Energy Transfer among Three Dye Components in a NanosheetâDye

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Energy Transfer among Three Dye Components in a Nanosheet–Dye Complex: An Approach to Evaluating the Performance of a Light-Harvesting System Yuta Ohtani, Shintaro Kawaguchi, Tetsuya Shimada, and Shinsuke Takagi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b10372 • Publication Date (Web): 03 Jan 2017 Downloaded from http://pubs.acs.org on January 5, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Energy Transfer among Three Dye Components in a Nanosheet–Dye Complex: An Approach to Evaluating the Performance of a LightHarvesting System Yuta Ohtani, Shintaro Kawaguchi, Tetsuya Shimada and Shinsuke Takagi* Department of Applied Chemistry, Graduate Course of Urban Environmental Sciences, Tokyo Metropolitan University, Minami−ohsawa 1−1, Hachioji, Tokyo 192−0397, Japan. KEYWORDS. Porphyrin; Organic–Inorganic Complex; Inorganic Nanosheet, Energy Transfer Reaction, Artificial Light-Harvesting System

ABSTRACT. Energy transfer among three dye components, namely, p-2,4,5,7-tetrakis(Nmethylpyridinium-4-yl)-6-potassium-oxy-3-fluorone (Fluorone), meso-tetra(N-methyl-3-pyridyl) porphine

(m-TMPyP),

and

meso-tetra(N-methyl-4-pyridyl)porphine

(p-TMPyP),

was

investigated for the purpose of utilizing a wide range of sunlight wavelengths for clay nanosheets. In this paper, we define a new parameter, the enhancement ratio of the excitation frequency (Γ380-780 nm) of the dye, in order to comprehensively represent the performance of the light-harvesting system (LHS). Γ380-780 nm is defined as the enhancement ratio of the excitation

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

frequency of dye that has the lowest excitation energy in the system (p-TMPyP in this system), in terms of the frequency of p-TMPyP without the use of light-harvesting dyes (Fluorone and mTMPyP), when the visible-light region of sunlight (380–780 nm) is used for irradiation light. Γ380-780

nm

was calculated from the absorption spectra of dyes, the results of energy transfer

experiments, and the sunlight spectrum (380–780 nm). We found that Γ380-780 nm in our LHS is 2.4, which implies enhancement of the excitation frequency of p-TMPyP by 2.4 times relative to that of p-TMPyP without a light harvesting system. We believe that Γ380-780 nm is an important standard parameter of the performance of artificial LHSs.

Introduction Plants function by harvesting sunlight through their light-harvesting system (LHS) and by producing a charge separation state at their reaction center (RC), which leads to CO2 reduction and water oxidation.1–6 The LHS of plants absorbs sunlight and increases the excitation frequency of the RC. One of the most important functions of the LHS is concentrating the dilute solar photon density, leading to the enhancement of the excitation frequency. The reaction converting solar to chemical energy (i.e., photosynthesis) has been evaluated in terms of its conversion efficiency (ηC; ηC = Jgµproϕcon/S,7 where Jg is the absorbed photon flux (photons s−1 m−2), µpro is the chemical potential of the product (J photon−1), ϕcon represents the quantum yield for the conversion of the absorbed photons into products, and S is the total incident solar energy (W m−2)). The importance of the photon absorption step in the sequence of photosynthesis is indicated by the ηC value; therefore, artificial LHSs are evaluated using this value in order to improve upon this step.


2

Page 3 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Many researchers have constructed artificial LHSs in various ways.8–19 Artificial LHSs have been constructed using covalently bonded donor and acceptor systems8–14 and supramolecular systems in which mesoporous organosilica15 and clay minerals16–19 are used as host materials. In previous research done in this field, researchers have noticed that there is no standard way of expressing the performance of artificial LHSs. One of the typical parameters used to evaluate the performance of an artificial LHS is the enhancement ratio of the photochemical reaction for the LHS achieved by using a monochromatic excitation light at a specific wavelength. In this method, the difference in enhancement ratios may be observed by the change in the excitation wavelength. For example, the enhancement ratio is theoretically infinite at the excitation wavelength where the energy acceptor does not absorb. The number of energy donor molecules that transfer excitation energy to one energy acceptor molecule has also been measured in order to evaluate the ability of the LHS. In this method, the enhancement ratio of the excitation frequency cannot be estimated. Therefore, we propose in this paper a new parameter, the enhancement ratio of the excitation frequency of the energy acceptor (Γ380-780 nm), to estimate the overall performance of the LHS. Γ380-780 nm indicates how the excitation frequency of the dye with the lowest excitation energy in the system increases in comparison with that without lightharvesting dyes under sunlight in the visible-light region (380–780 nm). Γ380-780

nm

may be

calculated using the absorption spectra of the dyes, the results of energy transfer experiments, and the sunlight spectrum (380–780 nm).20 AM (Air Mass) indicates the amount of air through which the sunlight passes, and AM1.5 is the sunlight at an incidence angle of 41.8°. The Γ380-780 nm

value includes the energy transfer efficiency and the extension of the absorption wavelength

region of the LHS. Thus, the performance of an LHS can be comprehensively evaluated by Γ380780 nm.


