Enhanced One-Photon Cycloreversion Reaction of Diarylethenes near

ARTICLE pubs.acs.org/JPCC

Enhanced One-Photon Cycloreversion Reaction of Diarylethenes near Individual Gold Nanoparticles Hiroyasu Nishi,† Tsuyoshi Asahi,‡ and Seiya Kobatake*,† †

Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan ‡ Department of Material Science and Biotechnology, Ehime University, 10-13 Dogohimata, Matsuyama, Ehime 790-8577, Japan ABSTRACT: The photocycloreversion reaction of a diarylethene upon irradiation with visible light was found to be accelerated in proximity to a gold nanoparticle covered with diarylethene polymers (Au-poly(DE)) dispersed in a solution. Enhancement of the reaction rate by the gold nanoparticle was quantitatively evaluated by kinetic analysis on the basis of absorption spectroscopy. Multicomponent bleaching of the closed-ring form of poly(DE) was observed around the gold nanoparticle upon irradiation with visible light; the irradiation time dependence of the absorbance could be explained using a reaction model with two decay components rather than one. The results indicate that the cycloreversion reaction was enhanced only in the vicinity of the gold nanoparticle. The faster reaction inside the polymer shell was confirmed by numerical spectral simulation of Au-poly(DE) using a double shell model based on Mie theory. The enhancement factor determined as the ratio of the enhanced reaction rate to the nonenhanced rate was estimated to be 2-5, and the enhanced region was evaluated to be 9-12 nm from the surface of the gold nanoparticle. The enhancement factor tended to increase with irradiation at longer incident wavelength, which did not correlate with the spectral shape of the local surface plasmon resonance (LSPR) band of the gold nanoparticle.

’ INTRODUCTION Hybrid heterostructures of noble metal nanoparticles and organic molecules have a significant impact in fields such as photonics and molecular sensors because the fluorescence and Raman scattering of a molecule close to the nanoparticle surface are strongly modified by the local surface plasmon resonance (LSPR) of the nanoparticle.1-8 LSPR is a phenomenon of resonance between the collective oscillation of conduction electrons and incident light. At the resonance frequency, LSPR results in enhanced electromagnetic fields that are confined to the nanometer scale on the particle surface. The local enhancement of electromagnetic fields is of significant importance for optical and spectroscopic applications because of the influence of LSPR modes on the optical transition of molecules near the nanoparticle surface. Thus, the localized electromagnetic enhancement effects of fluorescence and Raman scattering spectroscopy have been intensively examined and investigated recently.5-9 The local electromagnetic field generated by LSPR can be considered to act as a light-gathering antenna that leads to an increase of the optical transition probability of the molecule near the nanoparticle surface. Metallic nanoparticles have a potential for a specific photoreaction field that enhances photochemical reaction upon irradiation at the wavelength corresponding to the LSPR band. There have been several reports of these effects on the enhancement of photochemical processes such as solar energy conversion, photopolymerization, and photochromism.10-14 r 2011 American Chemical Society

Ueno et al. reported the two-photon polymerization of a UVreactive photoresist in the nanogaps of an ordered gold nanostructure upon irradiation by an incoherent visible light source.12 Hubert et al. demonstrated that mass transport induced by the photoisomerization reaction of azobenzene moieties in a polymer matrix was preferentially observed near a metallic nanostructure depending on the direction of polarized light.13 Although such research has attracted much attention from photochemists, the focus has been on the photochemical reaction in the solid state. It is difficult to evaluate reaction in the solid state because there are various heterogeneities, such as variation in the structural conformation of the reactive molecules and the distance between the molecule and the nanoparticle. Therefore, it is necessary to synthesize a well-defined heteronanostructure system of metal nanoparticle and photoreactive molecule with well-established photochemical properties to quantitatively investigate the mechanism of the LSPR enhancement effect on the photoreaction. One candidate for such a well-defined nanostructure is a gold nanoparticle with a photochromic diarylethene shell.15,16 Recently, we reported the synthesis and optical properties of the gold nanoparticle covered with diarylethene polymers (Au-poly(DE)) shown in Figure 1.15,16 Most diarylethenes undergo photochromic reaction with high thermal stability of both isomers, fatigue resistance, and Received: December 12, 2010 Revised: January 31, 2011 Published: March 01, 2011 4564

dx.doi.org/10.1021/jp111807k | J. Phys. Chem. C 2011, 115, 4564–4570

The Journal of Physical Chemistry C

Figure 1. Schematic illustration of Au-poly(DE).

