidized
dendrimer was stirred under an argon atmosphere for 10 min.
The solvents were evaporated in a vacuum, and the sample was
dried in a vacuum to constant mass.
Inelastic Incoherent Neutron Scattering. Inelastic
incoherent neutron scattering measurements in the 20−340
meV energy transfer range were carried out on a triple axis IN1
spectrometer at ILL (Grenoble). The spectrometer was used in
the configuration involving a Cu220 crystal monochromator (λ =
1278 Å) equipped with a 60′ collimator. The analyzer was a
BeF crystal. The samples were mounted in an aluminum foil flat
container which was placed at 90° respectively to the incident
beam. All spectra were recorded at 14 K. In such a
configuration, the expected energy resolution was around 5.5
meV for small energy transfers in between 20 and 140 meV and
then it linearly decreased to 7.5 meV for a 250 meV energy
transfer.
■
(1) Lau, T.; Lorenz, E.; Koyuncu, M. Lifetime of Poly(triaryl amine)
Based Organic Field Effect Transistors under Different Environmental
Conditions. Jpn. J. Appl. Phys. 2013, 52, 041601−041605.
(2) Rybakiewicz, R.; Zapala, J.; Djurado, D.; Nowakowski, R.;
Toman, P.; Pfleger, J.; Verilhac, J. M.; Zagorska, M.; Pron, A.
Naphthalene Bisimides Asymmetrically and Symmetrically N-sub-
stituted with Triarylamine−Comparison of Spectroscopic, Electro-
chemical, Electronic and Self-Assembly Properties. Phys. Chem. Chem.
Phys. 2013, 15, 1578−1587.
(3) Diallo, A. K.; Metri, N.; Brunel, F.; Sallenave, X.; Goubard, F.;
Margeat, O.; Ackermann, J.; Videlot-Ackermann, C. A Star-Shaped
Molecule as Hole Transporting Material in Solution-Processed Thin-
Film Transistors. Synth. Met. 2013, 184, 35−40.
(4) Song, Y. B.; Di, C. A.; Yang, X. D.; Li, S. P.; Xu, W.; Liu, Y. Q.;
Yang, L. M.; Shuai, Z. G.; Zhang, D. Q.; Zhu, D. B. A Cyclic
Triphenylamine Dimer for Organic Field-Effect Transistors with High
Performance. J. Am. Chem. Soc. 2006, 128, 15940−15941.
(5) Lee, J.; Cho, S.; Yang, C. Highly Reproducible Organic Field-
Effect Transistor from Pseudo 3-Dimensional Triphenylamine-Based
Amorphous Conjugated Copolymer. J. Mater. Chem. 2011, 21, 8528−
8531.
(6) Zhao, Z. J.; Li, Z. F.; Lam, J. W. Y.; Maldonato, J. L.; Ramos-
Ortiz, G.; Liu, Y.; Yuan, W. Z.; Xu, J. B.; Miao, Q.; Tang, B. Z. High
Hole Mobility of 1,2-bis[4-(Diphenylamino)Biphenyl-4-yl]-1,2-Diphe-
nylethene in Field Effect Transistor. Chem. Commun. 2011, 47, 6924−
6926.
A brief description of the neutron scattering theory can be
found in the Supporting Information.
(7) Cravino, A.; Roquet, S.; Aleveque, O.; Leriche, P.; Frere, P.;
Roncali, J. Triphenylamine-Oligothiophene Conjugated Systems as
Organic Semiconductors for Opto-Electronics. Chem. Mater. 2006, 18,
2584−2590.
(8) Yasuda, T.; Shinohara, Y.; Ishi-i, T.; Han, L. Y. Use of
Benzothiadiazole−Triphenylamine Amorphous Polymer for Reprodu-
cible Performance of Polymer−Fullerene Bulk-Heterojunction Solar
Cells. Org. Electron. 2012, 13, 1802−1808.
