Supporting Information.
Experimental details: Electronic spectra, STEM, AFM, and Photocurrent.
Supporting Information
Largely enhanced photocurrent via gap-mode plasmon resonance by a nanocomposite
layer of silver nanoparticles and porphyrin derivatives fabricated on an electrode
Katsuhiko Kanaizuka, Shigeta Yagyu, Manabu Ishizaki, Hiroki Kon, Takanari Togashi,
Masatomi Sakamoto, and Masato Kurihara
1. Procedures for the preparation of porphyrin-Ag NP nanocomposite layers
We prepared three types of photoactive films, ITO/(3-mercaptopropyl)trimethoxysilane
(MPTS)/Ag NPs/5-(4-carboxyphenyl)-10,15,20-triphenylporphyrins (1) (a), ITO/Ag
NPs/1 (b), and ITO/1 (c).
FIG. S1. Procedures for the preparation of ITO/MPTS/Ag NPs/1 (a), ITO/Ag NPs/1 (b),
and ITO /1 (c).
2. Electronic spectrum and STEM image of the Ag NPs
An electronic spectrum of Ag NPs used in this study is shown in Fig. S2(a). A scanning
transmission electron microscope (STEM) image of Ag NPs (Fig. S2(c)) and a picture
of an Ag NP dispersion solution of pentane (Fig. S2(b)) are also shown. The mean
particle size of the Ag NPs was estimated to be 7.9 nm. The preparation methods of this
Ag NPs have already been reported.S1
FIG. S2. Electronic spectrum (a) and a picture (b) of an Ag NP dispersion solution of
pentane, and a STEM image of the Ag NPs (c).
3. Electronic spectra and photo-action spectra of porphyrin-Ag NP nanocomposite
systems
To compare the intensity of the normal plasmon and the gap-mode plasmon bands in
ITO/Ag NPs/1 and ITO/MPTS/Ag NPs/1, normalized spectra are shown in the text.
Original spectra are shown in Fig. S3.
FIG. S3. (a) Electronic spectra of ITO/MPTS/Ag NPs (yellow) and ITO/Ag NPs (blue),
(b) electronic spectra of ITO/MPTS/Ag NPs/1 (yellow) and ITO /Ag NPs/1 (blue), and
(c) photocurrent action spectra of ITO/MPTS/Ag NPs/1 (yellow) and ITO /Ag NPs/1
(blue) in 0.1 M Na2SO4 at a potential of -0.1 V vs. Ag/AgCl.
4. Photocurrent generation of ITO/1 system
The UV-vis absorption spectrum and photoaction spectrum of ITO/1 are shown in Fig.
S4. The shape of the photoaction spectrum fitted nicely to the UV-vis absorption
spectrum; therefore, 1 acted as a trigger for the photocurrent generation.
FIG. S4. Electronic spectra of ITO/1 (green) and photocurrent action spectra of ITO/1
(yellow) in degassed 0.1 M Na2SO4 aqueous solution containing 10 mM ascorbic acid at
a potential of 0.1 V vs. Ag/AgCl.
5. Effect of oxygen molecules for photocurrent generation of ITO/MPTS/Ag NPs/1
Effect of oxygen molecules for the photocurrent generation was examined by nitrogen
bubbling of the electrolyte solution. The photocurrent responses of ITO/MPTS/Ag
NPs/1 upon the nitrogen bubbling are shown in Fig. S5. The photocurrent was reduced
via the nitrogen bubbling so that the oxygen molecules in the solution acted as an
electron- or energy acceptor.
FIG. S5. Photocurrent responses of ITO/MPTS/Ag NPs/1 in 0.1 M Na2SO4 aqueous
solution at -0.1 V vs. Ag/AgCl upon nitrogen bubbling for 0 min (black), 5 min (blue),
20 min (green).
6. AFM images of ITO/MPTS/Ag NPs/1 before and after light irradiation
The stability of the Ag NPs on ITO was determined by AFM measurement. Figs. S6(a)
and b shows AFM images before and after light irradiation for 20 min for
ITO/MPTS/Ag NPs/1 in 0.1 M Na2SO4 aqueous solution at 0 V vs. Ag/AgCl,
respectively. Removal or aggregation of Ag NPs was not observed; this also supports
the stable photocurrent detection (see Fig. S3).
FIG. S6. AFM images of before (a) and after light irradiation for 20 min (b) for
ITO/MPTS/Ag NPs/1 in 0.1 M Na2SO4 aqueous solution at 0 V vs. Ag/AgCl.
7. Calculation of quantum yields of photocurrent generation
The efficiencies were calculated using Equations 1 and 2, in which i is the photocurrent,
e is the elementary charge, I is number of photons and unit time,  is the irradiation
wavelength, A is the absorbance of ITO/1 or ITO/MPTS/Ag NPs/1 at  nm, c is the
velocity of light, W is the power of light irradiation at  nm (this value was monitored
by Advantest Q8230), and h is the Plank constant.S2,S3
(1)
(2)
For example, in the case of ITO/MPTS/Ag NPs/1, the values of , i, and W were 432
nm, 148 nA, and 345 W, respectively. Therefore the value of  was calculated to be
0.256 %.
8. References
S1. (a) M. Itoh, T. Kakuta, M. Nagaoka, Y. Koyama, M. Sakamoto, S. Kawasaki, N.
Umeda, M. Kurihara, J. Nanosci. Nanotechnol. 9, 6655 (2009).
(b) M. Kurihara, M. Sakamoto, Applied Jpn. Patent 2010-265543
S2. A. Aoki, Y. Abe, T. Miyashita, Langmuir 15, 1463 (1999).
S3. Y. Matsuo, K. Kanaizuka, K. Matsuo, Y.-W. Zhong, T. Nakae E. Nakamura, J. Am.
Chem. Soc. 130, 5016 (2008).