Selective functionalization of fullerenes with N,N-dihalosulfonamides as an N1 unit: Versatile syntheses of aza[60]fulleroids and aziridino[60]fullerenes and their application to photovoltaic cells

Article abstract of DOI:10.1002/chem.201201680

Highly selective and versatile methods for the synthesis of aza[60]fulleroids and aziridino[60]fullerenes from C₆₀ have been developed. The reactions utilized N,N-dihalosulfonamides as an N₁ source. The photophysical, electrochemical

Full text of DOI:10.1002/chem.201201680

FULL PAPER
DOI: 10.1002/chem.201201680
Selective Functionalization of Fullerenes with N,N-Dihalosulfonamides as an
N1 Unit: Versatile Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
and their Application to Photovoltaic Cells
Toshiki Nagamachi,[a] Youhei Takeda,[a, b] Kazuhisa Nakayama,[a] and
Satoshi Minakata*[a]
Dedicated to Professor FranÅois Diederich on the occasion of his 60th birthday
Abstract: Highly selective and versatile methods for the synthesis of aza[60]fulle-
roids and aziridino[60]fullerenes from C60 have been developed. The reactions uti-
lized N,N-dihalosulfonamides as an N1 source. The photophysical, electrochemical,
Keywords: fullerenes · halogens ·
and thermal properties of the iminofullerenes were investigated by means of UV/
photovoltaic devices · sulfonamides ·
Vis spectroscopy, cyclic voltammetry, and thermogravimetry, respectively. Further-
synthetic methods
more, photovoltaic cells based on the synthesized iminofullerenes were fabricated.
The power conversion efficiencies (PCEs) of the devices showed moderate values
ranging from 1.33 to 2.35%.
Introduction
Functionalized fullerenes have attracted a significant level
of interest from scientists because of their potential applica-
tions in the fields of organic electronics and the biological
sciences.[1,2] Among them, iminofullerenes, which have nitro-
gen-bridged fullerene cage structures, constitute a large
family of nitrogen-containing functionalized fullerenes. They
exist exclusively as either of two isolatable isomers: either
as a [5,6]-open cluster architecture with a 60 p-electron
system (aza[60]fulleroids) or a [6,6]-closed structure with a
Figure 1. Chemical structures of aza[60]fulleroids and aziridino[60]fuller-
enes.
58 p-electron system (aziridino[60]fullerenes; Figure 1).[1a]
They serve not only as the key synthetic precursors to
heteroACHTUNGTRENNUNG
fullerenes,[3] but also as promising new candidates for
n-type (electron-transporting) semiconducting materials. For
example, the groups of Wudl and Heeger have recently con-
ducted comparative studies of the performance of n-channel
organic field-effect transistors (OFETs) and bulk hetero-
junction (BHJ) solar cells that contain nitrogen analogues of
[6,6]-phenyl-C61-butyric acid methyl ester ([5,6]-open and
[6,6]-closed APCBM, A=aza; Figure 1).[4,5] They revealed
that the solution-processed OFET device based on [5,6]-
open APCBM exhibited a relatively higher electron mobili-
ty (me) than that of PCBM-based OFET.[4] Furthermore, the
solar cells based on the configurations of P3HT:
ACHTUNGTRENNUNG
APCBM [P3HT=poly-3(hexylthiophene)] and P3HT:ACHTUNGTRENNUNG
closed APCBM showed good power conversion efficiencies
(PCEs) of 2.8 and 2.3%, respectively, exceeding the efficien-
cies of the corresponding PCBM-based cells.[5] Therefore,
from the viewpoint of materials chemistry research, imino-
fullerenes are highly intriguing target molecules and numer-
ous efforts have been devoted to the development of meth-
ods for the synthesis of iminofullerenes.
[a] T. Nagamachi, Dr. Y. Takeda, K. Nakayama, Prof. Dr. S. Minakata
Department of Applied Chemistry
Graduate School of Engineering, Osaka University
Yamadaoka 2-1, Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-8402
The most widely used synthetic method for iminofuller-
enes involves the reaction of C60 with organoazides.[6,7]
A
E-mail: minakata@chem.eng.osaka-u.ac.jp
[b] Dr. Y. Takeda
representative protocol involves the 1,3-dipolar [3+2] cyclo-
Frontier Research Base for Global Young Researchers
Graduate School of Engineering, Osaka University
Yamadaoka 2-1, Suita, Osaka 565-0871 (Japan)
addition of organoazides with C60 followed by thermal ex-
[8]
trusion of N2 from the intermediately formed [6,6]-triazoli-
nes.[6c] This leads to the formation of [5,6]-open azafulleroids
as a major product, with [6,6]-closed aziridinofullerenes as a
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201680.
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minor product.[6] On the other hand, the [2+1] addition of
nitrenes to C=C double bonds at the [6,6] junction of C60 ex-
clusively provides [6,6]-closed aziridinofullerenes. These ni-
trenes can be generated by the thermolysis or photolysis of
azides,[7] by base-induced a-elimination from O-4-(para-ni-
trophenylsulfonyl)hydroxamic acids,[9] or by the treatment of
continuing exploration of fullerene functionalization meth-
ods, we found by chance that the treatment of C60 with two
equivalents of N-chloro-N-sodio-para-toluenesulfonamide
(chloramine-T) and an equimolar amount of I2 in toluene at
room temperature gave the [5,6]-open azafulleroid 1a as the
major product, together with trace amounts of the [6,6]-
closed aziridinofullerene 2a. The combined yield of the
products was 12% with an isomeric ratio of 97:3 [Eq. (1)].
Notably, compared to the results we have previously report-
ed, in which the reaction of C60 with an ammonium chlor-
amines with PbACHTUNGTRENNUNG
(OAc)4.[10]
In light of the facts that the aforementioned conventional
methods require highly toxic and explosive organoazides
and high reaction temperatures, and that the isomeric ratio
of the iminofullerenes being formed strongly depends on
the nature of the substituents on the nitrogen atom, there
remains considerable room for the development of alterna-
tive synthetic methods that allow selective access to isomeric
iminofullerenes from readily accessible and easily handled
reagents. In this context, some groups, including ours, have
recently developed such methods for the synthesis of imino-
fullerenes.[11–14] Akasaka and co-workers have reported the
[2+1] cycloaddition of C60 with nitrene, which was generated
by the photolysis of readily prepared N-para-toluenesulfo-
nylsulfilimine, to give N-tosylaziridinofullerene in a selective
manner.[11] Iminophenyliodinanes (RN=IPh) have also
emerged as alternative candidates for the synthesis of imino-
fullerenes. The group led by Gan reported the aziridination
of C60 by using alkyl-substituted iminoiodinane (R=
CH2CO2Me), which was generated in situ from a glycine
ester with a hypervalent iodine reagent and I2,[12] and the
Itami group developed a Cu-catalyzed variant by using
TsN=IPh to prepare N-para-tosylaziridinofullerene in suffi-
cient chemical yield.[13] As part of our efforts to develop re-
actions for the chemical modification of C60, we have previ-
ously developed an ionic aziridination of C60 that utilizes a
chlor
AHCTUNGTRENNUNG
amine salt exclusively gave aziridinofullerenes 2a,[14] the
ratio of the isomeric product was inversed in this reaction.
