Plasmon resonance-enhanced circularly polarized luminescence of self-assembled meso-tetrakis(4-sulfonatophenyl)porphyrin-surfactant complexes in interaction with Ag nanoparticles

Article abstract of DOI:10.1039/c4cc04477k

The chiroptical properties of an anionic meso-tetrakis(4-sulfonatophenyl) porphyrin (TPPS) complexed with cationic surfactants were enhanced by interaction with silver nanoparticles (AgNPs) in acidic solution. Improvement in chiroptical properties was rev

Full text of DOI:10.1039/c4cc04477k

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Plasmon resonance-enhanced circularly polarized
luminescence of self-assembled meso-tetrakis-
Cite this: Chem. Commun., 2014,
0, 11169
(4-sulfonatophenyl)porphyrin–surfactant
5
Received 12th June 2014,
Accepted 30th July 2014
complexes in interaction with Ag nanoparticles†
a
a
b
b
b
Takunori Harada,* Naoki Kajiyama, Kei Ishizaka, Reona Toyofuku, Katsuki Izumi,
DOI: 10.1039/c4cc04477k
b
c
c
a
Kazuo Umemura, Yoshitane Imai, Naoya Taniguchi and Kenji Mishima
www.rsc.org/chemcomm
The chiroptical properties of an anionic meso-tetrakis(4-sulfonato-
phenyl)porphyrin (TPPS) complexed with cationic surfactants were
enhanced by interaction with silver nanoparticles (AgNPs) in acidic
solution. Improvement in chiroptical properties was revealed by
circular dichroism (CD) and circularly polarized luminescence (CPL),
with |gabs| and |glum| values reaching 0.05 and 0.001 at 303 K,
respectively.
Materials that exhibit plasmon resonance enhancement are of
particular interest given their unique optical properties, including
their ability to exhibit electromagnetic field enhancement and to
1
undergo strong exciton plasmon coupling. Such properties allow
for various potential applications in chemistry, biology, and optics,
including use in ultrasensitive sensors and biological sensing and
imaging. In particular, much attention has been paid to the
optical and spectroscopic properties arising from the excitation of
Fig. 1 The structure of TPPS and the surfactants (1S,2R)-N-dodecyl-N-
methyl-ephedrinium bromide ((+)-DMEB), (1R,2S)-N-dodecyl-N-methyl-
ephedrinium bromide ((À)-DMEB) and cetyltrimethylammonium bromide
1h
the surface electromagnetic modes of noble metal nanoparticles (CTAB).
NPs). The enhanced electromagnetic field induced by localized
(
surface plasmon resonance (LSPR) can dramatically alter the
properties of molecules near noble metal surfaces, resulting in spectroscopic characteristics of well-ordered porphyrin assem-
many intriguing phenomena such as plasmonic circular dichroism blies because of their high photostability, strong Soret band
1
b,2
3
(CD),
surface-enhanced Raman scattering (SERS), and absorption in the visible region, and high quantum yield result-
1i,4
surface-enhanced fluorescence (SEF).
phenomena suggest that combining noble metal NPs with chiral p-electron system. Among various porphyrins, the chiroptical
These surface-enhanced ing from the strong stacking interaction of their large delocalized
6
molecules could aid in the development of novel molecular devices. properties of the water-soluble diprotonated 4-sulfonatophenyl
7
In this communication, we report a new example of plasmon- meso-substituted porphyrin (TPPS) (Fig. 1) have been studied
enhanced luminescence relating to circularly polarized lumines- extensively by several research groups due to the compound’s
cence (CPL), the differential emission DI (I
L
À I
R
) of right- unique chiral aggregation behaviour in acidic solution and the
8,9
circularly polarized light versus left-circularly polarized light solid state. As such, we have chosen this particular porphyrin
5
by chiral molecular systems. We focus specifically on the because it is more cost-effective to make a CPL material with
tunable chiroptical properties from achiral component(s) instead
a
of a relatively costly chiral compound.
