A tunable photosensor

Article abstract of DOI:10.1021/ja805393b

A pyrene-modified β-cyclodextrin (pyrenecyclodextrin)-decorated single-walled carbon nanotube (SWNT) field-effect transistor (FET) device was fabricated, which can serve as a tunable photosensor to sense a fluorescent adamantyl-modified Ru complex (ADA-Ru

Full text of DOI:10.1021/ja805393b

Published on Web 11/14/2008
A Tunable Photosensor
Yan-Li Zhao,† Liangbing Hu,‡ George Gru¨ner,*,‡ and J. Fraser Stoddart*,†,§
Department of Chemistry and Biochemistry, and Department of Physics and Astronomy, UniVersity of
California, Los Angeles, 405 Hilgard AVenue, Los Angeles, California 90095, and Department of
Chemistry, Northwestern UniVersity, 2145 Sheridan Road, EVanston, Illinois 60208
Received July 11, 2008; E-mail: ggruner@ucla.edu; stoddart@northwestern.edu
Abstract: A pyrene-modified ꢀ-cyclodextrin (pyrenecyclodextrin)-decorated single-walled carbon nanotube
(SWNT) field-effect transistor (FET) device was fabricated, which can serve as a tunable photosensor to
sense a fluorescent adamantyl-modified Ru complex (ADA-Ru). When the light is on (I ) 40 W m-2 and
λ ) 280 nm), the transfer curve of the pyrenecyclodextrin-SWNT/FET device shifts toward a negative gate
voltage by about 1.6 V and its sheet resistance increases quickly, indicating a charge-transfer process
from the pyrenecyclodextrins to the SWNTs. In contrast, the transfer curve of the pyrenecyclodextrin-
SWNT/FET device in the presence of the ADA-Ru complex shifts toward a positive gate voltage by about
1.9 V and its sheet resistance decreases slowly when the light is on (I ) 40 W m-2 and λ ) 490 nm),
showing a charge-transfer process from the pyrenecyclodextrin-SWNT hybrids to the ADA-Ru complex.
Because these photoresponse processes are recoverable following the removal of the light, the present
photosensor exhibits a promising application in the area of tunable light detection.
Introduction
remarkably improving their solubilities. For example, Guldi and
Prato et al.2f,7c,e,f have reported that the noncovalent combination
Increasing the selectivity, response speed, and sensing ability
of sensors for chemical and biological analytes has generated a
lot of interest1 recently. Because single-walled carbon nanotubes
(SWNTs) possess the advantages of biocompatibility, size
appropriateness, and sensitivity toward minute electrical per-
turbations, they have already exhibited2,3 considerable promise
for the electronic detection of biological species, as well as
simple gases. The insolubility4 of the SWNTs in the most
organic solvents and the difficulties of handling these highly
intractable carbon nanostructures, however, restrict real-life
applications of SWNTs to a considerable extent. To improve
upon the properties of the SWNTs, low cost and industrially
feasible approaches to their modification have been much sought
after2a,f,5-8 in recent years. Among the approaches, noncovalent
supramolecular modifications6-8 of the SWNTs can do much
to preserve the desired properties of the SWNTs, while
of the SWNTs with pyrene and porphyrin derivatives leads to
novel electron donor-acceptor nanohybrids, which, upon pho-
toexcitation, undergo fast electron-transfer, followed by the
generation of microsecond-lived charge-separated species. More-
over, success in the noncovalent functionalization of the SWNTs
has provided a further opportunity to employ these entities8 as
chemical and/or biological sensors. In these sensors, the SWNTs
are generally decorated by means of noncovalent bonding
interactions with bifunctional molecules that can be anchored,
on the one hand, onto the nanotubes, and, on the other hand, to
sense particular biomolecules, thus permitting their detection
with FET devices.
(3) (a) Collins, P. G.; Bradley, K.; Ishigami, M.; Zettl, A. Science 2000,
287, 1801–1804. (b) Kong, J.; Franklin, N. R.; Zhou, C.; Chapline,
M. G.; Peng, S.; Cho, K.; Dai, H. Science 2000, 287, 622–625. (c)
Chen, R. J.; Bangsaruntip, S.; Drouvalakis, K. A.; Kam, N. W. S.;
Shim, M.; Li, Y.; Kim, W.; Utz, P. J.; Dai, H. Proc. Natl. Acad. Sci.
U.S.A. 2003, 100, 4984–4989. (d) Goldoni, A.; Larciprete, R.; Petaccia,
L.; Lizzit, S. J. Am. Chem. Soc. 2003, 125, 11329–11333. (e) Li, J.;
Lu, Y.; Ye, Q.; Cinke, M.; Han, J.; Meyyappan, M. Nano Lett. 2003,
3, 929–933. (f) Li, Z.; Dharap, P.; Nagarajaiah, S.; Barrera, E. V.;
Kim, J. D. AdV. Mater. 2004, 16, 640–643. (g) An, K. H.; Leong,
S. Y.; Hwang, H. R.; Lee, Y. H. AdV. Mater. 2004, 16, 1005–1009.
(h) Heller, D. A.; Baik, S.; Eurell, T. E.; Strano, M. S. AdV. Mater.
2005, 17, 2793–2799. (i) Numata, M.; Asai, M.; Kaneko, K.; Bae,
A.-H.; Hasegawa, T.; Sakurai, K.; Shinkai, S. J. Am. Chem. Soc. 2005,
127, 5875–5884. (j) Robinson, J. A.; Snow, E. S.; Baˇdescu, S. C.;
Reinecke, T. L.; Perkins, F. K. Nano Lett. 2006, 6, 1747–1751. (k)
Hecht, D. S.; Ramirez, R. J. A.; Briman, M.; Artukovic, E.; Chichak,
K. S.; Stoddart, J. F.; Gru¨ner, G. Nano Lett. 2006, 6, 2031–2036. (l)
Star, A.; Tu, E.; Niemann, J.; Gabriel, J.-C. P.; Joiner, C. S.; Valcke,
C. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 921–926. (m) Numata,
M.; Sugikawa, K.; Kaneko, K.; Shinkai, S. Chem.-Eur. J. 2008, 14,
2398–2404.
