Conjugated Polymers with Sequential Fluorination for Enhanced

Subscriber access provided by Washington University | Libraries

Letter

Conjugated Polymers with Sequential Fluorination for Enhanced Photocatalytic H Evolution via Proton-coupled Electron Transfer 2

Yonggang Xiang, Xuepeng Wang, Li Rao, Pei Wang, Dekang Huang, Xing Ding, Xiaohu Zhang, Shengyao Wang, Hao Chen, and Yongfa Zhu ACS Energy Lett., Just Accepted Manuscript • Publication Date (Web): 14 Sep 2018 Downloaded from http://pubs.acs.org on September 15, 2018

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 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 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.

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 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

ACS Energy Letters

Conjugated

Polymers

with

Sequential

Fluorination for Enhanced Photocatalytic H2 Evolution via Proton-Coupled Electron Transfer Yonggang Xiang,§† Xuepeng Wang,§† Li Rao,§║ Pei Wang,† Dekang Huang,† Xing Ding,† Xiaohu Zhang,† Shengyao Wang,† Hao Chen*†, and Yongfa Zhu*‡ †

College of Science, Huazhong Agricultural University, Wuhan 430074, PR China

‡

Department of Chemistry, Tsinghua University, Beijing, 100084, P R China

║

College of Chemistry, Central China Normal University, Wuhan 430079, PR China

E-mail: [email protected] (H. Chen), [email protected] (Y. Zhu)

ABSTRACT The performance of D-A conjugated polymer based photocatalyts for solar hydrogen production is severely limited by poor charge mobility and weak reactive sites. Here, a series of D-A conjugated polymers with electronegative fluorine atoms on the backbone is presented and influence of fluorination on charge transfer and catalytic site activity is investigated. Theoretical calculation reveals that sequential fluorination on A unit benzothiadiazole will activate the catalytic site, and photocatalytic H2 generation process could be illustrated by proton-coupled electron transfer mechanism. Two series of fluorinated polymers were synthesized, and accelerated charge transfer was also verified. Among them, Linear B-FOBT-1,4-E and porous BFOBT-1,3,5-E with simultaneous electron-donating CH3O- and electron-withdrawing F-

ACS Paragon Plus Environment

1

ACS Energy Letters 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 17

substitution show 3.1 and 28.8 times higher H2 evolution rate than nonfluorinated counterparts, respectively, and AQY of 5.7% at 420 nm is obtained for B-FOBT-1,4-E. The results provide reciprocal understanding of activation nature of substituent-regulating polymers.

Conjugated polymers, consisting of alternating electron-donating (D) and electron-accepting (A) units, are one class of unique polymers which have been applied widely into construction of polymer solar cells (PSCs), and they are expected to exhibit strong visible light absorption ability and high photostability due to the push-pull intramolecular charge transfer.1-4 Very recently, DA conjugated microporous polymers developed by Cooper’s group were also found to exhibit modest H2 evolution rate (HER) under visible light irradiation (λ > 420 nm).5 In comparison to the most studied polymeric g-C3N4 with relatively fixed structures,6-9 the abundance of D and A contribute to tunable energy levels, as a result, more novel polymers by facile D or A units choice were prepared with superior HER and overall water splitting ability.10-19 However, D-A conjugated polymeric semiconductors still face drawbacks of low solar-to-H2 conversion efficiency, and their structures may be further optimized with regard to the three dominating steps in the process of photocatalytic water splitting: (i) absorption of photons to form electronhole pairs, (ii) charge separation and migration, (iii) surface proton reduction.20


2

Page 3 of 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

ACS Energy Letters

Among various strategies for optimizing structures of D-A conjugated polymers with high photovoltaic efficiency, a combination of “weak donors” and “strong acceptors” proves to benefit charge transport.21 To obtain a stronger acceptors, it has been widely reported that introduction of electronegative fluorine atoms on polymer backbone represents one effective method without changing light harvest ability significantly.22-25 We have recently synthesized two D-A conjugated polymers: linear B-BT-1,4-E and porous B-BT-1,3,5-E in which benzothiadiazole (BT) acted as A unit, and both of them exhibited moderate HER.26-28 In this regard, it is expected that further fluorination on BT of the above two polymers will accelerate photo-generated carrier separation in the second step of the photocatalytic process. On the other hand, regulation of catalytic reaction sites is another crucial factor to afford desired photocatalyts. Tian’s group prepared several types of BT based polymer nanoparticles (PDots),2930