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 24

In the present study, we used a complex consisting of three dyes and clay minerals in order to estimate the Γ380-780

nm

experimentally. The clay surface can be an excellent site for a

photochemical reaction.21–24 Furthermore, high-density adsorption structures of cationic dyes can be obtained without aggregation.23, 24 In our previous study on the excitation energy transfer reaction between two different kinds of adsorbed dyes on the clay surface, we found that the maximum efficiencies of the energy transfer from meso-tetra(N-methyl-3-pyridyl)porphine (mTMPyP) to meso-tetra(N-methyl-4-pyridyl)porphine (p-TMPyP) and from p-2,4,5,7-tetrakis(Nmethylpyridinium-4-yl)-6-potassium-oxy-3-fluorone (Fluorone) to p-TMPyP on the clay surface are ~100%.18, 19 In the present work, the energy transfer among three dyes (Fluorone, m-TMPyP, and p-TMPyP) was studied in order to utilize a wide spectrum of visible light and thus to increase the excitation frequency of p-TMPyP, which is the final energy acceptor in the system. The structures of Fluorone, m-TMPyP, and p-TMPyP are shown in Figure 1. The order of excitation energies of these dyes is Fluorone, > m-TMPyP > p-TMPyP. Therefore, the excitation energy is transferred from Fluorone and m-TMPyP to p-TMPyP.

N N

N

O

O

N

OK

N

N

N N H

4I

N

N H N

N H

4Cl

N

N H N

-

4Cl

N

N

N

N

N

Figure 1. The structures of p-2,4,5,7-tetrakis(N-methylpyridinium-4-yl)-6-potassium-oxy-3fluorone tetraiodide (Fluorone, left), meso-tetra(N-methyl-3-pyridyl)porphine tetrachloride (m-


4

Page 5 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TMPyP, center), and meso-tetrakis(N-methylpyridinium-4-yl)porphyrin tetrachloride (p-TMPyP, right).

Experimental Materials meso-Tetra(N-methyl-4-pyridyl)porphine tetrachloride (p-TMPyP) and meso-tetra(N-methyl3-pyridyl)porphine tetrachloride (m-TMPyP) were purchased from Frontier Scientific. p-2,4,5,7Tetrakis(N-methylpyridinium-4-yl)-6-potassium-oxy-3-fluorone

tetraiodide

(Fluorone)

was

synthesized by a method described in a previous paper.25 First, 2,4,5,7-tetrabromo-6-hydroxy-3fluorone, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) pyridine, tetrakis(triphenylphosphine) palladium, and potassium carbonic acid were added to degassed water under N2, and the mixture was heated to 80°C for 70 hours. The mixture yielded p-2,4,5,7-(pyridinyl)-6-potassium-oxy-3fluorone, which was then added along with iodomethane to degassed DMSO. The resulting mixture was stirred for 2 hours at room temperature to produce Fluorone. Water was deionized in an Organo BB-5A system (PF filter × 2 + G-10 column). The saponite clay, which was used in this experiment after the purification, was Sumecton SA (SSA; Kunimine Industries Co. Ltd). The stoichiometric formula of SSA is [(Si7.20Al0.80)(Mg5.97Al0.03)O20(OH)4]−0.77(Na0.49Mg0.14)+0.77, its surface area is 750 m2 g−1, and its cation exchangeable capacity (CEC) is 1.00 mmol g−1.23

Purification of clay25


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 24

SSA (2.0 g) was dispersed in water (300 ml), and the resulting colloidal dispersion was allowed to stand for 3 days. The supernatant liquid (150 ml) was then removed by decanting, and SSA was separated by centrifugation (20,000 rpm, 8 hours, 10°C). Deionized water was added to the supernatant. After the SSA was allowed to stand for 1 day, it was separated again by centrifugation (20,000 rpm, 8 hours, 10°C). It was then dried under vacuum and collected (0.9 g, 45% yield).