† Department of Chemistry and Biochemistry, University of California,
Los Angeles.
‡ Department of Physics and Astronomy, University of California, Los
Angeles.
§ Northwestern University.
(1) (a) Analytical Techniques in the Sciences: Chemical Sensors and
Biosensors; Eggins, B. R., Ed.; John Wiley & Sons, Ltd.: Chichester,
U.K., 2002. (b) McDonagh, C.; Burke, C. S.; MacCraith, B. D. Chem.
ReV. 2008, 108, 400–422.
(2) (a) Hirsch, A. Angew. Chem., Int. Ed. 2002, 41, 1853–1859. (b)
Ouyang, M.; Huang, J.-L.; Lieber, C. M. Acc. Chem. Res. 2002, 35,
1018–1025. (c) Avouris, P. Acc. Chem. Res. 2002, 35, 1026–1034.
(d) Dai, H. Acc. Chem. Res. 2002, 35, 1035–1044. (e) Niyogi, S.;
Hamon, M. A.; Hu, H.; Zhao, B.; Bhowmik, P.; Sen, R.; Itkis, M. E.;
Haddon, R. C. Acc. Chem. Res. 2002, 35, 1105–1113. (f) Guldi, D. M.;
Rahman, G. M. A.; Zerbetto, F.; Prato, M. Acc. Chem. Res. 2005, 38,
871–878. (g) Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M. Chem.
ReV. 2006, 106, 1105–1136. (h) Snow, E. S.; Perkins, F. K.; Robinson,
J. A. Chem. Soc. ReV. 2006, 35, 790–798. (i) Allen, B. L.; Kichambare,
P. D.; Star, A. AdV. Mater. 2007, 19, 1439–1451. (j) Kauffman, D. R.;
Star, A. Chem. Soc. ReV. 2008, 37, 1197–1206.
(4) Chen, J.; Hamon, M. A.; Hu, H.; Chen, Y.; Rao, A. M.; Eklund, P. C.;
Haddon, R. C. Science 1998, 282, 95–98.
9
16996 J. AM. CHEM. SOC. 2008, 130, 16996–17003
10.1021/ja805393b CCC: $40.75
2008 American Chemical Society

A Tunable Photosensor
A R T I C L E S
Scheme 1. Schematic Representation of the Pyrenecyclodextrin-Decorated SWNT Hybrids, How They Interact with Guest Molecules When
They Are Being Sensed in an FET Device, and Five Guest Molecules, 1-Adamantanol, 2-Adamantanol, 1-Adamantanecarboxylic Acid,
Sodium Cholate, and Sodium Deoxycholate
To carry out quantitative investigations on the sensitivities
offered by noncovalently functionalized SWNT/FET devices to
provide the interfaces that are selective toward the sensing of a
wide range of analytes, we have described the fabrication of
the FET devices (Scheme 1) in a recent work9 using the hybrids
of pyrene-modified ꢀ-cyclodextrin (pyrenecyclodextrin)-deco-
rated SWNTs, which serve as chemical sensors to detect
nonfluorescent organic molecules selectively, based on the
concept of molecular recognition. In the presence of certain
molecules, the transistor characteristics of the pyrenecyclodex-
trin-decorated SWNT/FET devices shift toward negative gate
voltage, exhibiting the following sequence of sensing abilities
for the guest molecules: 1-adamantanol > 2-adamantanol >
1-adamantanecarboxylic acid > sodium deoxycholate > sodium
cholate. The results indicate that the electrical conductance of
the device is highly sensitive to certain organic molecules and
varies significantly with changes in the surface adsorption of
these molecules. Satisfyingly, the magnitude of the transistor
characteristic movements in the pyrenecyclodextrin-SWNT/FET
devices in the presence of the organic molecules depends linearly
on the magnitudes of the complex formation constants (KS)
exhibited by the pyrenecyclodextrin derivative with these
molecules, a fact that demonstrates that the pyrenecyclodextrin-
decorated SWNT/FET devices serve as chemical sensors for
the detection of organic molecules in aqueous solution, not only
selectively but also quantitatively.
(5) (a) Holzinger, M.; Vostrowsky, O.; Hirsch, A.; Hennrich, F.; Kappes,
M.; Weiss, R.; Jellen, F. Angew. Chem., Int. Ed. 2001, 40, 4002–
4005. (b) Khabashesku, V. N.; Billups, W. E.; Margrave, J. L. Acc.
Chem. Res. 2002, 35, 1087–1095. (c) Sun, Y.-P.; Fu, K.; Lin, Y.;
Huang, W. Acc. Chem. Res. 2002, 35, 1096–1104. (d) Balasubrama-
nian, K.; Burghard, M. Small 2005, 1, 180–192. (e) Prato, M.;
Kostarelos, K.; Bianco, A. Acc. Chem. Res. 2008, 41, 60–68.
(6) (a) Star, A.; Stoddart, J. F.; Steuerman, D.; Diehl, M.; Boukai, A.;
Wong, E. W.; Yang, X.; Chung, S.-W.; Choi, H.; Heath, J. R. Angew.
Chem., Int. Ed. 2001, 40, 1721–1725. (b) Star, A.; Steuerman, D. W.;
Heath, J. R.; Stoddart, J. F. Angew. Chem., Int. Ed. 2002, 41, 2508–
2512. (c) Star, A.; Liu, Y.; Grant, K.; Ridvan, L.; Stoddart, J. F.;
Steuerman, D. W.; Diehl, M. R.; Boukai, A.; Heath, J. R. Macromol-
ecules 2003, 36, 553–560. (d) Chichak, K. S.; Star, A.; Altoe´, V. P.;
Stoddart, J. F. Small 2005, 1, 452–461.
Because the photosensing process2i is usually rapid and clean,
and can be executed at an electrode surface even in the solid
state, we have given particular attention to fabricating the
photosensitive SWNT-based FET devices, which are able to
(7) (a) Tang, B. Z.; Xu, H. Macromolecules 1999, 32, 2569–2576. (b)
O’Connell, M. J.; Boul, P.; Ericson, L. M.; Huffman, C.; Wang, Y.;
Haroz, E.; Kuper, C.; Tour, J.; Ausman, K. D.; Smalley, R. E. Chem.