and it indicated that heteroatoms nitrogen in the BT units was the reactive site in the process of

photocatalytic H2 evolution. Accordingly, surface proton reduction in the final step may also be assessed by theoretical prediction in terms of the catalytic site activity for fluorinated B-BT-1,4E and B-BT-1,3,5-E. To demonstrate the influence of F substitution on the photogenerated carrier mobility and catalytic active site. Theoretical Density functional theory (DFT) calculations31 are performed to predict the activation energy of H2 formation from interacting hydrogen atoms in two different polymer chains with heteroatoms N on BT units as active site, since it is the most difficult step of HER reaction.30 Previously, similar theoretical investigation was successfully used to reveal hydrogen evolution mechanism in Nitrogenase catalyzed N2 reduction.32 A series of linear fluorinated B-BT-1,4-E were designed with different number of fluorine atoms (0F, 1F, 2F, F/OCH3), and theoretic modeling indicates that photocatalytic H2 release process for the polymer


3


Page 4 of 17

follows proton-coupled electron transfer (PCET) facilitated route (Figure 1) which plays a vital role in a wide range of chemical and biological processes.33-37 As a result, It is predicted that BFOBT-1,4-E in which BT is simultaneously substituted by electron-donating methoxyl group (OCH3) and electron-withdrawing F has the strongest catalytic site. In the experimental part, and HER change of as prepared polymers obeys theoretical prediction. Moreover, same strategy could also be applicable to the microporous polymers B-BT-1,3,5-E system.

Figure 1. (a) Synthesis of linear and microporous polymers. (b) PCET- enhanced H2 release. (c) Energy profile of H2 formation reported in this study. The simulated reaction begins with two hydrogenated oligomer on nitrogen, and then one H2 molecule leaves the dimer through a transition state. For nonfluorinated B-BT-1,4-E, the two N atoms are identical, and activation energy barrier is calculated to be 1.75 eV between the energy of transition state and two hydrogenated monomers. However, the two N atoms in the BT unit are different in the monofluorinated B-FBT-1,4-E chain, and two models systems are evaluated. As shown in Figure 2b, positions of F substituent are regarded as para and meta relative to the position of hydrogenated N atom, and the models are named as m-B-FBT-1,4-E and p-B-FBT-1,4-E, respectively. A lower activation energy barrier is found for p-B-FBT-1,4-E


4

Page 5 of 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

ACS Energy Letters

(1.65 eV) in comparison to m-B-FBT-1,4-E (1.79 eV), thus p-B-FBT-1,4-E model is more kinetically favourable than m-B-FBT-1,4-E for H2 generation. The transition state structures and corresponding HOMO are further investigated, and the interaction between the two different hydrogenated polymers is far more interesting. In the transition state of B-BT-1,4-E, the p orbital of meta carbon in one polymer chain tends to approach p orbital of N atom in the other polymer chain, and then the resulted Hδ- attacks Hδ+ to form one H2 molecule. Similar to coupling between the proton motion and electron transfer that plays a key role in the proton pumping mechanism of photosynthetic reaction centers, the photocatalytic H2 release process here may follow typical PCET facilitated route due to different transfer way of proton and electron. However, there still exists a gap between the two approaching p orbitals for B-BT-1,4-E, which limits the PCET effect. As shown in Figure 2c, the induction effect of F atom at para position enlarges the p orbital of meta carbon, which will form a bridge with p orbital of N atom in the other polymer chain, and then PCET process is more favorable, revealing relatively lower activation energy of p-B-FBT-1,4-E. On the contrary, for mB-FBT-1,4-E, the induction effect of F atom at meta position has a negative impact on the PCET effect (Figure 2d). Therefore, it is reasonable that both meta and para fluorination result in a weaker PCET effect in comparison to sole para fluorination, as a result, activation energy of BDFBT-1,4-E is higher than p-B-FBT-1,4-E (Figure 2e). Above discussion sheds light on a way to improve the HER. Since we know electron-withdrawing F group at para site is beneficial to H2 evolution while it is bad at meta site, we hypothesize that the electron-donating OCH3 group at meta site along with the electron-withdrawing F atom at para site may favor the charge transfer between two interacting polymer chains. To our delight, B-FOBT-1,4-E with 4-OCH3-5-F-BT as A unit shows the lowest hydrogen release energy barrier at 1.54 eV among all the cases, thus it


5


Page 6 of 17

should be the most promising candidate for photocatalytic H2 evolution.

