Enhanced Solar Energy Harvest and Electron Transfer through Intra

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Enhanced Solar Energy Harvest and Electron Transfer through Intra- and Inter-Molecular Dual-Channel in Chlorosome-Mimicking Supramolecular Self-Assemblies Xiaoyuan Ji, Jie Wang, Yong Kang, Lin Mei, Zhiguo Su, Shaomin Wang, Guanghui Ma, Jinjun Shi, and Songping Zhang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b03105 • Publication Date (Web): 10 Oct 2018 Downloaded from http://pubs.acs.org on October 11, 2018

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Enhanced Solar Energy Harvest and Electron Transfer through Intra- and Inter-Molecular Dual-Channel in Chlorosome-Mimicking Supramolecular Self-Assemblies Xiaoyuan Ji1,2,3, Jie Wang1,4,Yong Kang1, Lin Mei2, Zhiguo Su1, Shaomin Wang4, Guanghui Ma1, Jinjun Shi3,*, Songping Zhang1,*

1Dr.

X. Ji, J. Wang, Y. Kang, Prof. Z. Su, Prof. G. Ma, Prof. S. Zhang

State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China E-mail: [email protected] 2Dr.

X. Ji, Prof. L. Mei

School of Pharmaceutical Sciences (Shenzhen), Sun Yat-sen University, Guangzhou 510275, China 3Dr.

X. Ji, Prof. J. Shi

Center for Nanomedicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115, USA E-mail: [email protected] 4J.

Wang, Prof. S. Wang

College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China

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ABSTRACT The direct connection between photosensitizer and electron mediator, achieved by precise arrangement based on chlorosome, provides photosynthetic bacteria the maximum efficiency in solar energy conversion. Herein, this study reports fabrication of bio-mimicking chlorosome for biocatalyzed artificial photosynthesis through self-assembly of simple molecules to functional systems. TCPP/EYx/Rh8-x macromolecules, synthesized through a sequential amidation reaction between porphyrin (TCPP), eosin Y (EY), and [Cp*RhCl2]2, was found to self-assemble into chlorosome-mimicking supramolecular assemblies through non-covalent interactions. Intra- and inter-molecular dual-channel for enhancing electron transfer was constructed in TCPP/EYx/Rh8-x supramolecular assemblies. Besides, the energy band structure of TCPP/EY4/Rh4 supramolecular assemblies also made a perfect coordination with oxidation and reduction potential of electron donor and NAD+, which led to a fast and orientated electron transfer along electron donor, TCPP/EY4/Rh4 and NAD+. Compared with the system using free components, the yield of NADH photo-regeneration was improved from 15% to 91% by TCPP/EY4/Rh4 supramolecular assemblies; by coupling this NADH photoregeneration process with dehydrogenases, 38 M methanol was synthesized for CO2 after 2 hours’ visible light irradiation, which was about 12fold higher than that obtained using free components. The chlorosome-inspired TCPP/EYx/Rh8-x supramolecular assemblies with intra- and inter-molecular electron transfer dual-channel represents a landmark for implementing highly effective solar energy conversion and selective methanol synthesis from CO2 in a green and sustainable manner.

KEYWORDS: Chlorosome, Molecular evolution, Artificial photosynthesis, Supramolecular assemblies, NADH regeneration


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1. INTRODUCTION Solar energy is a clean and sustainable resource that is considered to be a promising alternative to fossil fuels.1-6 It is well known that natural photosynthesis possesses a highly efficient light harvesting system that exhibits nearly 100% quantum efficiency. The natural photosynthesis realizing energy conversion via a cascade of photoinduced electron transfer and redox biocatalytic reactions to generate high-energy carbohydrates.7-8 Recently, biocatalyzed artificial photosynthesis (APS) using redox biocatalysts for mimicking the natural photosynthesis has been successfully constructed based on the light-driven regeneration of nicotinamide cofactors (NADH).9-11 Nevertheless, energy conversion efficiency of biocatalyzed APS is still rather low, owing to the complexity of kinetically coupling of photocatalysis with biocatalysis. According to previous studies, it had been revealed that electron transfer between the photosensitizer (PS) and the electron mediator (M) was the rate-limiting step for the overall reaction.10, 12-13 The slow and inefficient electron transfer between the PS and the M will result in fast recombination of photoinduced electron-hole pairs,14-15 which is considered as one of the most important reasons for the low NADH photo-regeneration yield.11 However, the electron transfer between PS and M is so complicated and enigmatic that it becomes the key challenge facing the advancement in APS. In natural photosynthesis, green photosynthetic bacteria is a representative of primitive photosynthesis with supramolecular antenna complexes called chlorosome, providing an exquisite inspiration from nature to mimic the configurable mechanisms (Scheme 1a).16-17 Selfassembled bacteriochlorophyll pigments (BChl c) in the chlorosome interior play a vital role in the efficient harvesting and funnelling of solar energy. While on the bottom of the chlorosome, another pigment, BChl a, provides the most effective pathway and direction for electron and energy transfer to the next reaction center through binding self-assembled BChl c pigments.16, 1819

The precise arrangement and direct connection among the key molecules enable the green 3 ACS Paragon Plus Environment

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photosynthetic bacteria to perform highly efficient photosynthesis, even in an extreme low-light environment. Nevertheless, programming and constructing functionalized molecular assemblies mimicking the unique features of photobacteria is still in its infancy for scientists. In general, molecular evolution with self-organization of PSs is identified as a significant process in the prebiotic photosystem evolution to mimicking chlorosome.20-21 Porphyrins with a macrocyclic tetrapyrrole core and multi functionalized substituents, exhibit remarkable physical, catalytic, and photochemical properties, which have been applied as PSs for APS.9, 22-24 In past few

decades,

self-assembled

nanostructures

formed

from

porphyrins

mimicking

bacteriochlorophyll pigments (BChl c) in the chlorosome interior have been presented.23, 25-27 The porphyrins in self-assembled formation have shown significantly increased activities for photocatalyzed hydrogen evolution and pollutants degradation as compared to the unassociated ones. However, their activity in biocatalyzed APS was rather low.9,

28

The dye-sensitizing

method has been proven effective in improving the whole photocatalytic activity through covalent cross-linking or absorpting onto the photocatalyst.29-32 So far, majority of studies on mimicking the primitive photobacteria focus on constructing nanostructures based on different porphyrin aggregates to enhance solar energy harvesting ability. The unique properties of the bottom of the chlorosome, however, are largely ignored. It was believed that the BChl a in the bottom provides the most effective pathway and direction for electron and energy transfer to the next reaction center through directly binding to the self-assembled BChl c pigments. As previous research shows, a rhodium-based organometallic complex, Cp*Rh(bpy)Cl (M, Cp*=pentamethylcyclodienyl, bpy=bipyridine), has been widely used as an efficient mediators to regenerate enzymatically active NAD(P)H from NAD(P)+ directly and specifically. This could be a promising candidate for mimicking the function of BChl a baseplate in chlorosome through binding to PS directly.33-35 Herein, we develop a scenario for molecular evolution towards 4 ACS Paragon Plus Environment

