High hole mobility and light-harvesting in discotic nematic dendrimers prepared: Via 'click' chemistry

Article abstract of DOI:10.1039/c8tc06142d

We report a new family of liquid crystalline porphyrin-core dendrimers with coumarin units at the periphery of the dendrimer. These compounds have been prepared by copper-catalyzed azide-alkyne "click" cycloaddition (CuAAC). The mesomorphic properties have been investigated via polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The peripheral coumarin units play a key role in the liquid crystal behavior, contributing to the appearance of discotic nematic mesophases with hole mobility values among the highest values reported for discotic liquid crystals (of the order of 1 cm² V^-1 s^-1). It has also been demonstrated that excitation of the coumarin moieties leads to energy transfer (antenna effect) to the luminescent porphyrin core. Therefore, this strategy, which involves 'click' chemistry, has been proven to be a powerful and elegant synthetic tool for the preparation of optoelectronic materials based on complex dendritic architectures.

Full text of DOI:10.1039/c8tc06142d

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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DOI: 10.1039/C8TC06142D
Journal Name
ARTICLE
High hole mobility and light-harvesting in discotic nematic
dendrimers prepared via ‘click’ chemistry
Received 00th January 20xx,
Accepted 00th January 20xx
a,‡
b
b
a
a
Alberto Concellón, Roberto Termine, Attilio Golemme, Pilar Romero, Mercedes Marcos, and
,
a,b
José Luis Serrano*
DOI: 10.1039/x0xx00000x
We report a new family of liquid crystalline porphyrin-core dendrimers with coumarin units at the periphery of the
dendrimer. These compounds have been prepared by copper-catalyzed azide-alkyne “click” cycloaddition (CuAAC). The
mesomorphic properties have been investigated by polarized optical microscopy (POM), differential scanning calorimetry
www.rsc.org/
(DSC) and X-ray diffraction (XRD). The peripheral coumarin units play a key role in the liquid crystal behavior, contributing
to the appearance of discotic nematic mesophases with hole mobility values among the highest values reported for
2
-1 -1
discotic liquid crystals (of the order of 1 cm ·V ·s ). It has also been demonstrated that excitation of the coumarin
moieties leads to energy transfer (antenna effect) to the luminescent porphyrin core. Therefore, this strategy, that
involves ‘click’ chemistry, has proven to be a powerful and elegant synthetic tool for the preparation of optoelectronic
materials
based
on
complex
dendritic
architectures.
the columns have been described.15-19 Despite this promising
properties, columnar mesophases still suffer from the
disadvantage that orientationally uniform domains that are
large enough to be used in most devices are often hard to
obtain. Nonetheless, very recently we reported a new family of
LC dendrimers with charge mobilities of the same order of
magnitude as those found in columnar phases, in spite of
Introduction
In the last few years the research field of organic electronics –
i.e. the use of conjugated molecules as active components in
electronic devices– has expanded impressively and diversified
into organic light-emitting diodes (OLEDs), organic field-effect
transistors (OFETs) or organic photovoltaic devices (OPVs). The
ideal organic semiconductor must have closely-packed
molecules with few defects between molecules or domains
2
0
D D
exhibiting a discotic nematic (N ) phase. The N mesophase
makes possible to obtain large homogeneously oriented
domains with very low density of defects due to its lower
order degree in comparison to columnar mesophases.
1
-4
because charge transport depends on molecular order. The
highest charge carrier mobility in organic systems has been
measured in single crystals of pentacene and rubrene (20
On the other hand, LC dendrimers have been recognized as an
attractive tool for the preparation of polymeric materials for
2
-1 -1 5
cm V s ), but the preparation of single-crystalline thin films
is very tedious and not applicable industrially. To overcome
this limitation, liquid crystals (LCs) offer an interesting
approach as they self-organize into nanostructured phases
that provide properties similar to those of organic single
crystals, while the dynamics is vital for the processability and
2
1-24
optoelectronic applications.
They combine in the same
molecule the structural and synthetic versatility of dendrimers
with the anisotropic properties of the LC state. The topology of
these molecules bearing several external reactive groups
allows the introduction of different active moieties that self-
assemble into a LC arrangement with a supramolecular order
6
-14
the self-healing of structural defects. In particular, columnar
LCs have attracted considerable attention because they
represent one-dimensional charge carrier pathways, whereby
the inner aromatic core is conducting and the outer alkyl
periphery has an insulating character. In such phases, charge
2
5-29
that facilitates charge transport.
Although the preparation
of dendrimers has been improved over the past decade, their
synthesis requires extremely efficient reactions. “Click”
chemistry provides efficient routes for the synthesis of
dendritic structures because it requires mild reaction
conditions, tolerates a wide range of functional groups, and
2
-1 -1
mobilities of the order of 1 cm ·V ·s along the direction of
3
0-34
leads to high yields.
a. Instituto de Ciencia de Materiales de Aragón, Departamento de Química
The aim of the work reported here is to exploit the ‘click’
chemistry as an effective and elegant approach for the
preparation of LC dendrimers with potential applications in
Orgánica, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain.
