Electropolimerization of Functionalizaed Carbazole End-Capped Dendrimers. Formation of Conductive Films

Article abstract of DOI:10.1016/j.electacta.2016.04.154

A series of peripherally carbazole functionalized dendrimeric starburst monomers were synthesized and characterized. The electrochemical polymerization over Pt and indium tin oxide electrodes of fully π-conjugated dendrimers allows the generation of elect

Full text of DOI:10.1016/j.electacta.2016.04.154

Accepted Manuscript
Title: Electropolimerization of Functionalizaed Carbazole
End-Capped Dendrimers. Formation of Conductive Films
´
Author: Marıa I. Mangione Rolando A. Spanevello Daniela
Minudri Daniel Heredia Luciana Fernandez Luis Otero
Fernando Fungo
PII:
S0013-4686(16)31006-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.electacta.2016.04.154
EA 27189
To appear in:
Electrochimica Acta
Received date:
Revised date:
Accepted date:
18-12-2015
19-4-2016
26-4-2016
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Please cite this article as: Maria I.Mangione, Rolando A.Spanevello,
Daniela Minudri, Daniel Heredia, Luciana Fernandez, Luis Otero,
Fernando Fungo, Electropolimerization of Functionalizaed Carbazole End-
Capped Dendrimers.Formation of Conductive Films, Electrochimica Acta
http://dx.doi.org/10.1016/j.electacta.2016.04.154
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Electropolimerization of Functionalizaed Carbazole End-Capped Dendrimers.
Formation of Conductive Films
María I. Mangione, Rolando A. Spanevello*
Instituto de Química Rosario, Facultad de Ciencias Bioquímicas y Farmacéuticas,
Universidad Nacional de Rosario – CONICET. Suipacha 531, S2002RLK Rosario,
Argentina.
Daniela Minudri, Daniel Heredia, Luciana Fernandez, Luis Otero, and Fernando
Fungo*
Departamento de Química, Universidad Nacional de Río Cuarto, Agencia Postal 3
(X5804BYA), Río Cuarto, Argentina.
Abstract
a series of peripherally carbazole functionalized dendrimeric starburst monomers
were synthesized and characterized. The electrochemical polymerization over Pt
and indium tin oxide electrodes of fully π-conjugated dendrimers allows the
generation of electro-active polymeric films. Dendrimers were design with and
without electroactive central core (triphenylamine) connected to peripherals
moieties, which influence the physicochemical characteristics of the
electrogenerated polymers. The versatile electropolymerization methodology
allows the generation of thin films of hyperbranched macromolecules with good
electrical conductivity, reversible electrochemical processes and electrochromic
properties.

Keywords: Dendrimeric Polymers, Electrodeposition, Optoelectronic.
Table of Contents/Abstract Graphic
1. Introduction
Dendrimers are highly branched organic macromolecules formed by multiple
chains emanating from a core, which hold a large number of applications in several
fields [1,2,3]. In particular, for the use as components in organic electronic devices,
these branches can be designed and synthetized as π-conjugated cables, to provide
adequate charge transport capabilities [4,5,6,7,8,9,10,11,12]. In addition, functional
groups such as chromophores, electron donor and/or electron acceptor moieties can be
introduced in selected positions (dendrimers´ core, branches or periphery), in order to
obtain the desired electronic or optoelectronic characteristics. In this way, dendrimeric
structures found numerous applications as light-harvesting antennas [13], organic light-
emitting material [4-56789], charge carriers transport layers [14], and as electron donor-
acceptor material [7,10,12,15]. However, the preparation of functional dendrimers is
usually a great challenge, since steric and solubility problems frequently appear during
the syntheses stages. Steric hindrance could arise during the connection of dendrons to
the focal point, and the solubility limitations often interfere in the production of high
generation dendrimeric polymers. Thus, for the production of π-conjugated dendrimers
it is important the search of alternative and efficient synthesis methods. During our
research program about the development of organic materials for electronic and
optoelectronic devices we demonstrated that hyperbranched π-conjugated polymeric
materials can be formed electrochemically from suitable functional dendrimeric
monomers [16,17,18,19,20,21,22]. The use of specially designed starburst dendrimer

allows not only the polymer formation by electropolymerization, but also the deposition
of the organic material over a conducting substrate as thin homogeneous films. In this
last sense, we also proved that by controlling the condition of the electrochemical film
formation, it is possible to optimize the film thickness and the surface morphology, with
the consequent effects over the film optoelectronic properties [21].
In order to obtain the desired starburst dendrimeric monomers, the branched
macromolecules must be carefully designed for to achieve the necessary electronic and
optoelectronic properties. Dendrimeric materials with well-defined structures may be
prepared by two main synthetic strategies, the convergent [23] and divergent [24]
routes. In a convergent synthesis, the dendrimer is built from the periphery inward. This
procedure gives rise to a precisely defined structure, monodisperse and with high purity
by avoiding incomplete end groups. One of the drawbacks of convergent strategy is that
it gives rise to a slow growth and, if high generation's dendrimers are needed, the
convergent route could be a problem. In contrast, the divergent route builds the
dendrimer from the core outward. This route often offers more drawbacks than the
convergent one. As the generation number increases, dendrimers´ purity and
polydispersity are more difficult to achieve, and restricts the repertory of reactions that
could be applied to a few number of high yielding ones [23,24,25].
In this article, we report the synthesis and properties of peripherally carbazole
(CBZ) functionalized starburst monomers, featuring the presence or absence of
electroactive central core triphenylamine (TPA) moieties connected by conjugated or
saturated branches (Fig. 1). The dendrimeric monomers are obtained by a convergent
strategy. In addition, the CBZ residues allow the formation of hyperbranched polymeric
films over conductive substrates by electrochemical polymerization. In fact, the radical
cation coupling of oxidized CBZ drives into the growing of the dendrimeric structures.