Raman Spectroscopy. Raman spectra of neutral and
oxidized dendrimers were recorded on a Jobin-Yvon T64000
spectrometer (λexc = 457, 514, and 647 nm, laser power = 10
mW, 2 μm diameter spot, typical exposure times 60 s) or on a
FT Raman Bruker RFS 100 spectrometer with the near-IR
excitation line (1064 nm, laser power = 50 mW).
5286
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
(9) Bian, L. Y.; Yang, D.; Yin, L. M.; Zhang, J.; Tang, W. H.
Carbazole Substituted Triphenylamine and Diketopyrrolopyrrole
Alternating Copolymer for Photovoltaic Cells. Macromol. Chem.
Phys. 2013, 214, 2136−2143.
(10) Roquet, S.; Cravino, A.; Leriche, P.; Aleveque, O.; Frere, P.;
Roncali, J. Triphenylamine-Thienylenevinylene Hybrid Systems with
Internal Charge Transfer as Donor Materials for Heterojunction Solar
Cells. J. Am. Chem. Soc. 2006, 128, 3459−3466.
(11) Zhang, Z. G.; Liu, Y. L.; Yang, Y.; Hou, K. Y.; Peng, B.; Zhao, G.
J.; Zhang, M. J.; Guo, X.; Kang, E. T.; Li, Y. F. Alternating Copolymers
of Carbazole and Triphenylamine with Conjugated Side Chain
Attaching Acceptor Groups: Synthesis and Photovoltaic Application.
Macromolecules 2010, 43, 9376−9383.
(12) Deng, D.; Shen, S. L.; Zhang, J.; He, C.; Zhang, Z. J.; Li, Y. F.
Solution-Processable Star-Shaped Photovoltaic Organic Molecule with
Triphenylamine Core and Thieno [3, 2-b] Thiophene−Dicyanovinyl
Arms. Org. Electron. 2012, 13, 2546−2552.
(13) Deng, D.; Yang, Y.; Zhang, J.; He, C.; Zhang, M. J.; Zhang, Z.
G.; Zhang, Z. J.; Li, Y. F. Triphenylamine-Containing Linear DAD
Molecules with Benzothiadiazole as Acceptor Unit for Bulk-
Heterojunction Organic Solar Cells. Org. Electron. 2011, 12, 614−622.
(14) Hu, B. B.; Chen, X. P.; Wang, Y. F.; Lu, P.; Wang, Y. G.
Structure-Property Investigations of Substituted Triarylamines and
their Applications as Fluorescent pH Sensors. Chem.Asian J. 2013, 8,
1144−1151.
(15) Shang, H. X.; Fan, H. J.; Liu, Y.; Hu, W. P.; Li, Y. F.; Zhan, X.
W. A Solution Processable Star Shaped Molecule for High
Performance Organic Solar Cells. Adv. Mater. 2011, 23, 1554−1557.
(16) Kwon, J.; Kim, M. K.; Hong, J. P.; Lee, W.; Lee, S.; Hong, J. I. A
Multifunctional Material Based on Triphenylamine and a Naphthyl
Unit for Organic Light-Emitting Diodes, Organic Solar Cells, and
Organic Thin-Film Transistors. Bull. Korean Chem. Soc. 2013, 34,
1355−1360.
(17) Zhan, Y.; Peng, J.; Ye, K. Q.; Xue, P. C.; Lu, R. Pyrene
Functionalized Triphenylamine-Based Dyes: Synthesis, Photophysical
Properties and Applications in OLEDs. Org. Biomol. Chem. 2013, 11,
6814−6823.
(18) Huang, J. H.; Su, J. H.; Li, X.; Lam, M. K.; Fung, K. M.; Fan, H.
H.; Cheah, K. W.; Chen, C. H.; Tian, H. Bipolar Anthracene
Derivatives Containing Hole- and Electron-Transporting Moieties for
Highly Efficient Blue Electroluminescence Devices. J. Mater. Chem.
2011, 21, 2957−2964.