LASCAMM CR-INSTM, CNR-NANOTEC Lab LiCryL, Dipartimento di Fisica,
b.
Universitá della Calabria, 87036 Rende, Italy.
c.
Instituto de Nanociencia de Aragón, Departamento de Química Orgánica, organic optoelectronic devices. Herein, we describe a new
Universidad de Zaragoza, 50009 Zaragoza, Spain.
approach which allows us to connect four azido-functionalized
dendrons with an alkyne functionalized porphyrin core. This
‡
Present adress: Department of Chemistry, Massachusetts Institute of Technology,
MA 02139, Cambridge, United States.
This journal is © The Royal Society of Chemistry 20xx
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 2 of 10
ARTICLE
Journal Name
strategy gives high yields and resulted in products that can be dendrimer was prepared to evaluate the role of coumarin
View Article Online
DOI: 10.1039/C8TC06142D
peripheral units in these supermolecular systems. It is formed
easily purified by non-chromatographic procedures.
Following this synthetic approach, three porphyrin-core by a first-generation dendron containing dodecyloxy alkyl
dendrimers have been synthetized and their chemical chains without coumarin moieties (ZnP-d C12). In this article,
1
structure are shown in Figure 1. Two of them are the first- and we report the synthesis, chemical and physical
second-generation dendrimers bearing coumarin moieties characterization of these porphyrin-core dendrimers, with the
(ZnP-d
1 2
Cou and ZnP-d Cou). The third porphyrin-core aim of assessing their possible use in organic electronics.
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
R
R
R
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
O
O
N
N
O
O
N
N
O
O
R
O
R
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
R
O
O
R
N
N
N
N
N
O
O
N
N
N
N
O
O
N
Zn
N
N
N
Zn
N
N
O
O
N
O
O
N
O
O
N
O
O
O
R
N
R
O
O
O
O
O
N
O
O
O
O
O
O
O
O
O
N
O
N
O
O
O
O
O
N
N
O
N
N
O
O
O
O
ZnP-d Cou: R =
O
O
O
1
O
O
O
O
O
O
O
ZnP-d C12: R = CH3
O
O
ZnP-d Cou
1
2
O
O
O
O
R
R
R
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Figure 1. Chemical structure of the porphyrin-core dendrimers prepared by ‘click’ chemistry.
O
O
O
O
O
O
O
O
O
O
O
O
O
Results and discussion
Synthesis and structural characterization
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
O
Zn
O
O
N
N
N
NN
O
O
O
O
O
The synthesis of the azido functionalized dendrons (N
3
-d
1
Cou,
O
O
O
O
O
O
O
O
O
O
3
N -d
2
Cou, and N
3
-d
1
C12) and the alkyne functionalized
O
O
O
O
O
O
N3
O
O
porphyrin core (ZnP-YNE) was described in the Supporting
Information.
4
O
Zn
O
ZnP-d2Cou
N
N
N
N
O
O
A convergent synthetic approach was used for the preparation
of the porphyrin-core dendrimers (Scheme 1). In the final
synthetic step, the azido functionalized dendrons and the
alkyne functionalized porphyrin were coupled by copper-
catalyzed azide-alkyne cycloaddition (CuAAC) using THF/water
O
O
N3
O
O
O
O
O
O
O
O
O
ZnP-YNE
O
O
O
O
O
O
O
O
N
N
O
O
O
O
Zn
O
O
O
O
O
O
N
N
N
N
N
O
as solvent and CuSO
4
·5H
2
O/sodium ascorbate as the catalytic
N3
O
O
N3-d1C12
O
O
system. An excess of the azide dendron (1.5 equivalents per
alkyne group) was employed to ensure the completeness of
CuSO4.H2O, sodium ascorbate
THF/H2O
ZnP-d1Cou
the reaction and was removed by using
a previously
O
synthesized alkyne-functionalized Wang resin. The efficiency of
the CuAAC coupling was determined by FTIR, NMR
spectroscopy (Figure 2a and Figures S1-S10), MALDI-TOF MS
O
O
O
N
N
N
N
Zn
O
N
NN
O
4
ZnP-d1C12
(Figures S11-S13), and size exclusion chromatography (SEC). All
Scheme 1. Convergent synthetic approach used for the
characterization methods indicated that the target porphyrin-
core dendrimers were monodisperse.
preparation
of
the
porphyrin-core
dendrimers.
2
| J. Name., 2012, 00, 1-3
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ARTICLE
View Article Online
DOI: 10.1039/C8TC06142D
(
a)
(b)
C
E
B
C≡C
F
L
J
O
≡C─H
O
O
H
N
K
O
O
M
N'
P
P
O
O
O
O
O
O
T
M'
N3
V
7
N
N
N
N
3
2
X
N
N
U
Zn
O
N
O
O
O
4
4
000 3500 3000 2500 2000 1500 1000 500
-
1
Wavenumber (cm )
P
L
(
(
c)
B
[
M]+
E
H
C
K, M
F
T
U
N -d Cou
3
1
F, F’, H, H’
P, E’
L
7
J
2
000
3000
4000
5000
6000
7000
V
B, B’
K, M
C
2
C’
E
N, N’
m/z
X
3
U
T
ZnP-d Cou
1
d)
7
X
3
2
≡C─H
ZnP-YNE
1
2
14
16
18
20
22
Elution time (min)
1
Figure 2. (a) H NMR spectra (400 MHz, CD
2
Cl
2
, 298K), (b) FTIR spectra, (c) MALDI mass spectrum, (d) SEC traces of ZnP-YNE
1 3 1
(red), ZnP-d Cou (black) and N -d Cou (blue).