This unexpected result prompted us to further explore the
new reaction. The results of a survey of reaction conditions,
other than reagents (see the Supporting Information, Table
S1), indicated that ortho-dichlorobenzene (o-DCB) was the
best solvent among those tested in terms of isomeric ratio
and “selectivity”[15] (21 and 100%, respectively).
The treatment of chloramine-T with iodine is expected to
generate the N,N-dihalo-para-tosylamide[16] (it remains un-
clear whether the compound exists as the N-chloro-N-iodo
or the N,N-diiodo form), thus implying that N,N-dihalo-
amine salt as an N1 unit to exclusively provide [6,6]-closed
aziridinofullerenes in high yield under mild reaction condi-
tions through an addition–cyclization pathway.[14] At the
same time, a unique rearrangement of aziridinofullerenes to
azafulleroids that is catalyzed by a chloramine salt in the
presence of 4 ꢁ molecular sieves was reported, although it
was not a straightforward route to azafulleroids. Turning our
attention to the synthetic repertoire for iminofullerenes, se-
lective and alternative synthetic reactions for the prepara-
tion of azafulleroids remain scarce, although the counter-
parts for aziridinofullerenes have been intensely developed.
Thus, we herein report on a highly selective synthetic
method for azafulleroids from C60 that features high effi-
ciency as well as high functional compatibility by utilizing
N,N-diiodosulfonamides, which can be readily generated
from simple sulfonamides and an iodinating reagent. The
complementary synthetic method that selectively leads to
aziridinofullerenes has also been developed.
AHCTUNGTREGaNNNU mide should play a key role in this new, selective reaction.
In light of the fact that sulfonamides have two acidic hydro-
gen atoms that are exchangeable with halogen atoms, we en-
visioned that the concomitant use of sulfonamides with an
appropriate halogenating reagent would generate dihalosul-
fonamides in situ. Furthermore, sulfonamides are more
readily available than the corresponding chloramine salts,
and thus their use is desirable from the viewpoint of syn-
thetic versatility and product diversity.
In this regard, we scrutinized different electrophilic halo-
genating reagents in the reaction of C60 with N-para-tolu-
AHCTUNGTREGeNNUN nesulfonamide (3a) at room temperature (Table 1). The
use of commonly available chlorinating reagents, such as N-
chlorosuccinimide (NCS) and tBuOCl, failed to give 1a and
2a; unreacted C60 was recovered quantitatively from these
reactions (Table 1, entries 1 and 2). Iodinating reagents com-
posed of diatomic interhalogen molecules (I2, IBr, ICl) were
also found to be ineffective for the reaction (Table 1, en-
tries 3–5). In the case of ICl, the recovery of C60 was moder-
ate, probably due to the production of C60Cln instead of the
formation of iminofullerenes.[17] Meanwhile, we were de-
lighted to find that the employment of tert-butyl hypoiodite
(tBuOI), which can be generated from tert-butyl hypochlor-
Results and Discussion
Discovery of the selective formation of [5,6]-open azafulle-
roids and an optimization study: During the course of our
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Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
FULL PAPER
Table 1. Effect of the halogenating reagent on the production of iminofullerenes.[a]
[d]
[d]
Entry
Reagent
Yield[b]
[%]
1a/2a[c]
C60
Entry
16
Reagent
Yield[b]
[%]
1a/2a[c]
C60
[%]
[%]
1
2
NCS
tBuOCl
0 (À)
0 (À)
–
–
98
99
BPIT
NBPI
11 (82)
89:11
86
3
4
5
6
I2
IBr
ICl
tBuOI
NIS
NIS
0 (À)
0 (À)
–
–
–
100
96
66
69
48
21
17
PhI
N
40 (64)
6 (13)
0 (À)
100:0
0:100
–
37
85
83
63
18[e]
19[e]
20[i]
NBS
Br2
AcOBr
0 (À)
16 (53)
52 (100)
45 (57)
100:0
100:0
97:3
0 (À)
–
7
8[e]
21[e]
0 (À)
–
100
9
52 (72)
36 (100)
100:0
100:0
28
64
10[f]
NIPI
NISac
DIH
22[i]
23[e]
24
NBSac
DBH
5 (12)
9 (23)
0 (À)
0 (À)
0:100
0:100
–
47
61
11
45 (63)
25 (96)
100:0
100:0
29
74
12[f]
13[g]
45 (61)
41 (77)
100:0
100:0
26
46
14[f,g]
Selectfluor
100
100
15[h]
TICA
4 (22)
100:0
82
25
–
[a] Reaction conditions: C60 (0.05 mmol), a halogenating reagent (0.1 mmol), and 3a (0.05 mmol) in o-DCB (25 mL) at room temperature for 3 h.
[b] Combined isolated yield of 1a and 2a; the values in parentheses indicate selectivity for the products. [c] Isomeric ratio of 1a/2a determined by
1H NMR spectral integration. [d] Recovery of unreacted C60. [e] Reaction time: 24 h. [f] Reaction time: 1.5 h. [g] One equivalent of DIH (0.05 mmol)
was employed; [h] 0.66 equivalents (0.033 mmol) of TICA were employed. [i] Reaction time: 12 h.
ite (tBuOCl) and sodium iodide in situ,[18] gave azafulleroid
1a as the sole product, albeit in low chemical yield (16%)
with moderate selectivity (53%; Table 1, entry 6). The reac-
tion with N-iodosuccinimide (NIS) provided 1a in high
chemical yield (52%) with perfect selectivity and isomeric
ratio, although prolonging the reaction time (to 24 h) not
only resulted in a slightly lower yield (45%) of products
with moderate selectivity (57%), but also caused the forma-
tion of trace amounts of aziridinofullerene 2a (Table 1, en-
tries 7 and 8). Benzene-fused variants of NIS (N-iodophtha-
limide (NIPI)[19] and N-iodosaccharin (NISac)[20]) and a hy-
dantoin-based bifunctional reagent (1,3-diiodo-5,5-dimethyl-
hydantoin (DIH)[21]) also afforded 1a exclusively and in
high yield, although selectivities were inferior to that of NIS
(Table 1, entries 9, 11, and 13). Improvements in selectivities
gained by using these reagents were observed when the re-
action time was reduced to 1.5 h, at the expense of a slight
decrease in chemical yields (Table 1, entries 10, 12, and 14).
