A novel phthalocyanine with two axial fullerene substituents

Article abstract of DOI:10.1016/j.tetlet.2005.08.038

A silicon phthalocyanine with two axial fullerene substituents was synthesized, and its electrochemical, absorption- and film-properties were characterized.

Full text of DOI:10.1016/j.tetlet.2005.08.038

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 6791–6795
A novel phthalocyanine with two axial fullerene substituents
Kun Nam Kim,a Chan Soo Choib and Kwang-Yol Kaya,*
aDepartment of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea
bDepartment of Applied Chemistry, Daejeon University, Daejeon 300-716, South Korea
Received 27 June 2005; revised 6 August 2005; accepted 10 August 2005
Abstract—A silicon phthalocyanine with two axial fullerene substituents was synthesized, and its electrochemical, absorption- and
film-properties were characterized.
Ó 2005 Elsevier Ltd. All rights reserved.
Phthalocyanines (Pcs) have long attracted enormous
interest owing to their intriguing electrical, optical, pho-
tochemical and catalytic properties.1 Among the various
electro- and photoactive chromophores utilized for
phthalocyanine chemistry,2 C60 has been proposed to
be a versatile building block and a growing interest in
fullerene-functionalized phthalocyanines is developing.1
Recently asymmetrical metal phthalocyanines contain-
ing a single fullerene (C60) substituent with rigid linkers
at the periphery3 and anotherasymmetrical zinc phtha-
locyanine–C60 hybrid with a flexible linker containing an
azacrown subunit4 were synthesized to study intramo-
lecular process such as electron transfer and energy
transfer between Pc donor and C60 accepter. Addition-
ally, supramolecular systems such as hydrogen bonded-5
and aggregated6 Pc–C60 dyads were reported for similar
studies. However, no phthalocyanine with more than
one fullerene substituent has been reported until now
to ourknowledge. On the otherhand, McKeown and
co-workers proved the glass-forming properties of axi-
ally substituted phthalocyanines with dendritic subunits,
and such compounds are further known to produce
glassy solids, which would allow the fabrication of the
sis of the soluble silicon phthalocyanine 1 with two axial
fullerene substituents by reaction between a bis-adduct
of C60 bearing an alcohol functionality and dichloro-
(phthalocyaninato) silicon in the presence of sodium
hydride.
k
j
i
h
O
O
O
O
O
f
O
O
O
e
H
H
g
d
O
c
b
a
O
Si
O
N
N
N
N
N
l
N
N
m
N
robust, nonscattering films for optical applications such
1,7
as nonlinearoptics and optical limiters.
With respect
to these aspects, the Pc 1 would also be a suitable com-
pound to exploit the optical and electronic properties of
the Pc macrocycle in solution as well as in solid state. In
line with these aspects, we report herein the first synthe-
O
O
O
O
O
O
O
O
O
Keywords: Si–phthalocyanine; Fullerene; Electrochemistry; Absorp-
tion spectrum; Glassy film.
15
*
Corresponding author. Tel.: +82 31 219 2602; fax: +82 31 219
1615; e-mail: kykay@ajou.ac.kr
1
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.08.038

6792
K. N. Kim et al. / Tetrahedron Letters 46 (2005) 6791–6795
OH
OH
OH
a
b
MeO2C
CO2Me
HO2C
CO2H
HOH2C
CH2OH
4
2
3
O
O
O
O
c
O
O
C18H37OH
HO
OC18H37
7
5
6
O
O
O
O
O
O
O
OC18H37
OC18H37
OC18H37
OC18H37
d
e
HO
HO
O
4
+
7
O
O
O
O
O
9
8
O
OC18H37
O
O
f
g
O
1
HO
O
O
OC18H37
O
10
Scheme 1. Synthesis of compound 1. Reagents and conditions: (a) MeOH, H2SO4, reflux 24 h, 97%; (b) LAH, THF, reflux, 24 h, 85%; (c) 110–
120 °C, 1 h, 93%; (d) DCC, DMAP, HOBT, THF, 3 h, 53%; (e) K2CO3, 18-crown-6, 3-bromo-1-propanol, acetone, reflux, 12 h, 72%; (f) C60, I2,
DBU, toluene, rt, 24 h, 23%; (g) silicon phthalocyanine dichloride, NaH, toluene, reflux 10 h, 32%.