Phys. Lett. 2001, 342, 265–271. (c) Guldi, D. M.; Rahman, G. M. A.;
Jux, N.; Tagmatarchis, N.; Prato, M. Angew. Chem., Int. Ed. 2004,
43, 5526–5530. (d) Guldi, D. M.; Rahman, G. M. A.; Sgobba, V.;
Ehli, C. Chem. Soc. ReV. 2006, 35, 471–487. (e) Guldi, D. M.; Rahman,
G. M. A.; Jux, N.; Balbinot, D.; Hartnagel, U.; Tagmatarchis, N.; Prato,
M. J. Am. Chem. Soc. 2005, 127, 9830–9838. (f) Ehli, C.; Rahman,
G. M. A.; Jux, N.; Balbinot, D.; Guldi, D. M.; Paolucci, F.; Marcaccio,
M.; Paolucci, D.; Melle-Franco, M.; Zerbetto, F.; Campidelli, S.; Prato,
M. J. Am. Chem. Soc. 2006, 128, 11222–11231. (g) Britz, D. A.;
Khlobystov, A. N. Chem. Soc. ReV. 2006, 35, 637–659. (h) Kurppa,
K.; Jiang, H.; Szilvay, G. R.; Nasibulin, A. G.; Kauppinen, E. I.;
Linder, M. B. Angew. Chem., Int. Ed. 2007, 46, 6446–6449. (i) Guldi,
(8) (a) Star, A.; Gabriel, J.-C. P.; Bradley, K.; Gru¨ner, G. Nano Lett. 2003,
3, 459–463. (b) Besteman, K.; Lee, J.-O.; Wiertz, F. G. M.; Heering,
H. A.; Dekker, C. Nano Lett. 2003, 3, 727–730. (c) Chen, R. J.; Choi,
H. C.; Bangsaruntip, S.; Yenilmez, E.; Tang, X.; Wang, Q.; Chang,
Y.-L.; Dai, H. J. Am. Chem. Soc. 2004, 126, 1563–1568. (d) Zhang,
M.; Smith, A.; Gorski, W. Anal. Chem. 2004, 76, 5045–5050. (e) Joshi,
P. P.; Merchant, S. A.; Wang, Y.; Schmidtke, D. W. Anal. Chem.
2005, 77, 3183–3188. (f) Li, C.; Curreli, M.; Lin, H.; Lei, B.; Ishikawa,
F. N.; Datar, R.; Cote, R. J.; Thompson, M. E.; Zhou, C. J. Am. Chem.
Soc. 2005, 127, 12484–12485. (g) Staii, C.; Johnson, A. T.; Chen,
M., Jr.; Gelperin, A. Nano Lett. 2005, 5, 1774–1778. (h) Tang, X.;
Bansaruntip, S.; Nakayama, N.; Yenilmez, E.; Chang, Y.-I.; Wang,
Q. Nano Lett. 2006, 6, 1632–1636. (i) Barone, P. W.; Strano, M. S.
Angew. Chem., Int. Ed. 2006, 45, 8138–8141. (j) Ogoshi, T.;
Takashima, Y.; Yamagushi, H.; Harada, A. J. Am. Chem. Soc. 2007,
129, 4878–4879.
´
D. M. Nature 2007, 447, 50–51. (j) Herranz, M. A.; Ehli, C.;
Campidelli, S.; Gutie´rrez, M.; Hug, G. L.; Ohkubo, K.; Fukuzumi,
S.; Prato, M.; Mart´ın, N.; Guldi, D. M. J. Am. Chem. Soc. 2008, 130,
66–73.
(9) Zhao, Y.-L.; Hu, L.; Stoddart, J. F.; Gru¨ner, G. AdV. Mater. 2008, 20,
1910–1915.
9
J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008 16997

A R T I C L E S
Zhao et al.
Scheme 2. Schematic Representation of the ADA-Ru Complex and How the Pyrenecyclodextrin-Decorated SWNT Hybrids Interact with the
ADA-Ru Complex When They Are Being Sensed in an FET Device
serve as photosensors using the light-controlled charge-transfer
(CT) principle. Specifically, the photosensitive SWNT/FETs
have promising applications as the essential components of light-
emitting diodes (LEDs) or photovoltaic devices (PVDs). How-
ever, research that introduces luminescent metal complexes
during the fabrication of photosensitive carbon nanotube hybrids,
or photosensitive carbon nanotube-based FET devices, has been
the subject of very few reports10 to date. Herein, we describe
our recent results obtained with pyrenecyclodextrin-decorated
SWNT/FET devices as tunable photosensors. In such SWNT/
FET devices (Scheme 2), the pyrenecyclodextrin derivatives on
the surfaces of the SWNTs serve as the sensing host. A
ruthenium complex with an adamantyl tether (ADA-Ru) as the
sensing guest can be immobilized by binding the adamantyl
group into the cavity of the pyrenecyclodextrin derivative in
aqueous solution. It is this molecular recognition event that
renders the CT between the ADA-Ru guest and the pyrenecy-
clodextrin-decorated SWNT hybrids practicable.
by means of π-π stacking interactions.11 The synthesis of the
ADA-Ru complex, the sensing guest, is outlined in Scheme
3. In the procedure, 1,10-phenanthroline-5,6-dione (7) was
formed by oxidation of 1,10-phenanthroline (6). This dione was
transformed into an imidazo[4,5-f]-1,10-phenanthroline deriva-
tive (8) by reacting it with an adamantyl-modified benzaldehyde
(5). Reaction of 8 with (1,10-phenanthroline)2RuCl2 (9) afforded
the ADA-Ru complex in a yield of 71%. The fact that the
adamantyl group of the ADA-Ru complex can be included in
1
the cavity of the ꢀ-CD ring is demonstrated by a H NOESY
experiment. Because the aqueous solubility of pyrenecyclodex-
1
trin is too low to perform the H NOESY experiment, we
pursued the 1H NOESY experiment using ꢀ-CD with ADA-Ru
complex in D2O at 25 °C. NOE crosspeaks (A-C) between
the protons of the adamantyl group and the H3 and H5 protons
on the inside of the ꢀ-CD ring are observed [Figure S1 in the
1
Supporting Information] in the H NOESY spectrum. These
observations indicate that the adamantyl group of the ADA-Ru
complex is included in the hydrophobic cavity of the ꢀ-CD ring
as illustrated in Scheme 2.