Analysis The absorption spectra were obtained on a Shimadzu UV-2600 spectrophotometer, and corrected fluorescence spectra were recorded on a Jasco FP-6500 spectrofluorometer. In the absorption and fluorescence measurements, a plastic cell (PMMA) was used for the aqueous clay/dye solutions. TG/DTA measurements were carried out with a Shimadzu DTG-60H analyzer to determine the water content of the dyes and clay.

Preparation methods for the clay/dye complexes The typical procedure for preparing the energy transfer samples is as follows. Aqueous solutions of Fluorone, m-TMPyP, and p-TMPyP were combined. The obtained solutions were mixed with an aqueous clay solution (9.9 mg L−1) under vigorous stirring. The total concentrations of Fluorone, m-TMPyP, and p-TMPyP were set at 1.0 × 10−7 M, and the clay loadings were varied. The Fluorone/m-TMPyP/p-TMPyP molar ratio was modulated to 3:1:2.


6

Page 7 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Under these conditions, the clay sheets existed as individually exfoliated sheets, and the obtained solution was highly transparent.

Method of estimating energy transfer efficiency and rate of energy loss Elementary steps between the three dyes in the system are shown in Figure 2.

kfp kpf kfm

kmp

Fluorone*

m-TMPyP*

kmf a

p-TMPyP*

kpm b

c

Figure 2. Elementary steps between the three dyes. In the figure, a, b, and c are generation rate constants for excited Fluorone, excited m-TMPyP, , , , and respectively represent deactivation by and excited p-TMPyP, respectively.

intersystem crossing, vibration, fluorescent reaction, the photochemical reaction due to collision with i dye molecules in the ground state. kxy represents the rate constant of energy transfer from x to y. The fitting equation was derived from the rate constants of these elementary steps in order to evaluate the energy transfer efficiency and rate of energy loss. The derivation of these equations is described in the Supporting Information.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 24

By using the fluorescence intensities of Fluorone/clay, m-TMPyP/clay, p-TMPyP/clay, and Fluorone/m-TMPyP/p-TMPyP/clay complexes, the energy transfer efficiency and the loss of the energy transferred was calculated from the fitting equation (1). The total fluorescence of the Fluorone/m-TMPyP/p-TMPyP/clay complex (FET(ν)) may be expressed as equation (1): = + +

(1)

where Ff(ν), Fm(ν), and Fp(ν) are the fluorescence spectra of the Fluorone/clay, m-TMPyP/clay, and p-TMPyP/clay complexes, respectively. ν is the wavelength of fluorescence. α, β, and γ indicate the ratios of the fluorescence intensity of the Fluorone/m-TMPyP/p-TMPyP/clay complex to the fluorescence intensity of the Fluorone/clay, m-TMPyP/clay, and p-TMPyP/clay complexes respectively. α, β, and γ are expressed in terms of equations (2), (3), and (4), respectively. = 1 − − − β = 1 + γ=

! "

! "

# "

+ ( "

(2)

$ %1 − − & ! "

( "

+

# " ( "

(3)

+ 1

(4)

where ηfm, ηfp, and ηmp are the efficiencies of the energy transfer reaction from Fluorone to mTMPyP, Flourone to p-TMPyP, and m-TMPyP to p-TMPyP, respectively. qf and qm are the losses of energy transfer with Fluorone and m-TMPyP, respectively. Af(λ), Am(λ), and Ap(λ) are, respectively, the absorbances of the Fluorone/clay, m-TMPyP/clay, and p-TMPyP/clay


8

Page 9 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


complexes at the excitation wavelength (λ). FET(ν), Ff(ν), Fm(ν), and Fp(ν) were measured at two excitation wavelengths (520 and 540 nm). On the basis of equation (1), the fluorescence spectrum FET(ν) was simulated using the respective reference fluorescence spectra Ff(ν), Fm(ν), and Fp(ν). Using the two kinds of coefficients obtained by measuring the fluorescence spectra, simultaneous equations were then solved, and parameters for the energy transfer efficiencies and the loss of the energy transfer were obtained from the spectral simulation. The energy-harvesting functionality was evaluated from the observed γ (γobs). γobs was calculated from the observed energy transfer efficiencies ηfm, ηfp, and ηmp. When γobs was larger than 1, the excitation frequency of p-TMPyP in the energy transfer system increased in comparison with that of the system using only p-TMPyP.

Results and Discussion Energy transfer reaction between two components in a dye/clay complex We found that the absorption spectrum of the Fluorone/m-TMPyP/p-TMPyP/clay complex is identical to the sum of the individual absorption spectra of the Fluorone/clay, m-TMPyP/clay, and p-TMPyP/clay complexes (Figure 3). This comparison suggests complete suppression of aggregation and the existence of three types dyes as single molecules even as they coexist on the clay surface.


