Design and Synthesis of Cycloplatinated Polymer Dots as

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Design and Synthesis of Cycloplatinated Polymer Dots as Photocatalysts for Visible Light–Driven Hydrogen Evolution Po-Jung Tseng, Chih-Li Chang, Yang-Hsiang Chan, Li-Yu Ting, Pei-Yu Chen, Chia-Hsien Liao, Ming-Li Tsai, and Ho-Hsiu Chou ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b01678 • Publication Date (Web): 13 Jul 2018 Downloaded from http://pubs.acs.org on July 13, 2018

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ACS Catalysis

Design and Synthesis of Cycloplatinated Polymer Dots as Photocatalysts for Visible Light–Driven Hydrogen Evolution Po-Jung Tsenga,‡, Chih-Li Changa,b,‡, Yang-Hsiang Chana, Li-Yu Tingb, Pei-Yu Chenb, Chia-Hsien Liaoa, Ming-Li Tsaia, and Ho-Hsiu Choub,*

‡

a

These authors contributed equally to this work

P.-J. Tseng, C.-L. Chang, Prof. Y.-H. Chan, C.-H. Liao, Prof. M.-L. Tsai

Department of Chemistry, National Sun Yat-sen University No. 70, Lienhai Rd., Kaohsiung 80424, Taiwan

b

C.-L. Chang, L.-Y. Ting, P.-Y. Chen, Prof. H.-H. Chou

Department of Chemical Engineering, National Tsing Hua University No. 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan

*Corresponding author. E-mail: [email protected]

ACS Paragon Plus Environment

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Abstract

By mimicking natural photosynthesis, generating hydrogen through visible light–driven splitting of water would be an almost ideal process for converting abundant solar energy into a useable fuel in an environmentally friendly and high-energy-density manner. In a search for efficient photocatalysts that mimic such a function, here we describe a series of cycloplatinated polymer dots (Pdots), in which the platinum complex unit is pre-synthesized as a co-monomer and then covalently linked to a conjugated polymer backbone through Suzuki–Miyaura cross-coupling polymerization. Based on our design strategy, the hydrogen evolution rate (HER) of the cycloplatinated Pdots can be enhanced 12-times higher than that of pristine Pdots under otherwise identical conditions. Compared to the Pt complex blended-counterpart Pdots, the HER of cycloplatinated Pdots still exhibit over 2-times higher than that of physically blended one. Furthermore, the enhancement of the photocatalytic reaction time with high eventual hydrogen productions, and low efficiency roll-off are observed by utilizing the cycloplatinated Pdots as photocatalysts. Based on the exceptional performance, our cyclometallic Pdot systems appear to be a new type of promising photocatalysts for visible light–driven hydrogen evolution.

Keywords Semiconducting polymers, Polymer dots, Photocatalysts, Visible light, Hydrogen evolution


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Introduction Converting abundant solar energy into chemical energy is one of the most promising

approaches for future energy production. Developing efficient visible light–driven photocatalytic systems that generate hydrogen from water, an earth-abundant source, should lead to many applications of this clean and renewable fuel. Although inorganic semiconductors have been used more widely for photocatalytic hydrogen evolution,1–5 organic photocatalytic semiconductors have recently gained enormous attention because of their capability for diverse molecular modification, tunable band gaps, and tailorable properties upon selecting appropriate donor and acceptor units. In 2009, Antonietti and coworkers reported the first example of a graphitic carbon nitride (gC3N4) as an organic photocatalyst for hydrogen production.6 Although the photocatalytic ability of g-C3N4 itself is poor, it can be improved significantly upon adding platinum nanoparticles as cocatalysts.7 Several organic semiconducting polymers have been investigated as potentially promising

photocatalysts

for

hydrogen

evolution,

including

poly(p-phenylene),8–10

polyazomethine,11 poly(2,2´-bipyridine),12,13 polytriazine,14 polyheptazine,15,16 polyhydrazine,17 polypyrene,18 polybenzothiadiazoles,19,20 and poly[(9H-carbazole-2,7-diyl)-1,4-phenylene].21 Because pristine organic semiconducting polymers are generally insoluble in water, organic solvents are necessary to increase their dispersibility in the reaction phase.19 Most recently, Tian and coworkers reported an efficient approach for dramatically improving the photocatalytic performance without using organic solvents by incorporating polymer dots (Pdots).22,23 Their PFBT and PFODTBT Pdots displayed impressive hydrogen evolution rates (HERs) of 8.3 and 50 mmol h–1 g–1, respectively, providing the significant enhancements in HERs over those of the pristine polymers. We considered that Pdots are particularly attractive as photocatalysts because of their highly efficient HERs, excellent water dispersibility (organic solvent free), facile structural