Evidence for the formation of the dendrimers was collected clearing point (Table 1). Thermal transitions and mesomorphic
from the 1H NMR spectra (Figure 2a), where new peaks properties were studied by POM, DSC and XRD, and the results
corresponding to the formed triazol ring appeared at around are listed in Table 1. Three cycles were carried out in DSC
7
V
.95 ppm (H ) and the ethynyl proton signal of the alkyne experiments and data were taken from the second cycle. In
functionalized porphyrin core disappeared upon CuAAC some cases, temperatures were taken from POM observations
1
coupling. Furthermore, there were changes in the H shift of because transition peaks were not detected in DSC curves
the methylenic protons linked to the new formed triazol (H
and H ).
FTIR spectra also confirmed the coupling, the bands at around Table 1. Thermal Stability and Transition Temperatures.
U
(Figures S14-S17).
T
3
280 (≡C-H), 2120 (C≡C) and 2110 (N
3
) disappeared after the
2% (°C)[a]
Phase transitions[b]
T
CuAAC reaction (Figure 2b). Further confirmation of the
coupling was provided by SEC analysis and MALDI-TOF mass
spectroscopy. The MALDI-TOF mass spectra showed the
expected peak and no other signals corresponding to
dendrimers with a partial functionalization were detected
N
N
N
3
3
3
-d
-d
-d
1
2
1
Cou
Cou
C12
213
230
241
344
309
335
g 20 Cr 61 I
g 11 N 73[c]
I
Cr 30 I
ZnP-d
ZnP-d
ZnP-d
1
Cou
2
Cou
1
C12
g 24 N
g 21 N
112[c]
I
D
(
Figure 2c). The SEC curves showed monomodal molar mass
distributions and residual precursors were not detected
Figure 2d). As can be observed, CuAAC coupling of the
98[c]
D
I
g 122 Cr 151[c] M 155[c]
I
(
[
a] Temperature at which 2% mass lost is detected in the
precursors blocks gave rise to a shift of the molar mass
distribution towards lower retention times that indicates the
porphyrin-core dendrimers’ formation.
thermogravimetric curve. [b] DSC data of the second heating
process at a rate of 10 °C/min. Temperatures are read at the
maximum of the peak. g: glass, Cr: crystal, N: nematic
mesophase, N
mesophase, I: isotropic liquid. [c] POM data.
D
: discotic nematic mesophase, M: unidentified
Thermal stability and liquid crystalline properties
The thermal stability of all the compounds was studied by TGA.
All of the samples showed good thermal stability with the 2%
weight loss temperature (T2%) more than 150 ºC above the
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Only the azido-functionalized second generation dendron (N
Cou) exhibited LC behavior. The other azido-functionalized nematic behavior can be explained by taDkOinI:g10in.1t0o39a/cCc8oTuCn0t61t4h2aDt
dendrons (N -d Cou and N -d C12) were not mesomorphic. the flexibility of the ester bonds allows adopting a rod-shaped
-d Cou showed a birefringent texture by POM at room geometry that locates the two dendrons in opposite
temperature on applying mechanical stress (Figure 3a).
3
-
nematic mesophase which has only orientationaVlieworAdrteicrle.OTnhlinies
d
2
3
1
3
1
N
3
2
3
5
directions. On the other hand, functionalization of the
porphyrin core with the coumarin-containing dendrons gives
(a)
(b)
3
6-38
rise to disk-like structures.
Thus, the XRD pattern recorded
for ZnP-d Cou is characteristic of a discotic nematic (N )
1
D
mesophase. It displayed one relatively strong reflection in the
low-angle region corresponding to the presence of a certain
degree of short-range columnar order within the nematic
3
9-
phase, as has been previously described in other N
D
phases,
and a broad halo in the high-angle region which corresponds
to the liquid-like order of the disordered alkyl chains (Figure
a). The calculated d-spacing (26 Å) for the signal in the low-
4
1
(c)
(d)
4
angle region represents the average inter-disk distance and
approximates the diameter of the porphyrin core. The spacing
from the high-angle diffraction is 4.6 Å, which mainly
originates from the liquid-like correlations between the
conformationally disordered alkyl chains.
2
On the other hand, the XRD pattern of ZnP-d Cou only showed
diffuse scattering in the low-angle region, and a broad diffuse
Figure 3. POM microphotographs for: (a) N
room temperature in the second cooling process, (b) ZnP-
Cou taken at room temperature in the second cooling, (c)
ZnP-d Cou taken at room temperature in the second cooling
process, and (d) ZnP-d C12 at 152 ºC in the second heating
1
process.