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mimicking the structure and function of chlorosome in primitive photobacteria

by self-

organization of a porphyrin (TCPP)-based macromolecules functionalized with eosin Y (EY) and electron mediator (M, Cp*RhCl2). Scheme 1b depicts structure of TCPP/EYx/Rh8-x macromolecules, which was synthesized by sequential amidation of the TCPP core structure by melamine, sensitization by EY, and final covalent linking of [Cp*RhCl2]2. The fabricated TCPP/EYx/Rh8-x macromolecules were found to self-assemble into supramolecular assemblies in water. It was expected that the TCPP sensitized by EY not only improve the absorbance in visible regions, but also have a perfect coordination of valence for an efficient energy harvesting and electron transfer. The M, which is covalently bound to EY-sensitized TCPP, will be responsible for the direction of the energy transfer, so that the electron transfer can be accelerated and recombination of the photoexcited holes and electrons can be retarded. By coupling the photoregeneration of NADH catalyzed by this chlorosome-mimicking supramolecular self-assemblies with the enzymatic synthesis of methanol from CO2, a biocatalyzed APS is developed. Besides the intra-molecular electron transfer channel mediated by covalent bond in TCPP/EYx/Rh8-x macromolecules, there are plenty of inter-molecular channel among adjacent macromolecules in their supramolecular assemblies, these intra- and inter-molecular dual-channel for electron transfer enable more efficient solar energy harvesting and electron transfer in the biocatlayzed APS. 2. RESULTS AND DISCUSSION 2.1 Synthesis and characterization of TCPP/EYx/Rh8-x Recently, porphyrin-based nanomaterials with different structures, such as nanofibers, nanobelts, nanotubes, and so on, have been succussfully fabricated through noncovalent interactions driven self-assembly of porphyrin molecules.36-38 Herein the present work, in order to achieve precise arrangement and molecular coordination mimicking the structure and function of chlorosome, 5 ACS Paragon Plus Environment

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TCPP was selected as core molecule and firstly functionalized with melamine to link different numbers of EY and M. A diagrammatic representation of the synthetic route is shown in Figure 1. Briefly, carboxyl groups on TCPP were firstly functionalized with multi-amino groups via melamine. With excess melamine and enough reaction time, all of the four carboxyl groups on TCPP were functionalized with melamine, introducing totally 8 amino groups to one TCPP molecule. The introduced amino groups were then used to react with carboxyl groups on EY or BPCC through facial EDC/NHS mediated cross-linking reaction. Lastly, the Rh compound [Cp*RhCl2]2 bind to the EY-sensitized TCPP directly through reacting with BPCC. In order to investigate the molecular coordination between PS and M, a series of TCPP/EYx/Rh8-x monomer molecules was designed and prepared, in which the subscript “x” indicates the number of EY molecules cross-linked to each of melamine-functionalized TCPP molecule; the amino groups left for Rh compound binding will therefore be “8-x”. According to the synthetic route illustrated in Figure 1, reactivity of carboxyl groups in EY and BPCC should be similar, therefore, the numbers of EY and BPCC linked to the amino groups in TCPP could be controlled by adjusting their molar ratios in the reaction mixture. Meanwhile, considering the steric effects, EY and BPCC tend to bind to different amino groups. With EY and BPCC applied at four different molar ratios of 0:8, 2:6, 4:4, and 6:2, four functionalized TCPP intermediates compounds,

namely,

TCPP/BPCC8,

TCPP/EY2/BPCC6,

TCPP/EY4/BPCC4,

and

TCPP/EY6/BPCC2 were synthesized, with their molecular structures shown in Figure S1. Lastly, the Rh compound [Cp*RhCl2]2 was attached to the EY-sensitized TCPP directly through reacting with BPCC. After each of above reaction step, the unreacted substrates and cross linkers were removed by dialysis with proper membrane molecular weight cut off, and the TCPP/EYx/Rh8-x macromolecule final products were purified by gel permeation chromatography (GPC) (Figure S2). TCPP, EY and Rh has characteristic absorbance at 420, 500, and 310 nm, respectively 6 ACS Paragon Plus Environment

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(Figure S3), therefore, the synthesized TCPP/EYx/Rh8-x, should show absorbance at all these three wavelengths. Figure S4 present a typical elution profile of the synthesized TCPP/EY4/Rh4 from GPC, which were recorded at 420, 500, and 310 nm simultaneously. Two elution peaks were detected with the major one at about 18.7 min. The ratio of peak areas detected at 420 nm (related to TCPP moiety), 500 nm (related to EY moiety), and 310 nm (related to Rh moiety) is about 1:6:2. The UV-Vis-NIR absorbance spectra of the purified TCPP/EYx/Rh8-x were presented in Figure 2 (a)-(d). Comparison of the spectra of TCPP/EYx/Rh8-x and their component units at same molar concentrations also demonstrated the successful incorporation of the TCPP, EY, and Rh into the macromolecules. The absorbance of TCPP/Rh8, TCPP/EY2/Rh6, TCPP/EY4/Rh4, and TCPP/EY6/Rh2 at 420, 500, and 310 nm read from each of their spectra were listed in Figure 2e. Meanwhile, the absorbance of the synthesized TCPP/EYx/Rh8-x macromolecules at 420, 500, and 310 nm could also be theoretically calculated by weighting the absorbance of TCPP, EY and Rh at each wavelength, based on their molar numbers in macromolecule formulas and standard curves established between absorbance against concentration (Figure S3). The predicted absorbances of TCPP/EYx/Rh8-x macromolecules were in accordance with the experimentally determined values, thus confirms the chemical composites and structures of the TCPP/EYx/Rh8-x supramolecular assemblies. The ratio of the theoretical values of absorbance at 420 nm (related to TCPP moiety), 500 nm (related to EY moiety), and 310 nm (related to Rh moiety), was roughly at 1: 6: 2.5, taking the TCPP/EY4/Rh4 as an example. This ratio was approximately consistent with the ratio of peak areas from GPC detected at these three wavelengths; thus further confirm the successful synthesis of macromolecules with desired chemical structure. The molecular structure of the synthesized macromolecules was further proved by matrixassisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) analysis 7 ACS Paragon Plus Environment