Recently, we reported chiral control of a highly stable TPPS
complex formed at the air–water interface that results by reacting
Department of Chemical Engineering, Fukuoka University, 8-19-1 Nanakuma,
Jonan-ku, Fukuoka 814-0180, Japan. E-mail: tharada@fukuoka-u.ac.jp;
Fax: +81 3 5465 7654
b
c
Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo, 162-8601, Japan
Department of Applied Chemistry, Faculty of Science and Engineering,
Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
Electronic supplementary information (ESI) available: Experimental section
10
the porphyrin with a cationic chiral surfactant. Specific surfac-
tants, such as chiral (1S,2R)- and (1R,2S)-N-dodecyl-N-methyl-
ephedrinium bromide ((+)-DMEB and (À)-DMEB, respectively)
†
1
1
and Fig. S1–S8. See DOI: 10.1039/c4cc04477k
as well as achiral cetyltrimethylammonium bromide (CTAB)
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Fig. 2 Circular dichroism (CD) and electronic absorption spectra of
(
TPPS)
DMEB (red) in acidic aqueous solution (pH = 2.3) 40 minutes after adding
DMEB to a solution of (TPPS)
n
complexed with (+)-DMEB (green), (À)-DMEB (blue) and racemic
n
Fig. 3 CPL and fluorescence emission spectra of the composite (TPPS) –
DMEB/AgNP solution ((+)-DMEB: green solid line, (À)-DMEB: blue solid line);
[TPPS] = 0.01 mM, [(+)-DMEB, (À)-DMEB] = 0.01 mM, [AgNPs] = 0.05 mM,
excitation wavelength (Ex = 430 nm), optical path length = 10 mm. The inset
shows the fluorescence emission spectra before (dotted line) and after (solid
line) adding AgNPs, and photographs show colour before (left) and after
n
; [TPPS] = 0.01 mM, [(+)-DMEB, (À)-DMEB or
(Æ)-DMEB] = 0.01 mM, optical path length = 10 mm.
(right) adding AgNPs under a black light.
(as a control), were selected based on their properties as well-
known chromophores that do not exhibit any electronic absorp-
tion in the visible range (B and Q-band), an important feature observation using AFM (Fig. S8, ESI†), while binding of the AgNPs
J
given the potential of surfactant molecules to limit absorption by was also correlated with an increase in the |gabs| value (= De/e;
the CPL-active complex (Fig. 1). In these experiments, cationic 0.05 from 0.006 at 303 K) that was quantitatively consistent with
1
d
n
surfactants play a key role in the adsorption of citrate-capped the theoretical model. The size distribution of (TPPS) –DMEB
1
2
NPs to the helical TPPS assemblies, a process that is realized by hardly changed before and after the addition of AgNPs. Thus,
substitution of citrate with a surfactant on the NP binding sites it was speculated that the enhancement in the |gabs| value is
(see Fig. S2, ESI†). Furthermore, chiral surfactants allow for mainly induced by the LSPR effect and is not due to an increase
control of chirality of the aggregates as a whole. in the enantiomeric excess of the chiral aggregates, because the
1
5
The formation of self-assembled TPPS complexed with sur- g-value is directly proportional to the scaling laws for these
factants was tracked by FT-IR (Fig. S3, ESI†), UV-vis (Fig. S4, nanoassemblies. Complex formation was also implied by the
1
3
ESI†) and CD spectroscopy. The CD signals obtained for TPPS observed blue shift of the zero crossing and the Davydov
complexed to (+)- and (À)-DMEB ((TPPS) –DMEB), respectively, splitting peak at the Soret bands (483 nm and 488 nm com-
were mirror images of each other (Fig. 2), while complexation pared to 485 and 489 nm) from that observed for the unbound
with achiral CTAB showed no circular absorption, as per expecta- AgNPs (free (TPPS) –DMEB) (Fig. S6, ESI†).
tions. Control experiments using racemic DMEB showed no CD The plasmon resonance-enhanced chiroptical properties of
activity in the B band (Fig. 2). Meanwhile, kinetic data at lmax the formed complexes were then investigated by chiroptical
488 nm) fit well with theoretical equations for a first-order spectroscopic methods. The fluorescence emission before and
n
n
J
(
process, allowing determination of the pseudo-first-order rate after the addition of AgNPs to the (TPPS) –DMEB solution
n
constant Kobs (see Fig. S5, ESI†). The Kobs value was calculated to (Fig. 3) indicates that emission is enhanced for the AgNP compo-
À1
16
be 0.0147 min for [TPPS] = 0.09 mM and [DMEB] = 0.09 mM, site compared to the non-conjugated complex of AgNPs. The
indicating that supramolecular chirogenesis proceeds slowly composite exhibited two characteristic bands: the broad band at
upon the addition of chiral DMEB. Additionally, the maximum 670 nm is assigned to the monomeric form, while the low-energy