(19) Jiang, Z. Q.; Ye, T. L.; Yang, C. L.; Yang, D. Z.; Zhu, M. R.;
Zhong, C.; Qin, J. G.; Ma, D. G. Star-Shaped Oligotriarylamines with
Planarized Triphenylamine Core: Solution-Processable, High-Tg
Hole-Injecting and Hole-Transporting Materials for Organic Light-
Emitting Devices. Chem. Mater. 2011, 23, 771−777.
(20) Jiang, W.; Yang, W.; Ban, X. X.; Huang, B.; Dai, Y. Q.; Sun, Y.
M.; Duan, L.; Qiu, Y. Synthesis of New Bipolar Materials Based on
Diphenylphosphine Oxide and Triphenylamine Units: Efficient Host
for Deep-Blue Phosphorescent Organic Light-Emitting Diodes.
Tetrahedron 2012, 68, 9672−9678.
(21) Iwan, A.; Sek, D. Polymers with Triphenylamine Units:
Photonic and Electroactive Materials. Prog. Polym. Sci. 2011, 36,
1277−1325.
(22) Tao, Y. T.; Yang, C. L.; Qin, J. G. Organic Host Materials for
Phosphorescent Organic Light-Emitting Diodes. Chem. Soc. Rev. 2011,
40, 2943−2970.
(23) Anderson, J. D.; McDonald, E. M.; Lee, P. A.; Anderson, M. L.;
Ritchie, E. L.; Hall, H. K.; Hopkins, T.; Mash, E. A.; Wang, J.; Padias,
A.; et al. Electrochemistry and Electrogenerated Chemiluminescence
Processes of the Components of Aluminum Quinolate/Triarylamine,
and Related Organic Light-Emitting Diodes. J. Am. Chem. Soc. 1998,
120, 9646−9655.
(24) Bender, T. P.; Graham, J. F.; Duff, J. M. Effect of Substitution on
the Electrochemical and Xerographic Properties of Triarylamines:
Correlation to the Hammett Parameter of the Substituent and
Calculated HOMO Energy Level. Chem. Mater. 2001, 13, 4105−4111.
(25) Xiao, H.; Leng, B.; Tian, H. Hole Transport Triphenylamine−
Spirosilabifluorene Alternating Copolymer: Synthesis and Optical,
Electrochemical and Electroluminescent Properties. Polymer 2005, 46,
5707−5713.
(26) Cheng, H. C.; Chiu, K. Y.; Tu, Y. J.; Yang, T. F.; Su, Y. O.
Electrochemically Controlled Multiple Hydrogen Bonding between
Triarylamines and Imidazoles. Org. Lett. 2013, 15, 3868−3871.
(27) Casalbore-Miceli, G.; Esposti, A. D.; Fattori, U.; Marconi, G.;
Sabatini, C. A Correlation between Electrochemical Properties and
Geometrical Structure of some Triarylamines Used as Hole Trans-
porting Materials in Organic Electroluminescent Devices. Phys. Chem.
Chem. Phys. 2004, 6, 3092−3096.
(28) Song, Y.; Di, C.; Xu, W.; Liu, Y.; Zhang, D.; Zhu, D. New
Semiconductors Based on Triphenylamine with Macrocyclic Archi-
tecture: Synthesis, Properties and Applications in OFETs. J. Mater.
Chem. 2007, 17, 4483−4491.
(29) Tang, C. W.; Van Slyke, S. A. Organic Electroluminescent
Diodes. Appl. Phys. Lett. 1987, 51, 913−915.
(30) Seo, E. T.; Nelson, R. F.; Fritsch, J. M.; Marcoux, I. S.; Leedy, D.
W.; Adams, R. N. Anodic Oxidation Pathways of Aromatic Amines.
Electrochemical and Electron Paramagnetic Resonance Studies. J. Am.
Chem. Soc. 1966, 88, 3498−3503.
(31) Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for
Organometallic Chemistry. Chem. Rev. 1996, 96, 877−910.
(32) Shirota, Y. Organic Materials for Electronic and Optoelectronic
Devices. J. Mater. Chem. 2000, 10, 1−25.
