Selective two-photon-absorption-induced reactions of anthracene-2-carboxylic acid on tunable plasmonic substrate with incoherent light source

Article abstract of DOI:10.1166/jnn.2015.9501

In this research, we report the development, characterization and application of various plasmonic substrates (with localized surface plasmon resonance wavelength tunable by gold nanoparticle size) for two-photon absorption (TPA)-induced photodimerization of an anthracene derivative, anthracene carboxylic acid, in both surface and solution phase under incoherent visible light irradiation. Despite the efficient photoreaction property of anthracene derivatives and the huge number of publications about them, there has never been a report of a multiphoton photoreaction involving an anthracene derivative with the exception of a reverse photoconversion of anthracene photodimer to monomer with three-photon absorption. We examined the progress of the TPA-induced photoreaction by means of surface-enhanced Raman scattering, taking advantage of the ability of our plasmonic substrate to enhance and localize both incident light for photoreaction and Raman scattering signal for analysis of photoreaction products. The TPA-induced photoreaction in the case of anthracene carboxylic acid coated 2D array of gold nanoparticles gave different results according to the properties of the plasmonic substrate, such as the size of the gold nanoparticle and also its resultant optical properties. In particular, a stringent requirement to achieve TPA-induced photodimerization was found to be the matching between irradiation wavelength, localized surface plasmon resonance of the 2D array, and twice the wavelength of the molecular excitation of the target material (in this case, anthracene carboxylic acid). These results will be useful for the future development of efficient plasmonic substrates for TPA-induced photoreactions with various materials.

Full text of DOI:10.1166/jnn.2015.9501

Article
Journal of
Nanoscience and Nanotechnology
Vol. 15, 1171–1179, 2015
Copyright © 2015 American Scientific Publishers
All rights reserved
www.aspbs.com/jnn
Printed in the United States of America
Selective Two-Photon-Absorption-Induced Reactions of
Anthracene-2-Carboxylic Acid on Tunable Plasmonic
Substrate with Incoherent Light Source
Francesca Pincella1ꢀ2, Katsuhiro Isozaki1ꢀ∗ꢀ†, Tomoya Taguchi1ꢀ2,
Yeji Song1ꢀ2, and Kazushi Miki1ꢀ2ꢀ∗
1Functional Heterointerface Group, Polymer Materials Unit, National Institute for Materials Science,
1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
2Department of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai,
Tsukuba, Ibaraki 305-8571, Japan
In this research, we report the development, characterization and application of various plasmonic
substrates (with localized surface plasmon resonance wavelength tunable by gold nanoparticle size)
for two-photon absorption (TPA)-induced photodimerization of an anthracene derivative, anthracene
carboxylic acid, in both surface and solution phase under incoherent visible light irradiation. Despite
the efficient photoreaction property of anthracene derivatives and the huge number of publications
Delivered by Ingenta to: Nanyang Technological University
about them, there has never been a report of a multiphoton photoreaction involving an anthracene
IP: 5.62.159.86 On: Tue, 14 Jun 2016 04:47:48
derivative with the exception of a reverse photoconversion of anthracene photodimer to monomer
Copyright: American Scientific Publishers
with three-photon absorption. We examined the progress of the TPA-induced photoreaction by
means of surface-enhanced Raman scattering, taking advantage of the ability of our plasmonic
substrate to enhance and localize both incident light for photoreaction and Raman scattering signal
for analysis of photoreaction products. The TPA-induced photoreaction in the case of anthracene
carboxylic acid coated 2D array of gold nanoparticles gave different results according to the prop-
erties of the plasmonic substrate, such as the size of the gold nanoparticle and also its resultant
optical properties. In particular, a stringent requirement to achieve TPA-induced photodimerization
was found to be the matching between irradiation wavelength, localized surface plasmon resonance
of the 2D array, and twice the wavelength of the molecular excitation of the target material (in this
case, anthracene carboxylic acid). These results will be useful for the future development of efficient
plasmonic substrates for TPA-induced photoreactions with various materials.
Keywords: Gold Nanoparticle, Plasmonics, Two-Photon Absorption, Photoreaction.
