Synthesis, characterization, photophysical and photovoltaic properties of new donor–acceptor platinum(II) acetylide complexes

Accepted Manuscript Synthesis, characterization, photophysical and photovoltaic properties of new donor−acceptor platinum(II) acetylide complexes Dr. Qian Liu, Dr. Nianyong Zhu, Dr. Cheuk-Lam Ho, Yingying Fu, Wai-Sum Lau, Prof. Zhiyuan Xie, Prof. Lixiang Wang, Prof. Wai-Yeung Wong PII:

S0022-328X(15)30044-9

DOI:

10.1016/j.jorganchem.2015.06.017

Reference:

JOM 19119

To appear in:

Journal of Organometallic Chemistry

Received Date: 3 June 2015 Revised Date:

9 June 2015

Accepted Date: 10 June 2015

Please cite this article as: Q. Liu, N. Zhu, C.-L. Ho, Y. Fu, W.-S. Lau, Z. Xie, L. Wang, W.-Y. Wong, Synthesis, characterization, photophysical and photovoltaic properties of new donor−acceptor platinum(II) acetylide complexes, Journal of Organometallic Chemistry (2015), doi: 10.1016/ j.jorganchem.2015.06.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical abstract

new donor− −acceptor platinum(II) acetylide complexes

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Synthesis, characterization, photophysical and photovoltaic properties of

Qian Liu, Nianyong, Zhu, Cheuk-Lam Ho,* Yingying Fu, Wai-Sum Lau, Zhiyuan Xie,*

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Lixiang Wang, Wai-Yeung Wong*

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Six new solution-processable platinum(II) acetylide donor-acceptor (D-A) triads end-capped by 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were synthesized and characterized by photophysical and electrochemical methods. These compounds were also used as active

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layers in the fabrication of organic solar cells.

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Synthesis, characterization, photophysical and photovoltaic properties of new donor−acceptor platinum(II) acetylide

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complexes Qian Liu,[a] Nianyong, Zhu,[a] Cheuk-Lam Ho,*[a,c] Yingying Fu,[b]

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Wai-Sum Lau,[a] Zhiyuan Xie,*[b] Lixiang Wang,[b] Wai-Yeung Wong*[a,c]

[a] Dr. Q. Liu, Dr. N.-Y. Zhu, Dr. C.-L. Ho, W.-S. Lau, Prof. W.-Y. Wong Institute of Molecular Functional Materials, Department of Chemistry and Institute of Advanced Materials Hong Kong Baptist University Waterloo Road, Kowloon Tong, Hong Kong, P.R. China E-mail: [email protected], [email protected]

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[b] Y-Y. Fu, Prof. Z.-Y. Xie, Prof. L.-X. Wang State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences, Changchun 130022, P.R. China E-mail: [email protected] [c] Dr. C.-L. Ho, Prof. W.-Y. Wong HKBU Institute of Research and Continuing Education Shenzhen Virtual University Park, Shenzhen, 518057, P.R. China

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Abstract: Six new solution processable platinum(II) acetylide donor-acceptor (D-A) triads end-capped by 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) have been synthesized and characterized by

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photophysical and electrochemical methods. All these materials possess low bandgaps and strong UV/Vis absorption between 400−700 nm. Bulk heterojunction (BHJ) solar cells based on these molecules as donor materials were fabricated. The best power conversion efficiency (PCE) of 1.46%

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with the open-circuit voltage (Voc) of 0.70 V, short-circuit current density (Jsc) of 6.17 mA cm−2 and fill factor (FF) of 0.33 was achieved under illumination of an AM 1.5 solar cell simulator. These results

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suggest the potential use of solution-processable small molecular platinum(II)-acetylides for efficient generation in organic photovoltaic implementation.

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Keywords: bulk heterojunction solar cell · platinum · acetylide · crystal structure · photovoltaics

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1. Introduction Recently, more attention has been paid to the energy crisis and environmental protection. Renewable

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energy sources have become a hot topic in the research community [1−2]. Among these organic solar cells (OSCs) have attracted much interest owing to their advantages over traditional silicon based solar cells, including solution processability, flexibility, lightweight and large-area fabrication at low cost [3].