Results and Discussion
The SWNT/FET device was fabricated, using CVD-grown
SWNT networks as channels, on silicon wafers with a 500 nm
thick silicon dioxide (SiO2) dielectric (see a detailed procedure
for the fabrication of the SWNT/FET device in the Experimental
Section).12 The device with the SWNT networks was soaked
in a DMF solution of pyrenecyclodextrin (1.13 mM) overnight,
Fabrication and Characterization. The pyrenecyclodextrin
derivative was synthesized9 by the condensation of mono(6-
aminoethylamino-6-deoxy)-ꢀ-cyclodextrin (ꢀ-CD) with 1-pyre-
neacetic acid in N,N-dimethylformamide (DMF) solution, and
the hybrids of the pyrenecyclodextrin-decorated SWNTs were
prepared9 according to a previous report. The pyrene units
attached to ꢀ-CD rings associate with the surfaces of the SWNTs
(11) (a) Chen, R. J.; Zhang, Y.; Wang, D.; Dai, H. J. Am. Chem. Soc.
2001, 123, 3838–3839. (b) Guldi, D. M.; Rahman, G. M. A.; Sgobba,
V.; Kotov, N. A.; Bonifazi, D.; Prato, M. J. Am. Chem. Soc. 2006,
128, 2315–2323.
(10) (a) Frehill, F.; Vos, J. G.; Benrezzak, S.; Koo´s, A. A.; Ko´nya, Z.;
Ru¨ther, M. G.; Blau, W. J.; Fonseca, A.; Nagy, J. B.; Biro´, L. P.;
Minett, A. I.; in het Panhuis, M. J. Am. Chem. Soc. 2002, 124, 13694–
13695. (b) Khairoutdinov, R. F.; Doubova, L. V.; Haddon, R. C.; Saraf,
L. J. Phys. Chem. B 2004, 108, 19976–19981. (c) Chaturvedi, H.;
Poler, J. Mater. Res. Soc. Symp. Proc. 2006, 938, 0938-N07-09.
(12) (a) Hu, L.; Hecht, D. S.; Gru¨ner, G. Nano Lett. 2004, 4, 2513–2517.
(b) Unalan, H. E.; Fanchini, G.; Kanwal, A.; Du Pasquier, A.;
Chhowalla, M. Nano Lett. 2006, 6, 677–682. (c) Hu, L.; Zhao, Y.-L.;
Ryu, K.; Zhou, C.; Stoddart, J. F.; Gru¨ner, G. AdV. Mater. 2008, 20,
939–946.
9
16998 J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008

A Tunable Photosensor
A R T I C L E S
Scheme 3. Schematic Representation of the Preparation of the ADA-Ru Complex
washed with H2O briefly thereafter, and blown with N2 gas to
dryness. Atomic force microscopy indicates9 that the average
height of the pyrenecyclodextrin layer on the surfaces of the
SWNTs is ca. 2.5 nm. We have observed that the pyrenecy-
clodextrin molecules are coated uniformly only onto the surfaces
of the SWNTs and do not stick to the SiO2 surfaces. Because
the pyrene unit in the pyrenecyclodextrin is an organic semi-
conductor,13 it may cause the SWNT device to leak through
the pinholes of the SiO2 dielectric if the pyrenecyclodextrin
molecules stick to the SiO2 surfaces. The self-assembly of the
pyrenecyclodextrin molecules, only and specifically, onto
the SWNTs by means of π-π stacking interactions avoids the
leakage problems associated with the transistors after decorating
the SWNTs with these molecules, a benefit that increases the
sensitivity of the system. This method of casting a photoactive
compound onto a SWNT network has been reported3k previously
to provide a strong enough interaction to reveal evidence for
CT upon illumination. Any changes in the device characteristics
can be attributed to resistance changes occurring along the
SWNT channel and not in the Schottky barriers at the contacts.
The device configuration we have employed for transistors and
resistance measurements is illustrated in Figure 1.
red curve to the blue one in Figure 2a) by about 1.6 V. Note
that the conductance of the transistor is given by G ) nµe, where
n is the carrier concentration, µ is the carrier mobility, and e is
the elementary charge of an electron. The barrier concentration
(n) and the carrier mobility (µ) on the SWNTs remain unchanged
whether the light is on or off. Therefore, there should be a CT,
associated with e, from the pyrenecyclodextrins to the SWNTs
when the light is on, causing the transfer curve to shift even
further to the left. In DMF solution, the fluorescence intensity
(see Figure S3 in the Supporting Information) of the pyrenecy-
clodextrin solution (4.30 × 10-4 mol L-1) decreases on the
L-1) at 25 °C. Strong fluorescence emission of the pyrenecy-
clodextrin was observed from 370 to 425 nm. Under these
conditions, the competitive light absorption by the SWNTs was
too low to be determined and can be ignored in the fluorescence
experiments.14 The dependence of fluorescent quenching around
412 nm on the SWNT concentration implies3k,12c,15 that a CT
process exists in the pyrenecyclodextrin-SWNT system, an
implication that supports perfectly the result of the FET device
investigation. In such hybrid systems, the light generates
electron-hole pairs. The generated excitons tend to combine;
stepwise addition of a SWNT solution ((0 - 1.44) × 10-3
g
Sensing Process. The conductance transfer characteristics (Isd
versus Vg) of the transistor were measured by applying 100 mV
and sweeping the gate voltage between +20 and -20 V in steps
of 0.5 V. Figure 2a illustrates the transfer curves of the SWNT/
FET device before (black curve) and after (red curve) the self-
assembly of pyrenecyclodextrin molecules in the dark. The
threshold voltage of the pyrenecyclodextrin-SWNT/FET device
shifts toward a negative gate voltage by about 9.4 V, as
compared to bare SWNTs. Because the excitation wavelength
(λex) of pyrenecyclodextrin is 274 nm (see Figure S2 in the
Supporting Information), an LED with an intensity (I) of 40 W
m-2 and excitation wavelength (λex) of 280 nm is used as a
light source for the FET device. After the LED has been
switched on for 5 min, the transfer curve of the pyrenecyclo-
dextrin-SWNT/FET device shifts further to the left (from the
Figure 1. A model of the pyrenecyclodextrin-decorated SWNT/FET device
showing how the pyrenecyclodextrin molecules interact with the SWNT
and, at the same time, bind with guest molecules.
