Synthesis, characterization and optical properties of novel dendronized azo-dyes containing a fullerene C60 unit and well-defined oligo(ethylene glycol) segments

Article abstract of DOI:10.1039/c7ra00413c

Herein, we report the preparation and characterization of a novel series of dendronized azo-dyes containing a fullerene C₆₀ unit and well-defined oligo(ethylene glycol) spacers. The azobenzene units present in these dyes were substituted in the

Full text of DOI:10.1039/c7ra00413c

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Synthesis, characterization and optical properties
of novel dendronized azo-dyes containing
Cite this: RSC Adv., 2017, 7, 16751
a fullerene C unit and well-defined oligo(ethylene
6
0
glycol) segments†
a
b
a
Jesus Ortız-Palacios, Gerardo Zaragoza-Galan, Edgar Aguilar-Ortız,
´
´
´
´
a
a
Efraın Rodrıguez-Alba and Ernesto Rivera*
´
´
Herein, we report the preparation and characterization of a novel series of dendronized azo-dyes containing
a fullerene C60 unit and well-defined oligo(ethylene glycol) spacers. The azobenzene units present in these
0
dyes were substituted in the 4 -position with different functional groups (–H, –OCH
3 4 9
, –C H , –CN and
2
–NO ). The optical properties of these compounds were studied by absorption spectroscopy as a function
of the dipole moment of the azobenzene moieties. All fullerene C60-azobenzene derivatives exhibited
trans–cis photoisomerization and photoprotonation under irradiation with UV-light. The results were
compared to those obtained with their precursor azo-dyes without fullerene C60. It was found that the
presence of the fullerene unit significantly quenches the photoisomerization yield, whereas the
photoprotonation was not affected by the presence of this chromophore.
Received 10th January 2017
Accepted 9th March 2017
DOI: 10.1039/c7ra00413c
rsc.li/rsc-advances
1
1–13
literature.
Some of them led to the development of new
1
Introduction
9,10,14
materials for molecular photoswitching,
smart optoelec-
15
16,17
Fullerene C60 has been widely studied and employed in the tronic devices and organic solar cells.
elaboration of many opto-electronic and photovoltaic devices
Rau classied azobenzenes into three main categories based
18
because of its remarkable electronic properties. This chromo- on their photochemical behaviour. Unsubstituted photo-
phore is considered one of the best molecular electron-acceptor chromic azobenzene belong to the rst category, known as
groups able to participate in F ¨o rster Resonance Energy Transfer “azobenzenes”. The thermally stable trans isomer exhibits an
(
FRET) and Charge Transfer (CT) phenomena either in solution intense absorption band at 350 nm due to the p–p* transition,
1–3
or in the solid state. However, the applications of fullerene as well as a weak intensity band at 440 nm related to the n–p*
60 itself are very limited because of its poor solubility in transition, whereas the cis isomer undergoes similar transitions
C
organic solvents. The incorporation of alkyl chains and other but with a more intense n–p* band. Moreover, “azobenzenes”
functional groups into fullerene C60 has led to the development have a relatively poor overlap of the p–p* and n–p* bands. The
of novel molecular structures with enormous potential optical second category, known as “aminoazobenzenes” usually
4
–8
applications. Very recently, some hybrid systems based on includes azobenzenes that are substituted by an electron-donor
azo-dyes containing fullerene C60 units have been investigated group and are characterized by the signicant overlap of the
due to their synergistic effect. Wang et al. reported the func- p–p* and n–p* bands. Finally, azobenzenes bearing an electron-
tionalization of fullerene C60 via the addition of a substituted donor and an electron-acceptor group belong to the third cate-
9
azobenzene as a carbene active intermediate. Kay et al. re- gory, named “pseudostilbenes”, where the p–p* and n–p* bands
1
8
ported the synthesis and optical properties of a novel azo- are practically superimposed and inverted on the energy scale.
dendrimer bearing a fullerene C60 unit as core. Other related
10
When donor–acceptor substituted azobenzenes are incor-
structures combining azobenzene-fullerene, exhibiting inter- porated into a polymer backbone, they generate very versatile
esting optical properties, have been reported in the photoactive materials. In particular, the irradiation of these
polymers with linear polarized light produces rapid trans–cis
cis–trans photoisomerization of “pseudostilbene” azobenzenes.
In consequence, polarized light allows the selective activation of
a
Instituto de Investigaciones en Materiales, Universidad Nacional Aut ´o noma de
M ´e xico, Circuito Exterior Ciudad Universitaria, C. P. 04510, D.F, Mexico. E-mail:
“pseudostilbenes” bearing a polarization axis parallel to the
riverage@unam.mx
b
Facultad de Ciencias Qu ´ı micas, Universidad Aut ´o noma de Chihuahua, Campus absorbing radiation, which causes the photoalignment of the
Universitario, #2, Apartado Postal 669, Chihuahua, Mexico
azobenzene moieties until they become perpendicular to the
light polarization axis.
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c7ra00413c
16–22
1
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dried by distillation over calcium hydride and anhydrous
toluene was employed. Precursor azo-dyes were synthesized
23,24,30
according to the method previously reported by us,
whereas N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) aniline
Disperse Red-1, DR1) was purchased from Aldrich. The
fullerene C60 was incorporated into azobenzene derivatives as
(
3
1,32
described in the literature.
1
13
H and C NMR spectra of the intermediates and nal
compounds involved in the synthesis were recorded in CDCl
3
solution at room temperature on a Bruker Avance 400 MHz
1
spectrometer, operating at 400 MHz and 100 MHz for H and
1
3
C, respectively. All compounds were dissolved in spectral
quality solvents purchased from Aldrich, and their absorption
spectra were recorded on a Varian Cary 1 Bio UV-vis (model
8452A) spectrophotometer at room temperature, using 1 cm
width quartz cuvettes. MALDI-TOF mass spectra were obtained
on a Bruker Daltonic Felx Analysis, using dithranol as matrix.
Photoisomerization experiments were carried out in solution
and solid state (cast lm). For the disubstituted malonic deriva-
tives (9, 10, 11) and the fullerene C -azobenzene derivatives (15,
6
0
1
6, 17) the photoisomerization experiments were conducted in
ꢁ
4
DMF solution (2.5 ꢀ 10 M) at room temperature. Cast lms
were prepared by depositing a saturated solution of the azo-dye
on quartz substrates. Solutions and lms were irradiated using
a Compact UV lamp model UVGL-25, 254/365 nm (6 W). The
samples were irradiated with intervals of 10 s and the spectral
changes were monitored by absorption spectroscopy. Meanwhile,
photoprotonation experiments with the fullerene C -azobenzene
Fig. 1 Synthesis of the fullerene C60-azobenzene derivatives.
6
0
3
derivatives were carried out in CHCl solution. Compounds 15
Our research group has developed different series of azo- and 19 were irradiated at 254 nm and monitored by absorption
23–26
27,28
dyes
and azo-polymers
with different structures. Very spectroscopy with intervals of 10 and 30 s, respectively.
recently, we reported the preparation and optical properties of
some photoactive azo-dendrons and azo-dendrimers bearing
a liquid crystalline behaviour, which exhibited a photo-
2
.2 Synthesis
29
protonation phenomenon. In this work, we describe the
2.2.1 Synthesis of the 3-dodecyloxy-5-hydroxybenzyl alcohol
1
synthesis and characterization of a novel series of dendronized (1). First generation dendron G OH (1) was prepared according to
33
azo-dyes containing fullerene C60 units, exible alkyl and oli- the method previously reported by us. The coupling constants
go(ethylene glycol) spacers. The amino-azobenzenes reported in were conrmed according a previous work reported by Fr ´e chet
0
34
this work were substituted in the 4 -position with different et al.
1
1
functional groups (–H, –OCH
Bingel reaction was used in order to obtain novel fullerene C60
azobenzene branched systems (Fig. 1 vide infra), which exhibit PhOCH
trans–cis photoisomerization and photoprotonation under all CH
3
, –C
4
H
9
, –CN and –NO
2
). The
H NMR (400 MHz, CDCl
(t, J ¼ 2 Hz, 1H, H ), 4.61 (s, 2H, PhCH
3
): d ¼ 6.49 (t, J ¼ 2 Hz, 2H, H ), 6.37
2
-
2
OH), 3.93 (t, J ¼ 7 Hz, 4H,
2
), 1.79–1.72 (m, 4H, PhOCH
2
CH
2
), 1.47–1.26 (m, 36H,
) ppm.
): d ¼ 160.52 (2C, C ), 143.16 (1C,
2
of the aliphatic chain), 0.88 (t, J ¼ 7 Hz, 6H, CH
3
1
3
c
irradiation with UV-light. The optical properties of these
compounds were studied in detail by absorption spectroscopy. C ), 105.02 (2C, C ), 100.52 (1C, C ), 68.03 (2C, PhOCH
The aim of this work is to demonstrate the ability of these (1C, PhCH OH), 31.90, 29.61–29.18, 26.02, 25.70, 22.87 (20C, all
of the aliphatic chain), 14.09 (2C, CH ) ppm.
2.2.2 Synthesis of 3-(3,5-bis(dodecyloxy)benzyloxy)-3-oxopro-
C NMR (100 MHz, CDCl
3
a
b
d
2
), 65.44
2
compounds to modify their optical properties by photo- CH
protonation and their susceptibility to favor the energy transfer
2
3
phenomenon instead of the trans–cis photoisomerization due to panoic acid (2). The synthesis of the monosubstituted malonic
the strong acceptor character of the fullerene unit.
ester was achieved according to the method described in the
literature.
31
1
H NMR (400 MHz, CDCl
3
) d ¼ 6.47 (d, J ¼ 2 Hz), 6.42 (t, J ¼ 2
2
Experimental
Hz), 5.14, (s, 2H), 3.93 (t, J ¼ 6 Hz, 4H), 3.50 (s, 2H), 1.77 (m, 4H),
.26 (m, 36H), 0.88 (t, J ¼ 6 Hz, 6H) ppm.