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(Figure 3). The TCPP/Rh8, TCPP/EY2/Rh6, TCPP/EY4/Rh4, and TCPP/EY6/Rh2 has molecular weight about 4458, 4918, 5378, and 5838, respectively, which is consistent with the theoretical molecular weight of TCPP/EYx/Rh8-x macromolecules derived from the molecular formulas (Table S1). Taken all together, we can conclude that TCPP/EYx/Rh8-x macromolecules with expected chemical structure and high purity was successfully synthesized and purified by dialysis and GPC. Based on the initial amount of TCPP, the final yields of TCPP/Rh8, TCPP/EY2/Rh6, TCPP/EY4/Rh4, and TCPP/EY6/Rh2 were about 7.61%, 4.62%, 4.83%, and 5.04%, respectively. 2.2 Formation and Characterization of TCPP/EYx/Rh8-x Supramolecular Assemblies As Figure 1 and Figure S1 show, in this porphyrin-based TCPP/EYx/Rh8-x macromolecule, the TCPP and EY units provide photoactive and fluorescent functionality, the positively charged M units allow for dispersion in aqueous medium and provide the directionality for the electrons transfer. Moreover, with hydrophobic TCPP core and hydrophilic Rh compound, this TCPP/EYx/Rh8-x macromolecule will also be amphiphilic. Because of this unique chemical structure and amphiphilic nature, TCPP/EYx/Rh8-x macromolecules tend to self-organize into well-defined supramolecular assemblies in aqueous medium. By manipulating the molecular composition and ratio of EY and M in the TCPP/EYx/Rh8-x monomer, the TCPP/EYx/Rh8-x-based supramolecular assemblies would exhibit subsequent changes of morphology and optical properties. Therefore, this amphiphile provides an excellent model for better understanding the structure-performance relationship of the natural photosynthesis system. Figure 4a presents the transmission electron microscopy (TEM) images of the TCPP/EYx/Rh8-x supramolecular assemblies, which are generally monodispersed. The TCPP/Rh8 assemblies have a mean diameter about 133.6 nm; a remarkable larger size about 224.5 nm was observed for the assemblies of TCPP/EY6/Rh2 with more EY ligands were crosslinked (Figure 4b). The surface zeta potential of the TCPP/EYx/Rh8-x supramolecular assemblies measured in water by Zetasizer Nano ZS 8 ACS Paragon Plus Environment

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(Malvern Instruments, UK) was also influenced by the numbers of EY and Rh. With increase in the number of Rh from 2 to 8, the surface zeta potential of the TCPP/EYx/Rh8-x supramolecular assemblies increased from 9.3 to 32.1 mV, due to increase of positively charged Rh moieties [Cp*Rh(bpy)H2O]2+. The energy-dispersive X-ray spectroscopy (EDS) elemental mapping of supramolecular assemblies were detected and shown in Figure 4c. The presence of the C, N, Rh and Br, which are characteristic elements of the TCPP, M and EY respectively, demonstrated the uniform and precise assembly of Rh and EY onto the ligands of TCPP. Moreover, the changing of densities of color dark cyan (Rh) and blue (Br) also demonstrate different ratios of EY and M in these supramolecular assemblies. The element composition of TCPP/EYx/Rh8-x supramolecular assemblies was further investigated by employing X-ray photoelectron spectroscopy (XPS). Figure 5a reveals that there were C, O, N, Rh, Cl, and Br elements in the XPS survey spectra of TCPP/EYx/Rh8-x supramolecular assemblies. As shown in Figure 5b-d, the high-resolution XPS spectra of C1s, N1s, O1s and Rh 3d region of TCPP/EY4/Rh4 supramolecular assemblies, respectively. The C1s XPS spectrum consist of four peaks at 288.7, 286.5, 285.4, and 284.7 eV, which is originated from C=O, C-O, C-OH, and C-C, respectively. There were three peaks in N1s XPS spectrum at 401.7, 399.9, and 397.7 eV, which should be assigned to CO-NH, C-NH, and C=N, respectively. For the O1s XPS spectrum, there were three peaks at 533.8, 532.5, and 531.5, which could be attributed C-O, C-OH, and C=O. As Figure 5e shows, although the Rh3d XPS profile of the TCPP/EY4/Rh4 supramolecular assemblies exhibited two peaks at 309 and 313 eV, they were not from free Rh compound. According to previous reports,39-40 there were two characteristic peaks of Rh at 309 and 313 eV, respectively, which were originated from Rh 3d5/2 and Rh 3d3/2. More importantly, the element contents of C, N, Br and Rh in the four TCPP/EYx/Rh8-x supramolecular assemblies determined by XPS are coincidently consistent with the theoretical values calculated 9 ACS Paragon Plus Environment

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from the molecular formulas (Figure 5f and Table S1). These results further confirmed the successful synthesis of TCPP/EYx/Rh8-x molecular with expected number of EY and M ligands. The structure of the supramolecular assemblies was further investigated by solid-state

13C-

NMR. The chemical shift of C atom in TCPP/EYx/Rh8-x supramolecular assemblies were detected and shown in Figure 5g. And the exact chemical shifts of C atom in TCPP/EY4/Rh4 supramolecular assemblies were labeled in Figure 5h. Although lots of chemical shift of C atoms were overlapped, there were still mutual consistency between theoretical and measured values. In addition, there are some characteristic peaks of EY and M in spectra. For example, the peaks at 16.9 ppm in the 13C NMR spectra of TCPP/EYx/Rh8-x supramolecular assemblies are assigned to -CH3 in M (Figure 5h), which are decreasing with the decreasing ratio of M ligands in TCPP/EYx/Rh8-x supramolecular assemblies. The peaks at about 90-100 ppm in the

13C

NMR

spectra of TCPP/EYx/Rh8-x supramolecular assemblies are assigned to the C affected by -Br in benzene ring of EY, which are increasing with the increasing ratio of EY ligands in TCPP/EYx/Rh8-x supramolecular assemblies. Besides, the changing of EY and Rh ligands ratios of TCPP/EYx/Rh8-x supramolecular assemblies were also detected in the color change of TCPP/EYx/Rh8-x supramolecular assemblies’ solutions (Figure S5) and Fourier Transform infrared (FTIR) spectrum (Figure S6). 2.3 NADH Photoregeneration and Methanol Synthesis by TCPP/EYx/Rh8-x Supramolecular Assemblies The photo-regeneration of NADH by using different TCPP/EYx/Rh8-x supramolecular assemblies including TCPP/Rh8, TCPP/EY2/Rh6, TCPP/EY4/Rh4, TCPP/EY6/Rh2 and free TCPP/EY/M systems at concentrations of each functional components the same as in their corresponding supramolecular assemblies were investigated. The reaction system included the following components: 15 wt% of TEOA, 1 mM of NAD+, 0.01 mM of TCPP/EYx/Rh8-x 10 ACS Paragon Plus Environment