The Pc 1 has two symmetrical fullerene substituents axi-
ally to the Pc core, and this structural shape with bulky
k
j
5
i
fullerene substituents may help to achieve the steric iso-
lation of the Pc rings in the solid phase to diminish the
intermolecular interactions, which usually cause to
broaden and red shift the intense visible absorption
band(the Q-band) due to the excitonic effects of the
cofacial Pc rings. The Pc 1 was synthesized as depicted
in Scheme 1.
1
1
5
h
O
O
O
n
O
O
f
O
O
O
e
H
H
g
d
O
Commercially available 5-hydroxy-isophthalic acid (2)
was esterified to give diester 3 (97% yield) and subse-
quent reduction of 3 with LAH produced 3,5-bishydr-
oxy-methyl-phenol (4) in a yield of 85%. Octacdecanol
(5) reacted with MeldrumÕs acid (6) to afford malonic
acid monooctadecyl ester( 7) in 93% yield. Esterification
of 4 with the mono-ester 7 of malonic acid in the pres-
ence of N,N0-dicyclohexylcarbodiimide (DCC) yielded
bis-malonate 8 (53% yield). Phenol group of bis-malon-
ate 8 reacted with 3-bromo-1-propanol in the presence
of K2CO3 and 18-crown-6 to give alcohol-functionalized
derivative 9 (72% yield). The fuctionalization of C60 was
based on the highly regioselective Diederich reaction,8
which led to macrocyclic bis-adducts of C60 through a
macrocyclization reaction of the carbon sphere with
bis-malonate derivatives in a double Bingel addition.9
Treatment of C60 with 9, iodine, and 1.8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) in toluene at room temper-
ature afforded the bis-adduct 10 in 23% yield.10 The final
reaction of bis-adduct 10 with commercially available
c
b
a
O
Si
O
N
N
N
N
N
N
l
N
N
m
O
O
O
O
O
O
O
O
O
15
11

K. N. Kim et al. / Tetrahedron Letters 46 (2005) 6791–6795
6793
dichloro-Si–Pc went smoothly in the presence of NaH to
Deschenaux and co-workers13 found that the curve sug-
gests the presence of chemical reactions coupled to some
of the redox processes. These chemical reactions are
responsible for the presence of extra anodic peaks in
the reverse scan. However, we did not find the chemical
reactions from compounds 1, 10 and 11 in that sense.
Instead, we found that the E1/2 of the first reduction
of the phthalocyanine moiety in compound 1 was more
anodic (DE = 280 mV) than that of compound 11 (i.e.,
analogous fullerene-free materials). This observation is
related to the strong electron-withdrawing effect of the
two axial fullerene substituents, which could stabilize
the first reduced state of the phthalocyanine. The E1/2
values of the reductions of the fullerene moiety in com-
pound 1 are not substantially shifted by the phthalocy-
anine moiety when compared with compound 10 (i.e.,
analogous phthalocyanine-free materials). According
to the electrochemical curves of compound 1, only two
oxidation processes occur; the first one corresponds to
produce 1 in 32% yield.10
1
The structure of 1 was confirmed by H and 13C NMR
spectroscopies and MALDI-TOF MS. The 1H NMR
spectrum is particularly informative, because the strong
ring current of the Pc macrocycle helps to differentiate
protons of similar type. 13C NMR spectrum showed a
set of C60 nucleus peaks (136–149 ppm), two carbonyl
carbons (163 and 158 ppm), aromatic carbons (111–
131 ppm) and aliphatic carbons (14–68 ppm). Further
confirmation of the hybrid Pc–fullerene structure was
obtained from the IR and UV/vis spectra, which were
found to contain absorbances due to the Pc and fuller-
ene fragments. Compound 1 is soluble in common
aprotic solvents such as THF, toluene and chloroform
but not in diethyl etherand hexane. To compaer the
physical properties such as spectroscopic, electrical
and film properties with those of 1, we also synthesized
a Pc 11, which contains the same axial substituents
without C60 moieties, by an analogous synthetic
method.11
the reversible exchange of one electron (with E1/2
=
1.10 V) attributed to the phthalocyanine moiety, and
the second one corresponds to a partially reversible
two-electron oxidation (with E1/2 = 1.30 V) situated on
the fullerene moiety. Deschenaux and co-workers13
reported similar results from fullerene–ferrocene mate-
rial. The redox potential for the first oxidation of the
phthalocyanine moiety in compound 1 is almost the
same as that of compound 11. Nierengarten et al.14
found that the E1/2 value of the first oxidation of the
porphyrin moiety in a tetraphenylporphyrin with four
fullenrene subunits was significantly more anodic than
meso-tetrakis (3,5-di-tert-butylphenyl) porphyrin as a
model compound. They explained that theirobservation
could be related to the substantial de-stabilization of the
first oxidized state of the porphyrin moiety by the strong
electron-withdrawing effect of the four fullerene sub-
units. They also described that solvation effects caused
by the presence of the surrounding fullerene groups
could also be the source of the observed shift in poten-
tial. In our case, although the redox properties of the
phthalocyanine moiety of compound 1 are significantly
influenced by the two fullerene subunits in the negative
potential region, those of the fullerene moiety in the neg-
ative potential region and of the phthalocyanine in the
positive potential region remain almost unchanged.