3 2
-d Cou taken at
halo in the high-angle region (Figure 4b). This pattern also
4
2
confirms the presence of a N
the disappearance of the intense maximum in the low-angle
region in the XRD pattern of ZnP-d Cou (Figure 4c). The
greater number of alkyl chains in ZnP-d Cou could be
D
mesophase. It is noteworthy
d
1
2
2
2
responsible for these differences of XRD, since they may
hinder the lateral disk-disk interactions between
metalloporphyrin units, and consequently, prevent the
All the porphyrin-core dendrimers exhibited mesogenic
properties and the thermal behavior was different depending
on the compound. In the case of the porphyrin-core
dendrimers with coumarin functional units around the
formation of columnar alterations within the N
With ZnP-d C12, the DSC curve showed an exothermic peak at
22 ºC (cold crystallization) and an endothermic peak
D
phase.
1
1
1 2
porphyrin core (ZnP-d Cou, and ZnP-d Cou), enantiotropic LC
corresponding both to the crystal-to-mesophase transition and
the transition from mesophase to isotropic liquid. These two
transitions were observed by POM and detected as only one
endothermic peak in the DSC which corresponds to the sum of
the two transition peaks, and thus the nature of the
mesophase could not be identified by XRD. These results
confirm the key role of the coumarin terminal units in the
mesogenic behavior of these materials leading to the
apparition of the mesophase at room temperature and
increasing significantly the mesophase range. Both features
are fundamental parameters for their practical applications in
organic electronics.
mesophases were observed. The DSC curves showed only a
glass transition freezing the mesomorphic order at room
temperature, while clearing temperatures were established
from POM observations. All the compounds had a high
tendency to homeotropic alignment and the mesophase was
observed by POM on applying mechanical stress to the
samples showing birefringent textures (Figure 3).
The assignment of the mesophase type was carried out by
XRD. The XRD pattern of the coumarin-containing second
3 2
generation dendron (N -d Cou) showed only diffuse scattering,
suggesting the absence of long-range positional order in the LC
phase (Figure S18). This kind of pattern corresponds to a
(a)
(b)
(c)
ZnP-d Cou
1
ZnP-d Cou
2
1
0
-
1
q (nm
)
1 2
Figure 4. (a) Room temperature XRD pattern of ZnP-d Cou, (b) room temperature XRD pattern of ZnP-d Cou, (c) 1D profiles of
the XRD patterns.
4
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Journal Name
Table 2. Photophysical data in DCM solutions and in thin film.
ARTICLE
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DOI: 10.1039/C8TC06142D
λabs (nm)
λabs (nm)
λabs (nm)
λem (nm)
λ
em (nm)
λem (nm)
Q (0‒2)
Φ [
a]
Φ
ET
F
Coumarin
Soret band
Q-bands Coumarin
Q (0‒1)
ZnP-YNE
DCM
film
‒
426
426
‒
558, 599
560, 602
‒
-
600
606
‒
644
651
‒
0.09
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
N
N
3
-d
-d
1
Cou
Cou
DCM
film
324
314
323
314
322
322
321
322
‒
388
411
388
411
383
‒[b]
383
‒[b]
‒
‒
‒
‒
‒
3
2
DCM
film
‒
‒
‒
‒
‒
‒
‒
‒
ZnP-d
ZnP-d
ZnP-d
1
Cou
2
Cou
1
C12
DCM
film
426
434
427
436
417
424
552, 595
562, 603
552, 594
563, 604
540
603
605
601
605
600
611
643
649
642
648
644
650
0.12 16%
‒
‒
DCM
film
0.11 23%
‒
0.14
‒
‒
‒
‒
DCM
film
‒
544
‒
[
F
a] The Φ values were calculated from DCM solutions with tetraphenylporphyrin (0.11 in benzene) as standard, excitation at 420
nm. [b] Not detectable.
Absorption and emission properties.
The UV-Vis absorption and fluorescence spectra of porphyrin-
core dendrimers and precursors were collected on dilute
solutions (10-5 to 10 M) in DCM, and in thin films prepared by
casting DCM solutions onto quartz substrates. Relevant data
are presented in Table 2.
(a)
Soret band
Q(0-1)
-7
The two coumarin-containing dendritic precursors, N
and N -d Cou, showed an absorption band in DCM solution at
24 and 323 nm respectively, and an emission band at 388 nm.
3
-d
1
Cou
Coumarin band
3
2
Q(0-2)
3
Interestingly, in thin film the absorption bands showed a
hypochromic shift of about 10 nm, while the emission band
showed a significant bathochromic shift of 23 nm probably due
to the aggregation effect. The porphyrin precursor ZnP-YNE
showed in the UV-visible spectrum a Soret band at 426 nm,
and two Q bands at 558 and 599 nm. Excitation of the Soret
band resulted in the apparition of two emission bands at 606
2
00
300
400
500
600
700
800
Wavelenght (nm)
(b)
Soret band
(Q(0-1)) and 651 nm (Q(0-2)).
On the other hand, the UV-Vis absorption spectra of the three
porphyrin-core dendrimers in DCM solution are, within
experimental error, a combination of the spectra of the alkyne
functionalized porphyrin and the corresponding azido
functionalized dendron (Figure 5a). The absorption bands
corresponding to the coumarin units showed similar values
both in solution and in thin film, whereas the absorption bands
corresponding to the porphyrin core in thin film exhibited a
bathochromic shift of about 10 nm in relation to those in
solution, due to the aggregation effect.