Figure 2. (a) Structure of mono-hydrogenated B-BT-1,4-E, para and meta is nominated by its relative position to the hydrogenated nitrogen atom. (b-e) B-BT-1,4-E, p- B-FBT-1,4-E, m-BFBT-1,4-E, B-DFBT-1,4-E. Left: Transition state structure of H2 release. Right: HOMO of transition state structure. isovalue = 0.02. Inspired by theoretical predictions, non-fluorinated linear B-BT-1,4-E and three Fsubstituted B-FBT-1,4-E, B-DFBT-1,4-E and B-FOBT-1,4-E were synthesized according to the palladium catalyzed Sonogashira–Hagihara cross-coupling polycondensation (Figure 1a). In general, the mixture of two monomers, Pd(PPh3)2Cl2 and CuI in DMF/TEA was first degassed with Ar for 20 min and then stirred at 80 oC for 24 hours. The cooled mixture was filtered and washed thoroughly with methanol and CH2Cl2 in the Soxhlet for 48 hours, and the final product was dried at 60 oC overnight. More synthetic details are described in the supporting information, and it should be noted that all the as-prepared polymers are completely insoluble in all solvents


6

Page 7 of 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

ACS Energy Letters

investigated. As shown in Figure 3a, the structures are first characterized by solid-stated

13

C

cross cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance spectra (NMR). The main peaks at ≈ 96 ppm and 87 ppm and are identified to be C4 and C5 of the C≡C- group, respectively. Specifically, peaks at ≈ 153 ppm are assigned to C1, and the peaks for other aromatic carbons could be found ranging from 116 ppm to 132 ppm. In addition, the Fourier transform infrared (FT-IR) spectra for all the polymers reveal the characteristic signals of the C≡C group at around 2205 cm-1 (Figure S1). In compared to B-BT-1,4-E, new signals at around 1380 cm-1 in B-FBT-1,4-E, B-DFBT-1,4-E and B-FOBT-1,4-E can be assigned to C-F bonds, and C-O stretching bands of B-FOBT-1,4-E appears at 1200 cm-1. The Brunauer– Emmett–Teller (BET) surface area of B-BT-1,4-E, B-FBT-1,4-E and B-DFBT-1,4-E are determined to be 66, 207, 233 m2 g-1 respectively, and it indicates that sequential fluorination results in remarkable increase of surface areas (Figure S2). However, introduction of OCH3 reduces the surface area of B-FOBT-1,4-E to 58 m2 g-1, and pore volumes vary from 0.102 to 0.360 cm3 g-1 (Figure S3). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images illustrate change of the morphology (Figure S4 and Figure S5), and all the conjugated polymers show amorphous properties by power X-ray diffraction (PXRD, Figure S6). In addition, thermal gravimetric analysis (TGA) reveals their excellent stability up to 350 oC in air condition (Figure S7).


7


Page 8 of 17

Figure 3. (a) Solid-state 13C CP/MAS NMR spectra, and asterisks denote spinning sidebands. (b) UV–vis diffuse reflectance spectra (DRS) of linear polymers. The impact of fluorination on optical absorption properties is investigated by UV–vis diffuse reflectance spectra (DRS), and all of the polymers show broad light absorption spectra (Figure 3b). There only exists slight change among B-BT-1,4-E, B-FBT-1,4-E, B-DFBT-1,4-E, but B-FOBT-1,4-E has lower visible light absorption ability. The optical bandgaps (Eg) of B-BT1,4-E, B-FBT-1,4-E, B-DFBT-1,4-E and B-FOBT-1,4-E are determined to be 2.14 eV, 2.12 eV, 2.12 eV and 2.18 eV (Table 1) according to Kubelka–Munk function, respectively. The HOMO levels are estimated by cyclic voltammetry (CV) curves (Figure S8 and Figure S9), and then LUMO levels are further calculated by CV and Eg. It can be seen that sequential fluorination gradually downshifts the HOMO and LUMO levels simultaneously due to strong inductive electron-withdrawing property of F substituents, while B-FOBT-1,4-E exhibits higher lying HOMO level than B-DFBT-1,4-E due to less electron-deficiency of F- and CH3O- substituted BT.38 The changing trends of HOMO and LUMO levels by sequential fluorination are also confirmed by DFT calculation (Figure S10). Therefore, the fluorination of D-A conjugated polymers definitely provides an effective strategy for optimizing the photoredox potentials. Table 1. Basic optical, energy band levels and H2 production properties of polymers. Polymer