9


0.04 Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 24

Fluorone / m-TMPyP / p-TMPyP / clay m-TMPyP / clay

0.03

p-TMPyP / clay Sum of Fluorone / clay, m-TMPyP / clay and p-TMPyP / clay

0.02

Fluorone / clay

0.01 0 380

480 580 Wavelength / nm

680

Figure 3. Absorption spectra of Fluorone/clay (orange line; [Fluorone] = 1.0 × 10−7 M, 20% vs. CEC), m-TMPyP/clay (green line; [m-TMPyP] = 1.0 × 10−7 M, 20% vs. CEC), and pTMPyP/clay (blue line; [p-TMPyP] = 1.0 × 10−7 M, 20% vs. CEC) complexes; and sum of the individual absorption spectra (red broken line) and co-adsorption sample spectrum (black line; [Fluorone] = [m-TMPyP] = [p-TMPyP] = 1.0 × 10−7 M, 20% vs. CEC).

We believe that the mechanism of energy transfer reaction in this system is of a Förster type26. Before the experiment, we calculated the theoretical energy transfer rate constant, kET, using the Förster equation: ) *+ , - ./

= 012345 67

/8

9

:,

(5)

where κ is the orientation parameter (κ2 = 5/4 for in-plane orientation), ϕD is the fluorescence quantum yield of the energy donor (the fluorescence quantum yields of Fluorone, m-TMPyP, and p-TMPyP are 0.50, 0.081, and 0.048 respectively18, 25, 27), n is the refractive index of the bulk medium (n = 1.33 for water), N is the Avogadro constant, and τD is the excited-singlet lifetime of the donor on the clay surface (the excited-singlet lifetimes for Fluorone, m-TMPyP, and pTMPyP are 2.9, 8.9, and 5.6 ns, respectively18, 25, 27). R is the average center-to-center distance


10

Page 11 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


between the adsorbed dye molecules (2.4 nm under 100% vs. CEC condition), and J is the integral for the overlap between the fluorescence spectra of the donor and the absorption of the acceptor according to equation (6). According to the analysis of the overlap between the fluorescence of the donor molecule and the absorption of the acceptor based on equation (6), the spectral overlap integral J for each combination was calculated. : = ∑ < =>? ==@ Δ=,

(6)

where λ is the wavelength in cm, εA(λ) is the extinction coefficient of the acceptor at wavelength λ, and FD(λ) is the fraction of the total fluorescence intensity of the donor. J and kET for each combination in this system were calculated (results are shown in Table 1). The calculated deactivation rate constants (1/τ) of the energy donors Fluorone and m-TMPyP are 3.4 × 108 and 1.1 × 108 s−1, respectively. Since the kET values are larger than the 1/τ values, most of the excitation energy efficiently transfers to p-TMPyP.

Table 1. Calculated J and kET Values of Each Energy Transfer Reaction

Donor→Acceptor Fluorone→m-TMPyP Fluorone→p-TMPyP m-TMPyP→p-TMPyP

J / 10-14 M-1 cm-1 cm4 4.4 16 1.8

kET / 109 s-1 14 50 0.30


11


We evaluated the reactions of energy transfer from Fluorone to p-TMPyP and from m-TMPyP to p-TMPyP in previous studies.18,

23

In these studies, Fluorone and m-TMPyP were energy

donors and p-TMPyP was an energy acceptor. When m-TMPyP coexisted with Fluorone, mTMPyP behaved as an energy acceptor. The result of energy transfer from Fluorone to m-TMPyP is shown in the Supporting Information (Fig. S1 and S2), and the energy transfer efficiencies of these systems are summarized in Figure 4. The figure shows that the energy transfer efficiencies depend on the ratio of energy donors to energy acceptors. For example, the efficiency of energy transfer from m-TMPyP to p-TMPyP tends to decrease with the increase in m-TMPyP/p-TMPyP ratio because the rate of the donor adjacent to the acceptor decreased. On the basis of these results, the condition required for achieving efficient energy transfer among the three components is [Fluorone] > [p-TMPyP] > [m-TMPyP]. When the Fluorone/porphyrin ratio is too large, quantitative observation of the fluorescence intensity of porphyrins in the energy transfer sample is difficult because the fluorescence quantum yield of Fluorone (0.50) is larger than that of m-TMPyP and of p-TMPyP (0.081 and 0.048, respectively). Thus, the smallest Fluorone/porphyrin ratio in the energy transfer samples is required. We therefore set the smallest

Fluorone→p-TMPyP 1 0.8

Fluorone→m-TMPyP 0.6 0.4

m-TMPyP→p-TMPyP

0.2 0

2 4 6 8 [Donor]/[Acceptor]

Energy transfer efficiency

[Fluorone]/[m-TMPyP]/[p-TMPyP] integer ratio at 3:1:2.

