Fullerene sensors based on calix[5]arene

Article abstract of DOI:10.1039/b205048j

A new class of fullerene sensors based on calix[5]arenes has produced the highly sensitive detection of C₆₀ and C₇₀.

Full text of DOI:10.1039/b205048j

Fullerene sensors based on calix[5]arene
Takeharu Haino,a Hiromi Araki,a Yoshihisa Fujiwara,b Yoshifumi Tanimotob and Yoshimasa
Fukazawa*a
a Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama,
Higashi-Hiroshima 739-8526, Japan. E-mail: fukazawa@sci.hiroshima-u.ac.jp
b Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, 1-3-1
Kagamiyama, Higashi-Hiroshima 739-8526, Japan
Received (in Cambridge, UK) 27th May 2002, Accepted 2nd August 2002
First published as an Advance Article on the web 22nd August 2002
A new class of fullerene sensors based on calix[5]arenes has
produced the highly sensitive detection of C60 and C70.
The development of chemical sensors has received broad
attention in recent years. One of the most appealing approaches
involves the combination of supramolecular concepts and
luminescence techniques. A number of sensors1 have been
developed with a focus upon selective binding for metal ions,
phosphates and neutral molecules coupled with luminescence
signal modulation.
During our investigation on fullerene receptors, we have
developed calix[5]arene-based fullerene receptors, which show
high selective binding for C60 and/or C70.2 Among numerous
studies on developing fullerene receptors reported so far,3 the
fullerene sensor is limited. We envisioned developing fullerene
sensors. Our strategy for the fullerene sensor is based on the
introduction of a covalently attached lumophore onto the
fullerene binding site. Since it is well known that fullerene is a
good acceptor in an energy transfer reaction, it might act as a
good luminescence quencher. The luminescence of the sensor
can be quenched when fullerene is situated in close proximity to
the lumophore. This optical response should produce highly
sensitive detection for fullerenes. Along this concept, sensors 1
and 2 have been designed.
Sensors 1 and 2 are soluble in toluene. Strong orange
luminescence showed up when the solution of 1 was exposed to
365 nm UV light (Fig. 1). Addition of C60 or C70 to the solution
of 1 caused a dramatic change. The luminescence was
immediately extinguished upon the addition of C60 or C70. The
steady-state phosphorescence spectral change of 1 in toluene
(lexc = 400 nm) is shown in Fig. 2. The characteristic
luminescence band appearing around 600 nm was assigned to
the metal-to-ligand charge transfer (MLCT) band.8 Upon the
addition of C60 to the solution of 1 in toluene, the luminescence
intensity gradually decreased (Fig. 2). In order to discuss the
quenching quantitatively, Stern–Volmer analysis was carried
out for 1, 2 and Re(bpy)(CO)3Cl 12 with C60 or C70 in toluene.
Steady-state luminescence quenching studies with C60 yielded
two linear Stern–Volmer plots for 2 and 12, as shown in Fig. 3.
The results were interpreted in terms of diffusion-controlled
intermolecular quenching between C60 and the lumophore. For
1 with C60 or C70, the quenching is much more efficient than the
others. The quenching of 1 with C60 or C70 produced curved
Stern–Volmer plots (Fig. 3). There should be two luminescence
quenching processes associated with the energy transfer from
the lumophore to the fullerene: one is an intermolecular
quenching process arising from the simple collision between the
unbound fullerene and the lumophore, the other is an intra-
The synthesis of sensors 1 and 2 was started according to
Scheme 1. Coupling reaction of iodocalix[5]arene 34 with
methyl ester 45 through palladium catalysis, followed by
hydrolysis of ester groups produced double-calix[5]arene
carboxylic acid 5. Bipyridine 66 was introduced to 5 to give
double-calix[5]arene 7. Reaction of 7 with Re(CO)5Cl in
toluene at 100 °C produced sensor 1 in 60% yield. Bromobipyr-
idine 84 reacted with 97 through Suzuki conditions to give 10.