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supramolecular assemblies and irradiated with visible light. Figure 6a presents the kinetic curves for NADH regeneration by TCPP/EYx/Rh8-x supramolecular assemblies. The TCPP/Rh8 supramolecular assembly containing no EY moiety has the lowest NADH regeneration yield of 64% and quantum efficiency of 13.19%. With the sensitizing of two EY moieties, the NADH regeneration yield using TCPP/EY2/Rh6 increased remarkably to 84% with a quantum efficiency of 17.31%; these values increased further to the highest values about 91% and 18.76% when TCPP/EY4/Rh4 supramolecular assemblies containing equal numbers of EY and M were applied. These results clearly demonstrated the effectiveness of EY sensitizing on TCPP. Further increasing the numbers of EY to 6, however, led to certain degree decreases in both NADH regeneration yield (79%) and quantum efficiency (16.29%). By coupling the TCPP/EYx/Rh8-x supramolecular assemblies-driven regeneration of NADH with the cascade redox enzymatic reaction mediated by FateDH, FaldDH and ADH, synthesis of methanol from CO2 was successfully achieved. The dependence of methanol yield on structure of the TCPP/EYx/Rh8-x supramolecular assemblies exhibited the same trend as that of NADH photoregeneration. Two hours reaction with TCPP/EY4/Rh4 supramolecular assemblies produced the highest methanol concentration of 38 M (Figure 6b), and relative lower values of 10 M, 27 M, and 20 M were obtained from reactions with TCPP/Rh8, TCPP/EY2/Rh6, and TCPP/EY6/Rh2, respectively. NADH regeneration and methanol synthesis in the solution based systems with different molecular ratios of TCPP, EY and M, which was corresponding to each of their supramolecular assembly counterparts, showed similar trends (Figure S7). Nevertheless, both the NADH regeneration yield and methanol productivity were much lower than that of corresponding assemblies. The system with free TCPP, EY and M of same amount as in TCPP/EY4/Rh4 supramolecular assemblies only lead to about 16% NADH photo-regeneration yield (Figure S7a) with a quantum efficiency of 3.3%, or 3 M methanol in the reaction coupled with the three11 ACS Paragon Plus Environment

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dehydrogenases catalyzed CO2 reduction (Figure S7b). Table S2 summarizes the biocatalyzed methanol conversion from CO2 through the cascade redox enzymatic reaction coupling with bioor photo-catalyzed NADH regeneration reported in recent years. As shown in Table S2, TCPP/EY4/Rh4 supramolecular assemblies catalyzed methanol synthesis had the highest yield as compared with that obtained by using other bio- or photo-catalytic systems. The energy level of the APS schematically illustrated in Figure 6c provided new evidences to explain the high efficiency obtained in this work. According to the band structure of TCPP and EY, the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of TCPP (-1.1V, 0.9V) are higher than that of EY (-1.02V, 1.09V). The match of energy bands between TCPP and EY will generate a heterojunction structure in the TCPP/EYx/Rh8-x supramolecular assemblies.41-42 Under light irradiation, the photo-excited electrons from the HOMO of TCPP transferred to LUMO of TCPP directly, and then immigrated to LUMO of EY driven by the built-in potential in the heterojunction, and finally transferred to Mox (the oxidized formation of M) along with the photo-induced electrons from HOMO of EY. The Mox would be reduced to Mred,1 firstly, then the other reduced form of Mred,2 will be formed spontaneously by absorbing a proton from aqueous medium. At last, two electrons and one proton will be transferred from Mred,2 to NAD+ to regenerate NADH and Mox. The regenerated NADH will be consumed at stoichiometric ratio in FateDH/FaldDH/ADH catalysed synthesis of methanol from CO2. At the same time, the holes in the HOMO of TCPP and those transferred from the HOMO of EY can be consumed by the sacrificial agents (TEOA). Thus, EY not merely acted as a stepping-stone to facilitate the electron transfer between TCPP and M, but also applied as a second PS for photo-inducing electron by itself. This heterostructure of EY-sensitized TCPP is expected to accelerate the harvesting and transferring of solar energy, thus leading to superior photocatalytic activity. 12 ACS Paragon Plus Environment

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More detailed analyses on possible electron transfer pathways between the PS and the M in the APS were schematically illustrated in Figure 6d. For the free APS with PS and M dispersed in buffer solution, the transfer of electron photo-excited from TCPP or EY to M will only through random collision. This random electron transfer will result in facile recombination of electronhole pairs in PSs. The random electron transfer pathway was labelled as P1 in Figure 6d. When these functional compounds were synthesized into TCPP/EYx/Rh8-x supramolecular assemblies, two more efficient electron transfer pathways were set up. Firstly, the covalent linking between electron mediator M and EY-sensitized TCPP formed an integrated light-dependent reaction center. The electron transfer from PS and M could be realized within one molecule unit, thus generating an intra-molecular electron transfer channel labelled as P2 in Figure 6d. Secondly, the well-defined

supramolecular

assemblies

are

self-assembled

from

TCPP/EYx/Rh8-x

macromolecule through non-covalent interactions including - stacking and hydrogen bonding. These interactions bring significant proximity effects between PS and M from near molecules, therefore forming inter-molecular electron transfer channels labelled as P3 in Figure 6d. The newly developed intra- and inter-molecular electron transfer pathways in TCPP/EYx/Rh8-x supramolecular assemblies with the negligible electron transfer distance, oriented transfer direction, and stable connection, will not merely accelerate the electron transfer rate, but also will eliminate the re-combination of photoinduced electron-hole pairs of PSs. Last but not least, mimicking the structure of chlorosome antenna complexes, TCPP/EYx/Rh8-x supramolecular assemblies with irregular surface and nano-scale size, provide large specific surface areas and countless active sites for light energy harvesting and NADH regenerating. The quantum efficiency increased from 3.30% of free APS to 13.19% of the TCPP/EYx/Rh8-x supramolecular assemblies also demonstrated the substantial advantages of the presence of physical contact and covalent bond mediated electron transfer pathways. 13 ACS Paragon Plus Environment

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On the basis of above discussions, we can also preliminarily understand the differences in the performances for NADH regeneration and methanol synthesis observed by using TCPP/EYx/Rh8x

supramolecular assemblies with different molar ratio of EY and M. As shown in Figure 6a and

6b, TCPP/Rh6 supramolecular assemblies without sensitization by EY show the lowest yield of NADH regeneration and methanol synthesis, and TCPP/EY4/Rh4 supramolecular assemblies with equal number of EY and M show the highest photocatalytic efficiency. It was speculated that in this conformation, each EY molecule has one M molecule next to it, and the latter is responsible to accepting the energy and electron from EY through covalent bond mediated pathway and transfer it to the next acceptor immediately. With the efficient electron transport system, the risk of photogenerated electron-hole recombination will be decreased, leading to the superior photocatalytic activity. As for TCPP/EY2/Rh6, the PS TCPP was sensitized with only two EY, the generating of electrons might not be competent to the covalent-bond mediated transfer to mediator. Contrary to TCPP/EY2/Rh6, TCPP/EY6/Rh2 supramolecular assemblies have a high capability to generate electrons with six EY sensitized TCPP, however, there probably is traffic jams in the electron transfer pathway due to less amount of M, therefore, electrons back-flowing and recombination with holes in HOMO of TCPP or EY would occur. The energy band structures of the TCPP/EYx/Rh8-x supramolecular assemblies with different content of EY and M analysed by linear sweep voltammograms and solid UV-visible diffuse reflectance (UV-DRS) experiments supported the above assumptions. According to UV-DRS, the absorbance threshold (g) of TCPP/Rh8, TCPP/EY2/Rh6, TCPP/EY4/Rh4, and TCPP/EY6/Rh2 are approximately at 605, 720, 715, and 740 nm (Figure 7a). Their corresponding band gaps (Eg), estimated from Kubelka–Munk conversion,43-45 were 2.25, 1.82, 1.86, and 1.80V (Figure 7b), respectively, implying that the TCPP/Rh8 supramolecular assemblies have the light absorption ability weaker than three others. The LUMO of TCPP/EYx/Rh8-x supramolecular assemblies were 14 ACS Paragon Plus Environment