(Table 1, entry 15). The use of a highly electrophilic iodoni-
um reagent (bis(pyridine)iodonium tetrafluoroborate
AHCTUNGTRENNUNG
(BPIT)[23]) resulted in a lower chemical yield and isomeric
ratio (Table 1, entry 16). The concomitant use of I2 with a
hypervalent iodine reagent, which has emerged as a repre-
sentative nonmetal oxidant, gave 1a in good yield, indicat-
ing the involvement of a nitrogen-centered radical (Table 1,
entry 17).[24] To our surprise, the reaction with N-bromosuc-
cinimide (NBS) for 24 h produced aziridinofullerene 2a
without the formation of 1a, although both the chemical
yield and selectivity were quite low (Table 1, entry 18). This
encouraged us to further investigate the reaction system be-
cause the result indicated that switching the major isomeric
product would be feasible only by changing the applied hal-
ogenating reagents. No product formation was observed
when Br2 or AcOBr were employed, although small
amounts of C60 were consumed (Table 1, entries 19 and 20).
Brominated counterparts of NIPI, NISac, and DIH
(NBPI,[25] NBSac,[26] and DBH,[27] respectively) were exam-
ined for the synthesis of 2a (Table 1, entries 21–23), based
A
ternary iodinating reagent (triiodoisocyanuric acid
(TICA)[22]) did not improve the efficiency of the reaction
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S. Minakata et al.
on the successful results for the selective synthesis of azaful-
leroid 1a. At this point, DBH was found to be the best re-
agent to give 2a in terms of chemical yield (Table 1,
entry 23), although an improved method is discussed later.
Fluoronium (F+) sources, such as Selectfluor and N-fluoro-
pyridinium triflate, were ineffective for the reaction
(Table 1, entries 24 and 25).
sulfonamides were subjected to the optimal reaction condi-
tions to verify the versatility of the synthetic method
(Table 2). The reaction with benzenesulfonamide (3b) with
NIS proceeded efficiently to give the corresponding azaful-
leroid 1b as the sole product in high yield with excellent se-
lectivity (Table 2, entry 1). Although the reaction with 1-
naphthalenesulfonamide (3c) required a long reaction time
of 72 h, azafulleroid 1c was exclusively formed in good yield
with moderate selectivity (Table 2, entry 2). Electron-with-
drawing substituents on the benzene ring (3d–f) did not sig-
nificantly affect the chemical yield, selectivity, or isomeric
ratio, although the reaction time was strongly dependent on
the amide substrate (Table 2, entries 3–5). It should be
noted that sulfonamides with an electron-donating group,
such as OMe (3g) and NEt2 (3h), underwent the desired re-
action without being iodinated at all,[28] giving the corre-
sponding azafulleroids 1g and 1h in 53 and 25% yield, re-
spectively (Table 2, entries 6 and 7).
Selective synthesis of various azafulleroids: For the selective
synthesis of azafulleroid 1a, NIS was found to be the best
reagent among those tested in terms of chemical yield and
selectivity. Thus, having established reaction conditions for
the selective synthesis of azafulleroid 1a, a wide range of
Table 2. Amide scope for the selective synthesis of azafulleroids 1.[a]
In the case of the reaction with 3h, the use of one equiva-
lent of the alternative iodinating reagent DIH improved the
chemical yield to 36% (Table 2, entry 8). Six- and five-mem-
bered heteroarene-substituted sulfonamides 3i–k were also
found to be amenable to the reaction conditions (Table 2,
entries 9–11). Specifically, the bromothiophene-substituted
azafulleroid 1k is an intriguing molecule (Table 2, entry 11)
because it could serve as a versatile building block for
donor–acceptor (D–A) fullerene dyads, which could be ap-
plicable to photosynthetic systems or single-molecule organ-
ic solar cells (SMOCs).[29] Furthermore, [60]fullerene was
successfully transformed into alkylsulfone-substituted aza-
fulleroids 1l and 1m by the reactions with simple alkylsulfo-
namides 3l and 3m, respectively, in high yields (Table 2, en-
tries 12 and 13). It is worth noting that the Me3Si group was
compatible with the concomitant use of an electrophilic io-
dinating reagent to provide the corresponding azafulleroid
1n (Table 2, entry 14). In addition to a wide variety of
Entry RNH2
3
t
Yield[b] Selectivity[c] 1/2[d]
[h] [%]
[%]
1
2
3b
3c
7
54
96
100:0
95:5
72 43
60
3[e]
3d
3e
3 f
12 44
24 50
72 41
30 53
92
100
88
100:0
100:0
95:5
4
5
6
3g
3h
3i
81
95:5
sulfonACHTNUTRGNEaUNG mides, phosphoric amides, such as 3o and 3p, were
also amenable to the reaction conditions and gave the unfa-
miliar phosphorous-substituted azafulleroids 1o and 1p as
the single isomeric products in good yields (Table 2, en-
tries 15 and 16). In all cases, unreacted C60 was easily sepa-
rated from the resulting iminofullerenes by column chroma-
tography on silica gel and was reusable. The structures of all
synthesized azafulleroids were identified by standard spec-
7
24 25
36 36
96
82
100:0
100:0
8[e]
9[f]
6
62
98
75
91
100:0
100:0
100:0
10[e,g]
11[f]
3j
24 40
3k
3l
36 29
20 60
1
troscopic techniques, such as H and 13C NMR, IR, and UV/
12
13
14[g]
84
85
98:2
95:5
Vis spectroscopy, and FAB-MS.[30] The 13C NMR spectra of
azafulleroids 1 showed 32 signals ranging from 130 to
150 ppm that were assignable to sp2 carbon atoms of the C60
skeleton, thereby supporting the Cs symmetry of the [5,6]-
open structure.[6e]
3m 22 46
3n
6
35
67
100:0
15
3o
12 43
12 24
86
100:0
16[g]
3p
65
100:0
Notably, the treatment of C60 with NIS and bis(sulfona-
mide) 3q, which contains a fluorene moiety, exclusively pro-
vided an A–D–A dumbbell-shaped azafulleroid 1q as a
single isomer in high yield [Eq. (2)].[31]
Furthermore, the selective functionalization reaction was
successfully applied to C70 to give aza[70]fulleroids[6a,b] as a
mixture of regioisomers 4a ([2,3]-open) and 4a’ ([7,8]-open)
[a] Reaction conditions: C60 (0.05 mmol), NIS (0.1 mmol), and
3
(0.05 mmol) in o-DCB (25 mL) at room temperature for the time indicat-
ed. [b] Combined isolated yield of 1 and 2. [c] See ref. [15]. [d] Isomeric
ratio of 1/2 determined by 1H NMR spectral integration. [e] One equiva-
lent of DIH was used instead of NIS. [f] Three equivalents of NIS were
used. [g] Reaction was conducted at 08C.