(33) Louie, J.; Hartwig, J. F.; Fry, A. J. Discrete High Molecular
Weight Triarylamine Dendrimers Prepared by Palladium-Catalyzed
Amination. J. Am. Chem. Soc. 1997, 119, 11695−11696.
(34) Lambert, C.; Amthor, S.; Schelter, J. From Valence Trapped to
Valence Delocalized by Bridge State Modification in bis(Triarylamine)
Radical Cations: Evaluation of Coupling Matrix Elements in a Three-
Level System. J. Phys. Chem. A 2004, 108, 6474−6486.
(35) Lambert, C.; Noll, G. The Class II/III Transition in
̈
Triarylamine Redox Systems. J. Am. Chem. Soc. 1999, 121, 8434−8442.
(36) Lancarter, K.; Odom, S. A.; Thayumanavan, S.; Marder, S. R.;
Bredas, J. L.; Coropceanu, V.; Barlow, S. Intramolecular Electron-
Transfer Rates in Mixed-Valence Triarylamines: Measurement by
Variable-Temperature ESR Spectroscopy and Comparison with
Optical Data. J. Am. Chem. Soc. 2009, 131, 1717−1723.
(37) Amthor, S.; Noller, B.; Lambert, C. UV/Vis/NIR Spectral
Properties of Triarylamines and Their Corresponding Radical Cations.
Chem. Phys. 2005, 316, 141−152.
(38) Lovesey, S. W. Theory of Neutron Scattering from Condensed
Matter; Oxford University Press: Oxford, U.K., 1984.
(39) Kim, J-.S.; Ho, P. K. H.; Murphy, C. E.; Seeley, A. J. A. B.;
Grizzi, I.; Burroughes, J. H.; Friend, R. H. Electrical Degradation of
Triarylamine-Based Light-Emitting Polymer Diodes Monitored by
Micro-Raman Spectroscopy. Chem. Phys. Lett. 2004, 386, 2−7.
(40) Zhang, K.; Wang, L.; Liang, Y.; Yang, S.; Liang, J.; Cheng, F.;
Chen, J. A Thermally and Electrochemically Stable Organic Hole-
Transporting Material with an Adamantane Central Core and
Triarylamine Moieties. Synth. Met. 2012, 162, 490−496.
(41) Zhang, Y.; Sun, J.; Zhuang, G.; Ouyang, M.; Yu, Z.; Cao, F.; Pan,
G.; Tang, P.; Zhang, C.; Ma, Y. Heating and Mechanical Force-
Induced Luminescence on−off Switching of Arylamine Derivatives
with Highly Distorted Structures. J. Mater. Chem. C 2014, 2, 195−200.
(42) Ito, A.; Sakamaki, D.; Ichikawa, Y.; Tanaka, K. Spin-
Delocalization in Charged States of para-Phenylene-Linked Dendridic
Oligoarylamines. Chem. Mater. 2011, 23, 841−850.
(43) Zhang, S. L. Raman Spectroscopy and its Application in
Nanostructures; John Wiley & Sons: Chichester, U.K., 2012.
(44) Boyer, M. I.; Quillard, S.; Cochet, M.; Louarn, G.; Lefrant, S.
RRS Characterization of Selected Oligomers of Polyaniline in situ
Spectroelectrochemical Study. Electrochim. Acta 1999, 44, 1981−1987.
(45) Rai, G.; Kumar, A. K.; Rai, S. Infrared, Raman Spectra and DFT
Calculations of Chlorine Substituted Anilines. Vib. Spectrosc. 2006, 42,
397−402.
5287
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288

The Journal of Physical Chemistry B
Article
(46) Quillard, S.; Louarn, G.; Lefrant, S.; MacDiarmid, A. G.
Vibrational Analysis of Polyaniline: a Comparative Study of
Leucoemeraldine, Emeraldine, and Pernigraniline Bases. Phys. Rev. B
1994, 50, 12496−12508.
(47) Dollish, F. R.; Fateley, W. G.; Bentley, F. F. Characteristic Raman
Frequencies of Organic Compounds; John Wiley & Sons: New York,
1969.