Coupling reaction of 10 with 3, followed by basic hydrolysis of
acetyl groups furnished calix[5]arene derivative 11, which
reacted with Re(CO)5Cl in toluene at 100 °C, produced sensor
2 in 46% yield.
Scheme 1
This journal is © The Royal Society of Chemistry 2002
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of 2 for C60 is only 3 times as large as that of 12. This can be
rationalized by the complexation of 2 to C60.10 It appears that
the quenching is mainly due to the intermolecular collision;
however, a small portion of the intramolecular quenching
process should contribute to the quenching. A more obvious
contribution of the intramolecular quenching process in the
bound state is seen in the luminescence quenching of 1 with the
fullerenes. The apparent quenching rate constants (kqapp) are
expressed as follows:
app
kq
= kq[G]0 for 2 and 12
= kq[G] + kqA for 1
Fig. 1 Luminescence changes induced on sensor 1 (1.0 3 1025 mol L21):
(left) in the absence of fullerenes, (middle) with C60, (right) with C70
app
kq
.
where [G]0 and [G] denote the concentration of total and
unbound guests, respectively. The apparent quenching rate
constants (kqapp) were calculated using the Ka value and the total
fullerene concentration of 5.6 3 1026 mol L21 (12: kqapp(C60)
= 7.1 3 104 s21, kqapp(C70) = 4.9 3 104 s21; 2: kqapp(C60) =
21 3 104 s21; 1: kqapp(C60) = 200 3 104 s21, kqapp(C70) = 120
3 104 s21). The apparent luminescence quenching rate
constants of 1 for C60 and C70 are over 20 times higher than that
of 12 at that concentration. This suggests that the apparent
quenching rate constant is strongly associated with the concen-
tration of the bound fullerene; thus, the high binding ability of
1 toward C60 and C70 brings about the extremely high sensitivity
and selectivity11 to them even at concentrations of less than
1025 mol L21
.
We have demonstrated the first example of the highly
sensitive detection of fullerenes using calix[5]arene-based
sensors produced by the combination of the supramolecular
concept and the luminescence technique.
Fig. 2 Steady-state luminescence spectra (lexc = 400 nm) of 1 (5.6 3 1026
mol L21) in toluene upon the addition of C60: a; 0, b; 0.67, c; 1.3, d; 2.0, e;
3.3, f; 4.7, g; 6.0, h; 8.7 (3 1025 mol L21).
Notes and references
1 P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed.., 2001, 40, 486; E. V.
Anslyn and J. J. Lavigne, Angew. Chem., Int. Ed., 2001, 40, 3118.
2 T. Haino, M. Yanase and Y. Fukazawa, Angew. Chem., Int. Ed., 1998,
37, 997; T. Haino, M. Yanase and Y. Fukazawa, Tetrahedron Lett.,
1997, 38, 3739; T. Haino, M. Yanase and Y. Fukazawa, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 259.
3 D. Sun, F. S. Tham, C. A. Reed, L. Chker, M. Burgess and P. D. W.
Boyd, J. Am. Chem. Soc., 2000, 122, 100704; K. Tashiro, T. Aida, J.-Y.
Zheng, K. Kinbara, K. Saigo, S. Sakamoto and K. Yamaguchi, J. Am.
Chem. Soc., 1999, 121, 9477; J. L. Atwood, L. J. Barbour, P. J. Nichols,
C. L. Raston and C. A. Sandoval, Chem. Eur. J., 1999, 5, 990; M. J.
Hardie and C. L. Raston, Chem. Commun., 1999, 1153; H. Matsubara,
T. Shimura, A. Hasegawa, M. Semba, K. Asano and K. Yamamoto,
Chem. Lett., 1998, 1099; K. Tsubaki, K. Takayoshi, T. Kinoshita and K.
Fuji, Chem. Commun., 1998, 895; N. S. Isaacs, P. J. Nicholls, C. L.