high reactivity in the solid state as well as in solution.17-24 The photochromic reaction of Au-poly(DE) can also be repeated many times around the gold core, and the reaction can be easily followed by observation of the absorption spectral changes of the diarylethene polymer (poly(DE)) or the spectral shift of the LSPR band derived from the refractive index change around the gold core accompanied with the photochromic reaction.16 Au-poly(DE) is considered to be useful for evaluation of the enhancement effect of the gold nanoparticle on the photochromic reaction because of its well-defined structure. In this work, we evaluated the enhancement effect of a gold nanoparticle on the photocycloreversion reaction of a diarylethene using Au-poly(DE) with an 18 nm diameter gold nanoparticle and a 17 nm thick poly(DE) shell dispersed in solution. This paper is the first report focusing on enhancement of a one-photon photochemical reaction near an individual gold nanoparticle with a well-defined structure.

’ EXPERIMENTAL SECTION Measurements. Absorption spectra were measured using a UV/visible spectrophotometer (Jasco V-560). Photoirradiation was conducted using a 200 W mercury-xenon lamp (Moritex MUV-202) or a 300 W xenon lamp (Asahi Spectra MAX-301) as a light source. Monochromatic light was obtained by passing the light through a monochromator and glass filters. The relative intensity of irradiation was measured using a power meter (Neoark PM-245). Transmission electron microscopy (TEM; Hitachi H-7000) was performed at an accelerating voltage of 75 kV. TEM samples were prepared by dropping a solution of Aupoly(DE) on a carbon-coated copper grid. Dynamic light scattering (DLS; Sysmex Zetasizer Nano ZS) analysis was performed to determine particle size. Synthesis and Characterization of Au-poly(DE). Poly(DE) and Au-poly(DE) were prepared and characterized using previously reported methods.15,16,25 Chain-length-controlled poly(DE) was synthesized by the reversible addition-fragmentation chain transfer (RAFT) radical polymerization of DE (styrene monomer with a diarylethene pendant group; 2.9 mol dm-3) using 2,20 -azobis(2,4,4-trimethylpentane) (ATMP; 1.0 10-3 mol dm-3) and 1-phenylethyl dithiobenzoate (PEDB; 0.02 mol dm-3) as the initiator and RAFT agent, respectively, in toluene for 60 h at 100 °C. The dithiobenzoate-end group in the polymer

ARTICLE

Figure 2. TEM image of Au-poly(DE) (d = 18 nm, n = 107) prepared by citrate reduction.

was subsequently reduced by sodium borohydride in tetrahydrofuran (THF) and water. The degree of polymerization of the polymer (n) was determined to be 107 by gel-permeation chromatography (GPC) with calibration using poly(DE) of various chain lengths prepared in ref 15. Au-poly(DE) was synthesized by citrate reduction followed by a ligand exchange reaction. A TEM image of the resulting Au-poly(DE) is shown in Figure 2. The mean diameter of the gold core (d) was determined to be 18 nm from the TEM image using the image analysis program package ImageJ (http://rsb.info.nih. gov/ij/index.html). Numerical Simulation of Absorption Spectral Changes of Au-poly(DE). Extinction spectral changes of Au-poly(DE) were simulated by numerical calculation on the basis of Mie theory using the algorithm described in ref 26. Spectra were calculated for two types of core-shell sphere: a gold core (18 nm diameter) coated with a uniform poly(DE) shell (17 nm thick) and a gold core coated with a double shell of poly(DE) having different conversion of the diarylethene closed-ring form. The density of the poly(DE) shell was assumed to be uniform so that the density of the shell was not dependent on the distance from the gold core surface. The refractive index of the solvent was set to be 1.375 as determined from measurement of the THF/water (50/50 vol/ vol) mixed solution using an Abbe refractometer at 25 °C. Other experimental settings, such as the density of the shell and the refractive index of the colorless or colored poly(DE) shell, were the same as those described in ref 16.