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modification, tunable semiconductor properties, and suitability for visible light–driven processes. However, the PFBT and PFODTBT Pdots performed their photocatalytic functions for approximately 80 min and 4 h, respectively,22,23 with high efficiency roll-offs. The Pdots with high long-term photocatalytic reaction and low HER roll-offs, has yet to be demonstrated. Thus, we aim to develop new types Pdot-based platforms to enhance their utility as efficient and long photocatalytic function. Additionally, many research reports have noted that platinum nanoparticles or platinum(II) chloride can enhance the performance of hydrogen evolution.24–26 Even though the platinum has been applied widely in cocatalytic systems, typically the approach has been to directly add the platinum nanoparticles into the solution system. However, this approach cannot easily control the interaction between the Pt and semiconducting polymer. Another physically blended strategy can simply form the metal and ligand coordination to enhance the HERs with uniformly loading the metal chloride onto the polymers.26–28 The platinum(II) chloride can be chelated to bipyridine-based conjugated polymers through coordinate bonds, whereas it might have the weaker chelating effect between the ligand and metal due to the use of coordinate bond, and the lower diversity of the chelating ligands—currently only the examples of bipyridyl ligand. Additionally, the platinum might merely be dispersed in the organic/water mixed solvent system, and the toxicity of the solution might be a concern.20 Previously, we developed various semiconducting Pdots for use as highly luminescent biofluorescent probes for bio-medical imaging.29-33 In this study, we presented a series of cycloplatinated Pdots as promising photocatalysts for visible light-driven hydrogen evolution. To accomplish this work, we synthesized two different cycloplatinated complexes in which a Pt(C^N) chromophore was chelated with an O^O diketonate ligand for use as a co-monomer in subsequent polymerization34 This design strategy has flexibility in terms of tuning the photophysical


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properties of the polymers simply by varying the structure and ratio of the Pt-ligand chromophore. Importantly, the C^N ligand and Pt atom are linked by covalent bonds, providing a stronger chelating effect that mitigates bond dissociation between the metal and ligand, relative to that of ligands binding the metal through coordinate bonds. These Pt-based semiconducting polymers were then further transformed into cycloplatinated Pdots. Therefore, the Pt complex was introduced within the Pdots and was covered by the PS-PEG-COOH, considering the enhancement of performance of hydrogen evolution without increasing the toxicity of the solution system. Optimizing the content of Pt complexes allowed us to enhance the photocatalytic performance of the cycloplatinated Pdots as photocatalysts for hydrogen evolution.

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Results and Discussion We selected the polymer PFTFQ (poly[(9,9’-dioctylfluorenyl-2,7-diyl)-co-(6,7-difluoro-2,3-

bis(3-(hexyloxy)phenyl)-5,8-di(thiophen-2-yl)quinoxaline)]) as a starting point because we have demonstrated previously that PFTFQ Pdots have strong absorption in the visible region.31 Accordingly, we synthesized two series of conjugated cycloplatinated polymers through Suzuki– Miyaura coupling polymerizations of PF (2,7-dibromo-9,9’-dioctyl-9H-fluorene) and TFQ (5,8bis(5-bromothiophen-2-yl)-6,7-difluoro-2,3-bis(3-(hexyloxy)phenyl)-quinoxaline)

with

either

PtPy

(platinum(II)(5-bromo-2-(5-bromothiophen-2-yl)pyridinato-N,C3’)(2,4-pentane-dionato-

O,O))

or

PtIq

(platinum(II)(4-bromo-1-(5-bromothiophen-2-yl)isoquinolinato-N,C3’)(2,4-

pentanedionato-O,O)) as the co-monomer (Scheme S1). The bulky TFQ co-monomer is introduced to provide the large steric hindrance to reduce the phenomenon of aggregation during the photocatalytic process. These two Pt complexes were covalently linked to the PFTFQ conjugated polymer backbone at various ratios (5, 15, and 25 mol%), providing six polymers, designated


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PFTFQ-PtPy5, PFTFQ-PtPy15, PFTFQ-PtPy25, PFTFQ-PtIq5, PFTFQ-PtIq15, and PFTFQPtIq25, respectively (Figure 1). Pdots PFTFQ-PtPy H2