Energy transfer efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 24

m-TMPyP→p-TMPyP 1 0.9

Fluorone→p-TMPyP

0.8 0.7

Fluorone→m-TMPyP

0.6 0

0.2 0.4 0.6 0.8 1 [Donor]/[Acceptor]


12

Page 13 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Efficiencies of energy transfer between two components. The vertical and horizontal axes respectively indicate the energy transfer efficiency and the energy donor/acceptor ratio. The horizontal ordinate range on the left is 0–8, and that on the right is 0–1. Squares, circles, and triangles indicate the energy transfer efficiencies between Fluorone and m-TMPyP, Fluorone and p-TMPyP, and m-TMPyP and p-TMPyP, respectively.

Energy transfer reaction of the Fluorone/m-TMPyP/p-TMPyP/clay complex The energy transfer between Fluorone, m-TMPyP, and p-TMPyP on the clay surface was examined by recording steady-state fluorescence spectra. Individual fluorescence spectra of Fluorone/clay, m-TMPyP/clay, and p-TMPyP/clay complexes are shown in Figure 5. The dye loadings for each complex were 0.05% versus CEC. By using the individual fluorescence spectra and equations (1)–(4), the energy transfer efficiency and loss of energy transfer were determined. For example, the fluorescence spectrum of the Fluorone/m-TMPyP/p-TMPyP/clay complex with total dye loading set at 40% vs. CEC is shown in Figure 6. The Fluorone/m-TMPyP/p-TMPyP molar ratio in the Fluorone/m-TMPyP/p-TMPyP/clay complex was set at 3:1:2. The fluorescence spectral shape of the energy transfer sample could be fitted with the linear combination of individual fluorescence spectra, as shown in Figure 6. In order to evaluate the energy transfer efficiency and loss of energy transferred for these three components, the fluorescence spectra of the energy transfer samples were measured at two different excitation wavelengths (520 and 540 nm).


13

400

1

Fluorone p-TMPyP m-TMPyP

300 200

Page 14 of 24

0.8 0.6 0.4

100

0.2

0

0 550

650

750

Wavelength / nm Figure 5. Individual fluorescence spectra of Fluorone/clay ([Fluorone] = 5.0 × 10−8 M; 0.05% vs. CEC), m-TMPyP/clay ([m-TMPyP] = 1.7 × 10−8 M; 0.05% vs. CEC), and p-TMPyP/clay ([pTMPyP] = 3.3 × 10−8 M; 0.05% vs. CEC) complexes in water. The spectra were obtained at an excitation wavelength of 540 nm.

Fluorescence intensity Fluorescence Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fluorescence intensity


4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

Energy transfer sample

Fitting 550

650 750 Wavelength / nm Wavelength / nm

850

Figure 6. Fluorescence spectra of the Fluorone/m-TMPyP/p-TMPyP/clay complex (solid line; [Fluorone] = 5.0 × 10−8 M, [m-TMPyP] = 1.7 × 10−8 M, [p-TMPyP] = 3.3× 10-8 M; the total dye loading was 40% vs. CEC) and the sum of fluorescence spectra of the Fluorone/clay, mTMPyP/clay, and p-TMPyP/clay complexes (dashed line). Spectra were recorded at an excitation wavelength of 540 nm.