Two different fully π-conjugated dendrimeric polymers are formed, with and without
electroactive central core connected to peripherals moieties (structures 1 and 3, Fig. 1).
Also, structurally related homologues dendrimeric monomers non-conjugated or
without CBZ moieties (structures 4 and 2) are studied, in order to establish
physicochemical-properties/molecular structures relationships.
We showed that the new hyperbranched macromolecules obtained by the
versatile electropolymerization methodology exhibit interesting electronic properties
that yield thin films with good electrical conductivity, reversible electrochemical
processes and stability. The outlined strategy allowed us to obtain new materials
through a process simpler than flask synthesis, and provided one of the very few
examples of using starburst monomers application to form electrochemically active
polymers.
2. Materials and methods
2.1 Instrumentation and Characterization Techniques.
Melting points were taken on a Leitz Wetzlar Microscope Heating Stage, Model
1
13
350 apparatus and are uncorrected. H and C NMR spectra were recorded on Bruker
Avance-300 spectrometer with Me4Si as the internal standard and chloroform-d as
solvent. Abbreviations: s =singlet, d = doublet, t = triplet, and m = multiplet expected
but not resolved. Mass spectra of dendrons were recorded in a Shimadzu QP2010 Plus
instrument, ion source temperature = 300 °C, and detector voltage = 70 kV. Samples
were analyzed by ultraviolet matrix assisted laser desorption-ionization mass
spectrometry (UV−MALDIMS) and by ultraviolet laser desorption-ionization mass
spectrometry (UV−LDI MS) performed on the Bruker Ultraflex Daltonics TOF/TOF
mass spectrometer Mass spectra were acquired in linear positive and negative ion

modes. Stock solutions of samples were prepared in chloroform. External mass
calibration was made using β-cyclodextrin (MW 1134) with nHo as matrix in positive
and negative ion mode. Sample solutions were spotted on a MTP 384 target plate
polished steel from Bruker Daltonics (Leipzig, Germany). For UV−MALDI MS matrix
solution was prepared by dissolving GA (gentisic acid, 1 mg/mL) in water and dry
droplet sample preparation was used according to Nonami et al. [26] loading
successively 0.5 µL of matrix solution, analyte solution and matrix solution after drying
each layer at normal atmosphere and room temperature. For UV-LDI MS experiments
two portions of analyte solution (0.5 µL × 2) were loaded on the probe and dried
successively (two dry layers). Desorption/ Ionization was obtained by using the
frequency-tripled Nd:YAG laser (355-nm). The laser power was adjusted to obtain high
signal-to-noise ratio (S/N) while ensuring minimal fragmentation of the parent ion sand
each mass spectrum was generated by averaging 100 lasers pulses per spot. Spectra
were obtained and analyzed with the programs FlexControl and FlexAnalysis,
respectively. Reactions were monitored by TLC on 0.25 mm E. Merck Silica Gel Plates
(60F254), using UV light (254 nm) and phosphomolybdic acid as developing agent.
Flash column chromatographies using E. Merck silica gel 60H were performed by
gradient elution of mixture of n-hexane and increasing volumes of dichloromethane or
ethyl acetate. Reactions were run under an argon atmosphere with freshly anhydrous
distilled solvents, unless otherwise noted. Yields refer to chromatographically and
spectroscopically homogeneous materials, unless otherwise stated.
For the optical characterization a Shimadzu UV-2401PC spectrometer and a Spex
FluoroMax fluorometer were used to measure the absorption and fluorescence spectra,
respectively. Spectra were acquire using quartz cells (path length: 1 cm) at room
temperature in 1,2-dichloroethane (DCE) and toluene (TOL) solutions.

The dendrimers electrochemical properties were studied in 0.5-1.0 mM range
concentration in DCE electrolyte containing 0.1 M tetra-n-butylammonium
hexafluorphosphate (TBAHFP) with an Autolab Electrochemical Instruments
potentiostat. The voltammetric experiments were carry out using as working electrode
an inlaid platinum disk (2.16 x 10-3 cm2) polished on a felt pad with 0.3 µm alumina and
sequentially sonicated in water and absolute ethanol, silver wire as pseudo-reference
electrode and a platinum coil as the counter electrode. Before each experiment
electrolyte blank was made to discard possible electrochemically active interferes. All
potential values reported are expressed relative to ferrocene/ferrocenium redox couple
(Fc/Fc+= 0.40 V vs SCE), which was used as an internal standard [27].
The spectroelectrochemical experiments were carried out in a homemade cell built from
a commercial UV-visible cuvette. The films were obtained by electropolimerized on
ITO (indium tin oxide, Delta Technologies, nominal resistance 10Ω/square) electrodes
by cyclic voltammetry technique under the experimental conditions described above.
The coated ITO- polymer film was used as working electrode, Pt as counter electrode
and a silver wire was used as pseudo-reference electrode. The homemade cell was
placed in the optical path of the sample light beam Hewlett Packard 8453 diode array
spectrophotometer, and UV-visible light absorption spectra were taken under potential
control. The background correction was obtained by taking an UV-visible spectrum of
an ITO working electrode without the polymer film. Surface analysis of
electrodeposited polymer films on ITO electrodes was performed by scanning electron
microscopy (SEM) with a Carl Zeiss EVO MA 10 with electron beam energy of 18 KV.
2.2 Synthetic Procedures.
Dendrimer 1: Dendron 9 (470.6 mg, 1.28 mmole) was dissolved in anhydrous toluene
(10 mL) under argon atmosphere. Pd(PPh3)Cl2 (11.6 mg, 0.02 mmole), CuI (6.1 mg,