𝒆"

H+

LUMO ~2.03eV

𝒆"

SA HOMO

SA+ 𝒆"

PFTFQ-PtIq

=

MeOH free

Figure 1. Schematic diagram of the structure and preparation of PFTFQ-PtPy- and PFTFQ-PtIqbased Pdots for visible light-driven hydrogen evolution. Gel permeation chromatography (GPC) revealed that the molecular weights of the designed polymers decreased upon increasing the ratio of the Pt complex. Thermogravimetric analysis (TGA) revealed that these cycloplatinated polymers had good thermal stability, with decomposition temperatures of greater than 340 °C (Table S1 & Figure S1). The preparation of these cycloplatinated Pdots was followed by our previous procedure,29–33 and was described in Supporting Information. Dynamic light scattering (DLS) revealed that the hydrodynamic diameter of these Pdots is in the range from 40 to 80 nm (Table S1, Figure 2 & S2). Importantly, to prove the Pt was contained in the cycloplatinated Pdots, the transmission electron microscopy (TEM)


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and energy-dispersive X-ray (EDX) measurements were provided. As shown in Figure 2 & S3, indeed the Pt atom was observed in the cycloplatinated Pdots, rather than in the PFTFQ Pdots. As a result, the first Pt-contained Pdots were obtained and demonstrated by our design strategy. The final amounts of the polymers in the cycloplatinated Pdot solutions were determined from UV– Vis spectroscopy, after removing the water and re-dissolving the residue in THF (Figure S4). PFTFQ Pdots

Number (Percent)

PFTFQ Pdots

20

10

0 10

50 nm

100

Size (d.nm) PFTFQ-PtPy15 Pdots

Number (Percent)

PFTFQ-PtPy15 Pdots

20

10

0 10

50 nm

100

Size (d.nm)

PFTFQ-PtIq15 Pdots

PFTFQ-PtIq15 Pdots

Number (Percent)

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

20

10

0 10

50 nm

100

Size (d.nm)

Figure 2. TEM (left), EDX (middle), and hydrodynamic diameter (right) spectra of PFTFQ, PFTFQP-PtPy15, and PFTFQ-PtIq15 Pdots. Figure 3a presents the UV–Vis absorption and photoluminescence spectra, and Table 1 and Table S1 summarize the photophysical properties of these Pdots. The absorption spectra of these cycloplatinated Pdots were similar to those of our previous PFTFQ Pdots,31 with two characteristic absorption bands near 380 and 515 nm. We assign the higher-energy absorption band to π–π* transitions from the PF units, and the longer-wavelength absorption band to intramolecular charge


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transfer from the PF units to the TFQ and Pt monomer moieties. The formation of Pdots resulted in slight red-shifting of the signals in the absorption spectra as compared with those of the pristine polymers (Figure S5), suggesting the aggregation of formed Pdots. The optical bandgap (Eg) of these Pdots were in the range of 2.01–2.03 eV. Such low values of Eg should be beneficial for photocatalysis from the point of view of light-harvesting. As evidenced by the photophysical properties of these Pdots, we observed no obvious differences in the LUMO/HOMO positions and optical bandgaps, suggesting that the optical absorption would not affect the catalytic efficiencies of the Pdots significantly. Interestingly, the emissions of these cycloplatinated Pdots exhibited slight red-shifts leading to larger Stokes shift relative to that of the PFTFQ Pdots (Table S1). We considered it is because the emission of these two Pt complex monomers (590, 685 nm) are more red-shifted compare to the emission of TFQ monomer (550 nm). Next, we examined the Pdots as photocatalysts for visible light–driven hydrogen evolution. A light emitting diode (LED) PAR30 lamp (20 W, 6500 K, λ > 420 nm) was used as the light source, and the emission spectrum of the LED lamp was exhibited in Figure S6a. Figure S7 displays the optimized amount of the polymer in the Pdot solution in water, and the effects of various sacrificial electron donors. Importantly, Figure S7c also demonstrated the linearity of the hydrogen production rate versus the amount of catalyst in our Pdots system. We eventually chose diethylamine (DEA) as the sacrificial electron donor (pH = 11). Additionally, we recorded the kinetic curve of hydrogen evolution of the most efficient PFTFQ-PtPy15 Pdots to confirm the photocatalytic process of the Pdots with DEA in water. Figure 3b reveals that the kinetic curve of the photocatalytic process was decreased promptly when the light was switched off, and again increased abruptly when the light switched on. This result presented a strong evidence to prove the