2.1 General conditions
1
1
3
All reagents used in the synthesis of the fullerene C -azo-
C NMR (100 MHz, CDCl ): d ¼ 171.38, 166.37, 160.39,
6
0
3
benzene derivatives were purchased from Aldrich and used as 136.88, 106.38, 101.22, 68.01, 67.46, 40.78, 31.87, 29.55–29.16,
received without further purication. Dichloromethane was 25.97, 22.62, 14.05 ppm.
16752 | RSC Adv., 2017, 7, 16751–16762
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2
.3 Synthesis of the precursor azo-dyes
2.4.2 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(4-((4-
butylphenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl-
malonate (10). Procedure described for the synthesis of 9, using
Precursor azo-dyes (4), (5) and RED-PEG-4 (7) were prepared
according to the method previously reported by us.
For the synthesis of azobenzenes (E)-2-(4-(phenyldiazenyl)
phenyl)-5,8,11-trioxa-2-azatridecan-13-ol (3) and (E)-4-((4-((2-(2-
3
0,33,35
4
(0.2 g, 0.5 mmol), DMAP (0.008 g, 0.07 mmol), 2 (0.329 g, 0.6
mmol) and DCC (0.120 g, 0.58 mmol) to give compound 10
(
Scheme 1b). Yield: 67%.
(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethyl)(methyl)amino)phenyl)
1
5
H NMR (400 MHz, CDCl ): d ¼ 7.83 (d, J ¼ 9 Hz, 2H, H ),
3
diazenyl)benzonitrile (6) (see ESI†).
4
6
7
9
5
.74 (d, J ¼ 8 Hz, 2H, H ), 7.26 (d, J ¼ 8 Hz, 2H, H ), 6.75 (d, J ¼
3 2 1
Hz, 2H, H ), 6.46 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ),
.09 (s, 2H, PhCH
2
OOC), 4.29 (t, J ¼ 5 Hz, 2H, OOCCH
2
of the
2
of the
2
of the tet-
2
.4 Synthesis of the disubstituted malonic ester
.4.1 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(4-(phenyl-
diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl-malonate (9).
(0.26 g, 0.67 mmol), N,N-dimethyl-4-aminopyridine (DMAP)
0.013 g, 0.1 mmol) and intermediate 2 (0.489 g, 0.87 mmol)
were dissolved in 10 mL of anhydrous CH Cl . Aer that,
tetra(ethylene glycol) chain), 3.92 (t, J ¼ 7 Hz, 4H, PhOCH
aliphatic chain), 3.69–3.60 (m, 14H, CH N y OCH
ra(ethylene glycol) chain), 3.45 (s, 2H, OOCCH COO), 3.09 (s,
H, CH N), 2.67 (t, J ¼8 Hz, 2H, PhCH ), 1.79–1.70 (m, 4H,
2
2
2
3
(
3
3
2
PhOCH CH ), 1.68–1.57 (m, 2H, Ph(CH ) ), 1.45–1.26 (m, 38H,
2
2
2 2
2
2
Ph(CH ) and all CH of the aliphatic chain), 0.95 (t, J ¼ 7 Hz,
2
3
2
a solution of N,N-dimethyl-4-aminopyridine (DCC) (0.18 g, 0.87
mmol) in 5 mL of anhydrous CH Cl was added dropwise. The
6
H, CH
3
), 0.89 (t, J ¼ 6 Hz, 3H, Ph(CH
2 3
)CH ) ppm.
2
2
13
g
C NMR (100 MHz, CDCl
3
): d ¼ 166.37 (1C, C ), 166.21 (1C,
reaction mixture was stirred at room temperature for 8 h. Then,
the crude product was ltered on Celite many times until the
urea was completely removed. The crude product was concen-
trated at reduced pressure and puried by column chromatog-
raphy on silica gel using hexanes/ethyl acetate (8 : 2) as eluent to
yield compound 9 (Scheme 1a). Yield: 55%.
e
b
h
l
C ), 160.43 (2C, C ), 151.38 (1C, C ), 151.14 (1C, C ), 144.63 (1C,
C ), 143.68 (1C, C ), 137.18 (1C, C ), 128.90 (2C, C ), 124.77 (2C,
C ), 122.09 (2C, C ), 111.38 (2C, C ), 106.39 (2C, C ), 101.10 (1C,
C ), 70.74–70.57, 68.76 (6C, OCH of the tetra(ethylene glycol)
o
k
d
n
m
j
i
c
a
2
chain), 67.17 (2C, PhOCH of the aliphatic chain), 68.52 (1C,
2
PhCH O), 68.05 (1C, N(CH ) ) 64.53 (1C, COOCH of the tet-
1
5
2
2 2
2
H NMR (400 MHz, CDCl ): d ¼ 7.87 (d, J ¼ 9 Hz, 2H, H ),
f
3
ra(ethylene glycol) chain), 52.15 (1C, NCH
1C, NCH ), 35.46 (1C, PhCH ), 33.48 (1C, PhCH
9.63–29.21, 26.01, 22.65 (20C, all CH of the aliphatic chain),
2.30 (1C, Ph(CH CH ), 14.08 (2C, CH ), 13.91 (1C,
CH ) ppm.
.4.3 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(4-((4-
methoxyphenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-
3-yl-malonate (11). Procedure described for the synthesis of 9,
using 5 (0.2 g, 0.5 mmol), DMAP (0.009 g, 0.7 mmol), 2 (0.309 g,
.6 mmol) and DCC (0.118 g, 0.7 mmol), to give compound 11
2
), 41.34 (1C, C ) 39.18
4
6
7
9
5
.84 (d, J ¼ 9 Hz, 2H, H ), 7.47–7.37 (m, 3H, H –H), 6.75 (d, J ¼
(
2
2
3
2
2
CH ), 31.88,
2
3 2 1
Hz, 2H, H ), 6.47 (d, J ¼ 2 Hz, 2H, H ), 6.41 (t, J ¼ 2 Hz, 1H, H ),
2
.09 (s, 2H, PhCH
2
OOC), 4.29 (t, J ¼ 5 Hz, 2H, OOCCH
2
of the
2
of the
2
)
2
2
3
tetra(ethylene glycol) chain), 3.92 (t, J ¼ 6 Hz, 4H, PhOCH
aliphatic chain), 3.68–3.59 (m, 14H, CH N y OCH
ra(ethylene glycol) chain), 3.46 (s, 2H, OOCCH COO), 3.07 (s,
H, CH N), 1.80–1.71 (m, 4H, PhOCH CH ), 1.46–1.39 (m, 4H,
Ph(CH
2
)
3
3
2
2
of the tet-
2
2
3
3
2
2
1
PhO(CH ) CH ), 1.36–1.27 (m, 32H, all CH of the aliphatic
chain), 0.90 (t, J ¼ 6 Hz, 6H, CH ) ppm.
2
2
2
2
3
0
1
3
g
C NMR (100 MHz, CDCl
3
): d ¼ 166.17 (1C, C ), 166.01 (1C,
(
Scheme 1c). Yield: 43%.
e
b
h l
C ), 160.28 (2C, C ), 153.00 (1C, C ), 151.22 (1C, C ), 143.45 (1C,
C ), 137.08 (1C, C ), 129.14 (1C, C ), 128.70 (2C, C ), 124.85 (2C,
C ), 122.02 (2C, C ), 111.21 (2C, C ), 106.20 (2C, C ), 100.94 (1C,
2
C ), 70.58–70.41, 68.37 (6C, OCH of the tetra(ethylene glycol)
chain), 68.59 (2C, PhOCH of the aliphatic chain), 67.85 (1C,
PhCH O), 66.96 (1C, NH (CH ) ), 64.35 (1C, COOCH of the
tetra(ethylene glycol) chain), 51.97 (1C, NCH ), 41.18 (1C, C ),
1
5
H NMR (400 MHz, CDCl
3
): d ¼ 7.83 (d, J ¼ 9 Hz, 2H, H ),
k
d
o
n
4
6
7
9
5
.81 (d, J ¼ 9 Hz, 2H, H ), 6.97 (d, J ¼ 9 Hz, 2H, H ), 6.76 (d, J ¼
j
m
i
c
3
2
1
Hz, 2H, H ), 6.46 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ),
.09 (s, 2H, PhCH OOC), 4.29 (t, J ¼ 5 Hz, 2H, OOCCH of the
a
2
2
2
tetra(ethylene glycol) chain), 3.92 (t, J ¼ 7 Hz, 4H, PhOCH of the
2
2
2
2 2
2
aliphatic chain), 3.86 (s, 3H, PhOCH
y OCH of the tetra(ethylene glycol) chain), 3.46 (s, 2H,
OOCCH COO), 3.08 (s, 3H, CH N), 1.78–1.75 (m, 4H, PhOCH
CH ), 1.44–1.26 (m, 36H, all CH
J ¼ 7 Hz, 6H, CH ) ppm.
3 2
), 3.69–3.61 (m, 14H, CH N
f
2
2
3 2
39.00 (1C, NCH ), 31.75, 29.50–29.07, 25.88, 22.52 (20C, all CH
2
3
2
-
3
of the aliphatic chain), 13.97 (2C, CH ) ppm.
2
2
of the aliphatic chain), 0.88 (t,
3
1
3
g
C NMR (100 MHz, CDCl ): d ¼ 166.35 (1C, C ), 166.19 (1C,
3
e
o
b
h
C ), 160.78 (1C, C ), 160.42 (2C, C ), 150.92 (1C, C ), 147.43
(
(
l
k
d
j
1C, C ), 143.64 (1C, C ), 137.18 (1C, C ), 124.53 (2C, C ), 123.76
m
n
i
c
2C, C ), 114.02 (2C, C ), 111.41 (2C, C ), 106.38 (2C, C ),
a
1
01.09 (1C, C ), 70.73–70.56, 68.75 (6C, OCH
ethylene glycol) chain), 68.52 (2C, PhOCH of the aliphatic
chain), 68.04 (1C, PhCH O), 67.15 (1C, N(CH ), 64.52 (1C,
COOCH of the tetra(ethylene glycol) chain), 55.43 (1C, NCH ),
2.16 (1C, OCH ), 41.33 (1C, C ), 39.15 (1C, NCH ), 31.87,
2
of the tetra(-
2
2
2 2
)
2
2
f
5
2
1
3
3
9.62–29.20, 26.00, 22.64 (20C, all CH of the aliphatic chain),
2
4.07 (2C, CH ) ppm.