1. INTRODUCTION
limitation and expand the applications for a wide range of
materials and weaker irradiation sources, because metallic
nanoparticles (MNPs), especially gold and silver nanopar-
ticles, possess intriguing plasmonic properties that allow
them to harvest and concentrate light at their surface.2ꢀ3
Multiphoton-induced photoreaction in the presence of a
plasmonic substrate (near-field enhanced photoreaction)
was recently reported for a limited class of materials,
such as diarylethenes,4–6 photoresist polymers,7ꢀ8 and more
recently, semiconductor photocatalysts.6ꢀ9 The plasmonic
substrate serves to make up for the low quantum efficiency
of the two-photon process (third-order quantum process)
by increasing the electric field in the proximity of the
metallic nanostructures.10–12 Up to now, the use of such
Multiphoton processes are attracting a great deal of atten-
tion due to their interesting properties such as 3D spatial
resolution, and shifting of excitation wavelengths from UV
to Vis or NIR; nevertheless, such photoreactions can only
be achieved with high-power pulsed lasers and molecules
with huge two-photon absorption cross sections (e.g., por-
phyrin derivatives), limiting their actual application.1 2D
or 3D metallic nanostructures are expected to break this
∗Authors to whom correspondence should be addressed.
†Present address: International Research Center for Elements Science,
Institute for Chemical Research, Kyoto University, Gokasyo, Uji, Kyoto
611-0011, Japan.
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 2
1533-4880/2015/15/1171/009
doi:10.1166/jnn.2015.9501
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Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Pincella et al.
metallic nanostructured substrates for TPA reactions suf-
fered from some major limitations linked to the fabrica-
tion method, mainly lithography or wet chemistry process
(colloidal MNPs). These limitations originate in the poor
control of optical properties of the metallic nanostructures
or small total area of the plasmonic substrates (typically
in the range of a few ꢁm2 for lithography). In the case
of colloidal MNPs attached to the target material for the
multiphoton process, the MNP loading is usually low6 and
Scheme 1. Selective TPA-induced reactions of anthracene-2-carboxylic
thus it is not possible to take advantage of the “hot spots”
(regions in the gap between particles) where MNPs exhibit
strong near-field enhancement. In the case of plasmonic
substrates prepared by top-down techniques, in addition to
size and cost issues, the range of applications is limited
to solid-state reactions. In order to apply plasmonic TPA
reactions to a wide range of photochemical processes, scal-
ability and generality need to be achieved by bottom-up
technique.13−16 Regarding scalability, we have already suc-
ceeded in solution-phase TPA reaction with an incoherent
light source11 with the advantage of large-area plasmonic
substrate prepared by a hybrid method developed by our
group.12 For generality, a different type of photoreaction
needs to be proven to verify the wide-range applicability
of our plasmonic TPA excitation system. Thus, we plan to
use plasmonic substrate with a localized surface plasmon
resonance (LSPR) wavelength that matches the optimal
condition for TPA in the anthracene derivative to induce
photodimerization in the molecule with visible light irra-
acid both on dried surface and in solution phase with AuNP array.
different photoproducts according to the reaction media
(Scheme 1).
2. RESULTS AND DISCUSSION
In order to obtain a large-scale and efficient plasmonic
substrate for TPA-induced photoreaction, a series of
gold nanoparticle (AuNP) arrays, dodecanethiol-capped
10-nm AuNP array (10Dod array) and mixed hexanethiol-
dodecanethiol-capped 23- and 39-nm arrays (23HexDod,
39HexDod arrays), was prepared by a hybrid deposition
method developed by our group (Fig. 1(a)).12 The high
density and close-packed morphology of these arrays were
characterized by SEM observation (Figs. 1(b), 2). Opti-
cal properties of the AuNP arrays were analyzed by UV-
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Vis-NIR extinction spectroscopy (Figs. 1(c), 3), where the
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LSPR lies in different regions, from 605 nm of the 10Dod
diation. Here, we demonstrate the successful fabrication of
different plasmonic substrates with high gap (“hot spots”)
density and LSPR in a wide range of wavelengths depend-
ing on the AuNP size.