14

Page 15 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Energy transfer efficiencies were evaluated by changing the loading. The Fluorone/mTMPyP/p-TMPyP molar ratio in the Fluorone/m-TMPyP/p-TMPyP/clay complex was set at 3:1:2, and the dye loadings were modulated to 1, 5, 10, 20, 30, 40, 50, and 70% vs. CEC of the clay. The obtained energy transfer efficiencies are plotted vs. the dye loadings in Figure 7. The obtained energy losses are plotted in the Supporting Information (Fig. S3). The efficiencies of the energy transfer from Fluorone (ηfm + ηfp) were 80–90% at 10–70% loadings vs. CEC. The maximum value of the sum of ηfm and ηfp is 1. ηmp was found to be >70% at 10–70% loading vs. CEC. These results, which are similar to those obtained for the energy transfer between two components, indicate that the dye molecules adsorb on the clay surface without separation of dyes in the energy transfer sample. The loss of energy transferred from mTMPyP was almost 0%, and the loss of energy transferred from Fluorone increased when the loading increased, as shown in the Supporting Information (Fig. S3). We hypothesize that this energy loss is caused by the collision between excited and ground-state Fluorone molecules on the clay surface.19, 25 In this system, the number of Fluorone molecules is larger than the number of porphyrin molecules. When the dye molecules adsorbed on the clay surface, the number of the adjacent Fluorone molecules on the clay surface tended to increase and the energy loss increased. The rate constant of a Förster-type energy transfer reaction is proportional to the sixth power of the center-to-center distance of the energy donor molecule from the energy acceptor molecule. Because the average distance between the donor and adjacent acceptor molecules on the clay surface diminished with increasing adsorption density of porphyrins on the clay surface, the frequency of the energy transfer increased. As shown in Figure 7, the energy transfer efficiencies were almost unchanged at high dye loadings. This result suggests that the adsorbed dye molecules assembled and segregated on the clay surface.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

Figure 7. Obtained values of the energy transfer efficiency at various loadings of Fluorone, mTMPyP, and p-TMPyP ([Fluorone] = 5.0 × 10−8 M, [m-TMPyP] = 1.7 × 10−8 M, [p-TMPyP] = 3.3 × 10−8 M; 10–70% loadings vs. CEC). Left, center, and right plots depict the efficiencies of the energy transfer from Fluorone to p-TMPyP, from Fluorone to m-TMPyP, and from mTMPyP to p-TMPyP, respectively.

Evaluation of the enhancement ratio of Γ380-780 nm γobs(λ) was evaluated by using equation (4) and the observed energy transfer efficiencies. γobs(λ) values indicate how much larger the excitation frequency of p-TMPyP in the energy transfer system is relative to the frequency for a p-TMPyP/clay complex at λ. γobs(λ) is shown in Figure 8. The maximum γobs(λ) was 38 at 513 nm excitation wavelength. This result indicates that Fluorone absorbs incident light that porphyrin cannot efficiently absorb and that it transfers excitation energy to p-TMPyP. If this system were used in a photochemical reaction, its reaction frequency would be larger than it would be without this energy transfer system. However, the result obtained at a specific excitation wavelength was not enough for evaluating the lightharvesting performance. Therefore, we adopted a novel method for evaluating the light-


16

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


harvesting performance. An important role of an LHS is concentrating sunlight energy in the photoreaction center. Thus, the light-harvesting functionality should be evaluated from Γ380-780 nm.

Γ380-780 nm is the ratio of excitation frequency, which can be defined in terms of equation 7:

ΓC1D1 4 =

TUV " EWUV FGHI JK ( L6IMNOPQRS JJ TUV " EWUV K ( L6IMNOPQRS JJ

(7)

where Nsunlight(λ) (m−2 s−1 nm−1) is the photon number of the sunlight spectrum in AM1.520 at λ, and Ap(λ) is the absorbance of p-TMPyP at λ in this system. Γ380-780 nm represents the ratio of the excitation frequency of p-TMPyP in the LHS (Fluorone, m-TMPyP, and p-TMPyP/clay system) C1

divided by ratio for the p-TMPyP/clay system. When [p-TMPyP] = 3.3 × 10−8 M, ED1 %1 − 10?( J &YZ4[\]^ =_= is 1.9 × 1018 m−2 s−1. The calculated results of this integral and Γ380-780 nm

therefore depend on the concentration of the samples. When the dye concentration in the

energy transfer samples increased, Γ380-780

nm

became smaller than that that for the dilute

condition because of saturation of the light absorption rate, as shown in the Supporting Information. For this system, we evaluated the energy transfer reaction at low concentration, neglecting the energy transfer via the trivial mechanism and the internal filter effect. In our LHS, the calculated Γ380-780 nm value is 2.4. In other words, the excitation frequency of p-TMPyP became 2.4 times higher because of the artificial LHS. Figure 8 shows that Γ380-780 nm is >2.4 with addition of the dye, which absorbs light in the 380–480 and 580–780 nm regions, to this system.


17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Ratio of excitation frequency


Page 18 of 24

40 30 20 10 0 380

480 580 680 Wavelength / nm

780

Figure 8. Ratio of the excitation frequency γobs(λ) of the Fluorone/m-TMPyP/p-TMPyP/clay complex ([Fluorone] = 5.0 × 10−8 M, [m-TMPyP] = 1.7 × 10−8 M, [p-TMPyP] = 3.3 × 10−8 M; 40% loading vs. CEC).