3
Scheme 1
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2
.4.4 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(4-((4- DCC (0.078 g, 0.2 mmol) to give compound 14 (Scheme 1f).
cyanophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl- Yield: 80%.
1
6
malonate (12). Procedure described for the synthesis of 9, using
H NMR (400 MHz, CDCl
3
): d ¼ 8.31 (d, J ¼ 9 Hz, 2H, H ),
5
4
6
(0.205 g, 0.5 mmol), DMAP (0.009 g, 0.8 mmol), 2 (0.363 g, 0.6 7.91 (d, J ¼ 9 Hz, 2H, H ), 7.89 (d, J ¼ 10 Hz, 2H, H ), 6.76 (d, J ¼
3
2
1
mmol) and DCC (0.133 g, 0.64 mmol) to give compound 12 9 Hz, 2H, H ), 6.46 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ),
(
Scheme 1d). Yield: 65%.
5.09 (s, 2H, PhCH
2
OCO), 4.36 (t, J ¼ 6 Hz, 2H, NCH
2
CH
of the aliphatic chain), 3.66 (t, J ¼
), 3.51–3.46 (m, 2H, OCOCH CH NCH
COO), 1.77–1.70 (m, 4H, PhOCH CH
of the 1.45–1.38 (m, 4H, PhO(CH CH ), 1.31–1.20 (m, 35H, all CH
of the the aliphatic chain and NCH
of the tet- CH ) ppm.
2
OCO),
1
5
H NMR (400 MHz, CDCl ): d ¼ 7.86 (d, J ¼ 9 Hz, 2H, H ), 3.91 (t, J ¼ 7 Hz, 4H, PhOCH
2
3
4
6
7
9
5
.85 (d, J ¼ 10 Hz, 2H, H ), 7.70 (d, J ¼ 9 Hz, 2H, H ), 6.75 (d, J ¼ 6 Hz, 2H, CH
3
CH
2
NCH
2
2
2
2
)
3
2
1
Hz, 2H, H ), 6.45 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ), 3.45 (s, 2H, OOCCH
2
2
2
),
of
.08 (s, 2H, PhCH
2
OOC), 4.29 (t, J ¼ 5 Hz, 2H, OOCCH
2
2
)
2
2
2
tetra(ethylene glycol) chain), 3.91 (t, J ¼ 7 Hz, 4H, PhOCH
aliphatic chain), 3.68–3.60 (m, 14H, CH N y OCH
ra(ethylene glycol) chain), 3.45 (s, 2H, OOCCH COO), 3.11 (s,
2
2
CH
3
), 0.88 (t, J ¼ 7 Hz, 6H,
2
2
3
1
3
e
C NMR (100 MHz, CDCl
3
): d ¼ 166.19 (1C, C ), 165.91 (1C,
2
g
b
l
h
3
H, CH N), 1.79–1.74 (m, 4H, PhOCH CH ), 1.45–1.25 (m, 36H, C ), 160.54 (2C, C ), 156.74 (1C, C ), 151.10 (1C, C ), 147.54 (1C,
3 2 2
o
k
d
n
all CH of the aliphatic chain), 0.88 (t, J ¼ 7 Hz, 6H, CH ) ppm. C ), 144.01 (1C, C ), 137.16 (1C, C ), 126.21 (2C, C ), 124.58 (2C,
2
3
1
3
g
j
m
i
c
C NMR (100 MHz, CDCl ): d ¼ 166.26 (1C, C ), 166.09 (1C, C ), 122.63 (2C, C ), 111.48 (2C, C ), 106.61 (2C, C ), 101.21 (1C,
3
e
b
l
h
a
2
C ), 160.36 (2C, C ), 155.31 (1C, C ), 152.24 (1C, C ), 143.48 C ), 68.15 (2C, PhOCH of the aliphatic chain), 67.26 (1C,
k
d
n
m
(
1
1C, C ), 137.11 (1C, C ), 132.90 (2C, C ), 125.77 (2C, C ), PhCH
2
O), 62.23 (1C, CH
), 45.67 (1C, CH
(CH ), 29.63–29.25 (14C, all CH
of 26.03 (2C, PhO(CH ), 22.64 (2C, CH
the aliphatic chain), 68.44 (1C, PhCH O), 67.97 (1C, N(CH ) ), 12.27 (1C, NCH CH ) ppm.
3
CH
CH
2
NCH
N), 41.43 (1C, C ), 31.88 (2C,
of the aliphatic chain),
CH ), 14.04 (1C, CH ),
2 2 3 2
CH O), 48.57 (1C, CH CH -
j
o
f
22.57 (2C, C ), 118.84 (1C, C ), 111.70 (1C, PhCN), 111.34 (2C, NCH
2
3
2
i
c
a
C ), 106.31 (2C, C ), 100.99 (1C, C ), 70.70–70.50, 68.68 (6C, CH
OCH of the tetra(ethylene glycol) chain), 67.07 (PhOCH
)
2
3
2
2
2
)
3
3
2
3
2
2
2
2 2
2
3
6
4.42 (1C, COOCH of the tetra(ethylene glycol) chain), 52.07
2
f
(
1C, NCH ), 41.27 (1C, C ), 39.18 (1C, NCH ), 31.80, 29.55–
2
3
2
.5 Synthesis of the fullerene C60-azobenzene derivatives
2.5.1 Synthesis of the fullerene C60-amino substituted
.4.5 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(4-((4- azobenzene (15). 9 (0.240 g, 0.3 mmol), I (0.065 g, 0.025 mmol)
2
9.13, 25.93, 22.56 (20C, all CH
2
of the aliphatic chain), 14.01
(
3
2C, CH ) ppm.
2
2
nitrophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl- and fullerene C60 (0.185 g, 0.3 mmol) were dissolved in 180 mL
malonate (13). Procedure described for the synthesis of 9, using of anhydrous toluene. Aer some minutes, 1,8-diazabicyclo
7
(0.208 g, 0.5 mmol), DMAP (0.009 g, 0.8 mmol), 2 (0.352 g, 0.6 [5,4,0]undec-7-ene (DBU) (0.185 g, 0.85 mmol) was added
mmol) and DCC (0.129 g, 0.62 mmol) to give compound 13 dropwise. The reaction mixture was stirred at room temperature
(
Scheme 1e). Yield: 77%.
for 6 h. Then, the crude product was ltered, concentrated at
1
6
H NMR (400 MHz, CDCl
3
): d ¼ 8.27 (d, J ¼ 9 Hz, 2H, H ), reduced pressure and puried by column chromatography on
5
4
7
9
5
.88 (d, J ¼ 9 Hz, 2H, H ), 7.86 (d, J ¼ 9 Hz, 2H, H ), 6.75 (d, J ¼ silica gel. In the rst column, a mixture toluene/hexane (1 : 1)
3
2
1
Hz, 2H, H ), 6.45 (d, J ¼ 2 Hz, 2H, H ), 6.38 (t, J ¼ 2 Hz, 1H, H ), was used as eluent in order to remove unreacted fullerene C60
.08 (s, 2H, PhCH
OCO), 4.29 (t, J ¼ 5 Hz, 2H, PhOCH
of the In the second column, a mixture of hexane/ethyl acetate (7 : 3
of the and 6 : 4) was employed to give the pure desired compound 15
aliphatic chain), 3.69–3.60 (m, 14H, CH N y OCH of the tet- (Scheme 2a). Yield: 31%. MALDI-TOF: C115 calcd: [M +
.
2
2
tetra(ethylene glycol) chain), 3.90 (t, J ¼ 7 Hz, 4H, PhOCH
2
H N O
83 3 9
2
2
+
+
ra(ethylene glycol) chain), 3.45 (s, 2H, OOCCH COO), 3.11 (s, H] 1650.90 found (m/z): [M + H] 1651.93.
2
1
3
H, CH N), 1.75–1.70 (m, 4H, PhOCH CH ), 1.45–1.38 (m, 4H,
H NMR (400 MHz, CDCl
3
) (Scheme 2a): d ¼ 7.85 (d, J ¼ 9 Hz,
3
2
2
5
4 6
PhO(CH
chain), 0.87 (t, J ¼ 7 Hz, 6H, CH
2
)
2
CH
2
), 1.33–1.24 (m, 32H, all CH
) ppm.
): d ¼ 166.21 (1C, C ), 166.06 (1C, 1H, H ), 5.43 (s, 2H, PhCH
2
of the aliphatic 2H, H ), 7.83 (d, J ¼ 8 Hz, 2H, H ), 7.48–7.38 (m, 3H, H –H), 6.75
3
2
(d, J ¼ 9 Hz, 2H, H ), 6.58 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz,
1
3
1
3
e
C NMR (100 MHz, CDCl
3
2
OCO), 4.63 (t, J ¼ 5 Hz, 2H, OOCCH
2
g
b
l
h
C ), 160.45 (2C, C ), 156.74 (1C, C ), 152.54 (1C, C ), 147.34 (1C, of the tetra(ethylene glycol) chain), 3.89 (t, J ¼ 6.50 Hz, 4H,
o
k
d
j
C ), 143.77 (1C, C ), 137.21 (1C, C ), 125.99 (2C, C ), 124.50 (2C, PhOCH
2
of the aliphatic chain), 3.83 (t, J ¼ 5, 2H, OCH
C ), 122.49 (2C, C ), 111.46 (2C, C ), 106.42 (2C, C ), 101.18 (1C, 3.62 (m, 14H, CH N y OCH of the tetra(ethylene glycol) chain),
N), 1.77–1.73 (m, 4H, PhOCH CH ), 1.43–1.25
2
), 3.68–
n
m
i
c
2
2
a
C ), 70.77–70.57, 68.74 (6C, OCH of the tetra(ethylene glycol) 3.09 (s, 3H, CH
2
3
2
2
chain), 67.08 (2C, PhOCH2 of aliphatic chain), 68.55 (1C, (m, 36H, all CH
PhCH O), 68.06 (1C, N(CH ), 64.44 (1C, COOCH
of the tet- CH ) ppm.
ra(ethylene glycol) chain), 52.17 (1C, NCH ), 41.31 (1C, C ), 39.17
1C, NCH ), 31.81, 29.56–29.19, 25.97, 22.57 (20C, all CH
aliphatic chain), 13.98 (2C, CH ) ppm.