0.03 mmole) and PPh3 (6.7 mg, 0.03 mmole) were added and the mixture was stirred for
30 minutes at room temperature. After the solution became orange, anhydrous
trimethylamine (10 mL) was added and the reaction was stirred for additional 15
minutes. Triethynylbenzene 7 (48.0 mg, 0.32 mmole) was added and the mixture was
stirred 48 hs at 76ºC. The solvents were concentrated under vacuum and the crude
product was purified by flash chromatography (hexane:dichloromethane) yielding
dendrimer 1 as white solid (257.2 mg, 0.29 mmole). mp: 297− 299 °C
(dichloromethane:hexane); 1H NMR: (300 MHz, CDCl3, TMS): 8.15 (d, J = 7.59 Hz,
6H), 7.84 – 7.73 (m, 6H), 7.70 – 7.54 (m, 8H), 7.51 – 7.36 (m, 13H), 7.31 (dd, J =
13
6.36Hz, 6H); C NMR:
(75 MHz, CDCl3, TMS): 140.52, 138.06, 135.36, 133.28,
126.94, 126.13, 124.07, 123.65, 121.66, 120.44, 120.34, 109.77, 90.08, 88.66. MALDI-
TOF MS: calcd for C66H39N3, (MH+) m/e 875., m/e 875.2 (MH+).
Dendrimer 2: To a mixture of 6 (64.8 mg, 0.07 mmol) in dry toluene were added
triethylamine 1:1 (14 mL) Pd(PPh3)4 (11.4 mg, 0.01 mmol), CuI (2.4 mg, 0.01 mmol),
and triphenylphosphine (2.5 mg, 0.01 mmol), and the mixture was stirred 15 min under
argon atmosphere. Commercial phenylacetylene 13 (0.05 mL, 0.43 mmol) was added
and the reaction was stirred overnigthat 80 °C. The solvent was evaporated and the
crude product was purified by column chromatography yielding 51.7 mg (0.06 mmol,
87%) of dendrimer 2 as yellow solid. mp: 122− 125 °C. 1H NMR, δ (300 MHz, CDCl3,
TMS): 7.56−7.52 (m, 7H), 7.50 (d, J = 4.6 Hz, 9H), 7.47−7.40 (m, 8H), 7.38−7.32 (m,
13
9H), 7.16−7.07 (m, 9H), 7.01 (d, J = 16.3 Hz, 3H). C NMR, δ (75 MHz, CDCl3,
TMS): 146.81, 137.48, 132.06, 131.95, 131.60, 128.90, 128.37, 128.25. 127.63, 126.75,
126.26, 124.31, 123.34, 122.00, 90.28, 89.64. MALDI−TOF (m/e): calcd for C90H63N3,
1186.5 (MH+); obsd, 1186.4 (MH+).

Dendrimer 3: Core 6 (44.0 mg, 0.05 mmole) was dissolved in anhydrous toluene (7.0
mL) under argon atmosphere. Pd(PPh3)4 (5.4 mg, 0.005 mmole) and CuI (1.6 mg, 0.008
mmole) were added and the solution was stirred 30 minutes at room temperature. Then,
anhydrous trimethylamine (5 mL) was added and the yellow mixture was stirred for
additional 15 minutes. Dendron 12 (56.8 mg, 0.22 mmole) was added and the reaction
was stirred and heated to reflux during 48 hs. At the end, the mixture became orange.
Solvents were concentrated under vacuum and the crude product was purified by flash
chromatography (hexane:dichloromethane) affording dendrimer 2 (52.2 mg, 0.039
mmole, 82%) as orange solid. mp: 183 - 186°C (dichloromethane:hexane); 1H NMR:
(300 MHz, CDCl3, TMS): 8.16 (d, J = 7.65 Hz, 6H), 7.77 (d, J = 8.25 Hz, 6H), 7.61 –
7.50 (m, 18H), 7.49 – 7.42 (m, 17H), 7.35 – 7.27 (m, 7H), 7.19 – 7.10 (m, 9H), 7.04 (d,
13
J = 16.48 Hz, 3H); C NMR:
(75 MHz, CDCl3, TMS): 146.85, 140.57, 137.74,
137.55, 135.23, 133.09, 132.05, 130.25, 129.08, 127.68, 126.87, 126.35, 126.08,
124.34, 123.58, 122.32, 121.74, 120.40, 120.24, 109.77, 90.63, 89.61. MALDI-TOF
MS: m/e 1346.4 (M+).
Dendrimer 4: Dendrimer 3 (38.0 mg, 0.028 mmole) was dissolved in distilled THF (9.0
mL) at room temperature affording a bright green solution. Catalyst Pd/C 10% (23.3
mg) was added and the mixture was submitted under hydrogen pressure (9 atmospheres)
for 3 days. After this reaction time, green color of the suspension remained and more
Pd/C 10% (29.0 mg) was added and the reaction was stirred under 9 atmospheres for 2
additional days. Finally, the reaction mixture showed no fluorescence and was filtered
over a short pad of Celite, washing with dichloromethane. Solvents were concentrated
under reduce pressure and the crude product was purified by flash chromatography
(hexane:dichloromethane) to afford dendrimer 4 (33.6 mg, 0.024 mmole, 86%) as
colorless oil. 1H NMR: d (300 MHz, CDCl3, TMS): 8.15 (d, J 7.7 Hz, 6H), 7.47 (d, J 8.4