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Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
FULL PAPER
tive were screened (Table 3).
We were delighted to find that
the addition of an equimolar
amount of
a metal salt en-
hanced the reaction efficiency,
although the use of an organic
salt was ineffective (Table 3, en-
tries 1–6). Among the salts ex-
amined, NaI was found to be
Table 3. Optimization study for the selective synthesis of aziridinofuller-
enes 2.[a]
in 41% combined yield [Eq. (3)]. Although control over the
regioselectivity was difficult in this case, it is worth noting
that the chemical yield was considerably improved com-
pared with the reaction that utilizes organoazides.[6a]
[d]
Entry Solvent
t
T
Additive Yield[b]
[%]
2a/1a[c] C60
[min] [8C]
[%]
1
2
3
4
5
6
7
8
9
10
11
12
13
o-DCB
o-DCB
o-DCB
o-DCB
o-DCB
o-DCB
30
30
30
30
30
30
25
25
25
25
25
25
25
25
25
25
60
0
NaBr
NaI
LiI
13 (33)
31 (94)
8 (32)
21 (66)
13 (33)
0 (À)
100:0
100:0
100:0
100:0
100:0
–
78:22 83
56:44 55
–
60
67
75
68
61
91
KI
CuI
nBu4NI
NaI
NaI
NaI
NaI
NaI
NaI
NaI
Cl2CHCHCl2 30
3 (18)
8 (18)
0 (À)
C6H5Cl
toluene
o-DCB
o-DCB
o-DCB
o-DCB
30
30
60
30
30
50
91
61
53
76
44
Selective synthesis of [6,6]-closed aziridinofullerenes: After
having established the selective synthetic method for azaful-
leroids, we turned our attention to the development of a se-
lective synthesis of the aziridinofullerenes that would serve
as a complementary method to the sulfonamide/NIS system.
In light of the fact that the reaction of C60 with some bromi-
nating reagents, such as NBS, NBSac, and DBH, exclusively
provided aziridinofullerene 2a instead of azafulleroid 1a,
(e.g., entries 18, 22, and 23 in Table 1), we assumed that
N,N-dibromo-para-toluenesulfonamide (TsNBr2; 5a) would
be the key chemical species in the reaction. To test this hy-
pothesis, we conducted the reaction of C60 with 5a, which
can be readily prepared by treating amide 3a with Br2 and
NaOH or by treating chloramine-T with Br2 in water.[32] As
anticipated, aziridinofullerene 2a was produced as the sole
product in 10% yield, albeit in low selectivity, without the
formation of azafulleroid 1a [Eq. (4)].
27 (69)
7 (15)
24 (100) 100:0
41 (74) 100:0
100:0
100:0
0
[a] Reaction conditions: C60 (0.05 mmol), 5a (0.05 mmol), and an additive
(0.05 mmol) in a solvent (25 mL) at the reaction temperature for the
time indicated. [b] Combined isolated yield of 2a and 1a; the values in
parentheses indicate selectivity for products. [c] Determined by 1H NMR
spectral integration. [d] Recovery of unreacted C60.
the most effective (Table 3, entry 2). The choice of the or-
ganic solvent had a significant influence on not only the
chemical yield, but also the isomeric ratio of 2a/1a, al-
though the reason for the solvent effect remains unclear at
this point (Table 3, entries 7–9). The fact that the use of tol-
uene, which is a sufficient solvent for the dissolution of full-
erene, failed to consume C60 might suggest the involvement
of a radical species in the reaction pathway (Table 3,
entry 9). A prolonged reaction time (60 min) resulted in a
decrease in chemical yield, as well as in selectivity, which is
probably attributable to the formation of multiadducts as
the reaction proceeded (Table 3, entry 2 vs. 10). The reac-
tion that was conducted at a higher temperature (608C) did
not improve the chemical yield or the selectivity (Table 3,
entry 11). In sharp contrast, the reaction that was conducted
at a lower temperature (08C) was beneficial in terms of pro-
viding good chemical yield and selectivity, probably due to
the suppression of further reactions, such as multiaddition
(Table 3, entry 12). Lastly, the reaction that was carried out
To improve the chemical yield and selectivity for 2a, the
reaction parameters of solvent, time, temperature, and addi-
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S. Minakata et al.
Table 4. N,N-Dibromoamide scope for the selective synthesis of aziridi-
Table 3, entry 8], possible isomerization routes between aza-
fulleroid and aziridinofullerene were taken into considera-
tion. Isolated 1a and 2a were separately subjected to the re-
action conditions that produced each isomer: 1a was treated
with two equivalents of I2 and N-chloro-N-sodiosulfonamide
in toluene at room temperature; 2a was treated with an
equimolar mixture of NaI and DBT in chlorobenzene. No
isomerization was observed in either case. These results are
consistent with the fact that isomerization between N-tosyl
iminofullerenes 1a and 2a requires photochemical (from 1a
to 2a)[6a] or thermal stimuli (from 2a to 1a),[11b] although the
ease of isomerization of other iminofullerenes would strong-
ly depend on their N-substituents.[34] Thus, iminofullerenes
1a and 2a would be independently formed directly from C60
in both cases, and not by way of these isomerization path-
ways.