2
of the aliphatic chain), 0.89 (t, J ¼ 7 Hz, 6H,
2
2
)
2
2
3
13
f
g
C NMR (100 MHz, CDCl
3
) (Scheme 2a): 163.46 (1C, C ),
2
e
b
h
l
(
3
2
of the 163.29 (1C, C ), 160.47 (2C, C ), 153.17 (1C, C ), 151.34 (1C, C ),
145.20, 145.16, 145.11, 144.97, 144.83, 144.63, 144.60, 144.55,
3
2
.4.6 Synthesis of (E)-3,5-bis(dodecyloxy)benzyl-2-(ethyl(4- 144.48, 144.41, 143.80, 143.78, 143.64, 143.01, 142.96, 142.89,
(
(4-nitrophenyl)diazenyl)phenyl)amino)ethyl malonate (14). 142.13, 141.85, 141.77, 140.84, 140.82, 139.34, 138.66 (fullerene
d
o
n
Procedure described for the synthesis of 9, using DR1 (0.1 g, 0.2 carbons), 136.55 (1C, C ), 129.31 (1C, C ), 128.87 (2C, C ),
j
m
i
c
mmol), DMAP (0.006 g, 0.02 mmol), 2 (0.184 g, 0.2 mmol) and 125.02 (2C, C ), 122.17 (2C, C ), 111.38 (2C, C ), 107.15 (2C, C ),
a
1
01.64 (1C, C ), 71.40 (fullerene carbon), 70.75–70.64, 68.91,
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anhydrous toluene, and DBU (0.077 g, 0.51 mmol) to obtain
compound 17 (Scheme 2c). Yield: 34%. MALDI-TOF:
+
+
C116H N O calcd: [M + H] 1680.93 found (m/z): [M + H]
85
3 10
1
681.90.
1
5
H NMR (400 MHz, CDCl
3
): d ¼ 7.82 (d, J ¼ 9 Hz, 2H, H ),
4
6
7
¼
.81 (d, J ¼ 9 Hz, 2H, H ), 6.98 (d, J ¼ 8.98 Hz, 2H, H ), 6.76 (d, J
3
2
9 Hz, 2H, H ), 6.58 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H,
1
H ), 5.43 (s, 2H, PhCH
2
OOC), 4.62 (t, J ¼ 5 Hz, 2H, OOCCH
2
of
of
the tetra(ethylene glycol) chain), 3.89 (t, J ¼ 7 Hz, 4H, PhOCH
2
the aliphatic chain), 3.82 (t, J ¼ 5 Hz, OCH ), 3.87 (s, 3H,
2
PhOCH ), 3.69–3.62 (m, 14H, CH N y OCH of the tetra(ethylene
3
2
2
glycol) chain), 3.08 (s, 3H, CH N), 1.77–1.70 (m, 4H, PhOCH -
3
2
CH
2
), 1.45–1.25 (m, 36H, all CH
) ppm.
C NMR (100 MHz, CDCl
2
of the aliphatic chain), 0.89 (t, J
¼
7 Hz, 6H, CH
3
Scheme 2
13
g
3
): d ¼ 163.47 (1C, C ), 163.31 (1C,
e
o
b
h
C ), 160.85 (1C, C ), 160.54 (2C, C ), 150.98 (1C, C ), 147.54 (1C,
l
C ), 145.24, 145.21, 145.16, 145.06, 144.88, 144.68, 144.60,
6
(
(
8.66 (7C, OCH
2C, PhOCH
1C, NCH ), 52.15 (1C, C ), 39.24 (1C, NCH
6.10, 22.67 (20C, CH2 of the aliphatic chain), 14.12 (2C,
CH ) ppm.
2
of the chain tetra(ethylene glycol) chain), 68.53
1
1
1
1
7
44.54, 144.46, 143.85, 143.06, 143.00, 142.18, 141.90, 141.83,
d
2
of the aliphatic chain), 68.11 (1C, PhCH
2
O), 66.18
40.89, 139.38, 138.71 (fullerene carbons), 136.61 (1C, C ),
f
), 31.90, 29.67–29.26,
j
m
n
i
2
3
24.60 (2C, C ), 123.83 (2C, C ), 114.10 (2C, C ), 111.50 (2C, C ),
2
c
a
07.26 (2C, C ), 101.78 (1C, C ), 71.50 (fullerene carbon), 70.77–
0.70, 68.71 (6C, OCH of the tetra(ethylene glycol) chain), 68.96
of the aliphatic chain), 68.63 (1C, PhCH O), 68.20 (1C,
of the tetra(ethylene glycol) chain), 66.23 (1C, NCH ),
), 31.93, 29.70–
9.31, 26.13, 22.69 (20C, all CH of the aliphatic chain), 14.11
3
2
2
.5.2 Synthesis of the fullerene C60-amino-butyl substituted
azobenzene (16). Procedure employed for the synthesis of 15,
using 10 (0.091 g, 0.1 mmol), I (0.023 g, 0.1 mmol), fullerene C60
0.066 g, 0.1 mmol) dissolved in 70 mL of anhydrous toluene, and
DBU (0.046 g, 0.3 mmol), to obtain compound 16 (Scheme 2b).
(PhOCH
2
2
OOCCH
2
2
f
2
3 3
55.50 (1C, OCH ), 52.26 (1C, C ), 39.21 (1C, NCH
(
2
2
(2C, CH ) ppm.
3
+
Yield: 40%. MALDI-TOF: C119
found (m/z): [M + H] 1708.59.
H N O
91 3 9
calcd: [M + H] 1707.01
2
.5.4 Synthesis of the fullerene C -amine-cyano substituted
60
+
azobenzene (18). Procedure employed for the synthesis of 15,
using 12 (0.19 g, 0.21 mmol), I (0.052 g, 0.21 mmol), fullerene C60
0.148 g, 0.21 mmol) dissolved in 150 mL of anhydrous toluene,
and DBU (0.103 g, 0.68 mmol) to yield product 18 (Scheme 2d).
1
5
H NMR (400 MHz, CDCl ): d ¼ 7.83 (d, J ¼ 9 Hz, 2H, H ),
3
2
4
6
7
9
5
.75 (d, J ¼ 8 Hz, 2H, H ), 7.27 (d, J ¼ 7 Hz, 2H, H ), 6.75 (d, J ¼
(
3 2 1
Hz, 2H, H ), 6.58 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ),
.43 (s, 2H, PhCH
2
OOC), 4.62 (t, J ¼ 5 Hz, 2H, OOCCH
2
of the
of the
+
Yield: 34%. MALDI-TOF: C116
found (m/z): [M + H] 1676.83.
H N O
82 4 9
calcd: [M + H] 1675.91
tetra(ethylene glycol) chain), 3.89 (t, J ¼ 6 Hz, 4H, PhOCH
aliphatic chain), 3.83 (t, J ¼ 5 Hz, OCH
CH N y OCH of the tetra(ethylene glycol) chain), 3.09 (s, 3H,
2
+
), 3.69–3.62 (m, 14H,
1
5
2
H NMR (400 MHz, CDCl ): d ¼ 7.88 (d, J ¼ 9 Hz, 2H, H ),
3
4
6
2
2
7
9
.86 (d, J ¼ 9 Hz, 2H, H ), 7.73 (d, J ¼ 8 Hz, 2H, H ), 6.76 (d, J ¼
CH N), 2.67 (t, J ¼ 8 Hz, 2H, PhCH ), 1.77–1.70 (m, 4H,
3
2
3
2
Hz, 2H, H ), 6.58 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H,
1
PhOCH CH ), 1.67–1.60 (m, 2H, Ph(CH ) ), 1.42–1.25 (m, 38H,
2
2
2 2
H ), 5.43 (s, 2H, PhCH
the tetra(ethylene glycol) chain), 3.90 (t, J ¼ 6 Hz, 4H, PhOCH
), 3.68–3.62 (m,
of the tetra(ethylene glycol) chain), 3.12 (s,
H, CH N), 1.78–1.68 (m, 4H, PhOCH CH ), 1.45–1.25 (m,
2
OOC), 4.62 (t, J ¼ 6 Hz, 2H, OOCCH
2
of
Ph(CH
H, CH
2
)
3
and all CH
), 0.89 (t, J ¼ 6 Hz, 3H, Ph(CH
2
of the aliphatic chain), 0.95 (t, J ¼ 7 Hz,
2
6
3
2 3
)CH ) ppm.
of the aliphatic chain), 3.83 (t, J ¼ 5 Hz, OCH
2
1
3
g
C NMR (100 MHz, CDCl
3
): d ¼ 163.46 (1C, C ), 163.31 (1C,
1
3
3
2 2
4H, CH N y OCH
e
b
h l
C ), 160.54 (2C, C ), 151.46 (1C, C ), 151.18 (1C, C ), 144.67 (1C,
C ), 143.84 (1C, C ), 145.24, 145.20, 145.15, 145.05, 145.02,
3
2
2
o
k
6H, all CH2 of the aliphatic chain), 0.89 (t, J ¼ 6 Hz, 6H,
1
1
1
1
44.87, 143.05, 143.00, 142.17, 141.89, 141.82, 140.88, 139.37,
38.71 (fullerene carbons), 136.60 (1C, C ), 128.91 (2C, C ),
24.82 (2C, C ), 122.16 (2C, C ), 111.46 (2C, C ), 107.24 (2C, C ),
01.77 (1C, C ), 71.49 (fullerene carbon), 70.76–70.69, 68.94 (6C,
CH ) ppm.