Hz, 6H), 7.44 – 7.36 (m, 18H), 7.33 – 7.26 (m, 6H), 7.17 (s, 12H), 7.07 (d, J 8.6 Hz,
6H), 7.00 (d, J 8.5 Hz, 6H), 3.03 (s, 12H), 2.90 (s, 12H). 13C NMR: d (75 MHz, CDCl3,
TMS): 37.41, 37.47, 37.60, 37.70, 109.79, 119.76, 120.27, 123.26, 123.87, 125.85,
127.02, 128.45, 128.51, 129.11, 129.86, 135.46, 135.94, 139.03, 139.66, 141.01,
141.26, 146.01.
3. Results and discission
3.1 Synthesis and Characterization. All dendrimers (Fig. 1) were obtained by
Sonogashira coupling between the cores 1,3,5-triethynylbenzene (TEB) 5 or tris{4-[(E)-
2-(4-iodophenyl)vinyl]phenyl}amine 6 and the corresponding dendrons by exception of
dendrimer 4 which was obtained by hydrogenation of dendrimer 3. The synthesis of
cores 5 and 6 were previously described by our group (Fig. 2) [22].
Synthesis of phenyl carbazole dendrons 9 and 12 were accomplished starting
from commercial carbazole 7. Under modified Ullmann´s conditions 7 was coupled
with 1,4-diiodobenzene 8 to afford 9 in 76% yield. Sonogashira type coupling reaction
of 9 with commercially available reagent 10 generates protected alkyne 11 with 97% of
yield. Finally, 11 was deprotected under basic conditions to produce free alkyne 12 in
86 % of yield. All the compounds were purified by flash column chromatography and
all the synthetic steps gave very good yields (Scheme 1).
Dendrimers were obtained by coupling between core 5 and dendron 9 and core 6
with dendron 12 and commercial phenylacetylene 13. Palladium catalyst Pd(PPh3)2Cl2
catalyst was employed for the coupling reactions of core 5 with dendron 9 (Schemes 2
and 3).
Pd(PPh3)4 was an efficient catalyst when performing the cross-coupling reaction
between core 6 and dendrons 12 and 13. As depicted in Scheme 3 reactions yields were

good to very good. All dendrimers were purified by flash chromatography and
recrystallized producing white to orange solids for the compounds with extended π-
conjugation. Dendrimer 4 was prepared by catalytic hydrogenation of 3 under 9
atmosphere of hydrogen pressure using Pd/C as catalyst and distillated tetrahydrofuran
as solvent. Product 4 was obtained as colorless oil in 86% yield.
1
13
The cores and dendrons structures were confirmed by HNMR, CNMR and
FTIR spectroscopy, and compared with the corresponding bibliographic reference when
1
it is necessary. Structures of the dendrimers were also characterized by HNMR,
13CNMR, FTIR spectroscopy and MALDI-TOF mass spectrometry experiments. In the
conjugated macromolecules 1, 2 and 3 the observation of two alkyne signals and the
13
total number of different carbon atoms signals in the CNMR spectrum allowed us to
confirmed the “starburst” shape of the dendrimers. Dendrimer 4 showed no alkyne
signals in 13CNMR spectrum and four new methylene peaks were observed. In the
1HNMR spectrum broad signals at 2.90 and 3.03 ppm corresponding to a total of 24
protons demonstrated the completed hydrogenation of all the unsaturated bonds present
in the starting macromolecule 3. MALDI-TOF data confirmed the expected molecular
mass calculated for each dendrimer. Experimental details and NMR spectra are
described in the Supporting Information.
3.2 Starburst Dendrimeric Monomers Optical Properties:
The dendrimers electronic transitions were investigated by measuring their absorption
and fluorescence spectra in diluted solutions. Fig. 3 shows the absorption and
photoluminescence spectra in DCE and TOL solutions.
The monomers light absorption energies are nearly solvent polarity independent,
and exhibit similar profiles. In general, the optical behavior can be analyzed and