nofullerenes.[a]
Entry
1
RNBr2
5
t
Yield[b]
[%]
Selectivity[c]
[%]
[h]
5b
5r
0.75
0.5
40
33
70
2[d]
100
3
4
5
5d
5e
5 f
6
1
2
39
42
29
65
68
63
6[d]
7
5l
1
2
46
46
66
82
5n
Regarding the reactive species in the selective reactions,
the involvement of N,N-dihalosulfonamides or related spe-
cies should be considered. We have previously reported that
tert-butyl hypoiodite (tBuOI) is a powerful iodinating re-
agent for compounds containing acidic hydrogen atoms,
such as carboxamides[18d] or N-alkenyl sulfonamides.[18f] It is
reasonable to speculate that proton exchange with iodine is
a favored process because the acidity of the amine-bonded
hydrogen atom of the arylsulfonamides is much higher than
that of arylcarboxamides (e.g., the pKa values of PhSO2NH2
and PhC(O)NH2 in DMSO are 16.1 and 23.3, respective-
ly).[35] In fact, when sulfonamide 3a was treated with two
equivalents of tBuOI in CD3CN at room temperature, the
[a] Reaction conditions: C60 (0.05 mmol),
5 (0.05 mmol), and NaI
0.05 mmol) in o-DCB (25 mL) at 08C for the time indicated. [b] Isolated
yield. [c] See ref. [15]; [d] The reaction was carried out at room tempera-
ture.
at 08C for 50 min was found to give 2a exclusively in 41%
yield with 74% selectivity; this result provides the most effi-
cient value for the preparation of [6,6]-closed N-Ts aziridi-
nofullerene 2a from C60 under these mild conditions.[13]
To test the versatility of the method, we examined the
substrate scope of the reaction (Table 4). The N,N-dibromo-
sulfonamides 5 were prepared according to reported meth-
ods.[32] Electronically neutral and deficient dibromoamides
were amenable to the reaction, providing the corresponding
aziridinofullerenes 2b, 2r, and 2d–f as the sole products in
good yields in all cases (Table 4, entries 1–5). The presence
of an alkyl substituent on the sulfonyl group did not affect
the efficiency of the reaction (Table 4, entries 6 and 7). In
all cases, no formation of the azafulleroid was observed. All
aziridinofullerenes 2 were characterized in a similar way to
azafulleroids.[30] In particular, 13C NMR spectroscopic mea-
1
broad singlet signal at around d=5.6 ppm in the H NMR
À
spectrum, which is attributable to the two N H protons,
completely disappeared, and an aromatic signal shifted from
d=7.74 to 7.82 ppm (see the Supporting Information, Fig-
ure S2), indicating the formation of diiodoamide A or its oli-
gomeric species, such as [TsN]3I4 (Scheme 1).[36] Treatment
ACHTUNGTRENNUNGsurements were useful for the identification of structural
symmetry. The existence of 15 signals in the region of d=
130–150 ppm indicated the C2v symmetric structure of the
[6,6]-closed monoadduct. At the same time, the peak at
around 80 ppm gave strong evidence for the presence of an
sp3-hybridized carbon in the fullerene sphere.[33] Also, the
UV/Vis spectra of compounds 2 showed characteristic ab-
sorption peaks at around 420 nm that indicate the [6,6]-
closed structure (see later).
Scheme 1. Preparation of N,N-diiodoamide A and its reaction with C60.
of the resulting solution with C60 in o-DCB gave azafulleroid
1a as the sole product in 30% yield with moderate selectivi-
ty. Furthermore, the reaction of C60 with p-NO2-C6H4SO2-
NI2 (p-NsNI2), which was readily prepared by halogen ex-
change of p-NsBr2 with I2 and is an isolatable compound,[36]
provided the p-Ns-substituted azafulleroid 1e in 26% yield
with 65% selectivity (see the Supporting Information,
Investigation of the reaction pathways, reactive species, and
mechanisms: Based on the fact that the isomeric mixtures of
iminofullerenes were formed in some cases [see Eq. (1) and
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Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
FULL PAPER
Table 5. Reaction of C60 with TsNX2 in the presence/absence of ambient
light.
Scheme S1). These results support the suggestion that N,N-
diiodosulfonamide A or its oligomeric complex [TsN]3I4 is
the active species in the selective formation of azafulle-
roids.[37]
Although structure-defined N,N-dibromosulfonamides
were employed in the synthesis of aziridinofullerenes, under
the optimal conditions the involvement of N-bromo-N-so-
diotosylamide (bromamine-T (BT)) or halogen-exchanged
N-bromo-N-iodotosylamide B, which could be generated by
an SN2 reaction with IÀ at the Br or N center, respectively,
should be taken into consideration (Scheme 2). The possible
[b]
Entry
Reagents
hn or dark
Product
Yield[a]
[%]
C60
[%]
1[c]
2[c]
3[e]
4[e]
dark
hn[d]
dark
hn[d]
1a
1a
2a
2a
9 (100)
52 (100)
18 (86)
41 (74)
91
48
79
44
TsNH2/NIS
TsNBr2/NaI
[a] Isolated yield; the values in parentheses indicate selectivity for prod-
ucts. [b] Yield of recovered C60. [c] Reaction conditions: C60 (0.05 mmol),
NIS (0.1 mmol), and TsNH2 (0.05 mmol) in o-DCB (25 mL) at room tem-
perature for 3 h. [d] Under illumination of laboratory fluorescent light.
[e] Reaction conditions: C60 (0.05 mmol), TsNBr2 (0.05 mmol), and NaI
(0.05 mmol) in o-DCB (25 mL) at 08C for 50 min.
nofullerenes were remarkably decreased (Table 5, entries 1
and 3) compared to the results obtained in the presence of
ambient light (Table 5, entries 2 and 4). Furthermore, the
addition of stoichiometric amounts of Galvinoxyl, a repre-
sentative free-radical inhibitor, suppressed the reaction com-
pletely to provide quantitative recovery of C60 in both
cases.[40] These results indicated the involvement of radical
species in both selective reactions. To obtain further insight
into the character of these radical species, several experi-
ments were conducted. Bubbling O2 over the reaction of C60
with TsNX2 (X=Br, I) did not retard the reaction efficiency
(see the Supporting Information, Scheme S3), thus excluding
the involvement of the excited triplet state of C60 (3C60*),
which is highly susceptible to O2 and should be easily
quenched if O2 is present.[41] Furthermore, UV/Vis/NIR
spectroscopic analysis of the mixture of TsNX2 and C60 in
ortho-dichlorobenzene did not show any absorption bands
in the range of 850 to 1150 nm, which would be characteris-
Scheme 2. Exclusion of the possible involvement of other species.
involvement of either BT or B was excluded by the follow-
ing experiments: 1) the treatment of C60 with BT, which can
be readily prepared from chloramine-T and Br2,[38] did not
give any iminofullerene products, only unreacted C60 was re-
covered quantitatively; 2) no liberation of IBr was observed
in a UV/Vis spectroscopic study (see the Supporting Infor-
mation, Figure S3); and 3) the reaction of C60 with mixed di-
haloamide B, generated separately by the treatment of BT
with BPIT, which is the I+ provider, yielded azafulleroid 1a,
instead of aziridinofullerene 2a, in 7% yield (see the Sup-
porting Information, Scheme S2). Although details of the
exact species involved remain unclear at present, we pro-
pose that an iodide attack on the positive bromine to form
pseudopolyhalide complex [TsN(Br)Br-I]ÀNa+[39] is likely to
CÀ
tic for a fullerene radical anion (C60 , see the Supporting In-
formation, Figure S4).[42] These results suggest that the elec-
3
tron transfer from dihalosulfonamide to C60* to generate
CÀ
À
weaken the N Br bond enough for either homolytic or het-
the fullerene anion C60 is less likely to have occurred in
erolytic cleavage.
the reaction systems.