3
13
d
n
g
C NMR (100 MHz, CDCl
3
): d ¼ 163.47 (1C, C ), 163.33 (1C,
m
j
i
c
e
b
l
h
C ), 160.48 (2C, C ), 149.98 (1C, C ), 147.83 (1C, C ), 145.21,
a
1
1
1
1
45.17, 145.13, 144.99, 144.84, 144.65, 144.58, 144.43, 143.80,
42.97, 142.91, 142.15, 141.86, 141.78, 140.86, 140.83, 139.36,
36.56 (fullerene carbons), 129.33 (1C, C ), 128.90 (2C, C ),
OCH
2
of the tetra(ethylene glycol) chain) 68.52 (PhOCH
), 68.18 (1C, PhCH O), 66.22
), 52.23 (1C, C ), 39.22 (1C, NCH ), 35.49 (1C, PhCH ),
3.49 (1C, PhCH CH ), 31.92, 29.69–29.30, 26.13, 22.68 (20C, all
of the aliphatic chain), 22.33 (1C, Ph(CH CH ), 14.11 (2C,
2
of the
aliphatic chain), 68.61 (1C, PhOCH
2
2
d
n
f
(1C, NCH
2
3
2
m
j
o
25.03 (2C, C ), 122.18 (2C, C ), 118.01 (1C, C ), 111.39 (2C,
3
CH
2
2
i
c
a
PhCN), 111.34 (1C, C ), 107.18 (2C, C ), 101.66 (1C, C ), 72.87
fullerene carbon), 70.76–70.66, 68.67 (6C, OCH of the tetra(-
2
2
)
2
2
(
2
CH ), 13.93 (1C, Ph(CH ) CH ) ppm.
3
2 3
3
ethylene glycol) chain) 68.44 (2C, PhOCH
chain), 68.93 (1C, PhCH O), 68.54 (1C, PhCH
OOCCH of the tetra(ethylene glycol) chain), 66.19 (1C, NCH
2.16 (1C, C ), 39.25 (1C, NCH
20C, all CH of the aliphatic chain), 14.13 (2C, CH
2
of the aliphatic
O), 68.12 (1C,
),
), 31.91, 29.68–29.27, 26.11, 22.68
) ppm.
2
.5.3 Synthesis of the fullerene C -amino-methoxy
60
2
2
substituted azobenzene (17). Procedure employed for the
synthesis of 15, using 11 (0.149 g, 0.15 mmol), I (0.039 g, 0.15
mmol), fullerene C60 (0.11 g, 0.15 mmol) dissolved in 110 mL of
2
2
f
2
5
(
3
2
3
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2
.5.5 Synthesis of the fullerene C60-amino-nitro substituted (14C, all CH
azobenzene (19). Procedure employed for the synthesis of 15, 22.68 (2C, CH
using 13 (0.153 g, 0.15 mmol), I (0.039 g, 0.15 mmol), fullerene
60 (0.113 g, 0.15 mmol) dissolved in 120 mL of anhydrous
2
of the aliphatic chain), 26.10 (2C, PhO(CH
2 3
) ),
CH ), 14.13 (2C, CH ), 12.29 (1C, NCH CH ) ppm.
3
2
3
2
3
2
C
3
Results and discussion
toluene, and DBU (0.078 g, 0.51 mmol) to give the desired
compound 19 (Scheme 2e). Yield: 69%. MALDI-TOF: 3.1 Synthesis of the fullerene C60-azobenzene derivatives
+
+
C115H N O calcd: [M + H] 1695.90 found (m/z): [M + H]
82
4
11
60
Generally, the synthesis of the fullerene C -azobenzene deriv-
atives was carried out according to the synthetic sequence
illustrated in Fig. 1. Six different substituted azobenzenes
1
696.85.
1
6
H NMR (400 MHz, CDCl
3
): d ¼ 8.32 (d, J ¼ 9 Hz, 2H, H ),
5
4
7
9
5
.91 (d, J ¼ 9 Hz, 2H, H ), 7.88 (d, J ¼ 9 Hz, 2H, H ), 6.77 (d, J ¼
(amino, amino-butyl, amino-methoxy, amino-cyano, amino-
3
2
1
Hz, 2H, H ), 6.58 (d, J ¼ 2 Hz, 2H, H ), 6.40 (t, J ¼ 2 Hz, 1H, H ),
nitro, DR1) (3, 4, 5, 6, 7 and 8) bearing different dipole
moment values were prepared and incorporated into
a substituted malonate containing a phenyl group with
aliphatic chains, to give the corresponding precursor
compounds (9, 10, 11, 12, 13 and 14). The last step consisted on
the incorporation of fullerene C60 into the precursor malonates
by means of a Bingel reaction to give six different fullerene C -
azobenzene derivatives (15, 16, 17, 18, 19 and 20).
Precursor substituted azobenzenes 4, 5, and 7 have been
prepared according to the method previously reported by us,
whereas substituted azobenzenes 3 and 6 were synthesized
using a similar procedure. Intermediate 2-(2-{2-[2-(methyl-
phenyl-amino)-ethoxy]-ethoxy}-ethoxy)-ethanol was prepared
according to our method previously reported in the literature
and the diazonium salts were prepared in situ. Aniline (1 eq.)
.43 (s, 2H, PhCH
2
OCO), 4.63 (t, J ¼ 5 Hz, 2H, PhOCH
2
of the
2
of the
tetra(ethylene glycol) chain), 3.89 (t, J ¼ 7 Hz, 4H, PhOCH
aliphatic chain), 3.83 (t, J ¼ 5 Hz, OCH ), 3.69–3.62 (m, 14H,
2
CH N and OCH of the tetra(ethylene glycol) chain), 3.13 (s, 3H,
2
2
CH N), 1.76–1.70 (m, 4H, PhOCH CH ), 1.45–1.37 (m, 4H,
PhO(CH
chain), 0.89 (t, J ¼ 7 Hz, 6H, CH
3
2
2
2
)
2
CH
2
), 1.35–1.25 (m, 32H, all CH
) ppm.
2
of the aliphatic
6
0
3
1
3
e
C NMR (100 MHz, CDCl
3
): d ¼ 163.45 (1C, C ), 163.30 (1C,
g
b
l
h
C ), 160.56 (2C, C ), 156.83 (1C, C ), 152.55 (1C, C ), 147.44 (1C,
C ), 145.24, 145.23, 145.17, 145.04, 145.01, 144.88, 144.69,
30,33
o
1
1
1
1
44.64, 144.59, 144.46, 143.84, 143.06, 143.01, 142.95, 142.18,
41.90, 141.81, 140.88, 139.36, 138.71 (fullerene carbons),
36.59 (1C, C ), 126.12 (2C, C ), 124.65 (2C, C ), 122.60 (2C, C ),
11.54 (2C, C ), 107.27 (2C, C ), 101.75 (1C, C ), 71.49 (fullerene
of the tetra(ethylene
of the aliphatic chain), 68.62
O), 68.20 (1C, COOCH ), 66.20 (1C, NCH ), 52.25
1C, C ), 39.35 (1C, NCH ), 31.92, 29.69–29.30, 26.13, 22.68 (20C,
23
d
j
n
m
i
c
a
carbon), 70.85–70.71, 68.72 (6C, OCH
glycol) chain), 68.96 (2C, PhOCH
2
ꢂ
was reacted with NaNO (1 eq.) in an HCl solution (30%) at 0 C.
2
2
Aerwards, 2-(2-{2-[2-(methyl-phenyl-amino)-ethoxy]-ethoxy}-
ethoxy)-ethanol (1 eq.) was added dropwise to the reaction
mixture in order to obtain the amino substituted azobenzene (3)
with 68% yield. Similarly, the diazonium salt of 4-cyanoaniline
was used to give the corresponding amino-cyano substituted
azobenzene (ESI†).
Dendron GIOH (1) (1 eq.) was treated in the presence of
Meldrum's acid (1 eq.) to afford the monosubstituted malonic
ester (2). This intermediate was further reacted with interme-
diate (3) in the presence of N,N-dimethyl-4-aminopyridine
(
(
1C, PhCH
2
2
2
f
3
all CH of the aliphatic chain), 14.10 (2C, CH ) ppm.
30
2
3
2.5.6 Synthesis of the fullerene C -DR1 (20). Procedure
60
employed for the synthesis of 15, using 14 (0.1094 g, 0.13
mmol), I (0.032 g, 0.13 mmol) and fullerene C60 (0.091 g, 0.13
mmol) were dissolved in 100 mL of anhydrous toluene and DBU
2
(
(
0.006 g, 0.038 mmol) to obtain the desired compound 20
Scheme 2f). Yield: 70%. MALDI-TOF: C110
H
72
N
4
O
8
calcd: [M +
+
+
H] 1577.77 found (m/z): [M + H] 1578.47.