Coumarin band
Q(0-1)
Q(0-2)
2
00
300
400
500
600
700
800
Wavelenght (nm)
The fluorescence emission spectra of the three porphyrin-core Figure 5. a) UV-Vis absorption spectra in DCM solution (black
dendrimers (λexc= 425 nm) consisted of two bands with a Q(0- line) and emission spectra (λexc = 425 nm) in DCM solution
1
)-band at around 600 nm and a Q(0-2)-band at around 645 (blue line) and in thin film (red line) of ZnP-d
nm (Figure 5a). The fluorescence quantum yields were also absorption spectra in DCM solution (black line) and emission
measured with tetraphenylporphyrin as standard (Φ
= 0.11 in spectra (λexc = 320 nm) in DCM solution (blue line) and in thin
1
Cou. b) UV-Vis
F
1
benzene), obtaining low quantum yields. The fluorescence film (red line) of ZnP-d Cou.
spectra were also recorded in thin films. Compared to the data
from DCM solutions, the emission Q(0-1) and Q(0-2) peaks are Nonetheless, when peripheral coumarin units of the
red-shifted ca. 5-10 nm.
dendrimers were excited at 320 nm, significant differences in
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ARTICLE
Journal Name
the fluorescence emission spectra were observed between the significantly lower than the LUMO energy values VainewdAbrtieclceaOunslinee,
measurements in DCM solution and in thin film. In the first being transparent, it simplifies the DoObI:s1e0r.1v0a3t9io/Cn8TCo0f614th2De
case, the emission band at 388 nm (see blue line in Figure 5b) macroscopic orientation by POM. All the cells, with a thickness
slightly overlap the Soret absorption band of the porphyrin, in the 5-10 m range, were filled by capillarity by heating the
and thus the porphyrin core was excited. As a consequence, material above the temperature of the transition to the
emission from the porphyrin core was also observed, isotropic liquid. After sample filling, cells were cooled to room
indicating that intramolecular energy transfer occurs from temperature. POM observations of cells of ZnP-d
1
Cou, and
coumarins donors to the porphyrin acceptor (antenna effect). ZnP-d Cou showed strong tendency for homeotropic
2
a
The energy transfer efficiencies (ΦET) were calculated by alignment. That is, without any surface treatment, the samples
comparing the donor emission in the presence of the acceptor were perfectly oriented with the director (average direction
4
3-45
relative to that in the absence of the acceptor,
and are the short molecular axes) perpendicular to the substrate.
C12, which does not display
summarized in Table 2. Low ΦET efficiencies were obtained However, cells filled with ZnP-d
1
because of the low degree of overlap between the emission liquid crystal properties at room temperature, showed large
spectrum of the coumarin and the absorption spectrum of the crystalline domains of various orientations.
porphyrin. However, it is noteworthy that the ΦET value of the The current-voltage curves typically exhibited a linear region at
second generation dendrimer (ZnP-d
than that of the first generation dendrimer (ZnP-d
6%). This is probably because the higher number of limited, a quadratic dependence was observed. In this regime,
peripheral coumarin units increase the effectivity of the light- neglecting the effect of traps and the voltage dependence of
2
Cou, ΦET= 23%) is higher low applied voltages, where the behavior is ohmic. However,
1
Cou, ΦET at higher voltages, where the current becomes space-charge-
=
1
harvesting.
mobility, the current dependence on applied voltage is
4
2
The fluorescence spectra (λexc= 320 nm) were also recorded in described by the Mott-Gurney equation:
thin film and compared to the data from DCM solutions; the
coumarin emission band was totally suppressed and only 퐽 = 휀
emission from the porphyrin core was observed (see red line in
푉2
푑3
9
휀
푟
휇
0
8
Figure 5b). Therefore, the energy transfer from coumarin units where J is the measured current density, µ is the charge
to the porphyrin core is more efficient in the thin film than in mobility, ε is the free-space permittivity, ε is the dielectric
0
r
DCM solution. This behavior can be attributed both to a higher constant of the material, V is the applied voltage, and d is the
number of coumarin donors around porphyrin acceptors and thickness of the device. As the relative dielectric constant and
to the anisotropic nature of the films.
the sample thickness can be easily measured, by using this
equation charge mobilities can be extracted from J-V curves.
The resulting hole mobilities values (μhole) are summarized in
Electrochemical properties and hole mobilities.
Cyclic voltammetry experiments (CV) were performed to study Table 3.
the electrochemical properties of the porphyrin-core Figure 6 shows the typical J-V curves obtained for ZnP-d Cou
1
dendrimers. ZnP-d
similar cyclic voltammograms with reduction and oxidation 0.150.05 and (21)×10 cm ·V ·s , respectively. The low
processes. The HOMO and LUMO energy levels, referred to the hole mobility value of ZnP-d C12 can be explained by taking
vacuum level were estimated from the oxidation and into account that this compound does not display liquid crystal
1 2 1
Cou, ZnP-d Cou, and ZnP-d
1
C12 exhibited and ZnP-d C12 and the resulting hole mobilities were
-9
2
-1 -1
1
reduction waves (Table 3).
properties at room temperature and thus all the
measurements were carried out in macroscopically disordered
Table 3. Electrochemical parameters and hole mobilities.