It is interesting to note that the reaction of TsNX2 (X=
Br, I) with C60 required the presence of laboratory light for
the reaction to progress efficiently (Table 5). When the reac-
tion was conducted in the dark, chemical yields of the imi-
On the basis of these experimental results, we propose a
plausible reaction mechanism in Scheme 3. The first step
À
would involve the homolytic cleavage of the N X bond of
C [43]
RSO2NX2 to generate the amidyl radical RSO2(X)N ,
a
Scheme 3. Plausible reaction mechanism.
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S. Minakata et al.
process which should be promoted by visible light.[44] In
light of the quite small bond dissociation energy (BDE) for
330 nm peak and a slight redshift of the absorption edge,
suggesting the existence of a weak donor–acceptor interac-
tion in these compounds. Dumbbell-shaped azafulleroid 1q
showed an enhanced absorption coefficient due to the dou-
bled number of fullerene moieties per molecule. As for azir-
idino[60]fullerenes 2, diagnostic peaks at around 420 nm,
which are characteristic of the 1,2 adduct at the [6,6] junc-
tion, were identified in all cases.; however, no significant
changes in the shape of the absorption spectra or absorption
edges were observed.
À1 [45]
À
the N I bond (130 kJmol ),
reasonable. The addition of NaI should play an important
this assumption would be
À
role in the homolytic fission of the slightly stronger N Br
bond (BDE ꢀ220 kJmolÀ1), as discussed in the previous
sections. The possibilities are that IÀ coordinates to Br to
form [TsN(Br)Br-I]ÀNa+, facilitating the fission of weaker
À
À
N Br bonds; or that I functions as a reductant to form
À [46]
C
Ts(Br)N and Br .
The resulting amidyl radical would
react with C60 to generate fullerene radical C. Because the
highest spin density of the monoadduct fullerene radicals is
reportedly localized on the carbon adjacent to the [6,6]-junc-
tion substituent,[47] it is reasonable that the reaction would
proceed from this position. When a considerably bulky and
soft halogen substituent, such as iodine, is added to the ni-
trogen atom, the radical would attack the iodine atom
rather than the sterically congested nitrogen atom, giving an
N-centered radical with a 1,2 substituent on the fullerene
cage (D). The subsequent intramolecular cyclization at the
With the aim of applying the synthesized iminofullerenes
as n-type semiconducting materials in photovoltaic devices,
solubility, thermal stability, and electrochemical properties
of the products were investigated (Table 6). Solubility is an
Table 6. Summary of the properties of azafulleroids and aziridinofuller-
enes.
[b]
[c]
Compound
Solubility[a]
[wt%]
Td
redE1
[V]
LUMO[d]
[eV]
G
[8C]
C60
PC61BM
1a
1b
1c
1d
1e
1 f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
2a
2b
2d
2e
2 f
0.32[e]
–
0.33
0.29
0.51
0.76
>1.10
0.16
0.50
–
–
À1.010
À1.074
À0.927
À0.905
À0.937
À0.909
À0.846
À0.927
À0.913
À0.938
À0.910
À0.912
À0.898
À0.907
À0.914
À0.938
À0.974
À0.959
À0.860
À0.933
À0.906
À0.914
À0.865
À0.923
À0.917
À0.944
À0.860
À3.80
À3.72
À3.87
À3.89
À3.86
À3.89
À3.95
À3.87
À3.89
À3.86
À3.87
À3.89
À3.90
À3.89
À3.89
À3.86
À3.83
À3.84
À3.94
À3.88
À3.89
À3.89
À3.94
À3.88
À3.88
À3.86
À3.94
C
[5,6] junction and the corresponding liberation of I should
326
358
328
237
301
318
313
242
301
266
260
334
331
310
354
265
329
248
268
241
158
336
217
135
193
provide the [5,6]-closed iminofullerene E; and spontaneous
electrocyclization would provide the [5,6]-open azafulleroid
1. On the other hand, when the halogen substituent is bro-
mine, which is more electronegative and has a smaller size
than iodine, the fullerene radical would directly attack at
the nitrogen atom, leading to the [6,6]-closed aziridinofuller-
ene 2.
0.29
0.57
>1.10
>1.10
0.38
<0.10
>1.10
<0.10
0.50
0.08
0.76
0.57
0.69
Properties of the products: With a series of the iminofuller-
enes 1 and 2 in hand, their various properties were investi-
gated to asses the products as candidates for n-type semi-
conducting materials. Absorption spectra of dilute solutions
of iminofullerenes in CH2Cl2 were measured at a concentra-
tion of 10À5 m, and representative spectra are shown in
Figure 2.[48] As reported in the literature, all the azafulle-
0.76
0.12
0.57
0.76
2l
2n
2r
0.19
[a] The solubility in toluene at room temperature. [b] The degradation
temperature at which 5% weight loss occurs under N2 flow. [c] Measured
in a mixed solvent of o-DCB/CH3CN (4:1) by using nBu4NPF6 as an elec-
trolyte at a scan rate of 0.1 VsÀ1; the onset potentials of the first reduc-
tion peak versus Fc/Fc+ (Fc=ferrocene). [d] Estimated from the follow-
ing equation: LUMO=(4.8+redE1) eV. [e] See ref. [50].