(DCC) and N,N-dimethyl-4-aminopyridine (DMAP) in dry
1
6
H NMR (400 MHz, CDCl ): d ¼ 8.30 (d, J ¼ 9 Hz, 2H, H ),
3
dichloromethane to give the azobenzene containing disubsti-
tuted malonic ester (9). Finally, this compound was reacted with
fullerene C , iodine and 1,8-diazabicyclo[5.4.0]undec-7-ene
5
4
7
9
5
3
6
.88 (d, J ¼ 7 Hz, 2H, H ), 7.87 (d, J ¼ 7 Hz, 2H, H ), 6.83 (d, J ¼
3 2 1
Hz, 2H, H ), 6.60 (d, J ¼ 2 Hz, 2H, H ), 6.41 (t, J ¼ 2 Hz, 1H, H ),
.41 (s, 2H, PhCH CH OCO),
OCO), 4.68 (t, J ¼ 6 Hz, 2H, NCH
.89 (t, J ¼ 7 Hz, 4H, PhOCH of the aliphatic chain), 3.79 (t, J ¼
Hz, 2H, CH CH NCH ), 3.57–3.51 (m, 2H, OCOCH CH
), 1.76–1.68 (m, 4H, PhOCH CH ), 1.43–1.36 (m, 4H,
PhO(CH CH ), 1.34–1.24 (m, 35H, all CH of the aliphatic
chain and NCH CH ), 0.89 (t, J ¼ 6 Hz, 6H, CH ) ppm.
6
0
2
2
2
(DBU) in anhydrous toluene to give the corresponding
2
fullerene C -azobenzene derivative (15). The other fullerene
6
0
3
2
2
2
2
-
C
60-azobenzene systems were obtained according to the same
NCH
2
2
2
synthetic method, under the same reaction conditions
described above. In the same manner, compounds (10), (11),
(12), (13) and (14) were reacted under the Bingel reaction
conditions to give the corresponding fullerenes C -azobenzene
2
)
2
2
2
2
3
3
1
3
e
C NMR (100 MHz, CDCl ): d ¼ 163.35 (1C, C ), 163.18 (1C,
3
6
0
g
b
l
h
C ), 160.53 (2C, C ), 156.63 (1C, C ), 151.20 (1C, C ), 147.40 (1C,
C ), 145.21, 145.18, 145.11, 144.89, 144.83, 144.59, 144.56,
derivatives (16), (17), (18), (19) and (20), respectively (Fig. 1).
o
1
1
44.43, 143.99, 143.79, 143.76, 142.98, 142.86, 142.80, 142.11,
42.08, 141.81, 141.69, 140.78, 140.75, 139.21, 138.60 (fullerene
3
.2 Characterization of the fullerene C -azobenzenes
60
d
n
j
derivatives
carbons), 136.47 (1C, C ), 126.47 (2C, C ), 124.61 (2C, C ), 122.63
m
i
c
a
(
(
2C, C ), 111.56 (2C, C ), 107.33 (2C, C ), 101.52 (1C, C ), 71.18 The precursor disubstituted malonic azo-dyes and their corre-
fullerene carbon), 68.95 (1C, PhCH O), 68.15 (2C, PhOCH ), sponding fullerene C60-azobenzene derivatives were fully char-
2
2
f
1
13
6
3.96 (1C, NCH CH O), 51.59 (1C, C ), 48.23 (1C, CH CH - acterized by H and C NMR spectroscopies. The molecular
2 2 3 2
NCH ), 45.34 (1C, NCH ), 31.91 (2C, CH (CH ) ), 29.68–29.25 weights and purity of the nal products were conrmed by
2
2
3
2 2
MALDI-TOF mass spectrometry using dithranol as matrix.
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1
f
For instance, in the H NMR spectrum of compound 9 corresponding to carbons (PhCH
Fig. 2a), we observe six signals in the aromatic region at 7.87, respectively, were also observed. Finally, the signals due to all
.84, 7.47–7.37, 6.75, 6.47 and 6.41 ppm, due to the aromatic the CH and CH present in the aliphatic chains appeared at
2 2 3
O), (NCH ), (C ) and (NCH ),
(
7
2
3
protons present in the azobenzene unit and the phenyl group, 31.90, 29.67–29.26, 26.10, 22.67, and 14.12 ppm.
5
4
6
3
2
1
13
corresponding to H , H , H –H, H , H and H , respectively. In
the aliphatic zone, we can see a singlet at 5.09 (PhCH OCO), and derivative 15, the signals of the aromatic rings did not show any
two triplets at 4.29 (OOCCH ) and 3.92 ppm (PhOCH ). In signicant chemical shi with respect to its precursor
addition, we perceive a multiplet at 3.68–3.59 ppm related to the compound 9 (Fig. 3). However, we observe the appearance of the
In the C NMR spectrum of fullerene C60-azobenzene
2
2
2
2
2
protons OCH of the oligo(ethylene glycol) segments, as well as signals arising from the fullerene C60 sp carbons at 145.20,
two singlets at 3.46 and 3.07 ppm due to the a protons of the 145.16, 145.11, 144.97, 144.83, 144.63, 144.60, 144.55, 144.48,
malonate (OOCCH COO) and the methyl group (NCH ), 144.41, 143.80, 143.78, 143.64, 143.01, 142.96, 142.89, 142.13,
2
3
respectively. Finally, the protons corresponding to methylenes 141.85, 141.77, 140.84, 140.82, 139.34, and 138.66 ppm. Mean-
CH ) present in the aliphatic chain appear at 1.80–1.71, 1.46– while, in the aliphatic region, we can notice an additional signal
.39, 1.36–1.27 and 0.90 ppm.
(
1
2
3
of the fullerene C60 sp carbons and the carbon a to the carbonyl
1
f
In the H NMR spectrum of fullerene C60-azobenzene group (C ) at 71.40 and 52.15 ppm, respectively.
derivative 15, the chemical shis of the protons are very similar The structure and purity of these compounds were
Fig. 2b). As we can notice, the signal due to the a protons of the conrmed by MALDI-TOF mass spectrometry. All fullerene C60
(
-
malonate (OOCCH COO), previously observed at 3.46 ppm, azobenzene derivatives showed the expected molecular ion
2
totally disappeared. This is an indication that the Bingel peaks, which are in agreement with the calculated molecular
1
3
coupling reaction between the fullerene C60 and the precursor weights. The C NMR the fullerene-azobenzene derivatives re-
malonic azo-dye successfully occurred. ported here can be found in the ESI.†
1
3
On the other hand, in the aromatic region of the C NMR
spectrum of the malonic azo-dye 9, there are 14 signals at
3
.3 Optical properties of the fullerene C -azobenzene
60
1
1
63.46, 163.29, 160.47, 153.17, 151.34, 143.78, 136.55, 129.31,
28.87, 125.02, 122.17, 111.38, 107.15, 101.64 ppm, assigned to
derivatives
the aromatic carbons of the phenyl groups present in the The optical properties of the fullerene C -azobenzene deriva-
6
0
structure. Moreover, in the aliphatic region, we observe various tives were studied by absorption spectroscopy in the UV-vis
signals at 70.75–70.64, 68.91, 68.66 ppm due to the methylenes region; the results are summarized in Tables 1 and 2. The
present in the tetra(ethylene glycol) spacers. In addition, the absorption spectra of the precursor malonic azo-dyes without
carbons PhOCH
2
3
of the aliphatic chain appear at 68.53. Four fullerene were recorded in CHCl , MeOH and DMF solution,
more signals at 68.11, 66.18, 52.15 and 32.24 ppm, whereas those of the fullerene C -azobenzene derivatives were
6
0
3
carried out in CHCl and DMF.
The absorption spectra of the precursor malonic azo-dyes
without fullerene were normalized for a better comparison. As
we can notice, the absorption spectra of compounds 9, 10 and 11,
in CHCl solution, showed a maximum absorption band at l
¼
3
max
410 nm followed by red-shied shoulder at 421 nm due to the p–
p* and n–p* transitions, respectively. These compounds have
a low dipole moment value and belong to aminoazobenzenes
18,19
category, according to Rau's classication.
By contrast,
1
13
Fig. 2 H NMR spectra in CDCl
3
: (a) precursor malonic azo-dye 9, (b) Fig. 3
C NMR spectra of fullerene C60-azobenzene derivative 15 in
fullerene C60-azobenzene derivative 15.
3
CDCl .
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Table 1 Optical properties of the precursor malonic azo-dyes
CHCl
3
DMF
max (nm)
MeOH
max (nm)
Compound
l
max (nm)
Cut off (nm)
l
Cut off (nm)
l
Cut off (nm)
9
410
410
410
448
478
468
528
528
528
562
596
584
418
418
418
462
496
490
530
530
530
574
628
632
410
410
410
450
478
478
428
428
428
568
610
610
1
1
1
1
1
0
1
2
3
4
Table 2 Optical properties of the fullerene C60-azobenzene derivatives
%
photoisomerization
b
a
Compound
CHCl
3
lmax (nm)
DMF lmax (nm)
yield cis isomer Dabs /Dabs
Film lmax (nm)
15
16
17
18
19
20
408
408
408
446–450
480
416
416
416
462
492–494
488
6.4
3
15.5
—
—
—
408
408
408
446
480
476
470–472
a
b
Absorbance of the precursor malonic azo-dyes. Absorbance of the fullerene C60-azobenzene system.
compounds 12, 13 and 14 exhibited well dened absorption
bands at 448, 478 and 468 nm, respectively (Fig. 4a). These benzene derivatives, we noticed that in CHCl
Regarding the optical properties of the fullerene C60-azo-
solution the
3
compounds possess high dipole moment values and belong to the absorption band of compounds 15, 16 and 17 (low dipole
pseudostilbenes category, so that they exhibit a total overlap of the moment) are blue-shied by 2 nm with respect to their
p–p* and n–p* bands in other words, only one absorption band precursor malonic azo-dyes without fullerene (Table 2). These
1
8,19
can be observed in the UV-vis spectra.
However, the absorption compounds exhibited a maximum absorption band at lmax
¼
bands of these compounds in MeOH solution did not show any 408 nm with a red-shied shoulder at 422 nm arising from the
signicant red shi. On the contrary, compound 14 showed a red- p–p* and n–p* transitions, respectively. In addition, we note
shi of 10 nm in its absorption band with respect to that observed the presence of a blue-shied shoulder at 394 nm, which reveals
in CHCl
was observed. Compounds having low dipole moments (9, 10 and compounds bearing high dipole moment values (18, 19, 20)
1) showed a red-shi of 8 nm in their adsorption bands, whereas show adsorption bands at 448, 480 and 472 nm, respectively.