a)

B-BT-1,4-E B-FBT-1,4-E B-DFBT-1,4-E B-FOBT-1,4-E B-BT-1,3,5-E B-FBT-1,3,5-E B-DFBT-1,3,5-E B-FOBT-1,3,5-E

HOMO a) (eV) -5.87 -6.03 -6.07 -5.83 -6.24 -6.31 -6.40 -6.29

LUMO b) (eV) -3.73 -3.91 -3.95 -3.65 -3.78 -3.84 -4.00 -3.88 b)

Eg c) (eV) 2.14 2.12 2.12 2.18 2.46 2.47 2.40 2.41

HER d) (µmol h-1) 128 313 207 399 10 165 120 288

AQY d) (%) 0.85 2.3 1.3 5.7 0.07 0.8 0.5 1.8 Eg; c)Determined

Determined from cyclic voltammetry (CV); HOMO = LUMO by the absorption onset of from DRS spectra; d) conditions: 30 mg polymer, 30 mL 10% vol TEOA/H2O, λ > 420 nm or = 420 nm. Following the successful preparation of conjugated polymers, the photocatalytic hydrogen evolution activity are measured in a Pyrex top-irradiation reaction vessel connected to a closed


8

Page 9 of 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

ACS Energy Letters

gas system. In details, 30 mg polymer was dispersed in 30 mL aquous solution containing 3 mL TEOA as the sacrificial electron donor, and air was thoroughly removed by repeating degassing procedure. The 300 W Xe lamp (PLS SXE300, Beijing Perfectlight Inc., China) equipped with a 420 nm cut-off filter is used as light source, and HER was determined by gas chromatograph. As a result, HER of mono-fluorinated B-FBT-1,4-E is determined to be 327 µmol h-1, which is 2.6 times higher than that of nonfluorinated B-BT-1,4-E (Figure 4a). The second introduction of F atom decreases HER of B-FBT-1,4-E to 214 µmol h-1, and then it is not surprising that B-FOBT1,4-E exhibits the highest HER of 399 µmol h-1 (Table 1). Therefore, it is reasonable that photocatalytic H2 evolution process here follows the PCET mechanism based on the good correlation between experimental results and theoretical prediction. Subsequently, AQY measurement against light wavelength reveals that B-FOBT-1,4-E shows a broad light response region (Figure 4b). It renders an AQY of 5.7% at 420 nm, which is among the highest values for polymer photocatalyts, and an unprecedented AQY of 1.3% at 500 nm has also been achieved (Table S2). Moreover, the photostability of the fluorinated conjugated polymers is confirmed by running long-term H2 evolution experiments. As displayed in Figure 4c, steady HER could be observed for B-FOBT-1,4-E after 4 cycles over 20 hours without any obvious decay. FTIR and SEM of the recycled sample show structural preservation (Figure S11and Figure S12). Subsequently, same strategy is also applied into the structural modulation of microporous B-BT-1,3,5-E, and three F-substituted polymers B-FBT-1,3,5-E, B-DFBT-1,3,5-E and B-FOBT1,3,5-E are synthesized. The structures of the four new polymers are first characterized by

13

C

CP/MAS NMR, FTIR, DRS, TEM, SEM, PXRD and TGA (Figure S13 to Figure S23), and sequential fluorination of the microporous B-BT-1,3,5-E has similar impact on bandgap and HOMO/LUMO energy levels to the previous linear counterpart. As shown in Table 1 and Figure


9


Page 10 of 17

S24, monofluorination results in dramatic HER from 10 µmol h-1 to 165 µmol h-1. The second fluorination reduces the HER of B-DFBT-1,3,5-E to 120 µmol h-1, meanwhile, B-FOBT-1,3,5-E exhibits highest HER at 288 µmol h-1 which is 28.8 times higher than B-BT-1,3,5-E. Therefore, similar PCET mechanism may also be utilized to explain the light-driven H2 evolution process due to same alternating D and A units.