Nierengarten et al.14 also found that the redox proper-
ties of the fullerene moiety seemed to remain unchanged
by the porphyrin moiety in a tetraphenylporphyrin with
four fullerene subunits. Again these results were de-
duced when compared with the model compounds, 10
and 11. Based on ourdiscussion forthe molecule of
compound 1, we can deduce that the phthalocyanine
moiety would be positively charged and the fullerene
moiety would be negatively charged. This charge separa-
tion might cause significant solvation effects forthe
redox potentials to remain unchanged for the above
moieties. This charge separation will also modify spec-
troscopic, electronic characteristics.
To compare the detailed electrochemical behavior of
compounds 1, 10 and 11 have been used as model com-
pounds as they lack eitherphthalocyanine (i.e., 10) or
fullerene (i.e., 11) subunit. Compound 1 is found to have
13 redox reactions from the redox waves in a cyclic
voltammogram. The data suggests that three of these
reactions originate from the phthalocyanine moiety
(E1/2 = ꢀ0.74 V, ꢀ1.24 V, +1.10 V), and the remaining
reactions originate from the fullerene moiety. Compari-
sons were made with compounds 10 and 11, which are
phthalocyanine-free and fullerene-free, respectively (see
Table 1); although the E1/2 of ꢀ1.24 V presumably orig-
inated from phthalocyanine, the cyclic voltammogram
depicts a shoulderpeak on the fullerne peak at
ꢀ1.31 V. These E1/2 values coincide with the peak values
of the differential pulse voltammogram (DPV) within
the first decimal point.12
Table 1. Electrochemical properties of compounds, 1, 10 and 11
Compound
1
10
11
Negative potential region
ꢀ0.59(73)
ꢀ0.74(119)
ꢀ1.06(110)
ꢀ1.24
ꢀ0.57(94)
ꢀ1.02a
ꢀ1.00(118)
ꢀ1.31(210)
ꢀ1.59(169)
ꢀ1.80(119)
ꢀ2.12(133)
ꢀ2.37(96)
ꢀ2.60(105)
ꢀ2.80(137)
ꢀ1.35(85)
ꢀ1.59(118)
ꢀ1.78(105)
ꢀ2.08(109)
ꢀ2.39b
ꢀ2.56(118)
Positive potential region
1.10(60)
1.09a
1.30(146)
Cyclic voltammetric measurements: glassy carbon working electrode,
Pt wire counter electrode, Ag/Ag+ pseudo-reference electrode, degas-
sed THF, 0.1 M Bu4NClO4 and a scan rate of 100 mV/s. Values for
E1/2 as (Epa + Epc)/2 V and DEpm V (in parentheses) are given.
a Measured by DPV.
The UV/vis spectrum of compound 1 in CHCl3 (Fig. 1)
shows characteristic phthalocyanine absorption bands.
A intense Q-band in the visible region of 675 nm was
accompanied by more or less weak satelite bands at
b Irreversible.