’ RESULTS AND DISCUSSION Cycloreversion Reaction of Au-free Poly(DE). The cycloreversion quantum yields of Au-free poly(DE) in solution upon irradiation at various wavelengths were determined as a reference for evaluation of the photochromic reaction around gold nanoparticles as described later. The poly(DE) sample was synthesized by a conventional radical polymerization as described in our previous paper23 (Mn = 38 100, Mw/Mn = 2.49). The quantum yields of the polymer upon irradiation with visible light were determined using the following equation:27

logð10Aλ ðtÞ - 1Þ ¼ - Φcfo εI0 t þ logð10Aλ ð0Þ - 1Þ

ð1Þ

where Aλ(t) and ε are absorbance at irradiation time t and the molar absorption coefficient of poly(DE) at the irradiation 4565

dx.doi.org/10.1021/jp111807k |J. Phys. Chem. C 2011, 115, 4564–4570


Figure 3. Changes in the absorbance (A600) of Au-free poly(DE) in toluene upon irradiation at 600 nm. The solid line shows the regression of the experimental data.

wavelength λ, respectively. Φc fo is the cycloreversion quantum yield at the wavelength. I0 and Aλ(0) are the intensity of incident light and the initial absorbance of the polymer at the irradiation wavelength, respectively. 1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene was used as a reference to obtain I0. The Φc fo value for Au-free poly(DE) can be determined from the slope of the relationship between log(10Aλ(t) - 1) versus t in eq 1. Figure 3 shows a typical example of the relationship upon irradiation at 600 nm. The linear relationship indicates that the photoreactivity of Au-free poly(DE) in solution is constant during the reaction; the polymer undergoes homogeneous photochromic reaction in solution upon irradiation with visible light. The values of Φc fo at various wavelengths are summarized in Table 1. Φc fo increases slightly with shortening of the irradiation wavelength. The wavelength dependence is considered to be related to an electron excited to a higher excitation state or vibrational level by irradiation at shorter wavelength; however, the correlation between the photoreactivity and excitation energy is still under discussion.28-30 Cycloreversion Reaction of Poly(DE) around the Gold Nanoparticle. Figure 4a shows absorption spectra of Au-poly(DE) (d = 18 nm, n = 107) in THF/water (50/50 vol/vol) before and after irradiation at 313 nm. Au-poly(DE) in this solution has the LSPR band at ca. 530 nm before irradiation. The clear LSPR band indicates that the particles are not aggregated and are dispersed individually in the solution. The absorption spectral change upon irradiation with UV light corresponds to generation of the diarylethene closed-ring form in the poly(DE) shell. The difference spectrum of Au-poly(DE) after irradiation at 313 nm (Figure 4b) was obtained by subtracting the absorption spectrum in which all the diarylethene chromophores in the poly(DE) shell are in the open-ring form from the absorption spectrum in the photostationary state (PSS) upon irradiation at 313 nm. We previously reported that the difference spectrum of Au-poly(DE) in the PSS has a dip in the visible region, which is due to LSPR band shift by change in the refractive index of the poly(DE) shell accompanied with the photocyclization reaction.16 Once all the colored diarylethene chromophores are transformed into the open-ring forms, the LSPR band reverts to the original position upon irradiation with visible light. Figure 4b also shows the normalized difference spectrum of Au-free poly(DE) in the PSS. The difference spectrum for Aupoly(DE) in the visible region contains two spectral changes from the photochromic reaction: one is for the poly(DE) shell and the other is for the gold nanoparticle. This means that the changes of the difference spectrum of Au-poly(DE) in the visible