Figure 4. (a) Photocatalytic H2 evolution of linear polymers; (b) AQY values light wavelength of B-FOBT-1,4-E; (c) Long-term test of B-FOBT-1,4-E in 20 hours; (d) Transient photocurrent response of linear polymers. In order to gain insight into the influence of F substitution on the photogenerated transfer efficiency in the PCET process, the transient photocurrent response under visible light irradiation is compared. As shown in Figure 4d and Figure S25, the trend of generated photocurrent intensity for linear and microporous D-A conjugated polymers follows the order which is consistent with the photocatalytic HER. It is noteworthy that all the conjugated polymers


10

Page 11 of 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

ACS Energy Letters

exhibited photocatalytic H2 evolution ability without additional Pt as cocatalyst, but residual Pd may also act as a cocatalyst at low threshold.11 In our designed conjugated polymers, the residual Pd contents vary between 0.3% and 0.5% via inductively coupled plasma-mass spectrometry (ICP-MS), and linear B-FOBT-1,4-E with the highest HER contained the lowest Pd content at 0.3%. As discussed, F incorporation has no obvious impact on the light harvest ability, and BFOBT-1,4-E with the highest HER has smaller surface area than B-FBT-1,4-E and B-DFBT-1,4E. With regard to photocatalytic process, the stronger active site N and accelerated charge transfer by incorporation of F in the polymers are the dominating factors to enhance the photocatalytic activity. In conclusion, sequential fluorination of linear D-A conjugated polymer led to regular change of barrier activation energy of H2 formation by DFT calculation, and theoretical models indicates that the light driven H2 release process follows typical PCET facilitated route. Photocatalytic H2 evolution activity of the as-prepared linear and microporous polymers follows the same trend of predicted activation energy change. The novel B-FOBT-1,4-E exhibits 3.1 times higher HER (399 µmol h-1) than nonfluorinated B-BT-1,4-E with a record AQY of 5.7% at 420 nm, and HER of B-FOBT-1,3,5-E is also increased by 28.8 times. Moreover, a strong relationship between degree of fluorination and charge mobility was verified by photocurrent measurement. Therefore, F substitution proves to be an effective method to enhance the photocatalytic activity of D-A conjugated polymers in terms of enhanced active sites and accelerated charge transfer, and PCET mechanism is first utilized to explain the photocatalytic H2 evolution process of conjugated polymers. This study provides a simple but very attractive manner to rationally modulate structure of D-A conjugated polymers based on the DFT calculation.


11


Page 12 of 17

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXXX. Experimental methods, details on material synthesis and characterization, NMR spectra, FTIR, UV–vis diffuse reflectance spectra (DRS), powder X-ray diffraction measurements, elemental analysis, thermogravimetric analysis, gas sorption properties, CV measurements, Nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and theoretical calculations. Notes The authors declare no competing financial interest. Author Contributions §

Y.-G.X., X.-P.W. and L.R. contributed equally to this work.

ACKNOWLEDGMENT The research was financially supported by the National Natural Science Foundation of China (51572101 and 51802107), and the Fundamental Research Funds for the Central Universities (2662017JC021, 2662015PY047 and 2662016PY088). Reference: (1)

Kang, H.; Lee, W.; Oh, J.; Kim, T.; Lee, C.; Kim, B. J. From Fullerene-Polymer to All-

Polymer Solar Cells: The Importance of Molecular Packing, Orientation, and Morphology Control. Acc. Chem. Res. 2016, 49, 2424-2434. (2)

Benten, H.; Mori, D.; Ohkita, H.; Ito, S. Recent Research Progress of Polymer

Donor/Polymer Acceptor Blend Solar Cells. J. Mater. Chem. A 2016, 4, 5340-5365. (3)

Liu, C.; Wang, K.; Gong, X.; Heeger, A. J. Low Bandgap Semiconducting Polymers for


12

Page 13 of 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

ACS Energy Letters

Polymeric Photovoltaics. Chem. Soc. Rev. 2016, 45, 4825-4846. (4)

Jin, Y.; Chen, Z.; Dong, S.; Zheng, N.; Ying, L.; Jiang, X.-F.; Liu, F.; Huang, F.; Cao, Y.