Figure 2. UV/Vis absorption spectra of solutions of: a) azafulleroids 1a,
1h, 1p, and 1q, and b) aziridinofullerenes 2a, 2d, 2e, and 2l in CH2Cl2.
important factor for the realization of solution-processed
fabrication of organic optoelectronic devices.[49] The solubili-
ty of iminofullerenes was found to strongly depend on the
nature of the substituent on the amide group. Specifically,
para-nitrophenylsulfonyl- (1e), thienylsulfonyl- (1j and k),
and (trimethylsilyl)ethylsulfonyl-substituted (1n) azafulle-
roids exhibited sufficient solubility in toluene (over
1.1 wt%), which is more than three times higher than that
roids 1 showed distinct absorption at around 330 nm and a
broad peak centered at around 550 nm, which are character-
istic of the [5,6]-open aza[60]fulleroids (Figure 2a). It is
worth noting that azafulleroids containing NEt2 (1h) and
P(O)ACHTUNGTRENNUNG(OEt)2 (1p) groups exhibited a broadening of the
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Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
FULL PAPER
of pristine C60 (ca. 0.32 wt%).[50] Thermogravimetric analysis
(TGA) of the iminofullerenes (see the Supporting Informa-
tion, Figure S5) revealed that azafulleroids 1 are quite ther-
mally stable (Td >2308C), whereas the Td of aziridinofuller-
enes 2 varied, ranging from as low as 1358C (2n) to as high
as 3368C (2 f).
To evaluate electrochemical behavior and estimate the
LUMOs of the iminofullerenes, cyclic voltammetry (CV)
was conducted (see the Supporting Information, Figure S6).
Although many of the azafulleroids 1 showed a quasi-rever-
sible reduction peak at around À0.9 V against the Fc/Fc+
redox potential, a few compounds, such as PhSO2-substitut-
ed azafulleroid 1b and nBuSO2-substituted 1m, did not ex-
hibit any reversibility in the reduction cycle. Aziridinofuller-
enes 2 were less stable to electrochemical reduction in ho-
Figure 3. a) Device architecture of the p–n-heterojunction photovoltaic
device containing an iminofullerene 1 or 2; and b) current-density–volt-
*
)
age characteristics of the device containing 1g under dark conditions (
and under illumination (AM 1.5 G, 100 mWcmÀ2
;
~
).
mogeneous solution than azafulleroids 1, leading to difficul-
red
ty in determining the half-wave potential (
E
) for the
smooth electron-transfer from iminofullerenes to Al,[54] was
conducted by vacuum deposition. Representative current-
density–voltage (J–V) curves of the device based on azaful-
leroid 1g under dark conditions and under AM 1.5 G illumi-
nation are shown in Figure 3b.[55] The distinct photocurrent
generation under light illumination clearly demonstrated
that the azafulleroid 1g functioned as an electron-transport-
ing material.
The parameters of device performances of the voltaic de-
vices, including the open-circuit voltage (VOC), short-circuit
current density (JSC), fill factor (FF), and power conversion
efficiency (PCE), are summarized in Table 7 with those of a
1/2
first reduction. These results were in remarkable contrast to
the aza-analogues of PC61BM developed by Wudl et al.,
which showed clear, reversible electrochemical reduction
peaks.[4,5] This difference in behavior for the electrochemical
reduction could be ascribed to the existence of a strongly
electron-accepting sulfonyl moiety, which would function as
a good electron acceptor and immediately degrade from the
À
R2N·SO2 , making analysis of the results difficult.[51]
The LUMOs were estimated from the reduction potential
onsets (Table 6), together with those of C60 and PC61BM for
comparison. All of the iminofullerenes showed lower
LUMOs than those of C60 (À3.80 eV) and PC61BM
(À3.72 eV). However, APCBMs[4,5] exhibited slightly higher
LUMOs than those of PC61BM, and higher again than C60.
These lower LUMOs are probably due to the existence of
the strong electron-withdrawing sulfonyl group in 1 and 2,
which causes a lowering of the LUMOs by an inductive
effect.
Table 7. Summary of the performance of PVCs under AM 1.5 G illumi-
nation.
Compound
VOC
[V]
JSC
[mAcmÀ2
]
FF
PCE
[%]
U
PC61BM
1a
1e
1n
1g
1p
2a
2e
2n
0.73
0.53
0.44
0.55
0.55
0.50
0.58
0.51
0.61
6.2
8.1
7.8
7.6
7.5
6.2
7.7
5.8
5.8
0.45
0.53
0.56
0.47
0.57
0.43
0.49
0.45
0.46
2.05
2.29
1.94
2.00
2.35
1.33
2.19
1.34
1.61
Application to photovoltaic cells: Based on the information
about these physical and chemical properties, photovoltaic
cells containing iminofullerenes as an electron-transporting
material were fabricated. The iminofullerene samples for
the application were chosen according to the criterion that
their solubility was higher than that of C60 (0.32 wt% in tol-
uene), for the purpose of solution-processing of an n-type
material. The configuration of the device was based on a
simple p–n-heterojunction structure as shown in Figure 3a.
Molybdenum trioxide (MoO3) was deposited by a vacuum-
evaporation method onto an indium tin oxide (ITO) elec-
trode as an intermediate layer.[52] Tetravalent oxometal ti-
tanyl phthalocyanine (TiOPc) was fabricated by a vacuum-
deposition technique on this intermediate layer to act as a
hole-transporting layer.[53] The electron-transporting layer
was deposited by spin-coating with a solution of iminofuller-
ene 1 or 2 in chlorobenzene (0.5 wt%), followed by anneal-
ing at 1208C for 5 min under an inert atmosphere. The suc-
cessive deposition of a buffer layer of bathocuproine (BCP),
which would form an Ohmic contact between an Al elec-
trode and an electron-transporting layer to facilitate the
PC61BM-based device for comparison. Among the devices
fabricated, those based on 1j, 4a (and 4a’), and 2b did not
provide sufficient curves for assessment. For all devices, VOC
values were lower than that of the device with PC61BM
(0.73 V), reflecting the lower LUMOs compared to
PC61BM, although the precise correlation between LUMOs
and VOC was not obtained.[56] PCEs of the devices exceeded
1.0%. Notably, the devices using 1a, 1g, and 2a showed
higher PCEs than that of the PC61BM-based device
(2.05%). Although it could be hard to compare with the
performance of BHJ solar cells composed of other soluble
fullerene-based materials, the results shown here demon-
strate the high potential of the iminofullerenes as electron-
transporting materials.
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S. Minakata et al.
thors (Y.T.) would like to acknowledge support from the Frontier Re-
search Base for Global Young Researchers, Osaka University, on the
Program of MEXT.
Conclusion
We have developed highly selective methods for the synthe-
sis of azafulleroids and aziridinofullerenes under mild condi-
tions by using easily handled N,N-dihaloamides as the key
chemical species. The reactions tolerated various amide
functionalities and allowed isomeric iminofullerenes to be
obtained in high yields. Furthermore, we have demonstrated
that the iminofullerenes reported herein function as good
electron-transporting materials in p–n-heterojunction photo-
voltaic devices.