understood by taking into account the different chromospheres that composed the
molecular structures (CBZ, TPA and para-phenylenevinylene). Dendrimer 1 is
constituted by three CBZ moieties bonded through ethynylphenyl arms linked to the
meta-positions of the central phenyl ring. In its spectrum the three main transitions (See
Fig. 3a and Table 1) are characteristic of those found in 9-phenylcarbazole derivatives
compounds [28,29,30,31,32]. On the other hand, dendrimer 3 presents four identifiable
optical transitions with λmax at 238, 293, 342 and 418 nm (See Fig. 3b and Table 1).
The low energy band (not present in 1) can be attributed to the π–π* transition taking
place in the para-phenylenevinylene segment [22]. This band assignment is supported
by the comparison with the spectrum of the model dendrimer 2, which holds three
vinylene-modified phenyls linked to a TPA core (See Fig. 3c). Following this analysis,
the absorption spectrum of dendrimer 3 can be seen as a combination of those obtained
with molecular structures of dendrimers 2 and 1. In fact, the dendrimer core is the same
in molecules 3 and 2 and the external shell resembles to dendrimer 1. In comparison,
when the conjugated arms of dendrimer 3 are hydrogenated to produce compound 4, the
obtained electronic absorption spectrum lacks of the optical transition attributed to the
vinylene residues (See Fig. 3d).
The photoluminescence properties of dendrimers were studied in DCE and TOL
solution exciting the monomers at the wavelength maxima of the lower energy bands.
The obtained results are showed in Fig. 3 and summarized in Table 1. It is possible to
see that the dendrimers that hold para-vinylene moiety (dendrimers 2 and 3) prevail the
emission of this well known light emitting center, while hydrogenated dendrimer 4
shows blue emission typical of TPA and CBZ centers [22,31-3233]. In the case of
dendrimer 1 that holds in its structure ethynylphenyl moiety, the emission from CBZ
center is red shifted regarding unsubstitute carbazole in 9 position, due to the larger

conjugation extension [32]. In addition, from the analysis of the showed fluorescence
spectra, it can be observed differences between the dendrimers emission with the
changes in the solvent polarity. Analyzing Fig. 3 it could be observed that dendrimers 2
and 3 shown approximately 35 nm bathochromic shifts in their emission maxima when
the solvent polarity is increased from TOL to DCE. This effect is in agreement with a
decrease in the energy of the singlet excited states as a function of an increase in the
solvent polarity; originated from fluorophores that have larger dipole moments in the
excited state than in the ground state [22,32,34]. Similar solvent effect is observed in
dendrimer 1 fluorescence emission spectra. However, the fluorescence of dendrimer 4 is
almost insensitive to the solvent polarity. Thus, the extension of the conjugation through
the introduction of unsaturated multiple bonds confers to the dendrimers excited states a
higher polar character [32]. Furthermore, as it is shown in Fig. 3b, dendrimer 3
photoluminescent excitation spectrum measured at 505 nm in DCE solution (dashed red
line in Fig. 3b), presents similar spectral features as their corresponding absorption
spectrum. This observation is indicative that the nitrogenated chromospheres (CBZ)
efficiently contribute to the para-phenylenevinylene emission at 505 nm, proving the
existence of intramolecular energy transfer in dendrimer 3 branches [22,32,35].
3.3 Dendrimers Electrochemical Properties: Electropolymerization and Film
Formation
The electropolymerization of fully conjugated dendrimers (dendrimers 1 and 3)
allows the generation of hyperbranched macromolecules obtained as thin films over
both, Pt and ITO electrode surfaces, with good electrical conductivity and
electrochemical stability. The dendrimers electrochemical behavior and the radical ions
stability were studied by cyclic voltametry technique in DCE solution. Compound 1, as

it has been mentioned, possesses CBZ as unique electroactive center in their outer layer.
Therefore, it is expected that this moiety rules the dendrimers electrochemical behavior.
Fig. 4a shows the cyclic voltammograms of 1. It can be observed that in the first scan
from -0.25 V to positive potentials (blue line) an oxidation wave, with peak at 0.95 V, is
generated (Table 1). When the scan direction is inverted two reduction waves can be
detected; one at 0.86 V (complementary to the process at 0.95 V) and another at 0.56 V.
During the second cycle (red line) a new oxidation peak at 0.67 V is identified, which is
complementary to the reduction process at 0.56 V observed in the first cathodic sweep.
This electrochemical behavior is typical of carbazole derivates where the CBZ oxidation
leads to the formation of radical cations, which undergoes a dimerization reaction to
produce dicarbazole [17,18,20,33,36]. The obtained dimer is more conjugated, thus it is
more easily oxidizable than the starting monomers, producing a new voltamperometric
signal at 0.67 V. As dendrimer 1 holds in its molecular structure three CBZ residues, it
is possible the electrochemical generation of hyperbranched dendrimeric polymers
which are deposited as a conducting film [17,18,20,36]. This hypothesis is corroborated
when the electrode potential is continually cycled. The progressive growth of the peaks
current (Fig. 4a, black lines) denoted the development of a conducting and electroactive
film on the working electrode surface. Further confirmation can be reach when the
electrode is removed from the electrochemical cell, washed with solvent, and
transferred to free monomer supporting electrolyte solution. The redox response of this
modified electrode is shown in Fig. 4b. It can be observed two oxidation peaks at 0.68
V (onset potential 0.41 V, Table 1) and 1.01 V, and two cathodic waves at 0.49 and
0.77 V. Thus, the CBZ moieties oxidation process in 1 results in dimerization reactions,
which leads to the formation of a stable polymer on the electrode surface [17,18,20,36].