ARTICLE

region do not directly correspond to the absorption spectral changes of the poly(DE) shell, and the cycloreversion reaction of Au-poly(DE) cannot be evaluated directly using eq 1. The change in the UV region reflects only the spectral change of the poly(DE) shell as shown by the spectral shape in Figure 4b. Therefore, the rate of the photocycloreversion reaction around the gold nanoparticle can be compared with that of Au-free poly(DE) using Δabsorbance at 290 nm. The change in Δabsorbance of Au-poly(DE) at 290 nm upon irradiation at 600 nm is shown in Figure 5, where the solid line corresponds to the spectral changes for Au-free poly(DE) under the same experimental condition as for Au-poly(DE). Figure 5 shows the reaction rate of Au-poly(DE) larger than that of Au-free poly(DE), which indicates that the photocycloreversion reaction of poly(DE) around the gold nanoparticle is faster than that of Aufree poly(DE). Assuming that the spectral shape, the cycloreversion quantum yield, and the absorption coefficient of the diarylethene chromophore remain unchanged, even around the nanoparticle, then enhancement of the photocycloreversion reaction can be evaluated by a method similar to that for Au-free poly(DE) using the following equation: ΔA 0 λ ΔA290 ΔA 290 ðtÞ - 1 ¼ - EΦcfo εI0 t log 10 ΔA λ ΔA0 ð0Þ þ log 10ΔA290 290 - 1

ð2Þ

where ΔAλ and ΔA290 are Δabsorbance of Au-free poly(DE) at the irradiation wavelength and at 290 nm, respectively. ΔA0290(t) is Δabsorbance of Au-poly(DE) at 290 nm, and ΔA0290(0) is that prior to irradiation. E is defined as an enhancement factor that corresponds to the degree of enhancement for the cycloreversion reaction rate induced by the gold nanoparticle.31 This equation assumes a one-component reaction model, as shown in Figure 6a, in which the cycloreversion reaction in the entire polymer shell is homogeneously enhanced by the particle. The ΔAλ/ΔA290 value can be determined from the difference spectrum of Au-free poly(DE) shown in Figure 4b. Therefore, eq 2 can be described as follows: 0

0

logð10ΔA λ ðtÞ - 1Þ ¼ - EΦcfo εI0 t þ logð10ΔA λ ð0Þ - 1Þ ð3Þ where ΔA0λ represents the Δabsorbance of poly(DE) around the gold nanoparticle at the irradiation wavelength estimated from ΔA0290(t). Figure 7 shows the plot for Au-poly(DE) in the solution upon irradiation at 650 nm. The dotted line corresponds to Au-free poly(DE) under the same conditions as that for Aupoly(DE). The initial change in the vertical is larger than that for Au-free poly(DE), which indicates that the photocycloreversion reaction of poly(DE) is enhanced by the gold nanoparticle. The overall average of the enhanced reaction rate can be estimated from the slope of the regression line along the experimental data plotted by eq 3, that is, the enhancement factor can be obtained by dividing the slope of the regression line by the slope for Aufree poly(DE). The enhancement factors upon irradiation at various wavelengths determined using the one-component reaction model are summarized in Table 1. These results indicate that cycloreversion of the diarylethene moiety is promoted around an individual gold nanoparticle dispersed in solution. 4566



ARTICLE

Table 1. Molar Absorption Coefficient of the Closed-Ring Form (ε) and Photocycloreversion Quantum Yield (Φc fo) of Au-Free Poly(DE) in Toluene and Enhancement Factor (E) Determined by One-Component and Two-Component Fitting for Au-poly(DE) in THF/Water upon Irradiation at Various Wavelengthsa Au-free poly(DE)

Au-poly(DE) one-component fitting

wavelength/nm

ε/mol-1 dm3 cm-1

Φc fo

E

550

13 000

0.0060

1.34

575

16 000

0.0052

1.44

600

16 100

0.0048

625

14 200

650

9500

2b

two-component fitting E

FE

R2 b

0.975

3.2

0.41

0.994

0.985

2.4

0.53

0.994

1.41

0.980

2.9

0.48

0.997

0.0045

1.44

0.972

2.8

0.48

0.983

0.0042

1.52

0.975

5.0

0.32

0.997

R

a

FE is the volume percentage of the enhanced area in the poly(DE) shell before photoirradiation. b R2 represents the coefficient of determination for the fitting.

Figure 4. (a) Absorption spectra of Au-poly(DE) (d = 18 nm, n = 107) in THF/water before (solid line) and after (dotted line) irradiation at 313 nm. (b) Difference spectra of Au-poly(DE) in THF/water (dotted line) and normalized difference spectrum of Au-free poly(DE) in THF (broken line) in the PSS upon irradiation at 313 nm.