[1] For comprehensive books and reviews of the reactivity and function-
alization of fullerenes, see: a) A. Hirsch, M. Brettreich, Fullerenes:
Chemistry and Reactions, Wiley-VCH, Weinheim, 2005; b) Fuller-
enes: Chemistry, Physics, and Technology (Eds.: K. M. Kadish, R. S.
Ruoff), Wiley-Interscience, New York, 2000; c) K. Itami, Chem.
Rec. 2011, 11, 226; d) Y. Matsuo, E. Nakamura, Chem. Rev. 2008,
108, 3016; e) N. Martꢂn, M. Altable, S. Filippone, A. Martꢂn-Dome-
nech, Synlett 2007, 3077; f) N. Martꢂn, Chem. Commun. 2006, 2093.
[2] For comprehensive reviews of fullerene-based materials, see: a) C.-
Z. Li, H.-L. Yip, A. K.-Y. Jen, J. Mater. Chem. 2012, 22, 4161; b) A.
Montellano Lꢃpez, A. Mateo-Alonso, M. Prato, J. Mater. Chem.
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R. Kumar, F. Wudl, J. Mater. Chem. 2010, 20, 2934; e) D. M. Guldi,
B. M. Illescas, C. M. Atienza, M. Wielopolski, N. Martꢂn, Chem. Soc.
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D. M. Guldi, Chem. Soc. Rev. 2005, 34, 31; k) F. Wudl, J. Mater.
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1097.
Experimental Section
Typical procedure for the synthesis of azafulleroids by using amides and
N-iodosuccinimide: N-Iodosuccinimide (22.5 mg, 0.1 mmol) was added to
a solution of a fullerene (36 mg, 0.05 mmol) and an amide (0.05 mmol) in
o-DCB (25 mL). The resulting mixture was allowed to stir at room tem-
perature for the time indicated in Table 1. After completion of the reac-
tion, the mixture was passed through a short column on a silica gel pad
(3 g), and the solvent was evaporated under reduced pressure. The resi-
due was purified by column chromatography on silica gel.
Compound data for a representative azafulleroid, 1c: Black solid; Rf =
0.34 (1:1 toluene/hexane); 1H NMR (270 MHz, CDCl3): d=8.88 (d, 1H,
J=8.1 Hz), 8.57 (dd, 1H, J=1.4, 7.6 Hz), 8.19 (d, 1H, J=8.1 Hz), 7.98
(d, 1H, J=7.6 Hz), 7.71–7.77 (m, 1H), 7.61–7.70 ppm (m, 2H); 13C NMR
(125 MHz, CDCl3): d=147.9, 147.3, 144.7, 144.4, 144.3, 144.2, 144.14,
144.08, 144.0, 143.71, 143.69, 143.5, 143.3, 143.1, 143.0, 142.9, 142.7, 141.8,
141.7, 140.14, 140.06, 139.8, 138.7, 138.5, 138.4, 137.9, 136.03, 135.99,
134.9, 134.3, 133.54, 133.50, 131.8, 129.1, 128.9, 128.8, 127.3, 125.2 ppm;
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FTIR (KBr): n˜ =3434, 1509, 1338, 1164, 1134, 766 cmÀ1
; UV/Vis
(CH2Cl2): lmax =224, 258, 322 nm; HRMS (FAB): m/z calcd for
[5] S. H. Park, C. Yang, S. Cowan, J. K. Lee, F. Wudl, K. Lee, A. J.
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C70H7NO2S: 925.0234 [M]+; found: 925.0197.
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Typical procedure for the synthesis of aziridinofullerenes by using N,N-
dibromoamides and NaI: Sodium iodide (7.5 mg, 0.05 mmol) was added
to a solution of a fullerene (36 mg, 0.05 mmol) and an N,N-dibromo-
ACHTUNGTRENNUNGamide (0.05 mmol) in o-DCB (25 mL). The mixture was allowed to stir at
room temperature for the time indicated in Table 4. The solution was
passed through a short column on a silica gel pad (3 g), and the solvent
was evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel.
Compound data for a representative aziridinofullerene, 2d: Black solid;
1
Rf =0.38 (1:1 toluene/hexane); H NMR (270 MHz, CDCl3): d=8.61–8.64
(m, 1H), 8.12–8.15 (m, 1H), 7.96–8.02 ppm (m, 2H); 13C NMR (68 MHz,
CDCl3): d=147.4, 145.4, 145.3, 145.2, 144.6, 144.5, 144.0, 143.6, 143.3,
143.2, 143.1, 142.8, 142.3, 142.1, 141.2, 140.8 (2C), 134.8, 134.1, 133.2,
131.1, 125.7, 80.6 ppm; FTIR (KBr): n˜ =3434, 1539, 1363, 1169, 1121,
526 cmÀ1; UV/Vis (CH2Cl2): lmax =316, 253, 224 nm; HRMS (FAB): m/z
calcd for C66H4N2O4S: 919.9892 [M]+, found: 919.9927.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research on
Innovative Areas (Molecular Activation Directed toward Straightforward
Synthesis) from the Ministry of Education, Culture, Sports, Science, and
Technology (MEXT), Japan. We thank Dr. Takamichi Yokoyama and Dr.
Izuru Takei (Mitsubishi Chemical Group Science and Technology Re-
search Center, Inc.) for their assistance with fabrication of the photovol-
taic devices and measurement of their performance. We also acknowl-
edge fruitful discussions with Dr. Junya Kawai (Mitsubishi Chemical
Group Science and Technology Research Center, Inc). One of the au-
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Syntheses of Aza[60]fulleroids and Aziridino[60]fullerenes
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Received: May 14, 2012
Published online: && &&, 0000
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S. Minakata et al.
Fullerenes
T. Nagamachi, Y. Takeda,
K. Nakayama, S. Minakata* &&&& — &&&&
Selective Functionalization of Fuller-
enes with N,N-Dihalosulfonamides as
an N1 Unit: Versatile Syntheses of
Aza[60]fulleroids and Aziridino[60]-
fullerenes and their Application to
Photovoltaic Cells
Full steam ahead: Highly selective and
versatile syntheses of aza[60]fulleroids
and aziridino[60]fullerenes from C60,
which utilize N,N-dihalosulfonamides
as an N1 source, were developed. Pho-
tophysical, electrochemical, and ther-
mal properties of the iminofullerenes
were measured, and photovoltaic cells
based on these compounds were fabri-
cated. The power conversion efficien-
cies (PCEs) of the devices show mod-
erate values ranging from 1.33 to
2.35% (see scheme).
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These are not the final page numbers!