1
crystalline phases. In the case of ZnP-d Cou, the introduction
E
(
LUMO
eV)[a]
of coumarin units around the porphyrin core contributes to
the appearance of the discotic nematic mesophase, leading to
a remarkable increase of μhole by 8 orders of magnitude.
2
-1 -1
E
HOMO (eV)[a]
µhole (cm ·V ·s )
ZnP-d
ZnP-d
ZnP-d
1
Cou
2
Cou
1
C12
–4.92
–4.94
–4.92
–1.33
0.15±0.05
0.9±0.2[b]
(2±1)×10-9
1E-7
0.1
0.01
1E-3
–1.35
–1.56
(
a)
(b)
1E-8
[
a] EHOMO = ‒ (Eox ‒ E1/2, FOC + 4.8) eV. ELUMO = ‒ (Ered ‒ E1/2, FOC +
1
E-9
4
.8) eV. [b] Lower estimation of the charge carrier mobility
1
1
1
E-4
E-5
E-6
(measured in areas with the lowest currents).
1E-10
1
E-11
The charge carrier mobility measurements were performed by
using the space charge-limited current (SCLC) technique. The
SCLC method was chosen by considering the HOMO energy
value of the materials, which matches the work function of
gold electrodes (WAu≈ -5.1 eV) and thus ensures the formation
of an ohmic contact. As a counter-electrode, indium tin oxide
1
10
100
1
10
Voltage (V)
Voltage (V)
Figure 6. Typical J-V curves for: (a) ZnP-d
Cou (circles represent experimental data and the two
continuous lines represent ideal linear and quadratic
1
C12 and (b) ZnP-
d
1
dependence of J on V).
(ITO) was used because its work function (WITO≈ -4.6 eV) is
6
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On the other hand, very high currents were measured for ZnP- In conclusion, we have found that combining
a
View Article Online
d
2
Cou. However, the hole mobility values reported in Table 3 metalloporphyrin core with luminescentDcOoI:u1m0.a10r3in9/mC8oTiCe0t6ie1s42iDn
were obtained only in those areas of the samples with the the same dendritic scaffold is a good strategy for the
lowest currents. Within the areas exhibiting higher currents, preparation of polymeric materials for optoelectronic
an ohmic regime was observed at all applied voltages, applications. Particularly, the hole mobility values are one of
probably because the injected charges never reach a density the highest values reported for discotic liquid crystals to this
high enough for the set-up of the space-charge regime. Films date. Therefore, these porphyrin-core dendrimers have great
2
of ZnP-d Cou, with a thickness of the order of 100 nm, potential as semiconducting soft materials with high hole
between ITO and Au electrodes were also prepared by spin- mobility.
coating followed by electrode evaporation, as described in the
Supporting Information. However, also in this case only ohmic
Conflicts of interest
There are no conflicts to declare.
regimes and high currents were observed. This means that the
charge mobility that was possible to measure via the SCLC
technique is a lower estimation of the hole mobility in these
materials and thus the real μhole is probably much higher.
The results obtained in these dendrimers reveal the key role Acknowledgements
played by the coumarin units in the hole mobility properties,
This work was supported by the MINECO-FEDER funds (project
CTQ2015-70174), Gobierno de Aragón-FSE (Research Group
E04). Authors would like to acknowledge the use of the SAI
either directly through an involvement in the hopping process,
or indirectly through its promesogenic activity. Nevertheless, a
definitive explanation for the different hole mobility values
(UZ) and CEQMA (UZ-CSIC) Services. A. Golemme is grateful for
2 1
measured in ZnP-d Cou and ZnP-d Cou cannot be deduced
support from the ELIOTROPO project (PON03PE_00092_2). R.
Termine was supported by the MERAVIGLIE project (CUP
J28C17000080006).
with the reported data. However, a hint might be derived from
the XRD patterns that, as illustrated above, suggest the
presence of a certain degree of short-range columnar order
only in ZnP-d
mesophase compared to ZnP-d
spontaneous homeotropic alignment (i.e.
macroscopic orientation between electrodes),
homogeneity within the mesophase of ZnP-d Cou might favor
a more uniform alignment over large areas of the samples,
leading to an increase of hole mobility. In addition, the higher
2
number of coumarin units in ZnP-d Cou could also play an
1
Cou which results in a less homogeneous
Cou. Bearing in mind their
favorable
higher
2
References
a
1
2
.
.
O. Ostroverkhova, Chem. Rev., 2016, 116, 13279-13412.
A. Saeki, Y. Koizumi, T. Aida and S. Seki, Acc. Chem. Res., 2012,
a
2
4
5, 1193-1202.
M. Mas-Torrent and C. Rovira, Chem. Rev., 2011, 111, 4833-
856.
3
4
5
.
.
.