Copyright: American Scientific Publishers
array, to 722 nm of the 23HexDod array, and 966 nm of
the 39HexDod array, making them good candidates for
visible and NIR light irradiation. These AuNP arrays were
immersed in 5 mM ACA solution in H2O–DMSO contain-
ing 5.4 M NaOH to adsorb ACA molecules at the AuNP
surface by hydrophobic interaction with alkanethiols.25
Irradiation of samples proceeded under continuous Ar flow
in a 5-mL glass (cutoff wavelength 300 nm) vessel sealed
with a natural rubber septum (Aldrich). ACA-coated AuNP
array samples were irradiated from the top with UV light
(285–400 nm, 300–400 nm at the sample, 59 mW/cm2ꢂ
for 24 h, Vis light (422–750 nm, 220 mW/cm2ꢂ for 60 h,
and NIR light (750–1050 nm, 294 mW/cm2ꢂ for 48 h,
respectively.
First, we show the plasmonic TPA-induced photoreac-
tion ACA on a dried surface (Scheme 1). Due to low ACA
concentration on the surface, common spectroscopic tech-
niques (e.g., UV-Vis) could not be used to study the pho-
toreaction at the surface of the 2D array; therefore, taking
advantage of the intrinsic ability of our array to enhance
both incident (laser excitation) and scattered electromag-
netic fields, we used surface-enhanced Raman scattering
(SERS)26–29 to determine the progress of the two-photon-
induced photodimerization of dried ACA by comparing
the SERS spectra with that of the starting ACA, possible
photoreaction products such as anthraquinone-2-carboxylic
acid (AQCA), and photodimer of ACA (ACAD). The most
In this report, we demonstrate how plasmon-induced
two-photon reaction can be successfully applied to
the photodimerization of an anthracene derivative,
i.e., anthracene carboxylic acid. The photoreaction of
anthracene derivatives, which has been well investigated,
gives anthraquinone in the presence of O2,17ꢀ18 photodimer
in the absence of O2,19 and radical-mediated dihydroxy-
bianthryl in the absence of O2 under a diluted aqueous
condition,20 respectively, by UV irradiation for wave-
lengths longer than 300 nm. Among these photoreactions,
the photodimerization of anthracene18 is a well-known
reversible photoreaction that proceeds under UV irradi-
ation for wavelengths longer than 300 nm and can be
reversed thermally or under UV irradiation for wave-
lengths shorter than 300 nm, and thus is frequently used
as a probing reaction for asymmetric photoreactions in the
field of supramolecular photochemistry.21–23 Despite the
efficient photoreaction property of anthracene derivatives,
to our knowledge, there have been no reports about TPA-
induced photoreaction of anthracene, with the exception
of a reverse photoconversion of anthracene photodimer
to monomer with three-photon absorption.24 Here, we
demonstrate the first plasmonic TPA-induced photoreac-
tion of anthracene-2-carboxylic acid (ACA), which gave
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Pincella et al.
Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Figure 1. (a) Schematic illustration of sample structure, (b) SEM image; inset shows higher magnification, and (c) extinction spectrum of 25HexDod
array; UV spectrum of ACA is overlaid.
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Copyright: American Scientific Publishers
Figure 2. SEM image of (a) 10Dod 2D array, and (b) 50HexDod 2D array; insets shows higher magnification.
intense peaks for these compounds were observed at 756,
1409 cm−1 for ACA; 710, 1035, 1179 and 1608 cm−1
for ACAD; 1034, 1179, 1598 and 1667 cm−1 for AQCA
(Figs. 4(a)–(c)), respectively. When Vis light was irradi-
ated, the SERS spectra of both the 10Dod and 39HexDod
arrays still presented the typical features of ACA along
with a clear contribution from AQCA (Figs. 5, 6). Con-
trastingly, the Vis-irradiated 23HexDod array showed a
dramatic change in the SERS spectrum (Fig. 4(e)), which
has some features common to both ACAD and AQCA at
1040, 1179, 1608 cm−1, and almost no contribution from
ACA. This result suggests that ACA is completely con-
verted to photoproducts by TPA-induced photoreaction at
the surface of the 23HexDod array. As can be seen from
Figure 3, Vis light is capable of exciting LSPR in the
case of the 10Dod and 23HexDod arrays, while for the
39HexDod arrays Vis light can only excite the quadrupole
peak (500 nm) and the shoulder of the main LSPR peak,
thus explaining the photoreaction results of 23HexDod.