6794
K. N. Kim et al. / Tetrahedron Letters 46 (2005) 6791–6795
limiterwhich are now underinvestigation. In addition,
we are also working on the photo-induced electron
transfer studies.
0.8
0.6
0.4
0.2
0.0
Acknowledgement
K.-Y. Kay would like to acknowledge the Brain Korea
21 program of the Ministry of Education for financial
support.
References and notes
300
400
500
600
700
800
1. Mckeown, N. B. Phthalocyanine Materials: Synthesis,
Structure and Function; Cambridge University Press:
Cambridge, 1998.
2. Phthalocyanines-Properties and Applications; Leznoff, C.
C., Lever, A. B. F., Eds.; VCH: New York, 1989; Vol. 1,
1993; Vols. 2–3, 1996; Vol. 4.
Wavelength (nm)
Figure 1. UV/vis spectra of 1 in CHCl3 (—) and in spin-coated film
(---).
3. (a) Linßen, T. G.; Durr, K.; Hanack, M.; Hirsch, A. J.
Chem. Soc., Chem. Commun. 1995, 103; (b) Durr, K.;
Fiedler, S.; Linßen, T. G.; Hirsch, A.; Hanack, M. Chem.
Ber. 1997, 130, 1375; (c) Gouloumis, A.; Liu, S.-G.; Sastre,
A.; Vazquez, P.; Echegoyen, L.; Torres, T. Chem. Eur. J.
2000, 6, 3600; (d) Guldi, D. M.; Gouloumis, A.; Vazquez,
P.; Torres, T. Chem. Commun. 2002, 2056; (e) Loi, M. A.;
Denk, P.; Hoppe, H.; Neugebauer, H.; Winder, C.;
Meissner, D.; Brabec, C.; Sariciftci, N. S.; Gouloumis,
A.; Vazquez, P.; Torres, T. J. Mater. Chem. 2003, 13, 700;
(f) Guldi, D. M.; Zilbermann, I.; Gouloumis, A.; Vazquez,
P.; Torres, T. J. Phys. Chem. B 2004, 108, 18485.
4. Sastre, A.; Gouloumis, A.; Vazquez, P.; Torres, T.; Doan,
V.; Schwartz, B. J.; Wudl, F.; Echegoyen, L.; Rivera, J.
Org. Lett. 1999, 1, 1807.
5. Martinez-Diaz, M. V.; Fender, N. S.; Rodriguez-Mor-
gade, M. S.; Gomez-Lopez, M.; Diederich, F.; Echegoyen,
L.; Stoddart, J. F.; Torres, T. J. Mater. Chem. 2002, 12,
2095.
6. Guldi, D. M.; Gouloumis, A.; Vazquez, P.; Torres, T.;
Georgakilas, V.; Prato, M. J. Am. Chem. Soc. 2005, 127,
5811.
7. (a) Brewis, M.; Clarkson, G. J.; Helliwell, M.; Holder, A.
M.; McKeown, N. B. Chem. Eur. J. 2000, 6, 4630; (b)
Hassan, B. M.; Li, H.; Mckoewn, N. B. J. Mater. Chem.
2000, 10, 39; (c) Mckeown, N. B. Adv. Mater. 1999, 11,
67.
8. (a) Nierengarten, J.-F.; Gramlich, V.; Cardullo, F.;
Diederich, F. Angew. Chem. 1996, 108, 2242; Angew.
Chem., Int. Ed. 1996, 35, 2101; (b) Nierengarten, J.-F.;
Herrmann, A.; Tykwinski, R. R.; Ruttimann, M.; Diede-
rich, F.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M. Helv.
Chim. Acta 1997, 80, 293; (c) Nierengarten, J.-F.; Habi-
cher, T.; Kessinger, R.; Cardullo, F.; Diederich, F.;
Gramlich, V.; Gisselbrecht, J.-P.; Boudon, C.; Gross, M.
Helv. Chim. Acta 1997, 80, 2238.
Table 2. The UV/vis spectroscopic data of 1
kmax (nm)
kmax (nm)
Dmax (nm)
DWd (nm)
a
b
c
1
11
675
676
683
679
8
3
8
8
a In CHCl3.
b In spin-coated film.
c kmax (film) ꢀ kmax (solution).
d Width of peak at half height (film) ꢀ width of peak at half height
(solution).