Conclusion In the present study, we achieved quantitative, excited-singlet, multiple-step, energy-transfer reactions between three adsorbed dyes on the clay surface. The energy transfer efficiencies of the multiple-step processes were analyzed using novel analytical formulae. The efficiency of the energy transfer from Fluorone to m-TMPyP and to p-TMPyP was 90%, and that from m-TMPyP to p-TMPyP was 75% when the total dye loading was 40% vs. CEC of the clay. According to these results, the clay/porphyrin complexes are promising candidates for use in efficient artificial LHSs. We propose the use of a new parameter, Γ380-780 nm, in order to evaluate the performance of the artificial LHS. Γ380-780 nm indicates the ratio of the excitation frequency of the energy acceptor in the LHS to the frequency without the energy donor under sunlight irradiation. The calculated


18

Page 19 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Γ380-780 nm for our system is 2.4. An increase in the Γ380-780 nm was achieved using the artificial LHS.

ASSOCIATED CONTENT Supporting Information. 1. Method of evaluation of the energy transfer reaction between the three components 2. Energy transfer reaction between Fluorone and m-TMPyP 3. Energy loss in the system 4. Dependence of Γ380-780 nm on the dye concentration This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *[email protected] ACKNOWLEDGMENT This work was partly supported by the Grant-in-Aid for Scientific Research on Innovative Areas “All Nippon Artificial Photosynthesis Project for Living Earth (AnApple)” grant (no. 25107521) and by the Grant-in-Aid for Scientific Research (B) (no. 24350100) from the Japan


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

Society for the Promotion of Science (JSPS). This work was also supported by the JSPS KAKENHI Grant-in-Aid for JSPS Research Fellows (no. 15J06785). REFERENCES 1. Scholes, G. D.; Fleming, G. R.; Olaya-Castro, A. and Grondelle, R. V. Lessons from Nature about Solar Light Harvesting. Nature chemistry, 2011, 3, 763-774. 2. Kirmaier, C. and Holten, D. Primary Photochemistry of Reaction Centers from the Photosynthetic Purple Bacteria. Photosynthesis Research, 1987, 13, 225-260. 3. Umena, Y.; Kawakami, K.; Shen. J. R. and Kamiya, N. Crystal Structure of OxygenEvolving Photosystem II at a resolution of 1.9 Å. Nature, 2011, 473, 55-60. 4. Herek, J. L.; Wohlleben, W.; Cogdell, R. J.; Zeidler, D. and Motzkus, M. Quantum Control of Energy Flow in Light Harvesting. Nature, 2002, 417, 533-535. 5. Fassioli, F.; Olaya-Castro, A.; Scheuring, S.; Sturgis, J. N. and Johnson, N. F. Energy Transfer in Light-Adapted Photosynthetic Membranes: from Active to Saturated Photosynthesis. Biophysical Journal, 2009, 97, 2464-2473. 6. Mcdermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Crystal Structure of an Integral Membrane Light-Harvesting Complex from Photosynthetic Bacteria. Nature, 1995, 374, 517–521. 7. Bolton, J. R.; Stricker, S. J.; Connolly, J. S. Limiting and Realizable Efficiencies of Solar Photolysis of Water. Nature, 1985, 316, 495-500.


20

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8. Miyatake, T.; Tamiaki, H.; Holzwarth, A. R.; Schaffner, K.Artificial Light-Harvesting Antennae: Singlet Excitation Energy Transfer from Zinc Chlorin Aggregate to Bacteriochlorin in Homogeneous Hexane Solution. Photochem. Photobiol. 1999, 69, 448456. 9. Takahashi, R.; Kobuke, Y. Hexameric Macroring of Gable-Porphyrins as a Light-Harvesting Antenna Mimic. J. Am. Chem. Soc. 2003, 125, 2372-2373. 10. Schanze, K.; Silverman, E. E.; Zhao, X. Intrachain Triplet Energy Transfer in PlatinumAcetylide Copolymers. J. Phys. Chem. B 2005, 109, 18451-18459. 11. Kelley, R. F.; Lee, S. J.; Wilson, T. M.; Nakamura, Y.; Tiede,D. M.; Osuka, A.; Hupp, J. T.; Wasielewski, M. R. Intramolecular Energy Transfer within Butadiyne-Linked Chlorophyll and Porphyrin Dimer-Faced, Self-Assembled Prisms. J. Am. Chem. Soc. 2008, 130, 42774284. 12. Yoo, H.; Yang, J.; Nakamura, Y.; Aratani, N.; Osuka, A.; Kim, D. Fluorescence Dynamics of Directly Meso−Meso Linked Porphyrin Rings Probed by Single Molecule Spectroscopy. J. Am. Chem. Soc. 2009, 131, 1488-1494. 13. Miller, M. A.; Lammi, R. K.; Prathapan, S.; Holten, D.; Lindsey,J. S. A Tightly Coupled Linear Array of Perylene, Bis(Porphyrin), and Phthalocyanine Units that Functions as a Photoinduced Energy-Transfer Cascade. J. Org. Chem. 2000, 65, 6634-6649. 14. Gilat, S. L.; Adronov, A.; Frechet, Jean, M. J. Light Harvesting and Energy Transfer in Novel Convergently Constructed Dendrimers. Angew. Chem., Int.Ed. 1999, 38, 1422-1427.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