4
L. Wang, G. Nan, X. Yang, Q. Peng, Q. Li and Z. Shuai, Chem.
Soc. Rev., 2010, 39, 423-434.
J. Takeya, M. Yamagishi, Y. Tominari, R. Hirahara, Y. Nakazawa,
T. Nishikawa, T. Kawase, T. Shimoda and S. Ogawa, Appl. Phys.
Lett., 2007, 90, 102120.
enhancing role in the increase of the hole mobility values.
Conclusions
6
.
W. Pisula, M. Zorn, J. Y. Chang, K. Müllen and R. Zentel,
Macromol. Rapid Commun., 2009, 30, 1179-1202.
M. O’Neill and S. M. Kelly, Adv. Mater., 2011, 23, 566-584.
E. K. Fleischmann and R. Zentel, Angew. Chem. Int. Ed., 2013,
Herein, we have developed a convenient and highly versatile
route involving ‘click’ chemistry to prepare novel liquid
7
8
.
.
crystalline dendrimers based on
a porphyrin core and
coumarin units at the periphery of the dendrimer. In these
compounds we have demonstrated that excitation of
coumarin donors results in energy transfer to the porphyrin
central core. This antenna effect is more efficient in thin film
than in solution.
5
2, 8810-8827.
9
.
N. K. Minar, K. Hou, C. Westermeier, M. Döblinger, J. Schuster,
F. C. Hanusch, B. Nickel, G. A. Ozin and T. Bein, Angew. Chem.
Int. Ed., 2015, 54, 7577-7581.
10. T. Kato, M. Yoshio, T. Ichikawa, B. Soberats, H. Ohno and M.
Funahashi, Nat. Rev. Mater., 2017, 2, 17001.
1. T. Kato, J. Uchida, T. Ichikawa and T. Sakamoto, Angew. Chem.
Int. Ed., 2018, 57, 4355-4371.
2. Y. Zeng, L. Lu, T. Gao, Y. Feng, J.-F. Zheng, E.-Q. Chen and X.-K.
Ren, Dyes Pigm., 2018, 152, 139-145.
3. K. P. Gan, M. Yoshio, Y. Sugihara and T. Kato, Chem. Sci., 2018,
The peripheral coumarin units play a key role in the liquid
crystal behavior, contributing to the appearance of discotic
nematic mesophases with high hole mobility values (of the
1
1
1
1
2
-1 -1
order of 1 cm ·V ·s ). To confirm this point a dendrimer
analogue (i.e. without coumarin peripheral units) was
prepared, and a decrease of 8 orders of magnitude in hole
mobility was observed, stressing our hypothesis about the
decisive influence of coumarin moieties in the final properties
9
, 576-585.
4. Y. Hu, K.-Y. Wu, T. Zhu, P. Shen, Y. Zhou, X. Li, C.-L. Wang, Y. Tu
and C. Y. Li, Angew. Chem. Int. Ed., 2018, 57, 13454-13458.
of the dendrimers. In general, the second generation 15. R. Chico, E. de Domingo, C. Domínguez, B. Donnio, B. Heinrich,
dendrimer showed better optical (antenna effect) and
electronic properties (hole mobility) than the first generation
analogue. Thus, these results probe the importance of tuning
such properties upon modification of dendrimer’s generation.
R. Termine, A. Golemme, S. Coco and P. Espinet, Chem. Mater.,
017, 29, 7587-7595.
6. A. Benito-Hernández, U. K. Pandey, E. Cavero, R. Termine, E.
2
1
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 8 of 10
ARTICLE
Journal Name
M. García-Frutos, J. L. Serrano, A. Golemme and B. Gómez-Lor, 43. S. L. Gilat, A. Adronov and J. M. J. Fréchet, AngeVwiew. CArhtieclme O. nIlninte.
Chem. Mater., 2013, 25, 117-121. Ed., 1999, 38, 1422-1427.
7. T. Sakurai, K. Tashiro, Y. Honsho, A. Saeki, S. Seki, A. Osuka, A. 44. A. Adronov, S. L. Gilat, J. M. J. Fréchet, K. Ohta, F. V. R.
DOI: 10.1039/C8TC06142D
1
1
1
Muranaka, M. Uchiyama, J. Kim, S. Ha, K. Kato, M. Takata and
Neuwahl and G. R. Fleming, J. Am. Chem. Soc., 2000, 122,
T. Aida, J. Am. Chem. Soc., 2011, 133, 6537-6540.
1175-1185.
8. E. M. García-Frutos, U. K. Pandey, R. Termine, A. Omenat, J. 45. S. Hecht, N. Vladimirov and J. M. J. Fréchet, J. Am. Chem. Soc.,
Barberá, J. L. Serrano, A. Golemme and B. Gómez-Lor, Angew.
Chem. Int. Ed., 2011, 50, 7399-7402.
2001, 123, 18-25.
9. T. Sakurai, K. Shi, H. Sato, K. Tashiro, A. Osuka, A. Saeki, S. Seki,
S. Tagawa, S. Sasaki, H. Masunaga, K. Osaka, M. Takata and T.
Aida, J. Am. Chem. Soc., 2008, 130, 13812-13813.