Figure 3. Extinction spectra of 10Dod (blue line), 23HexDod (red line),
39HexDod (black line) 2D array on Au substrate.
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Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Pincella et al.
Figure 6. Raman spectra of (a) bare 39HexDod array on Au substrate,
(b) ACA/39HexDod array, (c) visible light irradiated ACA/39HexDod
array, and (d) NIR light irradiated ACA/39HexDod array.
Figure 4. Raman spectra of (a) ACA on 23HexDod 2D array,
(b) ACAD on Au substrate, (c) AQCA on 23HexDod 2D array, (d) UV-
(e) Vis- (f) NIR-irradiated ACA-coated 23HexDod arrays, and (g) bare
23HexDod 2D array.
the LSPR in the array (NIR light). NIR irradiation on
the ACA-coated 39HexDod array resulted in no detectable
change from the original ACA spectrum, suggesting that
excitation of the 2D array under resonant conditions alone
(ꢃex ≡ ꢃLSPR) is not sufficient to trigger photoreaction, and
that suitable irradiation wavelengths are needed to induce
any photoreaction in the dried ACA (overlapping between
ꢃex and ꢃTPA is small in the case of 39HexDod 2D array).
After comparing the photoreaction progress for var-
ious plasmonic substrates, we sought to identify the
photoproduct of the Vis-light-irradiated ACA-coated
23HexDod 2D array to gain further insight into the pho-
In order to explain the results for the 10Dod array, we
have to consider that small AuNPs show low plasmonic
enhancement30 and limited “hot spot” volume compared
to larger particle arrays. From these considerations we can
understand the role of AuNP size in the development of
efficient plasmonic reactors.
Once the role of metallic nanoparticle size had been
ascertained, we attempted to verify the importance of
matching the excitation wavelengths with the 2D arrays’
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toreaction mechanism. Thus, we performed DFT calcu-
IP: 5.62.159.86 On: Tue, 14 Jun 2016 04:47:48
lation of Raman spectra of all candidate products, such
LSPR or ꢃTPA. In detail, the 23HexDod array (2D array
with the best match between LSPR CanodpyꢃrTigPAh)t:wAamseirrircaa- n Scientific Publishers
as ACAD, AQCA, and 10,10ꢀ-dihydroxy-9,9ꢀ,10,10ꢀ-tetra-
diated with UV and NIR light (Figs. 4(d), (f)). It can be
clearly seen that the ACA contribution (red dotted line in
Fig. 4) is still dominant after NIR irradiation, which sug-
gests that no reaction occurred, as expected. In the case
of UV irradiation (wavelength range for one-photon reac-
tion), no clear peaks were observed, which was confirmed
by SEM measurement to have arisen from the sintering of
AuNPs caused by the cleavage of surface alkanethiols.31
Next, in the case of the 39HexDod array, irradiation was
also performed with light in a suitable range to excite
hydro-bianthryl-dicarboxylic acid (HBAC), see Figure 7
and Table I. Although DFT-calculated Raman spectra and
experimental data do not match completely for all com-
pounds under investigation (Table I), the formation of
HBAC could explain the appearance of several peaks
around 870–890 cm−1 (877–895 in DFT), 1140 cm−1 (1156
in DFT), 1179 cm−1 (1156 in DFT), 1250 and 1320 cm−1
(1237 and 1345 in DFT) without any increase in intensity
of the C O peak at 1660 cm−1 (strong peak of AQCA).
Figure 7. DFT-calculated Raman activity of (a) ACA, (b) AQCA,
(c) ACAD obtained by averaging the 4 stereomers of ACAD, and
(d) 10,10ꢀ-dihydroxy-9,9ꢀ,10,10ꢀ-tetrahydro-bianthryl-dicarboxylic acid
(HBAC).