1
3c
value of artifact-free |gabs| was found to be 0.006 at 303 K, shoulder emission band at 731 nm with moderate quantum yield
0 min following the addition of DMEB to the solution (Fig. S6, (F = 0.1) results from the J-bands of (TPPS) . Overall, AgNP binding
ESI†). The amplification of the |g | (4R/D; R = Im[m Ám ], D = resulted in an immediate five-fold increase in fluorescence inten-
4
n
abs
ij ji
2
2
|
m | + |m | ) value was found to be directly proportional to the sities arising from the coupling of optical molecular dipoles with
ij ji
17
increase in rotational strength defined by the scalar product AgNPs (Fig. 3, inset). This resulted in the observation of clear,
R because the total amount of self-assembled (TPPS) remains detectable CPL signal intensities for (TPPS) –DMEB/AgNPs (Fig. 3)
unchanged during the chirogenesis process, implying that the from concentrations of (TPPS) –DMEB that have a very low or
dipole strength D is constant. undetectable level. For example, the maximum value of artifact-
The surface plasmon resonance band for silver NPs (AgNPs), free |glum| (2DI/I + I ) is 0.001 at 303 K, 40 minutes after addition
approximately 10 nm in size, is located at about 400 nm, of AgNPs to a (TPPS) –DMEB solution. As expected, the CPL curve
demonstrating no overlap with the range of fluorescence for TPPS of (TPPS) –(À)-DMEB/AgNPs was the mirror image of (TPPS) –
n
n
n
L
R
n
n
n
(
Fig. S7, ESI†); as such, AgNPs were selected for complexation with (+)-DMEB/AgNPs. Overall, complexation appeared to modify the
14
(
TPPS)
produced by adding citrate-capped AgNPs to a solution of fully site; this likely results from the interaction of the TPPS–DMEB
formed (TPPS) –DMEB (see the experimental section in the ESI†). composite with the silver surface and a concomitant change in
The formation of the target complexes was confirmed by direct conformational distribution. These results clearly demonstrate
n n
–DMEB. These complexes ((TPPS) –DMEB/AgNPs) were intrinsic R of the induced CPL bands of the TPPS–DMEB compo-
n
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that signals observed for the enantiomeric composites are truly This research work was partially supported by a Grant-in-Aid for
1
8,19
CPL
and are enhanced by the LSPR effect on the surface Young Scientists (25870996) from the Japan Society for the
Promotion of Science, funds (135009 and 137104) from the
of AgNPs.
The enhancement contribution of the AgNPs indicates that Central Research Institute of Fukuoka University and the MEXT-
this effect is related to the plasmon-induced electromagnetic Supported Program for the Strategic Research Foundation at
enhancement responsible for other surface-enhanced optical Private Universities, 2014–2018.
3
1h
phenomena such as SERS and SEF. These changes in CPL
intensities are the combined results of two effects: (1) CD Notes and references
enhancement and (2) quantum yield change due to increased
excitation decay rates. The quantum theory of the CPL effect
1
(a) M. Schaferling, X. Yin, N. Engheta and H. Giessen, ACS Photonics,
2
2014, 1, 530; (b) Z. Li, Z. Zhu, W. Liu, Y. Zhou, B. H. Han, Y. Gao and
of a single molecule provides us with the general equation
Z. Tang, J. Am. Chem. Soc., 2012, 134, 3322; (c) J. M. Slocik, A. O.
Govorov and R. R. Naik, Nano Lett., 2011, 11, 701; (d) A. O. Govorov,
J. Phys. Chem. B, 2011, 115, 7914; (e) A. O. Govorov, Z. Fan,
P. Hernandez, J. M. Slocik and R. R. Naik, Nano Lett., 2010,
10, 1374; ( f ) A. Yoshida and N. Kometani, J. Phys. Chem. C, 2010,
5
CPLmol = Im[m Ám ]. Here, we show that in the presence of a NP,
ij ji
2
this equation takes the form CPL
= Im[( Pˆ Ám ) m ]/(o À o) +
mol-NP
ij
ji
0
F(mij, mji)/(o
0
À o), where Pˆ , F(mij, mji), o
0
and o are the electric-
1
14, 2867; (g) T. Sato, A. Omura and Y. kobayashi, Bull. Chem. Soc.
field enhancement matrix, the geometry of the complex, the
Jpn., 2010, 83, 1052; (h) J. N. Anker, W. Paige Hall, O. Lyandres,
N. C. Shah, J. Zhao and R. P. Van Duyne, Nat. Mater., 2008, 7, 442;
(i) L.-Q. Chu, R. Forch and W. Knoll, Angew. Chem., 2007, 119, 5032.
frequency of the absorption band of a molecule, and the incident
1b,d
ˆ
light frequency, respectively.
As the factor P in the first term of
ˆ
2 (a) B. M. Maoz, R. van der Weegen, Z. Fan, A. O. Govorov, G. Ellestad,
N. Berova, E. W. Meijer and G. Markovich, J. Am. Chem. Soc., 2012,
the equation affects the angle between the vectors PÁmij and mji
,
2
0
any change in this value results in the CPL signal being altered.