Figure 6. Models proposed to evaluate the enhancement effect of the gold nanoparticle on the photocycloreversion reaction of the poly(DE) shell. (a) One-component and (b) two-component reaction models.

Figure 5. Changes in the Δabsorbance (ΔA0290) of Au-poly(DE) (d = 18 nm, n = 107) in THF/water at 290 nm upon irradiation at 600 nm (solid circle). The solid line shows the spectral changes for Au-free poly(DE) upon irradiation at 600 nm under the same conditions as for Au-poly(DE).

The enhancement effect of gold nanoparticles on the cycloreversion reaction was estimated using eq 3. The one-component reaction model is a simple approximation of the effect; however, the experimental data in Figure 7 does not have a completely

linear relationship, which indicates that the reaction corresponds to a more complicated reaction model than the one-component model. In other words, the photocycloreversion reaction of the poly(DE) shell is heterogeneously enhanced around the gold nanoparticle. To take the heterogeneity into account, we proposed a twocomponent reaction model as shown in Figure 6b. The inside of the polymer shell is defined as the enhanced area in which the photocycloreversion reaction is promoted by the core nanoparticle, while the outside of the shell corresponds to a nonenhanced area in which the reaction rate is the same as that of Au-free poly(DE). Assuming that the density of the chromophore in the 4567



ARTICLE

Figure 7. Relationship between the irradiation time and the absorbance (A0650) of the diarylethene chromophore in Au-poly(DE) (d = 18 nm, n = 107) in THF/water upon irradiation at 650 nm. The solid and broken lines are regression lines fitted using eqs 6 and 3, respectively. The dotted line corresponds to the relationship for Au-free poly(DE) under the same conditions as that for Au-poly(DE).

poly(DE) shell does not depend on the distance from the gold surface, the relationship between absorbance at a certain irradiation wavelength and the reaction rate in each area can be described as follows: 0

logð10AE ðtÞ - 1Þ ¼ - EΦcfo εI0 t þ logð10FE ΔA λ ð0Þ - 1Þ ð4Þ 0

logð10AN ðtÞ - 1Þ ¼ - Φcfo εI0 t þ logð10FN ΔA λ ð0Þ - 1Þ ð5Þ Equation 4 is that for the photocycloreversion reaction in the enhanced area, and eq 5 is for reaction in the nonenhanced area. AE(t) and AN(t) are the absorbance of the chromophore at the irradiation wavelength in the enhanced and nonenhanced areas, respectively. The volume percentages of the enhanced and nonenhanced areas in the entire shell before photoirradiation are set to FE and FN, respectively (0 e FE e 1, FE þ FN = 1). Thus, the relationship for the entire photoreaction in the shell can be described as follows: logð10AE ðtÞ þ AN ðtÞ - 1Þ ¼ logfð10R4 þ 1Þð10R5 þ 1Þ-1g ð6Þ where R4 and R5 represent the right-hand side terms in eqs 4 and 5, respectively. The experimental value of the left-hand side term corresponds to that in eq 3. The two variables (E and FE) can be determined by numerical fitting using the nonlinear least-squares method with eq 6, and they are summarized in Table 1. Figure 7 also shows a typical example of the regression curve upon irradiation at 650 nm. The simulated line obtained from the two-component fitting is in better accordance with the experimental data than that obtained from the one-component model. These results indicate that the cycloreversion reaction is promoted in a specific area, such as in the vicinity of the gold nanoparticle. Interestingly, a larger enhancement factor was observed upon irradiation at longer wavelength. If the enhancement is derived from the local electric field near the gold nanoparticle, then the largest enhancement factor should be observed upon irradiation around the LSPR band (ca. 530 nm). It is considered that most of the electrons excited by irradiation around the LSPR band are used for an interband transition of Au rather than as an enhancement effect. Consequently, enhanced

Figure 8. Schematic illustration of the enhancement effect of gold nanoparticle on the photocyclization reaction investigated in this study.