(13) Coropceanu, V.; Cornil, J.; da Filho, D. A. S.; Olivier, Y.; Silbey, R.;
Bre´das, J.-L. Chem. ReV. 2007, 107, 926–952.
9
J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008 16999

A R T I C L E S
Zhao et al.
tance change. The light wavelength dependence of the pyrenecy-
clodextrin-SWNT/FET was investigated by monitoring the
changes in resistance of the device upon illumination by light
of different wavelengths with a fixed intensity (I ) 40 W m-2).
Light was applied in wavelength intervals of 20 nm from 260
to 420 nm. Each specific wavelength of light was left on for
10 s and off for 50 s to allow the device to recover. The results
show that the resistance of the device increases when it is
exposed to light and decreases when the light source is removed,
an observation that is consistent with the data presented in Figure
2b. The changes in resistance of the pyrenecyclodextrin-SWNT/
FET in response to light of varying wavelengths yet of constant
intensity are shown in Figure S4 in the Supporting Information,
overlaid with the absorption spectrum of the pyrenecyclodextrin
(5.64 × 10-5 mol L-1) recorded in DMF solution at 25 °C.
The clear correlation between the magnitude of the changes in
resistance of the pyrenecyclodextrin-SWNT/FET and the ab-
sorption spectrum of the pyrenecyclodextrin provides direct
evidence that the light-induced change of the pyrenecyclodex-
trin’s electronic structure is coupled to the CT process through
the SWNT network.3k
Next, the pyrenecyclodextrin-SWNT/FET device was soaked
in an aqueous solution of the ADA-Ru guest for 2 h, washed
briefly with H2O thereafter, and finally blown to dryness with
N2. The pyrenecyclodextrin molecules coating the surfaces of
the SWNTs act as the hosts and recognize the guest molecules.
When the guest molecules are included in the cavities of the
pyrenecyclodextrin hosts, the threshold voltage of the pyrenecy-
clodextrin-SWNT/FET device shifts even more toward a nega-
tive gate voltage by about 4.1 V in the dark, that is, from the
red curve to the orange one in Figure 3a. The change in the
transistor characteristic for the pyrenecyclodextrin-SWNT/FET
device reaches a maximum value in relation to the shift and
Figure 2. (a) The Isd-Vg curves of SWNT/FET before (black) and after
(red) assembling the pyrenecyclodextrin (1.13 mM) in the dark and the
Isd-Vg curve of the pyrenecyclodextrin-SWNT/FET when the light is on
(blue), λ ) 280 nm and I ) 40 W m-2. (b) The resistance of the
pyrenecyclodextrin-SWNT/FET device vs time monitored under zero gate
voltage, λ ) 280 nm and I ) 40 W m-2
.
meanwhile, the electrons or holes are transferred partially to
the SWNTs, depending on the distance and the energy barriers
between the pyrenecyclodextrin and the SWNTs. In other words,
the formation of the pyrenecyclodextrin-SWNT hybrids favors
the transfer of electrons or holes from the pyrenecyclodextrin
(donor) to the SWNTs (acceptor), such that the exited electrons
or holes enter the SWNTs.
We also measured the network resistance of the pyrenecy-
clodextrin-SWNT/FET device between the source and drain with
zero-gate voltage. The resistance measurement was carried out
by applying a 100 mV bias with a Keithley 2400 apparatus.
The network resistance responds (Figure 2b) quickly to the
turning on and off of the LED, where I ) 40 W m-2 and λ )
280 nm. When the light is on, the sheet resistance increases
and stays high until the removal of the light. The data in the
sharp-increase region were enlarged and shown to fit well to
an exponential equation, producing a time constant of 5.1 s.
The photoresponse is fully recoverable after removal of the light,
indicating complete recovery of the CT. To eliminate the
possibility that the change of the resistance was a result of the
response of the SWNT network itself, we carried out a control
experiment on the SWNT network without the coating of
pyrenecyclodextrins and did not observe any detectable resis-
(14) Nakayama-Ratchford, N.; Bangsaruntip, S.; Sun, X.; Welsher, K.; Dai,
H. J. Am. Chem. Soc. 2007, 129, 2448–2449.
(15) (a) Guldi, D. M.; Rahman, G. M. A.; Jux, N.; Balbinot, D.;
Tagmatarchis, N.; Prato, M. Chem. Commun. 2005, 2038–2040. (b)
Kongkanand, A.; Kamat, P. V. ACS Nano 2007, 1, 13–21. (c) Cioffi,
C.; Campidelli, S.; Sooambar, C.; Marcaccio, M.; Marcolongo, G.;
Meneghetti, M.; Paolucci, D.; Paolucci, F.; Ehli, C.; Rahman, G. M. A.;
Sgobba, V.; Guldi, D. M.; Prato, M. J. Am. Chem. Soc. 2007, 129,
3938–3945. (d) Ballesteros, B.; de la Torre, G.; Ehli, C.; Rahman,
G. M. A.; Agullo´-Rueda, F.; Guldi, D. M.; Torres, T. J. Am. Chem.
Soc. 2007, 129, 5061–5068.