(48) Cochet, M.; Louarn, G.; Quillard, S.; Buisson, J. P.; Lefrant, S.
Theoretical and Experimental Vibrational Study of Emeraldine in Salt
Form. Part II. J. Raman Spectrosc. 2000, 31, 1041−1049.
(49) Louarn, G.; Buisson, J. P.; Lefrant, S.; Fichou, D. Vibrational
Studies of a Series of alpha-Oligothiophenes as Model Systems of
Polythiophene. J. Phys. Chem. 1995, 99, 11399−11404.
(50) Cochet, M.; Louarn, G.; Quillard, S.; Boyer, M. I.; Buisson, J. P.;
Lefrant, S. Theoretical and Experimental Vibrational Study of
Polyaniline in Base Forms: Non Planar Analysis. Part I. J. Raman
Spectrosc. 2000, 31, 1029−1039.
(51) Louarn, G.; Lapkowski, M.; Quillard, S.; Pron, A.; Lefrant, S.
Vibrational Properties of Polyaniline Isotope Effects. J. Phys. Chem.
1996, 100, 6998−7006.
(52) Meijer, G.; Berden, G.; Meerts, W. L.; Hunziker, H. E.; de Vries,
M. S.; Wendt, H. R. Spectroscopy on Triphenylamine and its Van Der
Waals Complexes. Chem. Phys. 1992, 163, 209−222.
(53) Sobolev, A. N.; Belsky, V. K.; Romm, I. P.; Chernikova, N. Y.;
Guryanova, E. N. Structural Investigation of the Triaryl Derivatives of
the Group V Elements. IX. Structure of Triphenylamine, C18H15N.
Acta Crystallogr., Sect. C 1985, 41, 967−971.
(54) Wilson, E. B., Jr. The Normal Modes and Frequencies of
Vibration of the Regular Plane Hexagon Model of the Benzene
Molecule. Phys. Rev. 1934, 45, 706−714.
́
(55) Varsanyi, G. Vibrational spectra of benzene derivatives; Academic
Press: New York, 1969; pp 17−84.
(56) Selby, T. D.; Kim, K. Y.; Blackstock, S. C. Patterned Redox
Arrays of Polyarylamines I. Synthesis and Electrochemistry of a p-
Phenylenediamine and Arylamino-Appended p-Phenylenediamine
Arrays. Chem. Mater. 2002, 14, 1685−1690.
(57) Hirao, Y.; Ito, A.; Tanaka, K. Intramolecular Charge Transfer in
a Star-Shaped Oligoarylamine. J. Phys. Chem. A 2007, 111, 2951−2956.
(58) Hirao, Y.; Ino, H.; Ito, A.; Tanaka, K.; Kato, T. High-Spin
Radical Cations of a Dendridic Oligoarylamine. J. Phys. Chem. A 2006,
110, 4866−4872.
(59) Kim, K. V.; Hassenzahl, J. D.; Selby, T. D.; Szulczewski, G. J.;
Blackstock, S. C. Patterned Redox Arrays of Polyarylamines II. Growth
of Thin Films and Their Electrochemical Behavior. Chem. Mater. 2002,
14, 1691−1694.
(60) Li, J. C.; Kim, K. Y.; Blackstock, S. C.; Szulczewski, G. J.
Patterned Redox Arrays of Polyarylamines III. Effect of Molecular
Structure and Oxidation Potential on Film Morphology and Hole-
Injection in Single-Layer Organic Diodes. Chem. Mater. 2004, 16,
4711−4714.
(61) Maurel, V.; Jouni, M.; Baran, P.; Onofrio, N.; Gambarelli, S.;
Mouesca, J. M.; Djurado, D.; Dubois, L.; Jacquot, J. F.; Desfonds, G.;
et al. Magnetic Properties of a Doped Linear Polyarylamine Bearing a
High Concentration of Coupled Spins (S = 1). Phys. Chem. Chem.
Phys. 2012, 14, 1399−1407.
5288
dx.doi.org/10.1021/jp502735s | J. Phys. Chem. B 2014, 118, 5278−5288