photocycloreversion reaction is observed upon irradiation at longer wavelength. Considering the enhancement factors and enhancement areas shown in Table 1, we can describe a schematic illustration for the present enhancement effect as shown in Figure 8. The mean diameter of the core particle (18 nm) and the entire diameter including shell thickness (52 nm) were determined by TEM and DLS measurements, respectively, which indicated a shell thickness of 17 nm. The enhancement factor in the enhanced area was estimated to be 2-5 depending on the irradiation wavelength. The volume of the enhancement area was 30-50% of the entire shell, which corresponds to an area compassing 9-12 nm from the gold surface. Au-poly(DE) is dispersed well in the solution; therefore, internanoparticle interactions, such the nanogap effect,12,14 can be ignored in the present case. Thus, to the best of our knowledge, this is the first quantitative and comprehensive result focused on the enhancement effect in a one-photon photochemical reaction near an individual gold nanoparticle. It seems that the enhancement factor obtained from the twocomponent reaction model (2- to 5-fold) is quite small in comparison to that obtained by surface-enhanced Raman scattering (SERS)5,6 and by a two-photon reaction reported previously.12,14 Larger enhancement was induced from a larger sized metal particle or nanostructure with intended molecules in the solid state, which means that the strong electric field enhancement and the significant contribution of hot spots in gap-mode excitation strongly affect the enhancement. However, in this study, we used relatively small sized gold nanoparticles. The quenching effect of the nearest diarylethene chromophores around the gold core was not considered for either the photocyclization or the photocycloreversion reactions.15,32,33 Therefore, two-component fitting results in an averaged enhancement factor. Taking into account these factors, the small enhancement factor is more likely to characterize the enhancement effect around individual gold nanoparticles. An enhancement factor with similar order of magnitude was observed in single-gold nanoparticle-enhanced Raman scattering34 and fluorescent enhancement.35,36 The other possibility for the enhanced photochromic reaction is the photothermal effect. A reaction in the vicinity of the gold nanoparticle can be promoted by thermal energy released from the particle upon photoirradiation.37,38 However, in this study, the irradiation intensity in the sample cell is ca. 0.5 mW cm-2, which is too weak to cause a dominant photothermal process. Furthermore, the closed-ring form of the diarylethene moiety used has high thermal stability.39 Therefore, we can conclude that 4568



ARTICLE

Figure 9. Simulated changes in the difference spectra of Au-poly(DE) in THF/water along with the photocycloreversion reaction of the poly(DE) shell calculated using (a) a double-shell structure to explain heterogeneous enhancement in the shell, (b) a uniform single shell, and (c) experimental changes in the difference spectra for Au-poly(DE) (d = 18 nm, n = 107) upon irradiation at 600 nm. The right-hand figures show the normalized spectra of the left-hand figures.

the enhancement of the photocycloreversion reaction results from the localized electric field in the vicinity of the gold nanoparticle. Numerical Simulation of the Changes in the Differential Extinction Spectra During Photocycloreversion Reaction Using a Double-Shell Model. Two-component fitting revealed that the photocycloreversion reaction was heterogeneously enhanced inside the polymer shell. To confirm this observation, we simulated changes in the extinction spectra of Au-poly(DE) during the photocycloreversion reaction on the basis of Mie theory using the double-shell structure described in the Experimental Section. The inside and outside thicknesses were set to 10 and 7 nm, respectively. For the double-shell model, the enhanced reaction rate inside the shell was set to be 3 times faster than that outside the shell. Figure 9a and b shows simulated changes in the differential extinction spectra of Au-poly(DE) using the double-shell model and that for Au-poly(DE) with a uniform shell, respectively.40 In the former case, the spectral dip in the visible region corresponding to the LSPR band shift disappears as the reaction progresses, whereas in the latter case, the spectral shape is almost the same and is independent of photoirradiation. The experimental result

shown in Figure 9c reproduces the heterogeneous enhancement effect better, which strongly supports that the heterogeneous photocycloreversion reaction discussed in the previous section is derived from faster photocycloreversion reaction near the gold nanoparticle. Because the reaction model does not take into account the quenching effect on the photocyclization and photocyloreversion reactions near the particle,15,32,33 and because there is a possibility that the heterogeneous enhancement effect is derived from core-size dependence, a more complicated analytical method or theoretical simulation may be necessary to make an improved evaluation of the effect. However, we could propose a comprehensive reaction model to quantitatively evaluate the enhancement effect, and the heterogeneous enhancement of the photochemical reaction around the individual gold nanoparticle was confirmed. We believe that the proposed model is sufficient to obtain the degree of enhancement as a first approximation.