Figure 3. (a) The Isd-Vg curves of the pyrenecyclodextrin-SWNT/FET before
(red) and after (orange) binding the ADA-Ru complex (2.20 mM) in the dark
and the Isd-Vg curve of the ADA-Ru-pyrenecyclodextrin-SWNT/FET when
the light is on (green), λ ) 490 nm and I ) 40 W m-2. (b) The resistance of
the ADA-Ru-pyrenecyclodextrin-SWNT/FET device vs time monitored under
zero gate voltage, λ ) 490 nm and I ) 40 W m-2
.
9
17000 J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008

A Tunable Photosensor
A R T I C L E S
the tilt of the transfer curve in the presence of guest molecules.
A control experiment was conducted to demonstrate that the
threshold voltage of bare SWNT/FET device, that is, the device
without the coat of pyrenecyclodextrin molecules, did not show
any appreciable change in the presence of the ADA-Ru guests
under exactly the same conditions because the ADA-Ru guests
without the binding of attached pyrenecyclodextrins are not
immobilized on the surfaces of SWNTs. These results can be
explained by the fact that, as the guest molecules become
included in the cavities of the pyrenecyclodextrin hosts, two
possible phenomena can come into play: one is that the guest
molecules included in the ꢀ-CD cavities will cause a rearrange-
ment in the charge distribution of the pyrenecyclodextrin, which,
in turn, will induce a ground-state CT from the ADA-Ru guests
to the pyrenecyclodextrin-SWNT hybrids, that is, causing a
change in the charge carrier density (n) in the SWNTs, or the
other is that the guest molecules included in the ꢀ-CD cavities
could bring about a further decrease in the charge mobility (µ),
either by altering the scattering potentials of the pyrenecyclo-
dextrin molecules or by causing the further deformation16 of
the SWNTs.
the ADA-Ru guest was too weak to be determined and can be
ignored in the fluorescence experiments under this condition.
This fluorescent quenching phenomenon suggests (i) because
the decreased fluorescence intensity can be rationalized18 by
the decreased microenvironmental hydrophobicity of the ꢀ-CD
cavity and/or steric deshielding around the fluorophore (the
pyrene unit in the pyrenecyclodextrin) arising from the inclusion
complexation between the ꢀ-CD cavity (host) and the adamantyl
moiety of the ADA-Ru complex (guest), the fluorescent group
(the pyrene unit) of the host can be attacked efficiently by the
deactivating water molecules through the formation of the
host-guest inclusion complex, which consequently contributes
to the fluorescence decrease of the host, and/or (ii) a CT process
exists from the pyrenecyclodextrin to the ADA-Ru guest in
the system because the ADA-Ru complex can act as an electron
acceptor. Because we treated the pyrenecyclodextrin-decorated
SWNTs as single entities in the FET sensing device, this
observation is consistent with the conclusion that there is a CT
process from the pyrenecyclodextrin-SWNT hybrids to the
ADA-Ru complex in the FET device when the light is on.
As the maximum excitation wavelength (λex) of the ADA-Ru
guest is 490 nm (see Figure S5 in the Supporting Information),
an LED with an intensity (I) of 40 W m-2 and excitation
wavelength (λex) of 490 nm is used as a light source for the
FET sensing device. The fluorescence of the pyrenecyclodextrin
is too weak to be determined and can be ignored under this
excitation wavelength with the same conditions.17 Interestingly,
after the LED has been switched on for 5 min, the transfer curve
of the pyrenecyclodextrin-SWNT/FET device shifts back to the
right (from the orange curve to the green one in Figure 3a) by
about 1.9 V in the presence of the ADA-Ru guest. The response
of the device to the light is a shift of the threshold voltage toward
positive voltages, indicating hole-doping of the SWNTs.3k Thus,
photoexcitation of the device causes a CT from the pyrenecy-
clodextrin-SWNT hybrids to the ADA-Ru complex. An
explanation for this process is that the direction of the photo-
induced CT may depend on several factors including (i) the
orientation of the guest molecules along the SWNTs, (ii) the
functionalization method (covalent or noncovalent) to derivatize
the SWNTs, and (iii) the structure of the particular guest
molecule used. Because there was initially a ground-state CT
to the pyrenecyclodextrin-SWNT hybrids upon addition of the
ADA-Ru guest, the photoinduced CT simply indicates at least
partial recovery of these transferred charges. In other words,
upon photoexcitation of the ADA-Ru guest, some of the
charges that had been transferred to the pyrenecyclodextrin-
SWNT hybrids in the ground state are transferred back to the
ADA-Ru molecule in the excited state.
Figure 4. Fluorescence spectral changes of the pyrenecyclodextrin (3.10
× 10-6 mol L-1) upon addition of ADA-Ru (0, 0.42, 0.85, 1.27, 1.69,
2.11, 2.54, 2.96, 3.38, 3.81, 4.23, and 4.65 × 10-6 mol L-1 from a to l) in
aqueous solution at 25 °C, λex ) 274 nm.
Because we do not observe any appreciable threshold voltage
change in bare SWNT/FET device, the device without the coat
of pyrenecyclodextrin molecules, in the presence of the ADA-Ru
complex as demonstrated above, we performed the fluorescent
experiments on the ADA-Ru complex with the SWNTs in
solution to get some insight for the interaction between them.
Significantly, the fluorescence intensity (see Figure S6 in the
Supporting Information) of the ADA-Ru aqueous solution (3.76
× 10-6 mol L-1) increases on the stepwise addition of a SWNT
DMF solution ((0-0.67) × 10-3 g L-1) with an excitation
wavelength (λex) of 490 nm at 25 °C. Similar fluorescent
enhancement behavior of the ADA-Ru aqueous solution (3.76
× 10-6 mol L-1) with the stepwise addition of a pyrenecyclo-
dextrin aqueous solution ((0-6.58) × 10-6 mol L-1) can be
observed under an excitation wavelength (λex) of 490 nm at 25
°C. Under these conditions, the competitive light absorption of
the SWNTs or pyrenecyclodextrin was too low to be determined
and so can be ignored in the fluorescence experiments. The
fluorescent enhancement of the ADA-Ru complex upon the
addition of the SWNTs or the pyrenecyclodextrin supports3k,12c,15
firmly the fact that a CT process from the pyrenecyclodextrin-
SWNT hybrids to the ADA-Ru complex happens when the
light is on in the FET device.