In concordance, spectroelectrochemical studies also supported this conclusion (see
below).
Dendrimer 3 has peripheral CBZ groups like compound 1 but the core of the
dendrimeric structure holds a TPA residue, which resembles dendrimer 2 (see Fig. 1). In
Fig. 5a (blue line voltamogram) can be observed a first reversible wave at 0.37 V, and a
second oxidation process at 0.98 V. When the potential scan is inverted to cathodic
direction it is observed a main peak, centered around 0.55 V. Taking into account that
the CBZ groups have a higher oxidation potential than TPA unit [17,20,22,33,36], it is
possible to assign the first electrochemical process to the dendrimer core (TPA), and the
second anodic peak to the outer sphere residues (CBZ groups) oxidation. Moreover,
when the applied potential is swept until the first redox process, a reversible
electrochemical response is clearly observed (See inset in Fig. 5a), similar than those
obtained for dendrimer 2 [22]. In concordance, if the potential is successively cycled
until this first wave, a current growth associated with the electrodeposition of a
conducting film at the electrode surface is not detected. This is in agreement with the
tri-para-substituted TPA radical cation stability [17,20,22].
On the other hand, when the applied potential is driven until the second redox
process (assigned to the CBZ moieties oxidation), the dendrimer 3 starts an oxidative
polymerization, generating a hyperbranched electroactive structure. Thus, through
potentiodynamic cycles, a gradual increase of current is detected, indicating the
formation of a conducting film on the electrode surface (see Fig. 5a). In order to study
the redox behavior of the electrogenerated film, the working electrode was removed
from the electrochemical cell and washed with DCE to eliminate the monomer that
could remain on the electrode. Then, it was transferred to an electrolyte solution to
study the modified electrode electrochemistry. The obtained voltamogram showed in

Fig. 5b confirms that an electroactive film is irreversibly adhered to the electrode
surface. The film has two reversible oxidation processes with peaks potential at 0.72 V
(potential onset 0.44 V, Table 1) and 0.98 V, respectively. The polymeric film shows
great stability when the film is subjected to numerous oxidation-reduction cycles. This
behavior is similar to the one observed in other systems formed by electroactive
polymers derived from CBZ [17,20,22,33].
Fig. 6 shows the hydrogenated dendrimer 4 voltammetric response, which has a
non-conjugated structure between the CBZ peripheral groups and the TPA core (see
Fig. 1). The obtained waves are quite similar to those generated by parent dendrimer 3,
with two main oxidation processes at 0.36 V and 0.82 V (Table 1). As before, these
peaks can be assigned to the oxidation of TPA and CBZ centers, respectively. When the
electrode applied potential is cycled until the first oxidation wave, a reversible redox
process is generated, as can be observed in the black line voltammogram showed as
inset in Fig. 6a. In the same inset is also shown with blue line the complete potential
sweep until the second redox wave, where is possible to see the carbazole dimerization
process, as was already described. Consequently, if the potential scan is repetitively
cycled until the further oxidation peak, it is observed the characteristic growth and
deposition of an electroactive film. The electrochemical response of dendrimer 4 film is
shown in Fig. 6b, where two defined peaks are detected at 0.57 and 0.98 V, with a film
oxidation potential onset of 0.40 V (Table 1).
A comparative analysis of the electropolymerization processes between
dendrimer 4 with 1 and 3 (Fig.s 4a, 5a and 6a), allows to observe that in the former case
the current increase between successive voltammetric cycles is significantly lower than
the one for fully conjugated dendrimers. This effect is a clear indication that, under the
present experimental conditions, 4 is able to generated CBZ coupling, but the film

formation efficiency is much lower compare with others dendrimers structures. In the
case of dendrimer 4, it is necessary to applied nearly hundred of voltammetric cycles on
Pt electrode, to obtain a film with similar current characteristic than those generated
after five voltammetric cycles with dendrimer 1 and 3. This behavior has been already
observed in other structural related non-conjugated dendrimers, and has been attributed
to the higher solubility of the electrooxidation products, that avoids the necessary
electrode surface-organic molecule interaction necessary for the film formation [22].
The higher solubility of dimers and/or oligomers originated by the coupling of 4 radical
cations can be related to the rotational and conformational freedom degrees in the
dendrimers arms that allow the generation of globular shape products, which do not
remain on the electrode surface. Moreover, due to the low tendency of 4 to form
electrodeposited films, it was not possible to modified ITO electrodes; precluding the
possibility of studying its spectroelectrochemical properties (see below). These results
reinforce the fact that the presence of conjugate and rigid branches in the dendron
molecular structure is an important factor to obtain hyperbranched electropolymeric
films [22].
3.4 Spectrolectrochemical Properties of Electrodeposited Films
The spectrochemical experiments on hyperbranched polymers electrodeposited
as films over ITO electrodes were carried out in order to get information about the
polymeric structures, and its relationship with the optoelectronical properties of the new
materials. The films over semitransparent ITO electrodes were growth using the same
experimental conditions already described for Pt electrode. The electronic absorption
spectra at different applied potentials for dendrimer 1 are shown in Fig. 7a. The film
derivate from 1 in its neutral state is almost transparent in the visible region. It has one