1
34, 717807; (b) A. O. Govorov, Y. K. Gun’ko, J. M. Slocik, V. A.
Gerard, Z. Fana and R. R. Naik, J. Mater. Chem., 2011, 21, 16806;
c) I. Lieberman, G. Shemer, T. Fried, E. M. Kosower and
In other words, this mechanism may create an enhanced chiral-
field by the interaction of a chiral molecule with NPs.
(
G. Markovch, Angew. Chem., Int. Ed., 2008, 47, 4855.
Overall, we have demonstrated a new example of plasmon
3
(a) C. E. Talley, J. B. Jackson, C. Oubre, N. K. Grady, C. W. Hollars,
S. M. Lane, T. R. Huser, P. Nordlander and N. J. Halas, Nano Lett.,
resonance-enhanced CPL of the (TPPS)
n
–DMEB complex in
2
005, 5, 1569; (b) A. M. Michaels, J. Jiang and L. Brus, J. Phys. Chem.
B, 2000, 104, 11965; (c) J. Gersten and A. Nitzan, J. Chem. Phys., 1980,
3, 3023.
interaction with AgNPs. The interaction of AgNPs with (TPPS)
n
through the surfactant DMEB resulted in the enhancement of
7
the CD and CPL signals (enhanced De and DI) when compared
4 (a) A. Kinkhabwala, Z. F. Yu, S. H. Fan, Y. Avlasevich, K. Mullen and
W. E. Moerner, Nat. Photonics, 2009, 3, 654; (b) O. L. Muskens,
V. Giannini, J. A. Sanchez-Gil and J. G. Rivas, Nano Lett., 2007, 7, 2871.
with the pure (TPPS) –DMEB complex, a phenomenon which
n
can be explained by the plasmon-induced resonant chiral-field
enhancement arising from the coupling of optical molecular
dipoles with AgNPs. This excitation of AgNP surface plasmons
resulted in |gabs| and |glum| values that were several times greater
than in the unbound AgNPs. These results suggest a significant
interaction between excitons and surface plasmons (exciton–
plasmon coupling), with the potential for tuning the chiroptical
properties of organic–NP complexes. Such control of chiral assem-
blies, consisting of achiral fluorescent compounds, through LSPR
may ultimately result in high performance CPL materials.
5
H. P. J. M. Dekkers, in Circularly polarized luminescence. A probe for
chirality in the excited state, ed. N. Berova, K. Nakanishi and R. W. Woody,
Circular Dichroism: Principle and Application, Wiley-VCH, 2000.
O. Ohono, Y. Kaizu and H. Kobayashi, J. Chem. Phys., 1993, 99, 4128.
The driving force for the formation of aggregates is the inter-
molecular interaction between the positively charged centre of a
diprotonated porphyrin ring and the negatively charged peripheral
sulfate groups of another TPPS molecule.
6
7
8
9
(a) S. Jiang, L. Zhang and M. Liu, Chem. Commun., 2009, 6252;
(b) L. Posaria, A. D’Urso, A. Mammana and R. Purrello, Chirality, 2008,
2
0, 411; (c) H. Onouchi, T. Miyagawa, K. Morino and E. Yashima,
Angew. Chem., Int. Ed., 2006, 45, 2381; (d) C. Escudero, J. Crusats,
I. D-Perez, Z. El-Hacemi and J. M. Ribo, Angew. Chem., Int. Ed., 2006,
45, 8032; (e) T. Yamaguchi, T. Kimura, H. Matsuda and T. Aida, Angew.
Chem., Int. Ed., 2004, 43, 6350; ( f ) J. M. Ribo, J. Crusats, F. Sagues,
J. Claret and R. Rubires, Science, 2001, 292, 2063.
Many organic compounds that exhibit CPL cannot effectively
maintain both F and |glum| because of the nature of circularly
5
polarized fluorophores (CPF). Typically, efficient CPFs do not
(a) Z. El-Hachemi, O. Arteaga, A. Canillas, J. Crusats, C. Escudero,
R. Kuroda, T. Harada, M. Rosa and J. M. Ribo, Chem. – Eur. J., 2008,
exhibit sufficient |glum|, while those that do are not efficient.
Optimization of the CPF F-|glum| trade-off is therefore a key
consideration for the realization of desirable CPFs, with this
LSPR-enhanced CPL being the first approach to achieve this
goal. This was possible because this technique brings the values
of both De and DI up to detectable levels, forcing both relatively
14, 6438; (b) V. V. Borovkov, T. Harada, G. A. Hembury, Y. Inoue and
R. Kuroda, Angew. Chem., Int. Ed., 2003, 42, 1746; (c) V. V. Borovkov,
T. Harada, Y. Inoue and R. Kuroda, Angew. Chem., Int. Ed., 2002,
41, 1378.