Figure 5. Raman spectra of (a) bare 10Dod array on Au substrate,
(b) ACA/10Dod array, and (c) visible light irradiated ACA/10Dod array
(green line).
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Pincella et al.
Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Table I. Comparison of experimental (normal Raman NR and surface-enhanced Raman SERS) and DFT (B3LYP/6-31G(d)//B3LYP/6-31G(d))-
calculated intense Raman lines of ACA, AQCA, ACAD and HBAC. All experimental data except NR AQCA peaks (obtained from Ref. [38]) was
collected during this study.
ACA (NR-SERS on
2D array)
AQCA (NR38-SERS
on 2D array)
ACAD
(NR-SERS on Au)
ACA (DFT)
AQCA (DFT)
ACAD (DFT)
HBAC (DFT)
–
–
776
–
687–696
712
–
856
718–710
712
–
–
679
733
877
754–756
–
–
–
–
839–852
–
–
–
–
–
–
–
1072
1272
1352
–
–
944
1040
1192
1264
1320
–
958
1040
1168
1248
–
1456
1536
1600
1037–1034
1173–1179
1032–1035
1177–1179
1075
1156
1237
1345
–
1248(?)–1250
–
1406–1409
1556–1560
1631–1631
–
–
–
–
–
–
1605–1598
1668–1667
1608
1656 (1672)
1610–1608
–
–
1648
–
1660 (1696)
The formation mechanism of HBAC was previously sug-
gested to have originated from photo-induced one-electron
oxidation of anthracene backbone, following a reaction
with water and dimerization.20 As we recently reported,25
the alkanethiol-capped AuNP surface can trap molecules
inside the hydrophobic molecular interface where ACA and
water can be concentrated. Thus, once ACA is excited by
TPA, such sequential reaction is supposed to occur at the
AuNP surface. Also, placing ACA near the AuNP surface
is considered to accelerate the one-electron oxidation of
ACA by AuNP’s electron relay property.32
In order to confirm the SERS results, all photoreaction
products were analyzed by mass spectra. NIR-irradiated
ACA on the 23HexDod array was confirmed to have no
changes from the starting ACA (m/z 495.1 [Na-ACA +
ACA − CO2 +CH3OH+H2O+Na]+ꢂ similar to the SERS
result (Figs. 8(a), (f)). Mass analysis revealed that some
ACA content on the 23HexDod array was converted to
AQCA (m/z 491.3 [AQCA-H+AQCA-CO2 +CH3OH]−ꢂ
by UV irradiation (Figs. 8(c), (d)). Surprisingly, Vis-
irradiated ACA on the 23HexDod array gave a clear
mass spectrum with no remaining ACA, which strongly
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Copyright: American Scientific Publishers
Figure 8. ESI mass spectra of (a) ACA, (b) ACAD, (c) AQCA, reaction products of (d) UV-, (e) Vis-, and (f) NIR-irradiated ACA-coated 23HexDod
arrays.
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Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Pincella et al.
Figure 9. 1H NMR (300 MHz, DMSO-d6ꢂ spectra of Vis-irradiated ACA solution with (a) 25HexDod-array, (b) Au thin film, (c) ACA, and (d) ACAD.
suggests the formation of HBAC (m/z 803.5 [2BHAC-
2CO2 +Na]+ꢂ (Fig. 8(e)) as suggested by DFT calculation.
From these results, the 23HexDod array was found to act
as plasmonic substrate for TPA-induced photoconversion
of ACA.
reported photocatalytic oxidation with Au.33 Of course,
without Au substrates, the ACA solution alone did not
show any spectral change by Vis irradiation because of
the absence of absorption bands at this wavelength range
(Fig. 1(c)). Considering these results, although the back-
ground single-photon-based photocatalytic oxidation reac-
tion by Au film is dominant, conversion of ACA to ACAD
was successfully achieved by TPA-induced reaction by
Second, we show plasmonic TPA-induced photoreaction
ACA in the solution phase (Scheme 1). The best substrate,
the 23HexDod array, was applied to solution-phase TPA-
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induced reaction of ACA (Fig. 9), which is of greater inter-
AuNP array. Our discovery of solution-phase as well as
surface-phase TPA reactions paves the way for the selec-
tion of TPA reaction depending on the reaction media.