2
2
2
2
2
2
0. A. Concellón, M. Marcos, P. Romero, J. L. Serrano, R. Termine
and A. Golemme, Angew. Chem. Int. Ed., 2017, 56, 1259-1263.
1. X. Zeng, G. Ungar, Y. Liu, V. Percec, A. E. Dulcey and J. K. Hobbs,
Nature, 2004, 428, 157.
2. B. Donnio, S. Buathong, I. Bury and D. Guillon, Chem. Soc. Rev.,
2
007, 36, 1495-1513.
3. B. M. Rosen, C. J. Wilson, D. A. Wilson, M. Peterca, M. R. Imam
and V. Percec, Chem. Rev., 2009, 109, 6275-6540.
4. H. J. Sun, S. Zhang and V. Percec, Chem. Soc. Rev., 2015, 44,
3
900-3923.
5. S. Hernández-Ainsa, M. Marcos and J. L. Serrano, in Handbook
of Liquid Crystals, eds. J. W. Goodby, P. J. Collings, T. Kato, C.
Tschierske, H. Gleeson and P. Raynes, Wiley-VCH Verlag GmbH
&
Co. KGaA, Second edn., 2014, vol. 7, ch. 7, pp. 259-300.
2
6. A. Concellón, T. Liang, A. P. H. J. Schenning, J. L. Serrano, P.
Romero and M. Marcos, J. Mater. Chem. C, 2018, 6, 1000-
1
007.
2
2
7. A. Concellón, M. Bucoş, J. L. Serrano, P. Romero and M.
Marcos, RSC Adv., 2016, 6, 65179-65185.
8. V. Iguarbe, A. Concellón, R. Termine, A. Golemme, J. Barberá
and J. L. Serrano, ACS Macro Lett., 2018, DOI:
1
0.1021/acsmacrolett.8b00505, 1138-1143.
2
3
3
3
3
9. A. Concellón, S. Hernández-Ainsa, J. Barberá, P. Romero, J. L.
Serrano and M. Marcos, RSC Adv., 2018, 8, 37700-37706.
0. R. K. Iha, K. L. Wooley, A. M. Nyström, D. J. Burke, M. J. Kade
and C. J. Hawker, Chem. Rev., 2009, 109, 5620-5686.
1. M. V. Walter and M. Malkoch, Chem. Soc. Rev., 2012, 41, 4593-
4
609.
2. M. Arseneault, C. Wafer and J. F. Morin, Molecules, 2015, 20,
263.
9
3. S. Guerra, T. L. A. Nguyen, J. Furrer, J.-F. Nierengarten, J.
Barberá and R. Deschenaux, Macromolecules, 2016, 49, 3222-
3
231.
3
4. A. Lancelot, R. González-Pastor, A. Concellón, T. Sierra, P.
Martín-Duque and J. L. Serrano, Bioconjugate Chemistry, 2017,
2
8, 1135-1150.
3
3
3
3
3
4
4
4
5. M. Marcos, R. Martín-Rapún, A. Omenat and J. L. Serrano,
Chem. Soc. Rev., 2007, 36, 1889-1901.
6. B. Wu, K. Chen, Y. Deng, J. Chen, C. Liu, R. Cheng and D. Chen,
Chem. Eur. J., 2015, 21, 3671-3681.
7. L. Li, S. W. Kang, J. Harden, Q. Sun, X. Zhou, L. Dai, A. Jakli, S.
Kumar and Q. Li, Liq. Cryst., 2008, 35, 233-239.
8. A. Segade, M. Castella, F. López-Calahorra and D. Velasco,
Chem. Mater., 2005, 17, 5366-5374.
9. C. T. Imrie, Z. Lu, S. J. Picken and Z. Yildirim, Chem. Commun.,
2
007, DOI: 10.1039/B614922G, 1245-1247.
0. M. Gupta, S. P. Gupta, M. V. Rasna, D. Adhikari, S. Dhara and S.
K. Pal, Chem. Commun., 2017, 53, 3014-3017.
1. M. Gupta, S. P. Gupta, S. S. Mohapatra, S. Dhara and S. K. Pal,
Chem. Eur. J., 2017, 23, 10626-10631.
2. H. K. Bisoyi and S. Kumar, Chem. Soc. Rev., 2010, 39, 264-285.
8
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DOI: 10.1039/C8TC06142D
GRAPHICAL ABSTRACT
High hole mobility and light-harvesting in discotic nematic dendrimers prepared via
click’ chemistry
‘
Alberto Concellón, Roberto Termine, Attilio Golemme, Pilar Romero, Mercedes Marcos, and José Luis
Serrano*
We have developed a new strategy involving ‘click’ chemistry to to prepare porphyrin-core dendrimers that
have coumarin units around the porphyrin core. These dendrimers exhibit nematic discotic phases with hole
mobilities among the highest values described in liquid crystals. Moreover, we have also demonstrated that
excitation of the coumarin moieties leads to energy transfer (antenna effect) to the porphyrin core.
h+
+
h+
h
h+
h+
h+
h+
h+
h+
h+
h+
h+
h
+
h+
h
+
Light-Harvesting
Hole mobility
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