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photocatalytic reaction in our system. In addition, from two control experiments, each component exhibited no activity under otherwise identical conditions.

b)60

PFTFQ Pdots PFTFQ-PtIq5 Pdots PFTFQ-PtIq15 Pdots PFTFQ-PtIq25 Pdots

PFTFQ-PtPy15 Pdots + DEA + light PFTFQ-PtPy15 Pdots + light

50

H2 (mmol/g)

PFTFQ Pdots PFTFQ-PtPy5 Pdots PFTFQ-PtPy15 Pdots PFTFQ-PtPy25 Pdots

Normalized Emission

a) Absorption

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

DEA + water + light

40 30

20 10

0 400

500

600

700

Wavelength (nm)

800

0

2

4

6

8

10

Time (h)

Figure 3. a) Absorption (solid line) and emission (dotted line) spectra of the PFTFQ Pdots and the cycloplatinated Pdots in water. b) Different component systems of the light-driven hydrogen generation of PFTFQ-PtPy15 Pdots from water at ambient temperature by GC measurement. Figure 4a presents the HERs of these Pdots, measured using gas chromatography (GC). The HER was enhanced when up to 15 mol% of the Pt complex unit was linked to the backbone of the polymer conjugated. Indeed, the PFTFQ-PtPy15 Pdots provided an excellent HER of 12.7 ± 0.6 mmol h–1 g–1, approximately 12-times higher than that of PFTFQ Pdots (1.3 ± 0.1 mmol h–1 g–1) (Table 1). Surprisingly, when the ratio of Pt complex reached 25 mol%, the HER decreased to 7.7 ± 0.2 mmol h–1 g–1, presumably because of the saturation effect of the metal cocatalyst.35–37 The PFTFQ-PtIq15 Pdots also exhibited an excellent HER of 11.1 ± 0.3 mmol h–1 g–1. More Importantly, the 4-h average of the HERs of the PFTFQ-PtPy15 and PFTFQ-PtIq15 Pdots remained as high as 10.2 ± 0.3 and 9.3 ± 0.3 mmol h–1 g–1, respectively, from the first to the fifth hour; that is, the HER roll-offs in our Pdot systems were only approximately 16-19%. To the best of our knowledge, this is the lowest HER roll-off in the Pdots-based system so far. To further realized the capability of the Pdots under the weak acid condition, we used the ascorbic acid as the


9

ACS Catalysis

sacrificial electron donor (pH = 5.0, adjusted by 5 M NaOH(aq)) for photocatalytic reaction. As shown in Figure S8, the HER of PFTFQ Pdots and PFTFQ-PtPy15 Pdots using ascorbic acid is 0.94 and 6.91 mmol h–1 g–1, respectively. This result shows that the use of DEA as the sacrificial electron donor still has higher hydrogen evolution performance than that of ascorbic acid in our system. Importantly, the strong enhancement of the HER was still observed using our cycloplatianted Pdots compared to that of pristine Pdots in ascorbic acid system.

H2 (mmol/g)

50 40

30

b) 70

PFTFQ PFTFQ-PtPy5 PFTFQ-PtPy15 PFTFQ-PtPy25 PFTFQ-PtIq5 PFTFQ-PtIq15 PFTFQ-PtIq25

PFTFQ-PtPy15 PFTFQ-PtIq15

60

H2 (mmol/g)

a) 60

20 10

50 40 30 20 10

0

0 0

c) 60

1

2

3

4

Time (h)

5

2

4

d) Intensity (Counts)

PtPy-blended-counterpart PFTFQ Pdots

103

30

6

8

Time (h)

10

12

IRF PFTFQ Fit of PFTFQ PFTFQ-PtPy15 Fit of PFTFQ-PtPy15 PFTFQ-PtIq15 Fit of PFTFQ-PtIq15

104

PFTFQ-PtPy15 Pdots

40

0

6

PFTFQ Pdots

50

H2 (mmol/g)

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

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102

20

101

10 0 0

1

2

3

4

Time (h)

5

6

1

0

10

20

30

Time (ns)