IP: 5.62.159.86 On: Tue, 14 Jun 2016 04:47:48
est for future applications. The substrate of the 23HexDod
Copyright: American Scientific Publishers
array was immersed in 10 mM ACA solution containing
10.8 mM NaOH in H2O–DMSO, where Vis light was irra-
diated for 33 h. The resultant solution was neutralized
3. CONCLUSIONS
1
1
and extracted for H NMR analysis. The H NMR spec-
trum revealed the formation of trace amounts of ACAD
(1.1% yield) and AQCA (84.1% yield) as a major product.
A similar experiment was carried out to check the con-
tribution of Au thin film used for the substrate of AuNP
arrays, where complete conversion of ACA to AQCA was
confirmed, which would have originated from recently
We succeeded in expanding the applicability of plasmonic
metallic nanostructures to induce TPA reaction. We fabri-
cated a series of AuNP arrays bearing LSPR ranging from
UV, Vis, to NIR region depending on the AuNP size. Inco-
herent light in various wavelength ranges was irradiated
to ACA-coated AuNP arrays and the photoreaction prod-
ucts were analyzed by SERS measurement and mass spec-
troscopy. The results confirmed that TPA-induced reaction
requires matching between irradiation wavelength, LSPR,
and twice the wavelength (half photon energy) of molecu-
lar excitation (ꢃirr ≡ ꢃLSPR ≡ 2ꢃexꢂ. In addition, we found
that even when matched conditions are met, the size of the
AuNPs strongly affects the progress of the TPA-induced
reaction. It was suggested by both DFT-calculated Raman
analysis and mass spectra that the formation of HBAC
had occurred through TPA-induced reaction at the sur-
face of the 23HexDod array by Vis irradiation, while it
1
was demonstrated by H NMR that solution-phase TPA-
induced reaction of ACA gave ACAD. Although higher
reaction efficiency is necessary to apply TPA-induced reac-
tion for chemical synthesis, we consider that this limita-
tion can be overcome by combining AuNP array substrates
with microchannel reaction systems, making this system
Figure 10. Extinction spectra of colloidal solution of 10 (blue line), 23
(red line) and 39 nm (black line) AuNP.
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Pincella et al.
Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
a promising candidate for the development of an efficient
and cost-effective “lab-on-a-chip” for photoreactions.
immersed in a 1% v/v solution of Hexdt in ethanol for
12 h, rinsed with 2-propanol (IPA) three times and dried
under a nitrogen stream.
4. EXPERIMENTAL DETAILS
4.1. General
4.4. Gold Nanoparticle Synthesis
4.4.1. 10-nm Gold Nanoparticles
Extinction spectra were recorded with a Jasco V-670
double-beam spectrophotometer equipped with a liquid
cell holder module and a specular reflectance module,
and SEM images were acquired with a Hitachi S-4800
FE-SEM. Raman measurements were performed with a
Horiba Jobin Yvon T-64000 micro-Raman spectrometer
equipped with He/Ne laser (632.8 nm excitation line was
used), single monochromator with notch filter for laser
line rejection, 1800 gr/mm grating, and liquid nitrogen
Small gold nanoparticles were synthesized by a seed-
mediated method35 starting from a (3.5 0.7)-nm seed.
0.12 mL of ice-cold 0.1 M aqueous NaBH4 solution was
added to 4 mL aqueous solution containing 2ꢅ5×10−4
M
HAuCl4 · 3H2O and 2ꢅ5 × 10−4 M trisodium citrate while
continuously stirring.
The growth solution was prepared by adding 0.2 mL
of a 50 mM solution of HAuCl4 · 3H2O to 39.8 mL of
milli-Q water. Then, 1.2 g of solid CTAB was added to
the solution to reach a final concentration of 0.08 M. The
1
cooled CCD detector. H and 13C spectra were recorded
on JEOL JNM-AL300 and JNM-ECS400 spectrometers.