1
0 T. Harada, H. Takahashi, K. Umemura, H. Moriyama, H. Yokota,
R. Kawakami and K. Mishima, Appl. Spectrosc., 2014, 68, in press.
1 (+)-DMEB (Fig. 1) was prepared from (1S,2R)-(+)-norephedrine
according to a previously reported method (see the experimental
section and Fig. S1 in the ESI†). CTAB and (À)-DMEB were pur-
chased from Tokyo Kasei Co. Ltd., and used without any further
treatment.
1
À3
21
high |glum| (order 10 ) and F values. We plan to further
investigate the detailed mechanism of protean plasmon resonance-
enhanced CD and CPL for (TPPS) –DMEB/AgNP complexes. Such
n
investigations include tuning of chiroptical properties through 12 (a) H. Wang, J. Kundu and N. J. Halas, Angew. Chem., Int. Ed., 2007,
4
6, 9040; (b) Z. M. Sui, X. Chen, L. Y. Wang, L. M. Xu, W. C. Zhuang,
changing the size and species of the NP cores, the spectral overlap
between the J-band and the plasmon band, the stoichiometric ratio
of TPPS and the NPs, and the distance between the fluorophore and
the surface of the NPs.
The authors thank Mr H. Hayakawa and Dr M. Watanabe
of Jasco Corp. Ltd. for discussion and technical assistance.
Y. C. Chai and C. J. Yang, Physica E, 2006, 33, 308.
3 (a) T. Harada and R. Kuroda, Biopolymers, 2011, 95, 127; (b) T. Harada,
H. Hayakawa and R. Kuroda, Rev. Sci. Instrum., 2008, 79, 073103;
1
(
7
c) R. Kuroda, T. Harada and Y. Shindo, Rev. Sci. Instrum., 2001,
2, 3802.
1
4 NP binding was confirmed by Fourier Transform Infrared Spectro-
scopy (FT-IR), as shown in the ESI,† Fig. S3. The FT-IR spectrum
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showed the presence of IR stretching frequencies for the nCH
2
18 The signals could be obtained only by the Stokes–Mueller matrix
analysis for true CPL signals because of the varying heights
(B20 nm) and widths (Bhundreds nm) of the optically anisotropic
rod-like (TPPS)n aggregates.
À1
À1
(
3000–2800 cm
region) and nRSO
3
H (1080–1000 cm
region)
bands, which were shifted from those observed for the unbound
NPs and (TPPS) -DMEB-AgNPs, respectively.
n
1
5 (a) A. Romeo, M. A. Castriciano, I. Occhiuto, R. Zagami, R. F. 19 T. Harada, R. Kuroda and H. Moriyama, Chem. Phys. Lett., 2012,
Pasternack and L. M. Scolaro, J. Am. Chem. Soc., 2014, 136, 40; 530, 126.
(
b) M. A. Castriciano, A. Romeo, G. De Luca, V. Villari, L. M. Scolaro 20 The magnitude of g is related to the amount of magnetic dipole
À1
and N. Micali, J. Am. Chem. Soc., 2011, 133, 765.
6 The effect of the distance between the AgNP surface and the
fluorophore on the CD and CPL enhancements was investigated
using surfactants having different alkyl chain lengths, ranging from
character in the transition: high g values (order 10 ) are only
1
expected for m-allowed and m-forbidden transitions provided, of
course, that the chromophore is contained in a molecular structure
that is sufficiently dissymmetric. For m-forbidden and m-allowed
transitions, small values (order o10 ) are predicted.
À3
6
to 12 carbon atoms; however, we did not observe any effect on the
SPR enhancement for this range of alkyl chain lengths (data were 21 (a) B. A. San Jose, S. Matsushita and K. Akagi, J. Am. Chem. Soc.,
not provided).
2012, 134, 19795; (b) K. Watanabe, I. Osaka, S. Yorozuya and
K. Akagi, Chem. Mater., 2012, 24, 1011; (c) S. Abraham, S. Paul,
G. Narayan, S. K. Prasad and N. D. S. Jayaraman, Adv. Funct. Mater.,
2005, 15, 1579.
1
7 The enhancement of the CD and CPL signals induced by the LSPR
effect was also observed upon interaction with other gold nano-
particles (data were not provided).
11172 | Chem. Commun., 2014, 50, 11169--11172
This journal is ©The Royal Society of Chemistry 2014