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Therefore, many related research activities are now focusing on developing new photovoltaic materials and optimizing these device architectures [4–6]. Great progress has been made in the field of organic

donor-acceptor

(D-A)

systems

which

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bulk heterojunction (BHJ) solar cells since its inception in 1995 [7]. BHJ solar cells comprise of typically

contain

electron-donating

materials

and

electron-withdrawing fullerene derivatives. Since then, significant improvements on power conversion efficiencies (PCEs) were achieved by alternating the device structures and modifying the structures of

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donor materials. The PCEs of single BHJ solar cells near 10% have been achieved for polymer-based solar cells (PSCs) [8, 9] and small molecule-based solar cells (SMSCs) [10−12], respectively. In contrast to the polymeric system, small molecules employed for SMSCs are easier to be synthesized and purified

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as they possess well-defined structures. Although the PCEs of SMSCs are still slightly behind those of PSCs, the large structural variations in the molecular weight, polydispersity, and regioregularity in

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polymeric systems result in poor reproducibility of PCEs [13−16]. Platinum(II)-containing polyynes and their oligomers have been demonstrated to be useful in photovoltaic applications [17−23]. Solution-processable polymeric semiconductors with Pt(II) centers possessing D-A architecture in the backbone were shown to exhibit broad absorption bands due to the intramolecular charge transfer (ICT) between the donor and acceptor units and small bandgaps which are suitable for photovoltaic devices [24]. The complexation of an electron-rich platinum(II) ion with the

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conjugated chain was reported to enhance the intrachain charge transport of π-conjugated polymers [25]. To get rid of the uncertainty in PCE induced by polymeric materials, here we report the utility and

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utilize of molecular Pt(II) complexes with different electron-donating groups and electron-accepting di-2-thienyl-2,1,3-benzothiadiazole (DTBT) unit that can modify the ICT strength of the D-A component for BHJ solar cell applications. Oligothiophene component was employed to fine-tune the

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ICT strength of the D-A component within the system. These complexes can be synthesized easily in high purity. Their optical, electronic and photovoltaic properties have been studied and their

2. Results and discussion 2.1. Synthesis and characterization

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structure-photovoltaic property relationships with different spacers will be presented.

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Compounds L1-2Br−L6-2Br were prepared according to the procedures reported in the literature [26−31]. The synthetic routes for the preparation of the diethynyl ligands L1−L6 and a new series of bi(thienyl)benzothiadiazole end-capped platinum(II)-acetylide compounds PT1−PT6 are illustrated in

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Scheme 1. The trimethylsilylacetylenic compounds L1-2TMS−L4-2TMS were synthesized by the Sonogashira reaction between L1-2Br−L6-2Br and trimethylsilylacetylene under Pd(OAc)2, CuI and

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PPh3 catalytic system in the solvent mixture of CH2Cl2 and NEt3. Upon deprotection in basic MeOH solution, ligands L1−L4 were obtained in high synthetic yields. For ligands L5−L6, L5-2Br−L6-2Br were refluxed with triisopropyl((5-(tributylstannyl)thiophen-2-yl)ethynyl)silane in toluene in the presence of Pd(PPh3)4 to get the key precursors L5-2SiPr3−L6-2SiPr3, which were then reacted with tetra-n-butylammonium fluoride to obtain the diethynyl ligands L5−L6. On the other hand, compound 1 was prepared by CuI/KF-catalyzed reaction between ligand L-TMS

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and trans-[PtCl2(PBu3)2] in a molar ratio of 1:1. Platinum(II)-acetylide compounds PT1−PT6 were then prepared by CuI-catalyzed dehydrohalogenation reaction between corresponding diethynyl ligands

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L1−L6 and two stoichiometric amounts of compound 1. All the platinum(II) compounds were purified by column chromatography on silica gel easily and are soluble in common organic solvents, such as CH2Cl2, CHCl3, THF and toluene. They were fully 13

C and

31

P NMR

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characterized by common spectroscopic techniques including infrared, 1H,

spectroscopy and MALDI-TOF mass spectrometry. In their IR spectra, v(C≡C) characteristic bands