Mass spectra were measured by Fourier transform ion
cyclotron resonance mass spectrometry (FT-ICR-MS) cou-
pled with electron spray ionization (ESI) technique using
a SolariX FT-ICR-MS spectrometer (Bruker Daltonics
GmbH). An Asahi-Spectra 300 W Xe lamp (Max-302)
equipped with UV (250–385 nm), Vis (385–740 nm) and
IR (750–1050 nm) mirror modules and a visible bandpass
filter (422–750 nm) was used for the photodimerization
experiments. Laser power and Xe lamp power (low inci-
dent) were measured on an Si photodiode (Thorlabs Inc.
S120VC, wavelength range 200–1100 nm) power meter.
Xe lamp power (high incident) was measured with a ther-
mal power sensor (Thorlabs Inc. S302C). DFT calculation
was carried out using the Gaussian 03 program.34
ꢁ
solution was stored in an incubator at 40 C until it turned
to an orange color and then finally cooled to RT before use.
To obtain a final size of 10 nm, 2.07 mL of seed solution
was added to a pre-prepared solution of 99.5 ꢁL of freshly
prepared 0.1 M ascorbic acid solution and 17.83 mL of
growth solution. The extinction spectrum of the solution
is shown in Figure 10.
4.4.2. 23 nm and 39 nm Gold Nanoparticles
Large gold nanoparticles (AuNPs) were synthesized by
another seed-mediated method from a 13-nm seed. First,
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a gold seed solution was prepared by the citrate reduction
Copyright: American Scientific Publishers
method37 (average size 13 1.5 nm): a 50 mL solution of
0.5 mM HAuCl4 ·3H2O was brought to boiling in a round-
bottom flask while continuously stirring, then 2.5 mL of
a 38.8 mM aqueous sodium citrate solution was added
at once. The solution was refluxed for 20 min to allow
complete reduction (solution turned wine red). The col-
loidal solution was left to cool slowly and then was used
as the seed solution to obtain larger (23 or 39 nm) gold
nanoparticles.
4.2. Materials
Plastic-formed carbon counter electrodes were purchased
from Tsukuba Materials Information Laboratory Ltd.
(TMIL) and used after cutting and cleaning by son-
ication in DI water and hexane. 2-Anthracene car-
boxylic acid (ACA), 9,10-anthraquinone 2-carboxylic acid
(AQCA), hexadecyltrimethylammonium bromide (CTAB),
and 1-hexanethiol were purchased from TCI. 1,6-
Hexanedithiol (Hexdt), and chloroauric acid trihydrate
were purchased from Sigma–Aldrich. All other chemicals
were purchased from Nacalai-Tesque. All chemicals were
guaranteed reagent grade and were used as received. Ultra-
pure water (Milli-Q by Millipore Co., 18.2 Mꢄ cm) was
used throughout the experiments.
To prepare the growth solution, 0.8 mL of 20 mM aque-
ous HAuCl4 ·3H2O solution and 80 ꢁL of 10 mM aqueous
AgNO3 solution were added to 34 mL of milli-Q water.
To obtain the desired final size, 6.12 mL (23-nm
AuNPs) or 0.6 mL (39-nm AuNPs) of seed solution was
added to the growth solution while stirring vigorously, and
6 mL of aqueous ascorbic acid solution (5.3 mM) was
added dropwise (feeding rate 0.6 mL/min) to the solution
by means of a mechanical syringe pump (KD Scientific).
The extinction spectra of the colloidal solutions are shown
in Figure 10.
4.3. Substrate Preparation
Quartz substrates (1 × 1 cm2ꢂ were cleaned by immer-
sion for 15 min at RT in fresh piranha solution (H2SO4
30%: H2O2 = 2:1 v/v; handle with care: piranha solu-
tion is highly corrosive and reacts violently with organic
matter) and rinsed three times with milli-Q water. Quartz
substrates were then coated with Cr (10 nm) (adhesion
layer) and Au (40 nm) by electron beam deposition. After-
wards, samples were UV-ozone cleaned for 3 h and later
4.4.3. Alkanethiol-Capped AuNPs
AuNPs of 10, 23 and 39 nm were then capped with
alkanethiols:11 The colloidal solution of 10-nm AuNPs
was mixed with a 0.55% v/v dodecanethiol solution
(10 mL) in acetone. The colloidal solution of 23- and
39-nm AuNPs was mixed with a 0.55% v/v solution of
J. Nanosci. Nanotechnol. 15, 1171–1179, 2015
1177

Selective TPA-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate
Pincella et al.
hexanethiol:dodecanethiol = 3:1 (10 mL) in acetone. Stir-
ring was performed for 12 h at RT, and then alkanethiol-
capped AuNPs were extracted with methanol and hexane
and purified by sequential centrifuge and redispersion into
hexane three times.