defined absorption peaks at 346 nm, while that at higher energy wavelength the ITO
light absorption onset does not allow the data acquisition. When the applied potential is
moved to positive values, and reaches the first oxidation wave onset (0.41 V, Table 1),
new electronic transitions are evidenced as new bands; one with wavelength absorption
maxima at about 433 nm and a second broad band centered at 1016 nm. Also in Fig. 7a
can be observed how these bands become well defined peaks as the potential advances
through the first oxidation processes of dendrimer 1 film (see colored dots in Fig. 5b).
These bands can be assigned to the generation of bicarbazole radical cations formed by
oxidation of the polymeric film As the potential goes insides in the seconds oxidation
process, the former absorption bands starts to decrease in absorbance, while a new
broad band at 775 nm is develop, which is due to the light absorption by biscarbazole
dication species [17,20,36,37].
On the other hand, a suitable film of dendrimer 3 was grown over an ITO
electrode by cycling the potential in the conditions showed in Fig. 5b, in order to
develop spectroelectrochemical analysis. At 0 V (green line, Fig. 7b), the film exhibited
two identifiable light absorption waves at 335 and 657 nm (with a shoulder at 548 nm).
The band at 657 nm is not observed in polymer 1 spectroelectrochemical analysis (see
Fig. 5a), and consequently, it must be attributed to the presence of TPA group in
dendrimer 3 polymeric film. This last band can be assigned to the typical electronic
transition in TPA radical cations [22,36,37], which indicates that in the film generated
from 3, positive charges remain trapped or isolated in the dendrimer core, even at low
potential. As it was observed with 1, when the applied potential became more anodic,
first the biscarbazole radical cation optical signals start to growth at 437 nm and 1034
nm (see Fig. 5a and b), and then the biscarbazole dication is generated which exhibits a
broad absorption band centered at 722 nm [22,36,37] Thus, the spectroelectrochemical

analysis is in agreement with the electrochemical processes associated to the TPA
central core and peripheral CBZ units in hyperbranched polymeric structure.
Therefore, the described spectroelectrochemical behavior supports that CBZ-
CBZ electroactive centers is present as cross-linked in the molecular structure of
dendrimeric films. A proposed molecular structure is shown in Fig. 8, where the
dimerizations of CBZ moieties are involved in the electropolymerization processes of
both monomers.
On the other hand, the UV-vis absorption changes with the applied potentials
observed in dendrimeric films are fully reversible and associated with significant color
changes that can be appreciate by the naked eye. Fig. 9a shows photographic pictures of
a dendrimer 1 film in its neutral (applied potential, Eapp= 0.00 V), semioxidized (Eapp
=
0.60 V), and fully oxidized (Eapp = 1.25 V) states.
The film colorations (transparent, pale yellow, and green, respectively) exhibit a
homogenous spreading on the ITO surface, showing the electrochromic capability of the
material. Fig. 9b displays the sequential changes in transmittance at 772 nm when the
applied potential is step-switched between the neutral and oxidized states (Eapp 0.00 and
1.25 V). As can be seen, dendrimer 1 film possess a high contrast ratio, with
transmittances of around 90 and 10 % in the neutral and fully oxidized states,
respectively. Furthermore, Fig. 9c exhibit the current changes associate to the coloration
processes. These changes reflect the kinetics of the charge transport processes, and can
be correlated with the coloration response time. The elapsed time needed for 90% of full
transmittance changes at 772 nm were 7.0 s for the coloration step and 2.0 s for the
bleaching step, reflecting the different conductivities between the reduced and oxidized
forms of dendrimer 1 film. On the other hand, similar elecrochromic behavior was

obtained with 3 electropolymer. However, the observed chances in coloration are less
intense than those generated by the alteration of the redox state in film 1 electrodes.
On the other hand, it is known that the film surface morphology characteristics
are associated to their use as active layer in electronic and/or optoelectronic devices
[21,38] Fig. 10 shows SEM images of both 1 and 3 derivates electropolymer films
surfaces, obtained in the above described condition on ITO electrode. Both polymeric
films fully cover the ITO surface, but it is clearly seen that they exhibit different
morphologies. Besides that both films display granulate surfaces, polymer obtained
from 1 has a smaller grain size than the observed for the film produced by the
electropolymerization of dendrimer 3. The morphology differences could be originated
in the dendrimeric molecular characteristics. In the case of dendrimer 3, the relevant
fact is the presence of the TPA electroactive central core, which remains positively
charged during the electrodeposition processes. As it was already demonstrated the
presence of an oxidized core can influence the characteristic of the morphological
surface of the hyperbranched polymers obtained by electropolymerization [21,22].
4. Conclusion
We developed a versatile synthetic strategy for the construction of fully
conjugated dendrimeric structures using a Sonogashira cross coupling protocol as a key
reaction. The starburst dendrimers were built convergently with an electroactive TPA
core or a non electroactive TEB core. The branched structures undergo electrochemical
polymerization through the oxidation of the peripheral CBZ groups. By this
methodology hyperbranched polymers were deposited as conductive films over metallic
and semitransparent oxide electrodes. The effects of monomer structural characteristics
over the films morphological and physiochemical properties were elucidated. In this