’ CONCLUSION We have investigated the enhancement effect of gold nanoparticles on the photochromic reaction of a diarylethene using 4569


The Journal of Physical Chemistry C well-defined Au-poly(DE), a gold nanoparticle covered with poly(DE). Au-poly(DE) was prepared by citrate reduction to evaluate the enhancement effect of the gold nanoparticle on the photocycloreversion reaction of a diarylethene chromophore upon irradiation with visible light. The cycloreversion reaction was found to be enhanced even around the individual gold nanoparticle dispersed in solution. The degree of enhancement was determined using two different reaction models: one-component and two-component reaction models. The two-component reaction model was more appropriate for evaluation of the enhancement effect because of the heterogeneous reaction rate in the polymer shell, and the enhancement factor and enhanced area were determined to be 2- to 5-fold and the area 9-12 nm from the gold surface. These experimental results are consistent with the theoretical simulation based on Mie theory, assuming that the poly(DE) shell undergoes enhanced photocycloreversion reaction only inside the shell. Observation and quantitative evaluation of the enhancement effect in the vicinity of individual gold nanoparticle was successfully achieved using the proposed model. Although a more complicated multicomponent model may be required to better evaluate the enhancement effect, the two-component model is the best analytical method at the present time. The present results are considered to be useful for the development of efficient photochemical reactions.

’ AUTHOR INFORMATION Corresponding Author

*[email protected].

’ ACKNOWLEDGMENT This work was partly supported by a Grant-in-Aid for Scientific Research on Priority Area “Strong Photon-Molecule Coupling Fields” (470) (Nos. 19049011 and 21020032) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. H. N. thanks the Japan Society for the Promotion of Science for Young Scientists for the support of a Research Fellowship. ’ REFERENCES (1) Kelly, K. L.; Coronad, E.; Zhao, L. L.; Schatz, G. C. J. Phys. Chem. B 2003, 107, 668–677. (2) Eustis, S.; El-Sayed, M. A. Chem. Soc. Rev. 2006, 35, 209–217. (3) Ghosh, S. K.; Pal, T. Chem. Rev. 2007, 107, 4797–4862. (4) Miller, M. M.; Lazarides, A. A. J. Phys. Chem. B 2005, 109, 21556–21565. (5) Campion, A.; Kambhampati, P. Chem. Soc. Rev. 1998, 27, 241–250. (6) Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Chem. Rev. 1999, 99, 2957–2975. (7) Geddes, C. D.; Lakowicz, J. R. J. Fluoresc. 2002, 12, 121–129. (8) Lakowicz, J. R.; Geddes, C. D.; Gryczynski, I.; Malicka, J.; Gryczynski, Z.; Aslan, K.; Lukomska, J.; Matveeva, E.; Zhang, J.; Badugu, R.; Huang, J. J. Fluoresc. 2004, 14, 425–441. (9) Tam, F.; Goodrich, G. P.; Johnson, B. R.; Halas, N. J. Nano Lett. 2007, 7, 496–501. (10) Sugawa, K.; Akiyama, T.; Kawazumi, H.; Yamada, S. Langmuir 2009, 25, 3887–3893. (11) Arakawa, T.; Munaoka, T.; Akiyama, T.; Yamada, S. J. Phys. Chem. B 2009, 113, 11830–11835. (12) Ueno, K.; Juodkazis, S.; Shibuya, T.; Yokota, Y.; Mizeikis, V.; Sasaki, K.; Misawa, H. J. Am. Chem. Soc. 2008, 130, 6928–6929.