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determined by linear sweep voltammograms experiments (Figure 7c). The LUMO value is -0.95 V (TCPP/Rh8), -0.83 V (TCPP/EY2/Rh6), -0.91 V (TCPP/EY4/Rh4), and -0.86 V (TCPP/EY6/Rh2), respectively. Hence, the HOMO of each TCPP/EYx/Rh8-x supramolecular assemblies is 1.30 V (TCPP/Rh8), 0.99 V (TCPP/EY2/Rh6), 0.95 V (TCPP/EY4/Rh4), and 0.94 V (TCPP/EY6/Rh2), calculated from the differences between their LUMO and Eg. The energy band structure of each TCPP/EYx/Rh8-x and the electron transfer pathways of the APS were labeled in Figure 7d. In consideration of the oxidization and reduction potential of TEOA and NAD+ is 0.8V and -0.3 V, there is a match of energy bands among TEOA, TCPP/EYx/Rh8-x supramolecular assemblies, and NAD+. For example, the TCPP/EYx/Rh8-x supramolecular assemblies has HOMO lower than oxidization potential of TEOA, while its LUMO is higher than the reduction potential of NAD. Therefore, the photo-excited electrons from the HOMO of the integrated APS could be directly transferred to the LUMO of the TCPP/EYx/Rh8-x supramolecular assemblies and eventually transferred to NAD+ for its reduction. Meanwhile, the holes in the HOMO of the TCPP/EYx/Rh8-x supramolecular assemblies can be consumed by the sacrificial agents (TEOA). Furthermore, the efficacy of electron transfer might also be affected by the relative energy position. According to Figure 7d, although TCPP/Rh8 supramolecular assemblies have the highest driving force for electron transfer, the wide band gap make it less efficient in the light-harvesting and electron generation. Among the other three TCPP/EYx/Rh8-x supramolecular assemblies which have a similar light-absorbing ability, the ability to oxidize TEOA should be TCPP/EY2/Rh6 > TCPP/EY4/Rh4 > TCPP/EY6/Rh2, and the ability to reduce NAD+ should be TCPP/EY4/Rh4 > TCPP/EY6/Rh2 > TCPP/EY2/Rh6. The fluorescence spectra of TCPP/EYx/Rh8-x supramolecular assemblies were also analysed to explain the donor-acceptor relationship between TCPP, EY, and M in different TCPP/EYx/Rh8-x supramolecular assemblies (Figure 7e).

The EY and TCPP have maximum fluorescence 15

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emission at about 540 nm and 660 nm, respectively. The emission quenching of TCPP at 660 nm demonstates photo-exited electrons of TCPP transferred to EY or M rather than recombined with the holes in HOMO of TCPP. Likewise, the emission quenching of EY at 540 nm also suggested the photo-exited electrons of EY transferred to M. The largest decrease in TCPP and EY fluorescence intensity were detected for the TCPP/EY4/Rh4 supramolecular assemblies, which means the fastest electron transfer from TCPP and EY to Rh inside of TCPP/EY4/Rh4 supramolecular assemblies. All these above analyses provide solid basis for the highest performance of TCPP/EY4/Rh4 in NADH regeneration and methanol conversion. As illustrated in Figure 6e, the TCPP/EYx/Rh8-x supramolecular assemblies not only enhanced their catalytic activity, but also realized successful recycling and reusing of the whole system. After 10 times reusing, the methanol yield of TCPP/EY4/Rh4 supramolecular assemblies-based APS still retained about 85%. The outstanding stability of TCPP/EYx/Rh8-x supramolecular assemblies also demonstrated that the stability of PSs was improved largely via forming covalent bonds among TCPP, EY, and M. Moreover, the TCPP/EY4/Rh4 supramolecular assemblies also showed excellent stability against consecutive irradiation of 450 W Xenon lamp. As shown in Figure S8, the activity of TCPP/EY4/Rh4 supramolecular assemblies for NADH regeneration remained over 90% after 100 hs of continuous irradiation. Moreover, as shown in Figure S9, after reused for 10 times and continuous Xenon lamp irradiation for 100 hrs, neither FTIR spectra nor UV-vis-NIR absorbance spectra of TCPP/EY4/Rh4 supramolecular assemblies show noticeable change as compared with newly prepared samples. The electrochemical properties of TCPP/EYx/Rh8-x supramolecular assemblies were further analysed by cyclic voltammetry (CV) analysis. The reduction potentials at cathodic peak currents of TCPP, EY, and M are at about -0.82, -0.94 and -0.75 V (Figure 8a and b, Table S3), respectively. A different shifts of reduction potentials were observed after blending PSs (TCPP or 16 ACS Paragon Plus Environment

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EY) with M, indicating interactions between the PSs (TCPP and EY) with M. Adding NAD+ into the above mixture solution of TCPP, EY and M lead to strong increase in the reduction peak current, implying reduction of NAD+ to NADH by PSs and M (Figure 8a and b). When the prepared TCPP/EYx/Rh8-x supramolecular assemblies were tested, the reduction potentials also shift to approximately -0.90 V (Figure 8c). Although the shifts of PS reduction potential were the same as the free system, the cathodic peak currents at their shifted reduction potential were larger than that of free system (Figure 8c, Table S3). More importantly, when the supramolecular assemblies were mixed with NAD+, increases in the reduction peak currents were observed (Figure 8d), which also demonstrates that the supramolecular assemblies are able to catalyze the reduction of NAD+. TCPP/EY4/Rh4 supramolecular assemblies mixed with NAD+ showing the highest increase of the reduction peak currents implying that it has fast electron transfer speed and NADH regeneration rate. The photochemical properties of TCPP/EYx/Rh8-x supramolecular assemblies were further investigated through photocurrent curves measurement experiments under an applied potential of 50 mV s-1 and light irradiation (>420 nm). As shown in Figure 8e, the photocurrent response versus time of TCPP/EY4/Rh4 supramolecular assemblies is the highest among the four supramolecular assemblies. As shown in Figure S10, there is a good correspondence between the photocurrent working spectra and the absorption spectra ranging from 400 nm to 700 nm, indicating that the TCPP/EYx/Rh8-x supramolecular assemblies are the source of photocurrent. The photocurrent response of TCPP/EYx/Rh8-x supramolecular assemblies is reversible and stable, such as the current increased and quenched reproducibly following irradiation on and off. The high photocurrent of TCPP/EY4/Rh4 supramolecular assemblies is answerable for their photocatalytic activity. This indicates that the electrons excited by simulated solar light were transferred from sacrificial agent TEOA to the electrode through the TCPP/EY4/Rh4 17 ACS Paragon Plus Environment