563, 580, 607 and 645 nm. In the ultraviolet region of
354 nm, the characteristic Soret or B-band was also
observed. The remaining weak band at 430 nm was
found to contain absorbances due to the fullerene frag-
ment. As expected, the UV/vis spectrum of 1 is practi-
cally same as the sum of the peaks of both 10
(phthalocyanine-free)10 and 11 (fullerene-free).11 The
UV/vis spectrum of spin-coated thin film of compound
1 also illustrates the extent to which the axial fullerene
substituents suppress cofacial intermolecular excitonic
interactions. Only relatively weak edge-to-edge exciton
interactions are present in the solid film of 1, as indi-
cated by the relatively small red shift (Dkmax) of the Q-
band (8 nm) as compared to its position in the solution
absorption spectrum. Broadening (DW) of the Q-band
due to excitonic effects is also small (8 nm) (Table 2).
These values show that this spin-coated film resembles a
solid solution. Interestingly, these results are also in
good agreement to the previously reported results of
the Pcs, such as McKeownÕs phthalocyanine with den-
dritic substituents where similar small changes have
been observed.7 Atomic force microscopy (AFM) stud-
ies indicate that spin-coating from toluene results in
smooth films. Polarized optical microscopy suggests that
the film derived from 1 is uniform and isotropic (nonbi-
refringent). The Pc 1 displays a distinct glass transition
on cooling from the melt (Tg = 140.5 °C). Therefore,
the film can also be readily fabricated by melt process-
ing. This easily processable Pc 1 is a suitable material
foroptical studies, such as nonlinearoptics and optical
9. Bingel, C. Chem. Ber. 1993, 126, 1957.
10. Synthesis of 10: Fullerene (0.29 g, 0.40 mmol) was dis-
solved in dry toluene (250 mL), and to this solution were
added 9 (0.35 g, 0.40 mmol), I2 (0.13 g, 1.00 mmol), and
DBU (0.3 mL, 2.00 mmol) under nitrogen atmosphere and
stirred at room temperature for 24 h. After evaporation of
the solvent, the crude product was purified by column
chromatographic separation (silica gel, toluene and then
MeOH–CHCl3 = 1:50). Compound 10: Dark brown solid
(23.4%); mp: 67 °C; 1H NMR (500 MHz, CDCl3):
d = 0.85–0.92 (t, 6H, CH3), 1.23–1.36 (s, 60H, CH2),
1.69–1.72 (m, 4H, CH2), 2.08 (m, 2H, CH2), 3.88 (t, 2H,

K. N. Kim et al. / Tetrahedron Letters 46 (2005) 6791–6795
6795
CH2), 4.17 (t, 2H, CH2), 4.35 (t, 4H, CH2), 5.13 (d, 2H,
CH2), 5.78 (d, 2H, CH2), 6.81 (s, 2H, ArH), 7.19 (s, 1H,
ArH). 13C NMR (CDCl3): d = 163.05, 159.07, 148.87,
147.72, 147.68, 147.51, 146.34, 146.26, 145.95, 145.83,
145.57, 145.39, 145.23, 144.77, 144.57, 144.45, 144.37,
144.16, 143.95, 143.77, 143.47, 143.25, 142.49, 141.46,
141.22, 140.18, 138.32, 137.83, 136.40, 136.02, 134.92,
115.40, 112.50, 70.86, 67.46, 67.43, 67.15, 65.83, 60.33,
49.49, 32.11, 29.91, 29.86, 29.78, 29.76, 29.55, 29.34, 28.65,
26.05, 22.88, 14.33. IR (KBr): t = 3433, 2928, 2854, 1751,
1607, 1464, 1238, 1203, 1115, 1060 cmꢀ1. UV/vis (CHCl3,
10ꢀ5 M): kmax = 262, 321, 376, 438 nm.
136.49, 136.09, 131.07, 123.85, 123.70, 111.37, 67.60,
67.36, 32.15, 29.94, 29.86, 29.60, 29.45, 28.79, 26.17,
26.10, 22.93, 14.37. IR (KBr): t = 2917, 2847, 1751, 1623,
1464, 1239, 1208, 1122, 1080 cmꢀ1. MALDI-TOF MS:
m/z: 3751 (m + 1), 2145, 1870, 1806, 1096, 812, 809, 765,
717. UV/vis (CHCl3, 10ꢀ5 M): kmax = 259, 330, 354, 430,
563, 580, 607, 645, 675 nm.