way, the importance of the presences of an extended conjugation in the dendrimer
branches for efficient film formation has been evidenced. We have also shown that the
existence of an oxidized core in the dendrimeric structure affects both, the
electrochromic and film morphology properties. Thus, the electroactive hyperbranched
starburst polymeric films, with the capability to avoid staking or aggregation between
the redox centers, have a remarkable potential to find applications in the design and
construction of organic electro-optical devices.
ASSOCIATED CONTENT
Supporting Information Available
Synthetic Procedures and Characterization Data, 1H and 13C NMR spectra and MM+
calculation of the synthesized compounds.
ACKNOWLEDGMENTS
We thank Consejo Nacional de Investigaiones Cientificas y Tecnicas
(CONICET-Argentina), Agencia Nacional de Promoción Cientıfica y Tecnológica
(ANPCYT Argentina), Universidad Nacional de Rosario y Universidad Nacional de Río
Cuarto. M.I.M, R.A.S, D.H, L.F, L.O. and F.F. are scientific members of CONICET.
AUTHOR INFORMATION
Corresponding Authors
* spanevello@iquir-conicet.gov.ar and ffungo@exa.unrc.edu.ar
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Figures Caption
Fig. 1. Dendrimer structures
Fig. 2. Cores 5 (TEB) and 6.
Fig. 3: Normalized absorption () and emission (- - -) spectra of a) Dendrimer 1, b)
Dendrimer 3, c) Dendrimer 2 and d) Dendrimer 4 recorded in DCM (black) and TOL
(Blue). Since the dyes spectra are similar in DCM and TOL, only the light absorption
spectra in DCM are shown. In Fig. 3b the dendrimer 3 photoluminescent excitation
spectrum (measured at 505 nm in DCE) is showed with red dash line (- - -).
Fig. 4: a) first (blue) and second (red) cycles in repetitive voltammograms (black) of
dendrimer 1 solution (DCE, 0.1 M TBAHFP) on a Pt electrode, v = 0.1 Vs-1. b) Cyclic
voltammogram of the electro-deposited film derived from dendrimer 1 on Pt (DCE, 0.1
M TBAHFP). The superimposed colored dots on voltammogram trace correspond to the
potentials applied when the spectra showed in Fig. 7a were acquire.
Fig. 5: a) first (blue) and second (red) cycles in repetitive voltammograms (black) of
dendrimer 3 solution (DCE, 0.1 M TBAHFP) on a Pt electrode, v = 0.1 Vs-1. Inset
shows the cyclic voltammogram until the first oxidation wave. b) Cyclic voltammogram
of the electro-deposited film derived from dendrimer 3 on Pt (DCE, 0.1 M TBAHFP).

The superimposed colored dots on voltammogram trace correspond to the potentials
applied when the spectra showed in Fig. 7b were acquire.
Fig. 6: a) first (blue) cycles of repetitive cyclic voltammograms of a solution of
dendrimer 4 in DCE with 0.1 M of TBAHPP on a Pt at a scan rate of v = 0.1 Vs-1. Inset
shows in black line the cyclic voltammogram until the first oxidation wave. b) Cyclic
voltammogram of the electro-deposited film derived from dendrimer 4 on Pt in DCE
solution without monomer, v = 0.1 Vs-1.
Fig. 7: UV-visible absorption spectra of electrodeposited films on an ITO electrode as
function of applied potentials: a) dendrimer 1 and b) dendrimer 3. The potential applied
to the colored spectra corresponds to the superimposed dots on voltammogram trace
showed in Fig. 4b and 5b with the same color. The insets show pictures of the electrodes
at different redox states.
Fig. 8: Electrochemical polymerization of end-capped CBZ dendrimers.
Fig. 9: a) 1 film on an ITO electrode pictures at different applied potentials. b) Dynamic
transmittance changes upon switching the potential between 0 and 1.25 V with a pulse
width of 40 s applied to the electrodeposited ITO/film of 1 in DCE containing 0.1 M
TBAHFP. The absorption was recorded at 772 nm. c) Current generated by the step
potentials applied to the system.
Fig. 10: SEM photographs of dendrimeric electropolymer films surfaces obtained from
a) 1 and b) 3.
Schemes
Scheme 1: Synthesis of dendrons 9 and 12.
Scheme 2: Synthesis of dendrimer 1.
Scheme 3: Synthesis of dendrimers 2, 3 and 4.
Table
Table 1: Photophysical and electrochemical parameters of 1-4 dendrimers. The emission
spectra were measured by excitation at the maximum of the lower energy bands in nm. a
b
Irreversible peak. Half-wave potentials, obtained from reference [22].c Reversible

d
process. Onset potentials determined from intersection between the baseline and the
current signal. The potentials values are expressed in volt vs. Fc/Fc+.
PHOTOPHYSICAL
ELECTROCHEMICAL
Oxidation Potentials (V)
Absorption(λmáx
DCE
)
Emission(λmáx)
DENDRIMER
ꢀꢁ# ꢂꢃꢂꢄꢅꢆ
0.95a
ꢀꢇ#ꢈꢉꢄ
0.41d
DCE TOL
Dendrimer 1
Dendrimer 2
Dendrimer 3
Dendrimer 4
241/293/342
321/419
406
501
505
365
373
462
466
366
0.38b
-----
238/293/342/418
243/261/294
0.37c/0.98a
0.36c/0.82a
0.44d
0.40d
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