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supramolecular assemblies. Therefore, TCPP/EY4/Rh4 supramolecular assemblies act as a most efficient photoactive catalyst for generating photocurrent through a favourable energetic relationship with TEOA compared with the others. In order to confirm the suppressed recombination of electron-hole pairs in TCPP/EYx/Rh8-x, time resolved fluorescence decay analysis was further applied. The excited state electron radioactive decay lifetime (Figure 8f) show that the TCPP/EY4/Rh4 supramolecular assemblies own the longest fluorescence lifetime (8.753 ns) compared with that of TCPP/Rh8 (4.446 ns), TCPP/EY2/Rh6 (7.023 ns), and TCPP/EY6/Rh2 (5.638 ns), indicating that the incorporation of TCPP, EY, and M increased the photoelectron lifetime of TCPP/EY4/Rh4 supramolecular assemblies. This result further certified that TCPP/EY4/Rh4 supramolecular assemblies have the best coordination among TCPP, EY, and M for the most efficient and fastest photo-excited electrons transfer. 3. CONCLUSIONS In summary, precisely arranging TCPP/EYx/Rh8-x supramolecular assemblies were realized via the self-assembly of TCPP/EYx/Rh8-x macromolecule through - stacking, hydrogen bonding and ion-exchange reaction. The chlorosome-mimicking TCPP/EYx/Rh8-x supramolecular assemblies-based APS not only improve the light sensitivity by EY-sensitized TCPP, but also accelerated electron transfer efficacy and eliminated the re-combination of photogenerated electrons and holes ascribing to constructed intra- and inter-molecular dual-channel. Moreover, the energy band structure of TCPP/EY4/Rh4 supramolecular assemblies also made a perfect coordination with oxidation potential of electron donor and reduction potential of NAD+, which led to a quick and smooth electron transfer along electron donor → TCPP/EY4/Rh4 → NAD+. Therefore, there was nearly 91% of NADH regeneration and 38 M of methanol synthesis catalyzed by TCPP/EY4/Rh4 supramolecular assemblies coupling with biocatalyzed system 18 ACS Paragon Plus Environment

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within 2 h. The effect of TCPP/EYx/Rh8-x supramolecular assemblies was confirmed by photochemical and electrochemical properties detections. This concept of chlorosome-mimicking model provides a new dual-channel mediated electron transfer through light-harvesting system, which may provide an entirely new direction to design APS and exploit solar energy. 4. EXPERIMENT SECTION 4.1 Materials 4,4′,4′′,4′′′-(Porphine-5,10,15,20-tetrayl)tetrakis(benzoic

acid)

(TCPP),

Eosin

Y

(EY),

methanol, dimethyl sulfoxide (DMSO), 2,2′-bipyridine-4-carboxylic acid (BPCC), melamine, NHydroxysuccinimide (NHS), 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), triethanolamine (TEOA), formate dehydrogenase from Candida boidinii (FateDH, EC.1.2.1.2), formaldehyde dehydrogenase from Pseudomonas sp. (FaldDH, EC.1.2.1.46), yeast alcohol dehydrogenase (ADH, EC 1.1.1.1), reduced and oxidized nicotinamide adenine dinucleotide (NADH/NAD+, 98wt%), were purchased from Sigma-Aldrich. Dichloro (pentamethylcyclopentadienyl) rhodium (III) dimer, [Cp*RhCl2]2, was purchased from Alfa. 4.2 Preparation of TCPP/EYx/Rh8-x Macromolecule Briefly, TCPP (2 mM) and melamine (20 mM) were dissolved in DMSO (20 mL) in turn. Subsequently, NHS (20 mM) and EDC (20 mM) were added to above solution. The mixture was allowed to stir for 48 h at 40 oC to form melamine-binding TCPP with multi- amino via the amidation reaction between the amino group of melamine and the carboxylic acid groups of TCPP . This mixture was dialyzed with a MWCO 1000 Dalton for 48 h in DMSO. Then, EY/ BPCC mixed compound at molar ratios of 0:8, 2:6, 4:4, or 6:2 were added into the dialyzed melamine-binding TCPP solution. The EDC (20 mM) and NHS (20 mM) were added to this solution. The mixture was stirred for 48 h at 40 oC to form TCPP/EYx/BPCC8-x compounds via the amidation reaction between the amino group of melamine-binding TCPP and the 19 ACS Paragon Plus Environment

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carboxylic acid groups of EY and BPCC. Then the mixture was dialyzed with a MWCO 4000 Dalton for 48 h in DMSO. [Cp*RhCl2]2 with half molar of BPCC was added into the mixed solution to react with bipyridyl of BPCC. The mixture was stirred for 2 h at room temperature to form TCPP/EYx/Rh8-x macromolecule. Then the mixture was dialyzed with a MWCO 4000 Dalton for 48 h in DMSO. In order to purify the products deeply, gel permeation chromatography (GPC) was adopt to separate the TCPP/EYx/Rh8-x macromolecule from other by-products using C18 silica gel column (Φ55mm×H400mm) as stationary phase and ethanol-acetone- DMSO (at volumetric ratio of 2 : 2 : 1) as mobile phase (0.5 mL/min), the eluent was monitor at 310 nm, 420nm, and 500 nm simultaneously. 4.3 Preparation of TCPP/EYx/Rh8-x Self-Assembled Supramolecular assemblies The TCPP/EYx/Rh8-x supramolecular assemblies were prepared according to the following procedures: 2 mL of DMSO solution containing 0.2 mM TCPP/EYx/Rh8-x macromolecule was slowly added dropwise via a syringe pump into 10 mL of deionized water for about 2 h under vigorous stirring. Then, the resulting solution was left at room temperature with constant stirring for another 2 h after the addition was completed. Subsequently, the self-assembled solution enclosed in a dialysis membrane (MWCO = 10 kDa), was dialyzed against deionized water for 48 h to remove DMSO. Finally, the volume of the resulting aqueous solution was then made up to 2 mL to obtain an aggregate dispersion with a concentration of 0.2 mM for further experiments 4.4 Characterization The relative molecular mass of TCPP/EYx/Rh8-x macromolecules were detected by matrixassisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF). The morphology of the TCPP/EYx/Rh8-x supramolecular assemblies were studied using transmission electron microscopy (TEM, JEM-2100UHR, JEOL, Japan). The particle size and zeta potential of 20 ACS Paragon Plus Environment