Raston, C. A. Sandova and D. J. Young, Chem. Commun., 1997, 1839;
A. Drljaca, C. Kepert, L. Spiccia, C. L. Raston, C. A. Sandoval and T.
D. Smith, Chem. Commun., 1997, 195; T. Andersson, G. Westman, G.
Stenhagen, M. Sundahl and O. Wennerström, Tetrahedron Lett., 1995,
36, 597; J. L. Atwood, G. A. Koutsantonis and C. L. Raston, Nature,
1994, 368, 229; T. Suzuki, K. Nakashima and S. Shinkai, Chem. Lett.,
1994, 699; Z. Yoshida, H. Takekuma, S. Takekuma and Y. Matsubara,
Angew. Chem., Int. Ed. Engl., 1994, 33, 1597.
4 T. Haino, H. Araki, Y. Yamanaka and Y. Fukazawa, Tetrahedron Lett.,
2001, 42, 3203.
5 B. Förster, J. Bertran, F. Teixidor and C. Viñas, J. Organomet. Chem.,
1999, 587, 67.
6 I. Hamachi, S. Tanaka, S. Tsukiji, S. Shinkai and S. Oishi, Inorg. Chem.,
1998, 37, 4380.
7 M. H. Todd, S. Balasubramanian and C. Abell, Tetrahedron Lett., 1997,
38, 6781.
Fig. 3 Stern–Volmer plots of sensors 1, 2 and 12 (5.6 3 1026 mol L21) in
the presence of fullerenes in toluene. The symbols represent the experi-
mental data and the solid lines are given by curve-fitting analysis (1: C70 vs.
1; Ω: vs. 1; 3: C60 vs. 2; +: C60 vs. 12).
molecular quenching process between the bound fullerene and
the lumophore of the complex. It is known that the receptor
bearing two calix[5]arenes shows remarkably strong binding
ability to the fullerenes in toluene.2 Although these plots
qualitatively account for the effect of the fullerene complexa-
tion, more detailed understanding is required to discuss the
quenching properties. For this, luminescence lifetime measure-
ments and the determination of the quenching rate constants
were carried out.
The luminescence lifetimes (t0) of 1, 2 and 12 in toluene were
determined to be 41.4 ns (1), 39.3 ns (2), and 34.5 ns (12),
respectively, by nanosecond laser spectroscopy. The quenching
rate constants (kq)9 on 2 and 12 for C60 or C70 were determined
on the basis of the Stern–Volmer plots and the luminescence
lifetimes (2: kq(C60) = 37.4 3 109 M21 s21, 12: kq(C60) = 12.7
3 109 M21 s21 and kq(C70) = 8.8 3 109 M21 s21). On the other
hand, the non-linear curve fitting analysis of the Stern-Volmer
plots for sensor 1 with C60 or C70 yielded both the inter-
molecular (kq) and the intramolecular quenching rate constants
(kqA) in the bound state, and the binding constants (Ka) (kq(C60)
8 K. A. Walters, L. L. Premvardhan, Y. Liu, L. A. Peteanu and K. S.
Schanze, Chem. Phys. Lett., 2001, 339, 255.
9 The quenching rate conctants of 12 for C60 and C70 were determined by
Stern–Volmer plots of the fullerene concentration vs. t0/t.
10 2: Ka(C60) = 1100 M21; 11: Ka(C60) = 1060 M21, Ka(C70) = 170
M21
.
11 A control experiment with anthracene as a small guest was carried out
= 5.7 3 109 M21 s21, kqA(C60) = 0.0020 3 109 s21, Ka
=
to test the selectivity of 1. A Stern–Volmer plot of 1 produced kq (21.2
71000 M21; kq(C70) = 12 3 109 M21 s21, kqA(C70) = 0.0012
3 109 s21, Ka = 360000 M21).
3 109 M21 21) and kqapp (11.9 3 104 s21 at a total guest concentration
s
of 5.6 3 1026 mol L21) is 17 times as small as that of 1 with C60. This
indicates that sensor 1 shows selective detection of fullerenes even if a
small aromatic guest is present.
Slight enhancement of the quenching rate was observed
between 2 and 12 for C60. The relative quenching rate constant
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