A Novel Naphtho [1,2-c:5,6-c'] Bis(1,2,5 Thiadiazole)-Based Narrow-Bandgap π-Conjugated Polymer with Power Conversion Efficiency Over 10%. Adv. Mater. 2016, 28, 9811-9818. (5)

Sprick, R. S.; Jiang, J. X.; Bonillo, B.; Ren, S. J.; Ratvijitvech, T.; Guiglion, P.;

Zwijnenburg, M. A.; Adams, D. J.; Cooper, A. I. Tunable Organic Photocatalysts for VisibleLight-Driven Hydrogen Evolution. J. Am. Chem. Soc. 2015, 137, 3265-3270. (6)

Yu, Y.; Yan, W.; Wang, X. F.; Li, P.; Gao, W. Y.; Zou, H. H.; Wu, S. M.; Ding, K. J.

Surface Engineering for Extremely Enhanced Charge Separation and Photocatalytic Hydrogen Evolution on g-C3N4. Adv. Mater. 2018, 30, 1705060. (7)

Meng, N. N.; Ren, J.; Liu, Y.; Huang, Y.; Petit, T.; Zhang, B. Engineering Oxygen-

Containing and Amino Groups into Two-Dimensional Atomically-Thin Porous Polymeric Carbon Nitrogen for Enhanced Photocatalytic Hydrogen Production. Energy Environ. Sci. 2018, 11, 566-571. (8)

Kong, L.; Ji, Y.; Dang, Z.; Yan, J.; Li, P.; Li, Y.; Liu, S. g‐C3N4 Loading Black

Phosphorus Quantum Dot for Efficient and Stable Photocatalytic H2 Generation under Visible Light. Adv. Funct. Mater. 2018, 28, 1800668. (9)

Cao, S. W.; Low, J. X.; Yu, J. G.; Jaroniec, M. Polymeric Photocatalysts Based on

Graphitic Carbon Nitride. Adv. Mater. 2015, 27, 2150-2176. (10)

Yanagida, S.; Kabumoto, A.; Mizumoto, K.; Pac, C.; Yoshino, K. Poly(p-phenylene)-

Catalysed Photoreduction of Water to Hydrogen. J. Chem. Soc., Chem. Commun. 1985, 0, 474475. (11)

Li, L. W.; Cai, Z. X.; Wu, Q. H.; Lo, W. Y.; Zhang, N.; Chen, L. X.; Yu, L. P. Rational


13


Page 14 of 17

Design of Porous Conjugated Polymers and Roles of Residual Palladium for Photocatalytic Hydrogen Production. J. Am. Chem. Soc. 2016, 138, 7681-7686. (12)

Sprick, R. S.; Bonillo, B.; Clowes, R.; Guiglion, P.; Brownbill, N. J.; Slater, B. J.; Blanc,

F.; Zwijnenburg, M. A.; Adams, D. J.; Cooper, A. I. Visible-Light-Driven Hydrogen Evolution Using Planarized Conjugated Polymer Photocatalysts. Angew. Chem. Int. Ed. 2016, 55, 18241828. (13)

Yang, C.; Ma, B. C.; Zhang, L. Z.; Lin, S.; Ghasimi, S.; Landfester, K.; Zhang, K. A. I.;

Wang, X. C. Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis. Angew. Chem. Int. Ed. 2016, 55, 9202-9206. (14)

Bi, S.; Lan, Z.-A.; Paasch, S.; Zhang, W.; He, Y.; Zhang, C.; Liu, F.; Wu, D.; Zhuang,

X.; Brunner, E., et al. Substantial Cyano-Substituted Fully sp2-Carbon-Linked Framework: Metal-Free Approach and Visible-Light-Driven Hydrogen Evolution. Adv. Funct. Mater. 2017, 27, 1703146. (15)