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the prepared samples were measured by Zetasizer Nano ZS (Malvern Instruments, UK). Solidstate

13C

NMR spectra of the TCPP/EYx/Rh8-x supramolecular assemblies were recorded

with JNM-EDA600 (JEOL, Tokyo, Japan). The Fourier transform infrared spectrophotometer (FTIR) spectra were measured by a FTIR spectrometer (Nexus 470, Nicolet, Madison, WI, USA). The compositions of the TCPP/EYx/Rh8-x supramolecular assemblies were analyzed by X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Japan). Elemental mapping was carried out by energy dispersive X-ray spectroscopy (EDS) (Inca X-MAX, Oxford, UK) connected to a scanning electron microscope (JSM-7001F). The distribution of C, N, Br and Rh elements on the TCPP/EYx/Rh8-x supramolecular assemblies were mapped. The absorption bands of TCPP, EY, M and TCPP/EYx/Rh8-x supramolecular assemblies were recorded by an ultraviolet-visible (UVVis) spectrophotometer (U-3000, Hitachi). For cyclic voltammograms analysis, photocurrenttime (I-T) profiles, and quantum efficiency of TCPP/EYx/Rh8-x supramolecular assemblies, the protocols were as same as our previous reports46-47. 4.5 Photo-regeneration of NADH The photo-regeneration of NADH by free system, TCPP/EYx/Rh8-x supramolecular assemblies were carried out in a quartz reactor with a temperature-controlled water bath (25 oC). A 450 W Xenon lamp equipped with a 420 nm cut-off filter was used as simulated solar light (CEL-HXF 300, CEAULIGHT, Beijing, China). For photo-catalyzed NADH from MAD+, free system or TCPP/EYx/Rh8-x supramolecular assemblies based APS with final concentration of TEOA, TCPP, M, and NAD+ was 15% w/v, 0.025 mM, 0.1 mM, and 1 mM, respectively, dissolved in 10 mL phosphate buffer solution (100 mM, pH 7.0). Before the reaction, the above mixture solution was firstly kept in dark for 1 h. After that, the mixture solution was exposed to the irradiation of 450 W Xenon lamp equipped with a 420 nm cut-off filter. Every 30 minutes, 10 L reaction solution was taken out to detect the concentration of regenerated NADH via UV-Vis spectrophotometer. 21 ACS Paragon Plus Environment

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4.6 Conversion of Methanol from CO2 The photo-/bioconversion of methanol from CO2 was conducted in the quartz cuvette reactor with a temperature-controlled water bath (25 oC). A 450 W Xenon lamp with a 420 nm cut-offfilter was applied as simulated solar light. Firstly, phosphate buffer solution (10 mL, 100 mM, pH 7.0) was bubbled with CO2 gas for 0.5 h to get a CO2 saturated solution. For photo-/bioconversion of methanol, 15wt/v% of TEOA and 0.025 mM of TCPP/EYx/Rh8-x supramolecular assemblies coupling with 0.5 mM of NAD+ and 0.1 mg/mL FateDH/FaldDH/ADH was added into the above reaction solution and kept the reaction under constant pressure at 0.3 MPa using CO2 gas. After incubation in dark for 30 minutes, the reaction system was exposed to 450 W Xenon lamp irradiation. Every 30 minutes, 10 L reaction solution was taken out to detect the concentration of conversed methanol by gas chromatography (Agilent 7890A) equipped with a flame

ionization

detector

(FID)

and

an

Agilent

HP-FFAP

gas

column

(25m×0.320mm×0.50μm)48-51. 4.7 Reusability of the TCPP/EY4/Rh4 Supramolecular Assemblies Recycling capability of TCPP/EY4/Rh4 supramolecular assemblies was detected through measuring the methanol yield during repeated usages. For each usage, the reactions were allowed to react for 2 hrs. After that, the TCPP/EY4/Rh4 supramolecular assemblies were seperated from reaction solution via centrifuging at 5000 rpm. Then the precipitate was dispersed into another fresh reaction system after washed 3 times using buffer solution and paused for 1 h. The methanol yield using the freshly prepared TCPP/EY4/Rh4 supramolecular assemblies were defined as 100%.

ASSOCIATED CONTENT Supporting Information 22 ACS Paragon Plus Environment

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The Supporting Information is available free of charge on the ACS Publications website at DOI: The schematic illustration of purification of TCPP/EYx/Rh8-x molecules by GPC, the structures, theoretical molecular formulas, and molecular weight of molecular monomer of TCPP/EYx/Rh8-x supramolecular assemblies, the photos of TCPP/EYx/Rh8-x supramolecular assemblies solutions, FTIR spectrum of TCPP/EYx/Rh8-x supramolecular assemblies, time profiles of photocatalytic regeneration of NADH and methanol conversion of corresponding free systems, photo-stability of TCPP/EY4/Rh4 supramolecular assemblies, the cathodic peak current and reduction potential at cathodic peak current of TCPP, EY, M and TCPP/EYx/Rh8-x supramolecular assemblies (PDF). AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. *E-mail: [email protected]. ORCID Xiaoyuan Ji: 0000-0002-6768-2304 Jinjun Shi: 0000-0001-9200-5068 Songping Zhang: 0000-0001-5793-5286 Notes The authors declare no competing financial interest. Acknowledgements The authors thank the support from the National Natural Science Foundation of China (Grant Nos. 21676276, 91534126), and the National Basic Research Program of China (973 Program, 2013CB733604).


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Yadav, R. K.; Baeg, J. O.; Kumar, A.; Kong, K.; Oh, G. H.; Park, N. J. Graphene–Bodipy

as a Photocatalyst in the Photocatalytic–Biocatalytic Coupled System for Solar Fuel Production from CO2. J. Mater. Chem. A 2014, 2, 5068-5076. (35)

Ji, X.; Su, Z.; Wang, P.; Ma, G.; Zhang, S. Integration of Artificial Photosynthesis System

for Enhanced Electronic Energy ‐ Transfer Efficacy: A Case Study for Solar ‐ Energy Driven Bioconversion of Carbon Dioxide to Methanol. Small 2016, 12, 4753-4762. (36)

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Lee, J. S.; Lee, S. H.; Kim, J.; Park, C. B. Graphene–Rh-Complex Hydrogels for Boosting 27 ACS Paragon Plus Environment