To provide further support for our conclusions, we performed
some investigations in solution. We determined the fluorescent
change of the pyrenecyclodextrin in the presence of the
ADA-Ru guest with an excitation wavelength (λex) of 274 nm
at 25 °C. In aqueous solution, the fluorescence intensity (Figure
4) of the pyrenecyclodextrin solution (3.10 × 10-6 mol L-1
- 4.65) × 10-6 mol L-1). The competitive light absorption of
)
decreases on the stepwise addition of an ADA-Ru solution ((0
(16) (a) Hertel, T.; Walkup, R. E.; Avouris, P. Phys. ReV. B 1998, 58,
13870–13873. (b) Bower, C.; Rosen, R.; Jin, L.; Han, J.; Zhou, O.
Appl. Phys. Lett. 1999, 74, 3317–3319. (c) Qian, D.; Dickey, E. C.;
Andrews, R.; Rantell, T. Appl. Phys. Lett. 2000, 76, 2868–2870.
(17) (a) Chen, P.; Meyer, T. J. Chem. ReV. 1998, 98, 1439–1478. (b) Du¨rr,
H.; Bossmann, S. Acc. Chem. Res. 2001, 34, 905–917.
(18) (a) Connors, K. A. Chem. ReV. 1997, 97, 1325–1357. (b) Liu, Y.;
Zhao, Y.-L.; Chen, Y.; Ding, F.; Chen, G.-S. Bioconjugate Chem.
2004, 15, 1236–1245.
9
J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008 17001

A R T I C L E S
Zhao et al.
mass spectra were measured on an IonSpec FT-ICR mass spec-
trometer. Fluorescence spectra were recorded on LPS-220B fluo-
rescence spectrometer (Photon Technology International) with lamp
power supply at 25 °C.
Furthermore, the network resistance of the pyrenecyclodex-
trin-SWNT/FET device in the presence of ADA-Ru was also
measured by turning on and off of the LED (I ) 40 W m-2 and
λ ) 490 nm). When the light is on, the sheet resistance (Figure
3b) decreases and stays low position until the removal of the
light. The photoresponse is almost recoverable after removal
of the light, indicating the recovery of the CT. The resistance
responds to the turning on and off of the LED more slowly, as
compared to that of the pyrenecyclodextrin-SWNT/FET device.
The data in the decrease region were enlarged and shown to fit
well to an exponential equation, producing a time constant of
65.0 s. This long time constant, measured from the resistance,
may not reflect19 the CT dynamics from the pyrenecyclodextrin-
SWNTs to the ADA-Ru guests, simply because of the fact
that the charge reconfiguration over the entire network lasts until
it reaches an equilibrium state.
SWNT/FET. The FET device was fabricated using CVD-grown
SWNT networks as the channels on silicon wafers with a 500 nm
thick silicon dioxide (SiO2) dielectric.12 The density of the network
was chosen to be 1.5 tubes µm-2, just above the percolation
threshold to avoid too many conduction paths through the metallic
SWNTs, a situation that would reduce the ON/OFF ratio of the
transistor characteristics. The lift-off lithography process was used
to pattern the e-beam deposited Pd contact pads on top of the
SWNTs network. Oxygen plasma was used to etch away the
SWNTs outside the source-drain channels. Because the channel is
200 µm long and 1000 µm wide, approximately 100 times longer
than the SWNTs, the network resistance, rather than the contact
resistance between Pd and network, dominates the overall resistance.
During the sensing process, three independent measurement experi-
ments were performed to afford self-consistent parameters, the
changes of the threshold voltages and the resistances, and give the
averaged values.
Conclusion
We have demonstrated that the pyrenecyclodextrin-SWNT/
FET device can serve as a tunable photosensor for sensing a
luminescent Ru complex, backed up by fluorescent spectroscopic
experiments in solution. When the light is on (I ) 40 W m-2
and λ ) 280 nm), the transfer curve of the pyrenecyclodextrin-
SWNT/FET device shifts toward a negative gate voltage by
about 1.6 V and its sheet resistance increases quickly, indicating
a CT process from the pyrenecyclodextrins to the SWNTs. In
contrast, the transfer curve of the pyrenecyclodextrin-SWNT/
FET device in the presence of the ADA-Ru guest shifts toward
a positive gate voltage by about 1.9 V and its sheet resistance
decreases slowly when the light is on (I ) 40 W m-2 and λ )
490 nm), showing a CT process from the pyrenecyclodextrin-
SWNT hybrids to the ADA-Ru guests. These photoresponse
processes are recoverable after removal of the light. The results
reveal the SWNT/FET sensing devices can be tailored to meet
specific needs using rationally designed approaches to analyte
sensing. They raise the prospect of promising applications in
the area of tunable light detection, as in artificial eyes and PVDs.
5: A mixture of 4-(2-hydroxyethoxy)benzaldehyde 3 (1.16 g, 7.0
mmol), 1-adamantaneacetic acid 4 (1.27 g, 6.5 mmol), DCC (1.44
g, 7.0 mmol), and DMAP (10.0 mg, 0.1 mmol) in CH2Cl2 (50 mL)
was stirred for 5 h at room temperature in an atmosphere of Ar.
The resulting suspension was filtered, the filtrate was evaporated,
and the residue was subjected to column chromatography (SiO2,
CH2Cl2 eluent) to give compound 5 (1.46 g, 65%) as a colorless
1
solid. H NMR (500 MHz, CD2Cl2, 25 °C, TMS): δ 1.64-1.72
(m, 12H, ADA-H), 1.95-1.97 (m, 3H, ADA-H), 2.13 (s, 2H,
CO-CH2-ADA), 4.29-4.31 (m, 2H, OCH2), 4.45-4.47 (m, 2H,
OCH2), 7.05-7.07 (d, J ) 8.5 Hz, 2H, Ar-H), 7.86-7.88 (d, J )
8.6 Hz, 2H, Ar-H), 9.91 (s, 1H, CHO). 13C NMR (125 MHz,
CD2Cl2, 25 °C): δ 28.6, 30.4, 32.6, 36.5, 42.1, 48.6, 61.6, 66.2,
114.6, 130.2, 131.6, 163.3, 171.1, 190.3.