Woods, D. J.; Sprick, R. S.; Smith, C. L.; Cowan, A. J.; Cooper, A. I. A Solution-

Processable Polymer Photocatalyst for Hydrogen Evolution from Water. Adv. Energy Mater. 2017, 7, 1700479. (16)

Wang, L.; Wan, Y. Y.; Ding, Y. J.; Wu, S. K.; Zhang, Y.; Zhang, X. L.; Zhang, G. Q.;

Xiong, Y. J.; Wu, X. J.; Yang, J. L., et al. Conjugated Microporous Polymer Nanosheets for Overall Water Splitting Using Visible Light. Adv. Mater. 2017, 29, 1702428. (17)

Wang, L.; Zheng, X.; Chen, L.; Xiong, Y.; Xu, H. Van der Waals Heterostructures

Stacked by Ultrathin Polymer Nanosheets for Efficient Z-Scheme Overall Water Splitting. Angew. Chem. Int. Ed. 2018, 57, 3454-3458. (18)

Zhang, G. G.; Lan, Z. A.; Wang, X. C. Conjugated Polymers: Catalysts for Photocatalytic


14

Page 15 of 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

ACS Energy Letters

Hydrogen Evolution. Angew. Chem. Int. Ed. 2016, 55, 15712-15727. (19)

Xu, Y. F.; Mao, N.; Zhang, C.; Wang, X.; Zeng, J. H.; Chen, Y.; Wang, F.; Jiang, J. X.

Rational Design of Donor-π-Acceptor Conjugated Microporous Polymers for Photocatalytic Hydrogen Production. Appl. Catal. B: Environ. 2018, 228, 1-9. (20)

Eom, Y. K.; Nhon, L.; Leem, G.; Sherman, B. D.; Wang, D.; Troian-Gautier, L.; Kim, S.;

Kim, J.; Meyer, T. J.; Reynolds, J. R., et al. Visible-Light-Driven Photocatalytic Water Oxidation by a π-Conjugated Donor–Acceptor–Donor Chromophore/Catalyst Assembly. ACS Energy Letters 2018, 2114-2119. (21)

Jung, J. W.; Liu, F.; Russell, T. P.; Jo, W. H. Medium Bandgap Conjugated Polymer for

High Performance Polymer Solar Cells Exceeding 9% Power Conversion Efficiency. Adv. Mater. 2015, 27, 7462-7468. (22)

Yao, H.; Li, Y.; Hu, H.; Chow, P. C. Y.; Chen, S.; Zhao, J.; Li, Z.; Carpenter, J. H.; Lai,

J. Y. L.; Yang, G., et al. A Facile Method to Fine-Tune Polymer Aggregation Properties and Blend Morphology of Polymer Solar Cells Using Donor Polymers with Randomly Distributed Alkyl Chains. Adv. Energy Mater. 2017, 7, 1701895. (23)

Kranthiraja, K.; Kim, S.; Lee, C.; Gunasekar, K.; Sree, V. G.; Gautam, B.; Gundogdu, K.;

Jin, S. H.; Kim, B. J. The Impact of Sequential Fluorination of π-Conjugated Polymers on Charge Generation in All-Polymer Solar Cells. Adv. Funct. Mater. 2017, 27, 1701256. (24)

Jo, J. W.; Jung, J. W.; Jung, E. H.; Ahn, H.; Shin, T. J.; Jo, W. H. Fluorination on Both D

and A Units in D-A Type Conjugated Copolymers Based on Difluorobithiophene and Benzothiadiazole for Highly Efficient Polymer Solar Cells. Energy Environ. Sci. 2015, 8, 24272434. (25)

Lee, J.; Byranyand, M. M.; Kang, G.; Son, S. Y.; Song, S.; Kim, G. W.; Park, T. Green-


15


Page 16 of 17

Solvent-Processable, Dopant-Free Hole-Transporting Materials for Robust and Efficient Perovskite Solar Cells. J. Am. Chem. Soc. 2017, 139, 12175-12181. (26)

Xiang, Y. G.; Wang, X. P.; Zhang, X. H.; Hou, H. J.; Dai, K.; Huang, Q. Y.; Chen, H.