ARTICLE

(13) Hubert, C.; Rumyantseva, A.; Lerondel, G.; Grand, J.; Kostcheev, S.; Billot, L.; Vial, A.; Bachelot, R.; Royer, P.; Chang, S.-H.; Gray, S. K.; Wiederrecht, G. P.; Schatz, G. C. Nano Lett. 2005, 5, 615–619. (14) Tsuboi, Y.; Shimizu, R.; Shoji, T.; Kitamura, N. J. Am. Chem. Soc. 2009, 131, 12623–12627. (15) Nishi, H.; Kobatake, S. Macromolecules 2008, 41, 3995–4002. (16) Nishi, H.; Asahi, T.; Kobatake, S. J. Phys. Chem. C 2009, 113, 17359–17366. (17) Irie, M. Chem. Rev. 2000, 100, 1685–1716. (18) Nakashima, H.; Irie, M. Polym. J. 1998, 30, 985–989. (19) Kawai, T.; Fukuda, N.; Gr€oschl, D.; Kobatake, S.; Irie, M. Jpn. J. Appl. Phys. 1999, 38, L1194–L1196. (20) Stellacci, F.; Bertarelli, C.; Toscano, F.; Gallazzi, M. C.; Zotti, G.; Zerbi, G. Adv. Mater. 1999, 11, 292–295. (21) Kobatake, S.; Irie, M. Bull. Chem. Soc. Jpn. 2004, 77, 195–210. (22) Yamaguchi, T.; Nomiyama, K.; Isayama, M.; Irie, M. Adv. Mater. 2004, 16, 643–645. (23) Kobatake, S.; Kuratani, H. Chem. Lett. 2006, 35, 628–629. (24) Nishi, H.; Kobatake, S. Chem. Lett. 2010, 39, 638–639. (25) Nishi, H.; Kobatake, S. Chem. Lett. 2008, 37, 630–631. (26) Uwada, T.; Toyota, R.; Masuhara, H.; Asahi, T. J. Phys. Chem. C 2007, 111, 1549–1552. (27) Yokoyama, Y.; Kurita, Y. Synth. Org. Chem. Jpn. 1991, 49 364–372. (28) Irie., M.; Mohri, M. J. Org. Chem. 1988, 53, 803–808. (29) Yokoyama, Y.; Shiozawa, T.; Tani, Y.; Ubukata Angew. Chem., Int. Ed. 2009, 48, 4521–4523. (30) Nakamura, S.; Kobayashi, T.; Takata, A.; Uchida, K.; Asano, Y.; Murakami, A.; Goldberg, A.; Guillaumont, D.; Yokojima, S.; Kobatake, S.; Irie, M. J. Phys. Org. Chem. 2007, 20, 821–829. (31) The enhancement factor (E) is used as an E-fold of Φc fo, ε, or I0. In the present work, we are considering that ε is enhanced as E ε rather than the enhancement of Φcfo. (32) Kudernac, T.; van der Molen., S. J.; van Wees, B. J.; Feringa, B. L. Chem. Commun. 2006, 3597–3599. (33) Yamaguchi, H.; Ikeda, M.; Matsuda, K.; Irie, M. Bull. Chem. Soc. Jpn. 2006, 79, 1413–1419. (34) Tong, L.; Li, Z.; Zhu, T.; Xu, H.; Liu, Z. J. Phys. Chem. C 2008, 112, 7119–7123. (35) Kim, J.; Dantelle, G.; Revaux, A.; Berard, M.; Huignard, A.; Gacoin, T.; Boilot, J.-P. Langmuir 2010, 26, 8842–8849. (36) Rey, D. A.; Strickland, A. D.; Kirui, D.; Niamsiri, N.; Batt, C. A. ACS Appl. Mater. Interfaces 2009, 1, 2174–2180. (37) Biesso, A.; Qian, W.; Huang, X.; El-sayed, M. A. J. Am. Chem. Soc. 2009, 131, 2442–2443. (38) Chen, X.; Zhu, H.-Y.; Zhao, J.-C.; Zheng, Z.-F.; Gao, X.-P. Angew. Chem., Int. Ed. 2008, 47, 5353–5356. (39) Morimitsu, K.; Shibata, K.; Kobatake, S.; Irie, M. J. Org. Chem. 2002, 67, 4574–4578. (40) The LSPR band of individual gold nanoparticle depends on the particle size and shape. The spectral simulation of individual gold nanoparticle could be reproduced well on the basis of the theoretical simulation using the spherical model. The distribution of the particle size and shape is insignificant to simulate the experimental data in this study.

4570


Enhanced One-Photon Cycloreversion Reaction of Diarylethenes near

Recommend Documents