11. Phthalocyanine 11 was synthesized by the similarmethod
forthe synthesis of 1 in Scheme 1.
1H NMR (200 MHz, CDCl3): d = ꢀ1.95 (t, 4H, aCH2),
ꢀ0.97 (m, 4H, bCH2), 0.65 (t, 12H, kCH3), 0.82–1.90 (m,
132H, i,jCH2 and cCH2), 3.50 (s, 8H, nCH2), 4.15 (t, 8H,
hCH2), 4.62 (S, 4H, dArH), 5.05 (m, 8H, f,gCH2), 4.75 (s,
2H, eArH), 8.22–8.45 (m, 8H, lCH of Si–Pc), 9.55–9.78
(m, 8H, mCH of Si–Pc). IR (KBr): t = 2962, 2869, 1743,
1635, 1465, 1326, 1209, 1141, 1079 cmꢀ1. UV/vis (CHCl3,
10ꢀ5 M): kmax = 259, 277, 358, 381, 563, 580, 610, 647,
676 nm.
Synthesis of 1: Sodium hydride (7.80 mg, 0.33 mmol) was
added to a mixture of dichloro(phthalocyaninato) silicon
(28.5 mg, 0.05 mmol) and 10 (150 mg, 0.09 mmol) in dry
toluene (2 mL). After refluxing under nitrogen for 10 h,
the reaction mixture was cooled to room temperature, and
then the solvent was evaporated to dryness under reduced
pressure. The crude product was washed with water twice
and was purified by two successive column chromato-
graphic separations (silica gel, CH3CN–CHCl3 = 1:60).
Dark green glassy product (32.4%); mp: 172 °C.
12. Differential pulse voltammograms of compound 1 were
obtained underthe following conditions: 80 mV pulse,
50 ms pulse width, 100 ms periods, and a scan rate of
20 mV/s. The remaining conditions are the same as that of
CV measurements. For compound 1: ꢀ0.55, ꢀ0.72, ꢀ1.01,
ꢀ1.24, ꢀ1.33, ꢀ1.57, ꢀ1.79, ꢀ2.08, ꢀ2.37, ꢀ2.57, ꢀ2.77,
+1.06, and +1.34 V. Forcompound 10: ꢀ0.54, ꢀ0.98,
ꢀ1.32, ꢀ1.55, ꢀ1.76, ꢀ2.05, and ꢀ2.55 V. Forcompound
11: ꢀ1.02 and +1.09 V.
1H NMR (600 MHz, CDCl3): d = ꢀ1.93 (t, 4H, aCH2),
ꢀ0.97 (m, 4H, bCH2), 0.85–0.92 (t, 12H, kCH3), 1.08 (t,
4H, cCH2), 1.19–1.38 (m, 120H, iCH2), 1.74–1.77 (m, 8H,
jCH2), 4.42 (t, 8H, hCH2), 4.98 (d, 4H, gCH2), 5.65 (s, 4H,
dArH), 5.83 (d, 4H, fCH2), 6.95 (s, 2H, eArH), 8.33–8.36
(m, 8H, lCH of Si–Pc), 9.55–9.59 (m, 8H, mCH of Si–Pc).
13C NMR (CDCl3): d = 163.28, 158.45, 149.47, 149.32,
149.14, 147.82, 146.57, 146.39, 146.06, 145.95, 145.49,
145.36, 144.90, 144.71, 144.48, 144.33, 144.10, 143.89,
143.61, 143.42, 142.63, 141.59, 141.35, 140.34, 137.36,
13. Carano, M.; Chuard, T.; Deschennaux, R.; Even, M.;
Marcaccio, M.; Paolucci, F.; Prato, M.; Roffia, S. J.
Mater. Chem. 2002, 12, 829.
14. Nierengarten, J.-F.; Schall, C.; Icoud, J.-F. Angew. Chem.,
Int. Ed. 1998, 37, 1934.