15. Inagaki, S.; Ohtani, O.; Goto, Y.; Okamoto, K.; Ikai, M.;Yamanaka, K.; Tani, T.; Okada, T. Light Harvesting by a Periodic Mesoporous Organosilica Chromophore. Angew. Chem., Ind. Ed. 2009, 48, 4042-4046. 16. S. Takagi, D.A. Tryk, H.J. Inoue, Photochemical Energy Transfer of Cationic Porphyrin Complexes on Clay Surface. J. Phys. Chem. B. 2002, 106, 5455-5460. 17. Takagi, S.; Eguchi, M.; Tryk, D. A.; Inoue, H. Light-Harvesting Energy Transfer and Subsequent Electron Transfer of Cationic Porphyrin Complexes on Clay Surfaces. Langmuir, 2006, 22, 1406-1408. 18. Ishida, Y.; Shimada, T.; Masui, D.; Tachibana, H.; Inoue, H.; Takagi, S. Efficient Excited Energy Transfer Reaction in Clay/ Porphyrin Complex toward an Artificial Light-Harvesting System. J. Am. Chem. Soc. 2011, 133, 14280-14286. 19. Ohtani, Y.; Shimada, T.; Takagi, S. Artificial Light-Harvesting System with Energy Migration Functionality in a Cationic Dye/Inorganic Nanosheet Complex. J. Phys. Chem. C 2015, 119, 18896-18902. 20. http://pveducation.org/pvcdrom/appendices/standard-solar-spectra 21. Okada, T.; Ide, Y.; Ogawa, M.; Oraganic-Inorganic Hybrids Based on Ultrathin Oxide Layers: Designed Nanostructures for Molecular Recongnition. Chem. Asian J. 2012, 7, 19801992. 22. Boháč, P.; Crímerová, A.; Bujdák, J.; Enhanced Luminescence of 3, 3’-diethyl-2, 2’thiacyanine Cations Adsorbed on Saponite Particles. Applied Clay Sci. 2016, 127-128, 64-69.


22

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


23. Takagi, S.; Shimada, T.; Ishida, Y.; Fujimura, T.; Masui, D.; Tachibana, H.; Eguchi, M.; Inoue, H.; Size-Matching Effect on Inorganic Nanosheets: Control of Distance, Alignment, and Orientation of Molecular Adsorption as a Bottom-Up Methodology for Nanomaterials. Langmuir, 2013, 29, 2108-2119. 24. Takagi, S.; Shimada, T.; Yui, T.; Inoue, H. High Density Adsorption of Porphyrins onto Clay Layer without Aggregation: Characterization of Smectite-Cationic Porphyrin Complex. Chem. Lett. 2001, 30, 128-129. 25. Ohtani, Y.; Ishida, Y.; Ando, Y.; Tachibana, H.; Shimada, T.; Takagi, S. Adsorption and Photochemical Behaviors of the Novel Cationic Xanthene Derivative on the Clay Surface. Tetrahedron Letters, 2014, 55, 1024-1027. 26. Förster, T. Delocalized Excitation and Excitation Transfer. In Mordern Quantum Chemistry, Part III, Sinanoglu, O. Ed.; Academic Press: New York, 1965; 93-137. 27. Ishida, Y.; Shimada, T.; Tachibana, H.; Inoue, H.; Takagi, S. Regulation of the Collisional Self-Quenching of Fluorescence in Clay/Porphyrin Complex by Strong Host-Guest Interaction. J. Phys. Chem. A 2012, 116, 12065-12072.

Insert Table of Contents Graphic and Synopsis Here


23


Page 24 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

24

Energy Transfer among Three Dye Components in a NanosheetâDye

Recommend Documents

Energy Transfer among Three Dye Components in a NanosheetâDye