3
(Table 1), and in DMF a signicant solvatochromic effect the presence of H-aggregates (Fig. 5). Alternatively, azo-
1
compounds bearing high dipole moments (12, 13 and 14)
exhibited red-shis of 14, 18 and 22 nm, respectively (Fig. 4b,
Table 1). On the other hand, malonic azo-dyes bearing NO
acceptor group (13, 14) exhibited a maximum absorption band at
max ¼ 478 nm in MeOH solution, showing slight shis of 10 and
nm in CHCl and DMF solution, respectively (Table 1).
2
as
l
6
3
Fig. 4 Normalized absorption spectra of the precursor azo-dyes: (a) in Fig. 5 Absorption spectra of the fullerene C60-azobenzene derivatives
CHCl , and (b) in DMF solution. in CHCl solution.
3
3
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These compounds exhibited also a blue-shied shoulder at
4
32 nm, which indicates the presence of H-aggregation (Fig. 5,
36
Table 2).
As well, the optical properties of fullerene C -azobenzene
6
0
derivatives were studied in DMF solution (ESI, Fig. S6†). These
hybrid systems having low dipole moments (15, 16, 17) exhibi-
ted a maximum absorption band which is 8 nm red-shied with
respect to the absorption value in CHCl
3
solution. However,
fullerene 60-azobenzene derivatives bearing high dipole
C
Fig. 7 Absorption spectra upon irradiation with UV light at 365 nm for
moment values (18, 19 and 20) showed maximum absorption
bands at lmax ¼ 462, 492–494, 488, respectively. They also
exhibited a blue-shied shoulder at 428 nm, which can be due
1
0 minutes: (a) precursor azo-dyes 9, 10 and 11, (b) fullerene C60
-
ꢁ4
azobenzene derivatives 15, 16 and 17 (Conc. 2.5 ꢀ 10 M in DMF at
room temperature).
36
to intramolecular azobenzene–fullerene interactions.
3.4 Protonation effect upon irradiation
365 nm for 10 min. Aer this time, we noticed that the intensity
We decided to study the photoprotonation effect on the series of of the absorption band as well as the extinction molar coeffi-
azo-dyes containing rst generation Fr ´e chet type dendrons. In cient of compounds 9, 10 and 11 decreased, due to the photo-
these compounds, the formation of an azo-hydrazone via isomerization from the trans (E) to the cis (Z) isomer. Moreover,
tautomerism can be induced by irradiating with UV light at in the UV region of the absorption spectrum of these
29,37
254 nm.
Particularly, we investigated the photoprotonation compounds there is a shoulder at 450 nm, related to the n–p*
effect of the fullerene C60-azobenzene derivatives 15 and 19, transition of the cis isomer (Fig. 7a). Meanwhile, in the
having the lowest and the highest dipole moment value, respec- absorption spectra of the fullerene C60-azobenzenes derivatives
tively. Aer irradiation with UV light for 140 s, compound 15 15, 16 and 17 the intensity of the bands did not vary signi-
reached a photostationary state (PPS). However, over time we cantly (Fig. 7b). The photoisomerization yield in these
noticed that absorption band at 410 nm decreases drastically in compounds depends in large measure on the donor/acceptor
intensity and two new absorption bands appear in the visible character of the substituents present in the azobenzene units
region at 524 nm and 546 nm, respectively; the isobestic point (Table 2). Fullerene C60-azobenzene derivative 17 exhibited
was located at 430 nm (Fig. 6a). Similarly, fullerene C60-azo- a photoisomerization yield of 13%, which can attributed to the
3
benzene derivative 19, bearing a high dipole moment value, electron-donor effect of the (OCH ) group. Finally, compounds
exhibited the same photochromic effect as its homologue with 15 and 17 bearing low dipole moment values exhibited
low dipole moment 15. Upon irradiation the absorption band at
480 nm decreased drastically in intensity and the appearance of
two additional bands at 520 and 552 nm was observed; in this
case the isosbestic point was situated at 500 nm (Fig. 6b). This
fullerene C60-azobenzene system reached a photostationary state
(PPS) aer irradiation for 600 s. From these results, we can
remark that the photochromic behavior of this azo-dye was not
perturbed at all by the incorporation of the fullerene unit (Fig. 8).
3.5 trans–cis photoisomerization
Photoisomerization experiments were performed with the
samples in DMF solution, which were irradiated with UV light at
Fig. 6 Photoprotonation effect of [60] fullerene C60-azobenzene
derivatives irradiated with UV light at 254 nm: (a) derivative 15, and (b) Fig. 8 Photoisomerization and photoprotonation of C60-azobenzene
ꢁ4
derivative 19 (Conc. 2.5 ꢀ 10 M in CHCl
3
at room temperature).
derivative 19.
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at 410 nm, jointly with the appearance of a shoulder at 450 nm
due to the n–p* transition of the cis isomer (Fig. 10a). On the
contrary, when the fullerene C -azobenzene derivatives (15, 16,
6
0
17) were irradiated with UV light for 10 minutes, the absorption
bands did not change at all (Fig. 10b). This is certainly due to
a quenching of the photoisomerization process by the presence
of the fullerene unit in these derivatives.
4
Conclusions
Six different fullerene C60-azobenzene derivatives (15, 16, 17, 18,
9 and 20) were successfully synthesized and fully characterized
1
1
13
by H, C NMR and MALDI-TOF. The optical properties of the
fullerene C60-azobenzene dyes were studied by UV-vis spec-
troscopy and compared to those of their precursor malonic azo-
dyes without fullerene (9, 10, 11, 12, 13 and 14).
Fig. 9 Absorption spectra of fullerene C60-azobenzene derivatives 19
in CHCl , DMF and cast film.
3
Fullerene C60-azobenzene derivatives bearing low dipole
moment (15, 16 and 17) in CHCl
3
exhibited a maximum
absorption band at lmax ¼ 408 nm and a shoulder at 422 nm due
to p–p* and n–p* transitions, respectively. The presence of
a blue-shied shoulder at 394 nm revealed the presence of H-
photoisomerization yields of 6.4 and 3.0%, respectively (Table
). These low yields are due to the fact that the fullerene C60
strongly absorb in the UV region, which causes a partial
quenching the photoisomerization process (Fig. 8).
2
aggregates. Fullerene
C60-azobenzene derivatives bearing
a high dipole moment (18, 19 and 20) showed maximum
absorption bands between 448 and 472 nm; the presence of H-
aggregates was also detected.
3.6 Optical properties and trans–cis photoisomerization in
The photoprotonation effect in the fullerene C60-azobenzene
derivatives 15 and 19, having the lowest and the highest dipole
moment, respectively, was studied by absorption spectroscopy.
Compound 15 (lowest dipole moment) reached a photosta-
tionary state (PPS). The absorption band at 410 nm decreased
drastically in intensity and two absorption bands appeared at
cast lms
The optical properties of the fullerene C60-azobenzenes deriva-
tives were also studied in cast lms, and the results are
summarized in Table 2. The normalized absorption spectra of
the fullerene C60-azobenzene derivative 19 in CHCl , DMF and
3
cast lm are shown in Fig. 9. As we can see, the absorption band
in a cast lm did not show any signicant shi with respect to
the absorption band observed in CHCl solution. However, in
DMF this absorption band was red-shied by 8 nm, and we note
a shoulder at 524 nm due to the presence of J-aggregates,
followed by two discrete shoulders at 580 and 702 nm, respec-
tively (Table 2).
524 and 546 nm. Compound 19 (highest dipole moment)
behaved similarly and exhibited the same photochromic effect.
It was found that the photoprotonation behavior of these azo-
dyes was not perturbed by the incorporation of the fullerene
unit.
Photoisomerization experiments were performed with the
precursor dyes with low dipole moment (9, 10 and 11) in DMF
solution. A typical trans–cis photoisomerization behavior was
observed. The absorption band at 410 nm decreased in intensity
and a shoulder at 450 nm due to the n–p* transition (cis isomer)
appeared. On the contrary, in the UV-vis spectra of the fullerene
3
28
38
On the other hand, photoisomerization experiments were
carried out in cast lm samples. The precursor malonic azo-
dyes without fullerene bearing low dipole moments (9, 10 and
11) exhibited trans–cis photoisomerization when they were
irradiated with UV light at 365 nm for 10 minutes. Aer this
time, we noticed a decrease in intensity of the absorption band
C
60-azobenzenes derivatives (15, 16 and 17) the intensity of the
bands did not vary remarkably. It was found that the presence of
the fullerene moiety drastically decreases the photo-
isomerization yield because of a strong quenching effect.
The optical properties of the fullerene C60-azobenzenes
derivatives were also studied in cast lms, where the presence of
J-aggregates was detected. Malonic azo-dyes without fullerene
(9, 10 and 11) exhibited typical trans–cis photoisomerization,
whereas the fullerene C60-azobenzene derivatives (15, 16, 17)
did not since the fullerene moiety acts as quencher.
Acknowledgements
Fig. 10 Absorption spectrum in casted film of: (a) precursor azo-dye
We are grateful to Miguel Angel Canseco for his assistance with
UV-vis spectroscopy and Gerardo Cedillo for his help with H
9
, (b) fullerene C60-azobenzene derivative 15, after irradiation for 10
1
minutes.
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1
3
and C NMR spectroscopy. This project was nancially sup- 16 S. Ma, H. Ting, L. Zhang, Y. Ma, L. Zheng, L. Xiao and
ported by PAPIIT (Project IN-100316) and CONACyT (Projects
53155 and 222847).
Z. Chen, Reversible photoinduced bi-state polymer solar
cells based on fullerene derivatives with azobenzene
groups, Org. Electron., 2015, 23, 1–4.