(with a 5% ND filter), 0.42 NA objective lens (45×Super
Long Working Distance Plan APO from Photon Design),
integration time of 60 s and two acquisitions. For detection
of ACA Raman peaks with the 10-nm AuNP 2D array as
substrate, the power at the sample was set to 190 ꢁW (with
a 10% ND filter), and acquisition time was set to 180 s
(due to the low near-field enhancement of the substrate).
The Raman peaks relative to ACA, ACAD and AQCA
were identified by comparison of the SERS spectra with
DFT-calculated spectra of the same compounds, as shown
in Table I.
4.5. 2D Array Deposition
The 2D array of AuNPs was deposited on the gold sub-
strates by means of a hybrid method developed by our
laboratory.12 Briefly, a dithiol-functionalized gold substrate
was used as a cathode, while a plastic carbon electrode
was used as an anode. The distance between the elec-
trodes was kept at 1.2 mm, while the voltage applied was
1.1 V. Alkanethiol-capped AuNPs were redispersed in a
2-mL hexane:acetone (10:1 v/v) solution. The electrodes
were immersed in the colloidal solution (in a 3-mL plas-
tic vessel) and left in a nitrogen-purged environment until
complete evaporation of the colloidal solution took ꢁplace.
Afterwards, samples were put on a hot plate at 50 C for
24 h to induce chemisorption of the AuNPs on the sub-
strate and finally they were sonicated for 20 s to remove
multilayers. The extinction spectra of the 10-, 23- and
39-nm AuNP 2D arrays are shown in Figure 3.
Acknowledgments: We thank the Japan Society for the
Promotion of Science (JSPS) and the Ministry of Edu-
cation, Culture, Sports, Science and Technology of Japan
(MEXT) for financial support; Grant-in-Aid for Chal-
lenging Exploratory Research (Kazushi Miki, 24656040);
Grant-in-Aid for Scientific Research on Innovative Areas
“Integrated Organic Synthesis” (Kazushi Miki, 22106545
and 24106746); and Grant-in-Aid for Young Scientists
(Katsuhiro Isozaki, 30455274), Japan Science and Tech-
nology Agency (JST) for financial support of e-ASIA JRP.
Also, a part of this research was supported both by the
Research Foundation for Opto-Science and Technology
and by Grant for Environmental Research Projects from
The Sumitomo Foundation. We are grateful to Professor
M. Nakamura and Professor H. Takaya (Kyoto University)
4.6. Deposition of Anthracene Derivative
ACA, AQCA, and ACA photodimer (ACAD) were
deposited onto the AuNP 2D arrays by the immersion
Delivered by Ingenta to: Nanyang Technological University
for their assistance with the analysis and helpful discus-
IP: 5.62.159.86 On: Tue, 14 Jun 2016 04:47:48
method. Deposition by immersion was performed by intro-
ducing a substrate in a sealed vessel containing a nitro-
gen gas-purged (15 min bubbling with N2 gas) 5 mM
anthracene derivative solution prepared by adding 1 mL
of 50 mM solution in DMSO to 9 mL of 6 mM aque-
ous NaOH solution. The samples were kept overnight in
the anthracene derivative solution and then dried under a
nitrogen stream. The anthracene derivative-coated samples
were then characterized by Raman spectroscopy to verify
the effective deposition of the anthracene derivative.
Copyright: American Scientific Publishers
sions. This study was supported by NIMS Molecule and
Material Synthesis Platform in “Nanotechnology Platform
Project” operated by the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), Japan.
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Received: 17 December 2013. Accepted: 25 December 2013.
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Copyright: American Scientific Publishers
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