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Nanohollow Sphere Composite for Degradation of Methylene Blue and 4-Nitrophenol under Visible Light. Mater. Chem. Phys. 2016, 179, 35-41. (43) Imanaka, Y.; Anazawa, T.; Manabe, T.; Amada, H.; Ido, S.; Kumasaka, F.; Awaji, N.; Sanchez-Santolino, G.; Ishikawa, R.; Ikuhara, Y. An Artificial Photosynthesis Anode Electrode Composed of A Nanoparticulate Photocatalyst Film in A Visible Light Responsive GaN-ZnO Solid Solution System. Sci. Rep. 2016, 6, 35593. (44) Zeng, P.; Ji, X.; Su, Z.; Zhang, S. WS2/g-C3N4 Composite as An Efficient Heterojunction Photocatalyst for Biocatalyzed Artificial Photosynthesis. RSC Adv. 2018, 8, 20557-20567. (45) Yan, S. C.; Li, Z. S.; Zou, Z. G. Photodegradation of Rhodamine B and Methyl Orange over Boron-Doped g-C3N4 under Visible Light Irradiation. Langmuir 2010, 26, 3894-3901. (46) Ji, X.; Wang, J.; Mei, L.; Tao, W.; Barrett, A.; Su, Z.; Wang, S.; Ma, G.; Shi, J.; Zhang, S. Porphyrin/SiO2/Cp*Rh(bpy)Cl Hybrid Nanoparticles Mimicking Chloroplast with Enhanced Electronic Energy Transfer for Biocatalyzed Artificial Photosynthesis. Adv. Funct. Mate. 2018, 28, 1705083. (47) Ji, X.; Liu, C.; Wang, J.; Su, Z.; Ma, G.; Zhang, S. Integration of Functionalized TwoDimensional TaS2 Nanosheets and An Electron Mediator for More Efficient Biocatalyzed Artificial Photosynthesis. J. Mater. Chem. A 2017, 5, 5511-5522. (48) Ji, X.; Su, Z.; Ma, G.; Zhang, S. Sandwiching Multiple Dehydrogenases and Shared Cofactor between Double Polyelectrolytes for Enhanced Communication of Cofactor and 28 ACS Paragon Plus Environment

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Figures

Scheme 1. a) Cartoon showing the structure of chlorosome in the green photosynthetic and b) illustration of the structure mimicking chlorosome based on TCPP/EY4/Rh4 macromolecule.


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ACS Catalysis

EY

Melamine

BPCC

EY+ BPCC at molar ratio of 4:4

EDC+NHS

TCPP

[Cp*RhCl2]2

TCPP/EY4/BPCC4

TCPP/EY4/Rh4

Figure 1. Preparation of TCPP/EY4/Rh4 macromolecule via the amide reaction between TCPP and EY, BPCC and Rh compound in DMSO.


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Figure 2. UV-vis-NIR absorbance spectra of a) TCPP/ Rh8, b) TCPP/EY2/Rh6, c) TCPP/EY4/Rh4, d) TCPP/EY6/Rh2 and the corresponding free TCPP, EY, and M, e) the comparison of absorbance between TCPP/EYx/Rh8-x and their corresponding free molecule with the same concentrations at 310 nm, 420 nm, and 500 nm.


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5838.423

5379.685

TCPP/EY6/Rh2

TCPP/EY4/Rh4

RI

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 Catalysis

TCPP/EY2/Rh6 4918.011

TCPP/Rh8 4458.623

0

1000

2000

3000

4000

m/z

5000

6000

7000

Figure 3. The MALDI-TOF spectra of TCPP/EYx/Rh8-x macromolecules.


8000

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Figure 4. Characterization of TCPP/EYx/Rh8-x supramolecular assemblies. (a) TEM images, (b) size distribution, (c) SEM images and energy-dispersive X-ray spectroscopy (EDS) element mapping of C, N, Rh and Br of supramolecular assemblies from (1) TCPP/Rh8, (2) TCPP/EY2/Rh6, (3) TCPP/EY4/Rh4, and (4) TCPP/EY6/Rh2.


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ACS Catalysis

Figure 5. Characterization the chemical composition and structures of TCPP/EYx/Rh8-x supramolecular assemblies. XPS survey spectrum of a) TCPP/EYx/Rh8-x supramolecular assemblies and high-resolution spectra of b) C 1s, c) N 1s, d) O 1s, and e) Rh 3d, f) the contents of C, N, Br, Rh calculated by XPS curves and by their molecules theoretical analysis (brackets), g) solid state 13C CP/MAS NMR spectrum of TCPP/EYx/Rh8-x supramolecular assemblies, and h) 35 ACS Paragon Plus Environment

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the unit molecular structural formula of TCPP/EY4/Rh4 supramolecular assemblies.


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ACS Catalysis


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Figure 6. a) Time profiles of photocatalytic regeneration of NADH from NAD+ with different supramolecular assemblies. b) Time profiles of methanol synthesis yield under dark stage for 0.5 h, followed by a light stage for 2 h. c) Schematic diagram of energy-level and electron transfer in the biomimetic artificial photosynthesis system. d) Electron transfer pathway of TCPP/EY4/Rh4 supramolecular assemblies. Under visible-light irradiation, photo-excited electrons of EYsensitized TCPP encapsulated in supramolecular assemblies are transferred to M, generating reduction potentials for NADH regeneration. e) Reusability of TCPP/EY4/Rh4 supramolecular assemblies for methanol synthesis.


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ACS Catalysis

Figure 7. (a) Solid UV-visible diffuse reflectance spectra, (b) corresponding bandgap estimated from Kubelka–Munk equation, (c) linear sweep voltammograms, and (d) schematic energy-level and electron movement diagram of TCPP/EYx/Rh8-x supramolecular assemblies. For linear sweep voltammograms analysis, the scan rate was 100 mVs-1, glassy carbon (working), silver-silver chloride (reference), and platinum (counter) electrodes in sodium phosphate buffer (100 mM, pH 7.0). e) fluorescence spectra of TCPP/EYx/Rh8-x supramolecular assemblies with excitation wavelength of 430 nm.


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Figure 8. Cyclic voltammograms (CV) of (a) EY, M, EY-M and EY-M-NAD+, (b) TCPP, M, TCPP-M

and

TCPP-M-NAD+,

(c)

TCPP/EYx/Rh8-x

supramolecular

assemblies,

d)

TCPP/EYx/Rh8-x supramolecular assemblies-NAD+. The concentration of TEOA, TCPP (EY), M and NAD+ is 15wt%, 0.05 mM, 0.15 mM, and 1 mM, respectively. The potential was scanned at 100 mV s-1 using glassy carbon (working), silver-silver chloride (reference) and platinum 40 ACS Paragon Plus Environment

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ACS Catalysis

(counter) electrodes in sodium phosphate buffer (100 mM, pH 7.0), (e) photocurrent-time (I-T) profiles of TCPP/EYx/Rh8-x supramolecular assemblies under simulated solar light illumination; The concentration of TEOA, and TCPP/EYx/Rh8-x supramolecular assemblies is 15wt%, and 0.01mM. The scan rate is 50 mV s-1 and input power is 100 mW cm-2 using glassy carbon (working), silver-silver chloride (reference), and platinum (counter) electrodes in sodium phosphate buffer (100 mM, pH 7.0), and f) time-resolved fluorescence spectra of TCPP/EYx/Rh8x

supramolecular assemblies.


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TOC


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Enhanced Solar Energy Harvest and Electron Transfer through Intra

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