Enhanced Visible Light Photocatalytic Activity of TiO2 Assisted by Organic Semiconductors: A Structure Optimization Strategy of Conjugated Polymers. J. Mater. Chem. A 2018, 6, 153-159. (27)

Zhang, X. H.; Wang, X. P.; Xiao, J.; Wang, S. Y.; Huang, D. K.; Ding, X.; Xiang, Y. G.;

Chen, H. Synthesis of 1,4-Diethynylbenzene-Based Conjugated Polymer Photocatalysts and Their Enhanced Visible/Near-Infrared-Light-Driven Hydrogen Production Activity. J. Catal. 2017, 350, 64-71. (28)

Hou, H. J.; Zhang, X. H.; Huang, D. K.; Ding, X.; Wang, S. Y.; Yang, X. L.; Li, S. Q.;

Xiang, Y. G.; Chen, H. Conjugated Microporous Poly(benzothiadiazole)/TiO2 Heterojunction for Visible-Light-Driven H2 Production and Pollutant Removal. Appl. Catal. B: Environ. 2017, 203, 563-571. (29)

Wang, L.; Fernández-Terán, R.; Zhang, L.; Fernandes, D. L. A.; Tian, L.; Chen, H.; Tian,

H. Organic Polymer Dots as Photocatalysts for Visible Light-Driven Hydrogen Generation. Angew. Chem. Int. Ed. 2016, 128, 12494-12498. (30)

Pati, P. B.; Damas, G.; Tian, L.; Fernandes, D. L. A.; Zhang, L.; Pehlivan, I. B.;

Edvinsson, T.; Araujo, C. M.; Tian, H. An Experimental and Theoretical Study of an Efficient Polymer Nano-Photocatalyst for Hydrogen Evolution. Energy Environ. Sci. 2017, 1372-1376. (31)

Chai, J. D.; Head-Gordon, M. Long-Range Corrected Hybrid Density Functionals with

Damped Atom-Atom Dispersion Corrections. Phys. Chem. Chem. Phys. 2008, 10, 6615-6620. (32)

Rao, L.; Xu, X.; Adamo, C. Theoretical Investigation on the Role of the Central Carbon

Atom and Close Protein Environment on the Nitrogen Reduction in Mo Nitrogenase. ACS Catal.


16

Page 17 of 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

ACS Energy Letters

2016, 6, 1567-1577. (33)

Magnuson, A.; Anderlund, M.; Johansson, O.; Lindblad, P.; Lomoth, R.; Polivka, T.; Ott,

S.; Stensjo, K.; Styring, S.; Sundstrom, V., et al. Biomimetic and Microbial Approaches to Solar Fuel Generation. Acc. Chem. Res. 2009, 42, 1899-1909. (34)

Chang, X. X.; Wang, T.; Gong, J. L. CO2 Photo-Reduction: Insights into CO2 Activation

and Reaction on Surfaces of Photocatalysts. Energy Environ. Sci. 2016, 9, 2177-2196. (35)

Weinberg, D. R.; Gagliardi, C. J.; Hull, J. F.; Murphy, C. F.; Kent, C. A.; Westlake, B.

C.; Paul, A.; Ess, D. H.; McCafferty, D. G.; Meyer, T. J. Proton-Coupled Electron Transfer. Chem. Rev. 2012, 112, 4016-4093. (36)

Hammarstrom, L.; Styring, S. Proton-Coupled Electron Transfer of Tyrosines in

Photosystem II and Model Systems for Artificial Photosynthesis: the Role of a Redox-Active Link Between Catalyst and Photosensitizer. Energy Environ. Sci. 2011, 4, 2379-2388. (37)

Yuan, W.; Zhou, Z. J.; Gong, L.; Meggers, E. Asymmetric Alkylation of Remote C(sp3)-

H bonds by Combining Proton-Coupled Electron Transfer with Chiral Lewis Acid Catalysis. Chem. Commun. 2017, 53, 8964-8967. (38)

Jung, J. W.; Liu, F.; Russell, T. P.; Jo, W. H. Anthracene-Based Medium Bandgap

Conjugated Polymers for High Performance Polymer Solar Cells Exceeding 8% PCE Without Additive and Annealing Process. Adv. Energy Mater. 2015, 5, 1500065.


17

Conjugated Polymers with Sequential Fluorination for Enhanced

Recommend Documents