C O MMU N I C A T I O N S
citation of SAM I eventually results in degradation of the film and
loss of photocurrent after approximately 10 cycles, II and III did
not show any decrease in current over several hours of alternating
light/dark cycles.
We note that neither II nor III is an optimized system because
there is a mismatch between the spectral output of the excitation
lamp and the absorption spectrum of the pyrene chromophore. We
are currently investigating other complexing ligands and metal ions
as well as the effect that the distance of separation between pyrene
and the gold surface has on the magnitude of the photocurrent.
(
The current systems range from 2 to 3 nm in distance between
Figure 2. Photocurrent generated following exposure of III to ∼0.1 mW
at 350 nm at constant applied voltage ) 0 V versus SCE. Photocurrent is
pyrene and the surface according to modeling studies.) Clearly,
however, these preliminary results indicate that this noncovalent
strategy is a potentially efficient and facile means by which to
fabricate complex modular multicomponent supramolecular systems
for device functions, including conversion of incident light to
electric current.
Note Added after Print Publication: Due to a production error,
the structures in Figure 1 were incomplete in the version published
on the Web 2/14/2003 (ASAP) and in the March 12, 2003 issue
2
expressed as nA/cm .
concomitant decrease in impedance. Deposition of the pyrene-
containing ligand again results in attenuated conductivity and
increased impedance. Similar conductivity and impedance behaviors
were obtained for film III upon deposition of the second layer of
Cu(II) ions and capping with the pyrene-containing ligand.
Contact angle measurements and IR spectra confirm that
substantial changes in the surface occur following the addition of
each layer. The changes in contact angles mirror the changes in
hydrophobicity of each of the deposited components, while the IR
measurements show conclusively the presence of each of the added
layers. Conductivity, impedance contact angle, and IR data are
available as Supporting Information.
The electrochemical changes that take place with the sequential
exposure of the surface to each component in II and III indicate
that in addition to a possible electronic role, the Cu(II) ion aids in
organizing and stabilizing the film, probably by complexing with
the pyridyl and bipyridyl ligands present (Figure 1). That deposition
of the pyrene-containing ligand in II and III, as well as the bipyridyl
ligand in III, results in significantly attenuated current values and
enhanced impedance, indicates that the deposition of Cu(II) and
subsequent addition of ligand results in a specific Cu(II)-ligand
interaction rather than a nonspecific deposition. If the latter
occurred, a significant amount of disorder in the film causing
substantial defects and different CV behavior could be expected.
One of us has shown previously that complexation of Cu(II) by
(
Vol. 125, No. 10, pp 2838-2839); the correct electronic version
of the paper was published on 3/20/2003 and an Addition and
Correction appears in the April 16, 2003 issue (Vol. 125, No. 15).
Supporting Information Available: Synthetic details for SAM I,
II, and III, methods and results for CV, impedance, IR, contact angle,
photocurrent experiments, and preparation of SAMs and multilayered
films (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
References
(
1) Imahori, H.; Nishimura, Y.; Norieda, H.; Karita, H.; Yamazaki, I.; Sakata,
Y.; Fukuzumi, S. Chem. Commun. 2000, 661-662.
(
2) Imahori, H.; Norieda, H.; Nishimura, Y.; Yamazaki, I.; Higuchi, K.; Kato,
N.; Motohiro, T.; Yamada, H.; Tamaki, K.; Arimura, M.; Sakata, Y. J.
Phys. Chem. B 2000, 104, 1253-1260.
(3) Imahori, H.; Norieda, H.; Yamada, H.; Nishimura, Y.; Yamazaki, I.;
Sakata, Y.; Fukumuzi, S. J. Am. Chem. Soc. 2001, 123, 100-110.
(4) Uosaki, K.; Kondo, T.; Zhang, X.; Yanagida, M. J. Am. Chem. Soc. 1997,
119, 8367-8368.
(
5) Kondo, T.; Ito, T.; Nomura, S.; Uosaki, K. Thin Solid Films 1996, 284-
285, 652-655.
(
6) Kondo, T.; Yanagida, M.; Nomura, S.; Ito, T.; Uosaki, K. J. Electroanal.
Chem. 1997, 438, 121-126.
2
,6-pyridinedicarboxylic acid groups results in the formation of
(7) Morita, T.; Kimura, S.; Kobayashi, S.; Imanishi, Y. Bull. Chem. Soc. Jpn.
2000, 73, 1535-1540.
stable complexes in which the metal ion is fully encapsulated
between two of the ligands.15
(
8) Morita, T.; Kimura, S.; Kobayashi, S.; Imanishi, Y. J. Am. Chem. Soc.
2000, 122, 2850-2859.
(
9) Hong, H.-G.; Mallouk, T. E. Langmuir 1991, 7, 2362-2369.
Photoexcitation of SAM I and multilayered films II and III in
the presence of methyl viologen by an unfocused, unfiltered,
omnidirectional, 20 W, 350 nm Rayonet lamp (power incident on
sample ∼0.1 mW) causes generation of a cathodic photocurrent in
(
10) Yang, H. C.; Aoki, K.; Hong, H.-G.; Sackett, D. D.; Arendt, M. F.; Yau,
S.-L.; Bell, C. M.; Mallouk, T. E. J. Am. Chem. Soc. 1993, 115, 11855-
11862.
(
11) Ogawa, S.; Hu, K.; Fan, F.-R. F.; Bard, A. J. J. Phys. Chem. B 1997,
01, 5707-5711.
1
2
the range 5-30 nA/cm with II and III consistently exhibiting
(12) Brust, M.; Blass, P. M.; Bard, A. J. Langmuir 1997, 13, 5602-5607.
(
13) Moore et al. have deposited helical peptides horizontally on gold surfaces.
Strong, A. E.; Moore, B. D. Chem. Commun. 1998, 473-474. Strong, A.
E.; Moore, B. D. J. Mater. Chem. 1998, 9, 1097-1105.
2
higher values than SAM I (5-10 nA/cm for SAM I; 10-30 nA/
2
cm for II and III). Figure 2 shows the change in photocurrent for
(
14) Fox et al. have investigated optical and electrochemical properties of SAMs
in which pyrene chromophores are coupled to gold surfaces. Fox, M. A.;
Whitesell, J. K.; McKerrow, A. J. Langmuir 1998, 14, 816-820. Reese,
R. S.; Fox, M. A. Can. J. Chem. 1999, 77, 1077-1084.
III as a result of alternately shuttering and unshuttering the light
2
source. A photocurrent of 30 nA/cm is comparable to, although
7
,8
somewhat smaller than that reported by Imahori and co-workers
(
(
15) MacDonald, J. C.; Dorrestein, P. C.; Pilley, M. M.; Foote, M. M.;
Lundburg, J. L.; Henning, R. W.; Schultz, A. J.; Manson, J. L. J. Am.
Chem. Soc. 2000, 122, 11692-11702.
2
∼50-100 nA/cm ) and represents a quantum efficiency of ∼1%.
In addition to enhanced current generation, II and III also appear
to possess greater stability than SAM I. While repeated photoex-
JA0289548
J. AM. CHEM. SOC.
9
VOL. 125, NO. 10, 2003 2839