2
1
7 M. Wang, E. Chesnut, Y. Sun, M. Tong, M. Guide, Y. Zhang,
D. N. Treat, A. Varotto, A. Mayer, L. M. Chabinyc,
T.-Q. Nguyen and F. Wudl, PCBM Disperse-Red Ester with
Strong Visible-Light Absorption: Implication of Molecular
Design and Morphological Control for Organic Solar Cells,
J. Phys. Chem. C, 2012, 116, 1313–1321.
References
1
H. W. Kroto, A. W. Allaf and S. P. Balm, C :
60
Buckminsterfullerene, Chem. Rev., 1991, 91, 1213–1235.
2
B. C. Thompson and J. M. J. Fr ´e chet, Organic Photovoltaics
Polymer–Fullerene Composite Solar Cells, Angew. Chem.,
Int. Ed., 2008, 47, 58–77.
18 H. Rau, in Photochemistry and Photophysics, ed. J. K. Rabek,
3
D. M. Guldi and N. Martin, Fullerenes: From Synthesis to
CRC Press. Boca Raton, Florida, 1990, vol. 2, p. 119.
Optoelectronic Properties, Kluwer Academic Publishers, 19 A. Natansohn and P. Rochon, Photoinduced Motions in Azo
Dordrecht, The Netherlands, 2002. Containing Polymers, Chem. Rev., 2002, 102, 4139–4176.
F. Wudl, Fullerene materials, J. Mater. Chem., 2002, 12, 1959– 20 T. Todorov, L. Nikalova and N. Tomova, Polarization
4
5
1963.
Holography. 1: A new high-efficiency organic material with
reversible photoinduced birefringence, Appl. Opt., 1984, 23,
4309–4312.
A. M. L ´o pez, A. Mateo-Alonso and M. Prato, Materials
chemistry of fullerene C60 derivatives, J. Mater. Chem.,
2
011, 21, 1305–1318.
21 S. Xie, A. Natansohn and P. Rochon, Recent Developments in
Aromatic Azo Polymers Research, Chem. Mater., 1993, 5,
403–411.
6
7
M. Parto, [60] Fullerene chemistry for materials science
applications, J. Mater. Chem., 1997, 7, 1097–1109.
F. Wudl, The Chemical Properties of Buckminsterfullerene 22 N. K. Viswanathan, D. Y. Kim, S. Bian, J. Williams, W. Liu,
(
C ) and the Birth and Infancy of Fulleroids, Acc. Chem.
L. Li, L. Samuelson, J. Kumar and S. K. Tripathy, Surface
relief structures on azo polymer lms, J. Mater. Chem.,
1999, 9, 1941–1955.
6
0
Res., 1992, 25, 157–161.
S. A. Backer, K. Sivula, D. F. Kavulak and J. M. J. Fr ´e chet,
8
9
High Efficiency Organic Photovoltaics Incorporating a New 23 E. Rivera, M. Bellet ˆe te, A. Natansohn and G. Durocher,
Family of Soluble Fullerene Derivatives, Chem. Mater.,
007, 19, 2927–2929.
N.-X. Wang, C. H. Sun and W. Liu, Synthesis of fullerene
Synthesis, characterization, and optical properties of
a novel azo-dye bearing an oligo(ethylene glycol) methyl
ether side chain in solution and in the solid state, Can. J.
Chem., 2003, 81, 1076–1082.
2
azobenzene derivatives, Fullerene Sci. Technol., 2001, 9,
4
29–432.
24 E. Rivera, M. P. Carre ´o n-Castro, I. Buend ´ı a and G. Cedillo,
Optical properties and aggregation of novel azo-dyes
bearing an end-capped oligo(ethylene glycol) side chain in
solution, solid state and Langmuir–Blodgett lms, Dyes
Pigm., 2006, 68, 217–226.
1
0 K.-Y. Kay, K. J. Han, Y. J. Yu and Y. D. Park, Dendritic
fullerenes (C60) with Photoresponsive Azobenzene Groups,
Tetrahedron Lett., 2002, 43, 5053–5056.
1
1 D. I. Schuster, K. Li, D. M. Guldi, A. Palkar, L. Echegoyen,
C. Stanisky, R. J. Cross, M. Niemi, N. V. Tkachenko and 25 E. Rivera, M. P. Carre ´o n-Castro, L. Rodriguez, G. Cedillo,
H. Lemmetyien, Azobenzene-linked porphyrin fullerene
dyads, J. Am. Chem. Soc., 2007, 129, 15973–15982.
2 K. S. Kumar and A. Patnaik, Tunable One-, two-, and three
dimensional self assemblies from an acceptor–donor
S. Fomine and O. G. Morales-Saavedra, Amphiphilic azo-
dyes (RED-PEGM). Part 2: Charge transfer complexes,
preparation of Langmuir Blodgett lms and optical
properties, Dyes Pigm., 2007, 74, 396–403.
1
fullerene-N,N-dimethylaminoazobenzene dyad: Interfacial 26 C. Caicedo, E. Rivera, Y. Valdez-Hern ´a ndez and
geometry and temporal evolution, Langmuir, 2011, 27,
1017–11025.
3 K. S. Kumar and A. Patmaik, Solvent-polaritydimeric
association of fullerene (C60)-N,N-dimethylamino-
azobenzene dyad: Modulated electronic coupling of the
M. P. Carre ´o n-Castro, Synthesis and characterization of
novel liquid-crystalline azo-dyes bearing two amino-nitro
1
1
substituted azobenzene units and
a
well-dened,
a
oligo(ethylene glycol) spacer, Mater. Chem. Phys., 2011, 130,
471–480.
azochromophore with a substituted 3D fullerene, Chem.–Eur. 27 T. Garc ´ı a, M. P. Carre ´o n-Castro, A. Gelover-Santiago,
J., 2011, 17, 5327–5343.
P. Ponce, M. Romero and E. Rivera, Synthesis and
Characterization of Novel Amphiphilic Azo-Polymers
Bearing Well-Dened Oligo(Ethylene Glycol) Spacers, Des.
Monomers Polym., 2012, 15, 159–174.
1
4 Y. Shirai, T. Sasaki, J. M. Guerrero, B. C. Yu, P. Hodge and
J. M. Tour, Synthesis and Photoisomerization of Fullerene
and Oligo(phenyleneethynylene) Azobenzene Derivatives,
ACS Nano, 2008, 2, 97–106.
5 M. E. El-Khouly, J. H. Kim, K. Y. Kay and S. Fukuzumi,
Silicon phthalocyanine-azobenzene-[60] fullerene light
harvesting pendant: synthesis, characterization and
28 F. Tapia, J. M. Reyna-Gonz ´a lez, G. Huerta, S. Almeida and
E. Rivera, Synthesis and characterization of novel
polythiophenes bearing oligo(ethylene glycol) segments
and azobenzene units, Polym. Bull., 2010, 64, 581–594.
1
electron transfer reaction studied by laser ash photolysis, 29 J. Ort ´ı z-Palacios, E. Rodr ´ı guez-Alba, G. Zaragoza-Gal ´a n,
J. Porphyrins Phthalocyanines, 2013, 17, 1055–1063.
J. R. Le ´o n-Carmona, A. Mart ´ı nez and E. Rivera,
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 16751–16762 | 16761

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Paper
Incorporation of novel azobenzene dyes bearing
oligo(ethylene glycol) spacers into rst generation
dendrimers, Dyes Pigm., 2015, 116, 1–12.
0 E. Rivera, M. P. Carre ´o n-Castro, R. Salazar, G. Huerta,
C. Becerril and L. Rivera, Preparation and characterization
of novel graed polyethylene based azo-polymers bearing
lms and liquid-crystalline behaviour, Molecules, 2013, 18,
1502–1527.
34 C. J. Hawker and J. M. J. Fr ´e chet, Preparation of Polymers
with Controlled Molecular Architecture. A new Convergent
Approach to Dendritic Macromolecules, J. Am. Chem. Soc.,
1990, 112, 7638–7647.
3
oligo(ethylene glycol) spacers, Polymer, 2007, 48, 3420–3428. 35 J. Ort ´ı z-Palacios, E. Rodr ´ı guez-Alba, G. Zaragoza-Gal ´a n and
3
1 D. Felder, M. Guti ´e rrez-Nava, M. P. Carre ´o n-Castro,
J. F. Eckert, M. Luccisano, C. Schall, P. Masson,
J. L. Gallani, B. Heinrich and D. Gillonand, Synthesis of
amphiphilic fullerene derivatives and their incorporation
E. Rivera, Fr ´e chet-type dendrons bearing azobenzene units
and exible oligo(ethylene glycol) spacers: synthesis,
characterization, thermal and optical properties, Des.
Monomers Polym., 2013, 16, 578–591.
in Langmuir and Langmuir–Blodgett lms, Helv. Chim. 36 M. Kasha, Energy transfer mechanisms and the molecular
Acta, 2002, 85, 288–319.
2 X. Camps and A. Hirsch, Efficient cyclopropanation of C60
exciton model for molecular aggregates, Radiat. Res., 1963,
20, 55–71.
3
starting from malonates, J. Chem. Soc., Perkin Trans. 1, 37 K. S. Kumar and A. Patnaik, Tunable electronic properties of
997, 1595. proton-responsive N,N-dimethylaminoazobenzene
3 J. Ort ´ı z-Palacios, E. Rodr ´ı guez-Alba, M. Avelar, A. Mart ´ı nez,
fullerene (C60) dyad, ChemPhysChem, 2010, 11, 3645–3655.
M. P. Carre ´o n-Castro and E. Rivera, Synthesis and 38 S. K. Lin, L. L. Shiu, K. M. Chien, T. L. Luh and T. I. Lin,
1
a
3
characterization of novel dendrons bearing amino-nitro-
substituted azobenzene units and oligo(ethylene glycol)
spacers: thermal, optical properties, Langmuir Blodgett
Fluorescence of Fullerene Derivatives at Room
Temperature, J. Phys. Chem., 1995, 99, 105–111.
16762 | RSC Adv., 2017, 7, 16751–16762
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