Figure 4. a) Time course of produced H2 for PFTFQ Pdots, and the cycloplatinated Pdots. b) Time course of produced H2 for PFTFQ-PtPy15 and PFTFQ-PtIq15 Pdots for 12 hours. c) Comparison of hydrogen generation of chemically linked PFTFQ-PtPy15 pdots and physically PtPy-blendedcounterpart PFTFQ Pdots. d) Time-resolved fluorescence decay of IRF (black solid line), the PFTFQ Pdots and cycloplatinated Pdots. Notably, the 4-h average of the HERs of the PFTFQ-PtPy Pdot series were all slightly higher than those of the PFTFQ-PtIq Pdot series (Table 1). To better investigate this phenomenon, we


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ACS Catalysis

performed density functional theory (DFT) calculations (Figure S9). We found that the HOMOs of these polymers were delocalized to some extent over the conjugated systems, whereas the LUMOs were more localized over the TFQ, PtPy, and PtIq moieties. Accordingly, the dihedral angles between the 1-(thien-2-yl)isoquinoline and PF moieties of PFTFQ-PtIq (55.1°) were much greater than those between the 2-(thien-2-yl)pyridine and PF moieties of PFTFQ-PtPy (35.3°). The smaller dihedral angle in the PFTFQ-PtPy series suggests a more planarized polymer, with the higher HER attributed to the increased charge carrier mobility and a decreased Coulomb binding energy for dissociating electron/hole pairs and, hence, an enhancement in exciton dissociation yield.38–40 Notably, both the PFTFQ-PtPy15 and PFTFQ-PtIq15 Pdots displayed not only excellent HERs but also long-term photocatalytic reactions functioning for over 12 h with eventual hydrogen productions of 66.3 ± 1.0 and 59.8 ± 1.4 mmol g–1, respectively (Figure 4b). To the best of our knowledge, this PFTFQ-PtPy15 Pdot system presented the longest photocatalytic reaction time, which was three times longer than that of the previous Pdot systems for visible light-driven hydrogen evolution,21 with the highest eventual hydrogen productions in the Pdots system (Table S2). To illustrate the effect of the Pd introduced during the polymerization, we utilized ICP-MS to determine the residual Pd in these polymers. As shown in Table S1, the result showed that most of the residual Pd contents are in the ranges from 0.05-0.033%, while the PFTFQ-PtIq15 one is 0.126%, which is slightly higher than others. Notably, no obvious positive correlation is observed between the HER and residual Pd, considering the residual Pd has no significant effect on the hydrogen evolution. Notably, even though the Pt complexes were positioned within the Pdots and were covered by the copolymer PS-PEG-COOH, they could still serve as cocatalysts that dramatically enhanced the HER. The apparent quantum yield (AQY) of all of these Pdots were measured by the green laser at 515 nm (Figure S6b) and their AQY data were provided in Table


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S1. We found that the most efficient photocatalysts of both PFTFQ-PtPy15 and PFTFQ-PtIq15 Pdots could provide the highest AQY value of ca. 0.40%, which was about 10-times higher than that of PFTFQ Pdots, demonstrating that our design strategy can truly enhance the efficiency of hydrogen evolution. To further investigate the effect of the covalent linking of the Pt complexes to the backbone of the conjugated polymer PFTFQ, we simply added 15 mol% PtPy to the PFTFQ polymer to form the PtPy-blended-counterpart PFTFQ Pdots. Figure 4c reveals that the HER of the PtPy-blendedcounterpart PFTFQ Pdots was 5.46 mmol h-1 g-1—still higher than the HER of the PFTFQ Pdots alone, but less than half that of the PFTFQ-PtPy15 Pdots. Thus, the cycloplatinated Pdots, in which the chemically linking Pt complexes to the backbone of the semiconducting polymer, indeed dramatically improved the performance of hydrogen evolution, relative to the physical blended one. We suspect that electrons could undergo transport more smoothly through the polymer backbone to the Pt complex unit with this design strategy, leading to more efficient photoinduced charge separation, as well as an enhancement in the rate of the proton reduction reaction.41 In addition, because the outer surfaces of the Pt-based semiconducting polymers were covered by PS-PEG-COOH, the use of these cycloplatinated Pdots as photocatalysts can minimize the toxicity,28,30 relative to the approach that directly adding Pt nanoparticles into a solution system. To gain insight into the role of the cycloplatinated complex unit for electron transfer during the photocatalytic reaction, we recorded time-resolved transient photoluminescence decay spectra (Figure 4d). The lifetimes obtained when the Pdots contained the cycloplatinated complex units were shorter than those of the PFTFQ Pdot system, suggesting that the cycloplatinated complex units played the role of a cocatalyst lead that enhanced the charge transfer process. Surprisingly, PFTFQ-PtIq25 Pdot resulted in the fastest lifetimes, whereas the HER in this case was much lower