8: 1,10-Phenanthroline-5,6-dione 7 (0.80 g, 4.2 mmol) and
ammonium acetate (5.86 g, 133 mmol) were dissolved in hot glacial
MeCO2H (10 mL). While the mixture was stirred, a solution of 5
(1.43 g, 4.2 mmol) in glacial MeCO2H (10 mL) was added dropwise
to the mixture. The mixture was heated at 90 °C for 3 h and was
then poured into H2O (200 mL). The solution was neutralized with
ammonia to pH 7, before being cooled to room temperature. The
precipitate was filtered off and washed with large portions of H2O.
The product was dried to afford compound 8 (1.38 g, 62%) as a
Experimental Section
General. All reagents, including ꢀ-CD, 1-adamantaneacetic acid
(4), ruthenium(III) chloride hydrate, 4-hydroxybenzaldehyde (1),
and 1,10-phenanthroline (6), are commercially available and were
used without further purification. SWNTs were purchased from
Carbon Solutions Inc. and used without further purification. 4-(2-
Hydroxyethoxy)benzaldehyde (3), 1,10-phenanthroline-5,6-dione
(7), and (1,10-phenanthro-line)2RuCl2 (9) were prepared as de-
scribed previously.20-22 Pyrenecyclodextrin and pyrenecyclodex-
trin-decorated SWNT hybrids were synthesized according to our
previous report.9 Nuclear magnetic resonance (NMR) spectra were
recorded on Bru¨ker Avance 500 and 600 spectrometers at 25 °C.
Chemical shifts were reported in parts per million (ppm) downfield
from the Me4Si resonance, which was used as the internal standard
1
dark red solid. H NMR (500 MHz, (CD3)2SO, 25 °C, TMS): δ
1.46-1.56 (m, 12H, ADA-H), 1.85-1.87 (m, 3H, ADA-H), 2.04
(s, 2H, CO-CH2-ADA), 4.21-4.26 (m, 2H, OCH2), 4.33-4.37
(m, 2H, OCH2), 7.13-7.14 (d, J ) 8.6 Hz, 2H, Ar-H), 7.81-7.86
(m, 2H, Ar-H), 8.17-8.19 (d, J ) 8.6 Hz, 2H, Ar-H), 8.85-8.87
(d, J ) 8.0 Hz, 2H, Ar-H), 8.97-8.98 (d, J ) 7.6 Hz, 2H, Ar-H),
13.5 (s, NH). 13C NMR (125 MHz, CD2Cl2, 25 °C): δ 28.5, 32.8,
36.7, 43.2, 48.7, 62.1, 66.2, 112.5, 114.8, 121.6, 122.9, 124.3, 125.4,
126.6, 130.0, 132.5, 135.3, 150.1, 153.1, 154.4, 159.7.
ADA-Ru: 8 (0.15 g, 0.3 mmol) and 9 (0.15 g, 0.3 mmol) were
dissolved in absolute EtOH (100 mL). The solution was heated
under reflux for 6 h and was then filtered to remove unreacted
starting materials. The filtrate was concentrated under vacuum and
then poured into Et2O (30 mL). The solution was filtered, and the
obtained solid was washed with Et2O. The product was dried to
1
when recording H NMR spectra. Electrospray ionization (ESI)
(19) (a) Star, A.; Lu, Y.; Bradley, K.; Gru¨ner, G. Nano Lett. 2004, 4, 1587–
1591. (b) Robel, I.; Bunker, B. A.; Kamat, P. V. AdV. Mater. 2005,
17, 2458–2463.
1
give compound (0.21 g, 71%) as a magenta solid. H NMR (500
MHz, D2O, 25 °C, TMS): δ 1.31-1.43 (m, 12H, ADA-H),
1.67-1.69 (m, 3H, ADA-H), 1.91 (s, 2H, CO-CH2-ADA),
4.26-4.34 (m, 4H, OCH2CH2O), 7.32-7.34 (d, J ) 8.5 Hz, 2H,
Ar-H), 7.54-7.66 (m, 6H, Ar-H), 7.94-8.04 (m, 6H, Ar-H),
8.20-8.28 (m, 6H, Ar-H), 8.50-8.62 (m, 6H, Ar-H). MS (ESI):
(20) (a) Mao, P. C.-M.; Mouscadet, J.-F.; Leh, H.; Auclair, C.; Hsu, L.-Y.
Chem. Pharm. Bull. 2002, 50, 1634–1637. (b) Meng, F.; Hua, J.; Chen,
K.; Tian, H.; Zuppiroli, L.; Nu¨esch, F. J. Mater. Chem. 2005, 15,
979–986.
(21) (a) Hiort, C.; Lincoln, P.; Norden, B. J. Am. Chem. Soc. 1993, 115,
3448–3454. (b) Lenaerts, P.; Storms, A.; Mullens, J.; D’Haen, J.;
Go¨rller-Walrand, C.; Binnemans, K.; Driesen, K. Chem. Mater. 2005,
17, 5194–5201.
(22) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17,
3334–3341.
m/z ) 496.7 [M - 2Cl]2+
.
Acknowledgment. We thank Professor Jeffrey I. Zink in
UCLA for the valuable discussion regarding the charge-transfer.
9
17002 J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008

A Tunable Photosensor
A R T I C L E S
1
This work was supported by the Microelectronics Advanced
Research Corporation (MARCO) and its Focus Center Research
Program (FCRP), the Center for Functional Engineered NanoAr-
chitectonics (FENA), the Center for Nanoscale Innovation for
Defense (CNID), and the National Science Foundation (NSF)
Grant DMR-0404029.
Supporting Information Available: H NOESY NMR spec-
trum and figures of the fluorescent and UV-vis experiments.
This material is available free of charge via the Internet at http://
pubs.acs.org.
JA805393B
9
J. AM. CHEM. SOC. VOL. 130, NO. 50, 2008 17003