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ACS Catalysis

than that provided by the PFTFQ-PtPy25 Pdot. We suspect that this behavior arose because PFTFQ-PtIq25 polymer incorporating 25 mol% PtIq complex units had a molecular weight (ca. 9000 g mol–1) much lower than that of other Pdots (over 18,000 g mol–1). As a result, the amount of PF and TFQ units of PFTFQ-PtIq25 was less than that of other cycloplatinated Pdots, leading to lower activity of the catalyst.42

Table 1. Photophysical properties and HERs of various Pdots.

Absorption (nm)

HOMO (eV)a)

LUMO (eV)b)

Optical bandgap (eV)c)

Lifetime (ns)d)

AQY (%)e) at 515 nm

l > 420 nm

HER

(mmol h-1 g-1)f)

4-h average of HER (mmol h-1g-1)f)

PFTFQ

384, 517

-5.67

-3.64

2.03

1.57

0.04

1.3±0.1

1.1±0.1

PFTFQ-PtPy5

381, 516

-5.70

-3.68

2.02

0.90

0.02

4.1±0.1

3.5±0.1

PFTFQ-PtPy15

383, 509

-5.64

-3.61

2.03

0.79

0.40

12.7±0.6

10.2±0.3

PFTFQ-PtPy25

373, 496

-5.69

-3.67

2.02

0.67

0.09

7.7±0.2

4.9±0.5

PFTFQ-PtIq5

380, 512

-5.62

-3.61

2.01

0.89

0.05

4.2±0.1

3.2±0.1

PFTFQ-PtIq15

380, 519

-5.60

-3.59

2.01

0.67

0.42

11.1±0.3

9.3±0.3

PFTFQ-PtIq25

372, 504

-5.69

-3.66

2.03 b)

0.60

0.03

1.6±0.2

1.5±0.1

a)

Determined by photoelectron spectrometer. Derived by extracting the HOMO level from the optical bandgap. c)Calculated from the onset of absorption spectrum. d)Fluorescence lifetime. e) Apparent quantum yield is measured at 515 nm. f)Conditions: 10 mL diethylamine/Pdots solution (20 vol%), while LED light (l > 420 nm, 20W, 6500K).

n

Conclusion In summary, we have successfully demonstrated the cycloplatinated Pdots as efficient

photocatalysts for visible light-driven hydrogen evolution. This was accomplished via the introduction of Pt complex into the semiconducting polymer backbone through the covalent bonding. These Pt-based semiconducting polymers were then further transformed into cycloplatinated Pdots. After optimizing the ratio of the Pt complexes, the cycloplatinated Pdots provided impressive enhanced HERs compare to the pristine PFTFQ Pdots as well as the Pt


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complex blended-counterpart Pdots under otherwise identical conditions. More importantly, our molecular design strategy significantly improved the photocatalytic reactions functioning with high eventual hydrogen productions and low HER roll-off of the Pdot-based system. Furthermore, the use of these cycloplatinated Pdots as photocatalysts can minimize the toxicity of the solution system because the excellent water dispersibility (methanol free), and the Pt compelx is designed within the Pdot and was covered by the copolymer PS-PEG-COOH. We believe such cyclometallic Pdot systems will have promising applications in the generation of clean and renewable energy.

Supporting Information The supporting materials of polymer synthesis, photocatalytic method, optical and physical properties of polymers and Pdots, DLS, TEM, EDX spectra, quantity of Pdots analysis data, emission spectra of light source, and DFT calculations are available free of charge on the ACS Publication website http://pubs.acs.org.

Acknowledgements The authors gratefully acknowledge the financial support of the Ministry of Science and Technology of Taiwan (MOST 107-2636-E-007-001; MOST 106-2622-8-007-017), and also thank the National Center for High-Performance Computing of Taiwan for providing the computing time. The authors appreciate the Precision Instrument Support Center of National Tsing Hua University in providing the analysis and measurement facilities.


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AUTHOR INFORMATION Corresponding Author H.-H. Chou, *E-mail: [email protected]


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Table of Contents


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Design and Synthesis of Cycloplatinated Polymer Dots as

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