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ranging at 2075–2085 cm−1 were observed and the absence of terminal acetylenic C≡C–H stretching vibrations in L1−L6 is consistent with the formation of the coupling products PT1−PT6. All the proton signals of aromatic rings resonate in the downfield region (above 6.90 ppm) and those of alkyl group are located in the upfield region (below 2.3 ppm, around 4.0 ppm for the alkyl-CH2 group). The sharp

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signals of C≡C–H of ligands are located at around 3.5 ppm, which disappeare in the spectra of PT1−PT6, indicating the ligands were capped by two Pt(II) fragments. The expected features with correct integration ratios in the spectra of 1H NMR are in agreement with the symmetrical structures of

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PT1−PT6. There are four distinct peaks in the spectra of 13C NMR due to the presence of four acetylide units in these symmetric molecules. Besides, the strong P signals flanked with two satellites were

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observed in all 31P NMR spectra for the Pt(II) complexes. The 1JP-Pt values range from 2316 Hz to 2329 Hz for PT1−PT6, which are typical of those for related trans-PtP2 systems [32]. The respective molecular ion peaks [M]+ in their MALDI-TOF mass spectra further confirm the synthesis of targeted products .

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N

N

Br

TMS

Br

S

S

K2CO3

H

O Br

TMS

Br

C6H13 S

N

N

O

Br TMS

O

S

iPr

3Si

S

L5-2Br Bu3Sn

iPr

S

N

C6H13 L4 C4H9 N

H

S

S

H

L5

DCM

N

H

O

S

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3Si

SiiPr3

S

O

O

N

L6-2SiPr3

S

SiiPr3

N O

S O N

S

H

L6

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L6-2Br

Br

H

O

H

TBAF

Pd(PPh3)4, toluene, 110℃

N

N

S

N

L5-2SiPr3

SiiPr3

S

O O

O

L3 C6H13

C4H9 N

Br

N

TMS

L4-2TMS

C4H9 N

Br

S

N

C6H13

C6H13 L4-2Br

Br

O

L3-2TMS C6H13

L3-2Br

H

S

O

O

O

H

TMS S

S

H

S

S

S

S

S

CH2Cl2:CH3OH=1:1

O

CuI, Pd(OAc)2, PPh3

C6H13 N N

L2

L2-2TMS TMS

S

H

TMS

S

L2-2Br

H

S L1

N

S

N

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TMS

Br

S

S

C6H13 N N N S

Br

H

TMS

S L1-2TMS

S

O

N

N

S

L1-2Br C6H13 N N N Br

S

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S

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N

6

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Scheme 1 The synthetic procedures for ligands L1−L6 and Pt(II) complexes PT1−PT6.

2.2. X-ray structural analysis

The solid-state structure of PT1 was determined by the single-crystal X-ray diffraction analysis. Selected bond lengths and angles are listed in Table 1. It crystallizes in the triclinic space group and the inversion center of the crystal symmetry overlaps the symmetrical center of the oligomer. A perspective view of the molecule is depicted in Figure 1a. Three di(thienyl)benzothiadiazole units are linked by two

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Pt(PBu3)2 bis(acetylide) units forming the oligomer with the three organic units. The two terminal di(thienyl)benzothiadiazole units are parallel and atoms to plane distances are in the range of 2.8 to 3.1Å.

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The middle di(thienyl)benzothiadiazole unit rotates 31º away from the above two planes, while the square plane (P2C2) around Pt atom rotates 40º further. The two square planes are also parallel due to the symmetry and the plane distance is around 3.4(3) Å based on the four atoms to plane distances. The

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acetylide groups are located in trans position of the Pt square planar coordination geometry. The C≡C bond lengths are 1.23(2) Å for the middle unit and 1.22(2) Å for the two terminal units, which are π interactions

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similar. The steric influence of the big phosphine ligands exists, so there is no close π

for the middle unit. However, the two terminal di(thienyl)benzothiadiazole units show close contacts to its adjacent units (e.g. S S contacts of 3.28 and 3.49 Å), which are also the terminal units of the adjacent oligomers, respectively (Figure 1b).

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(b)

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(a)

Figure 1 (a) A perspective view and atomic labeling scheme for PT1 and (b) the formation of an infinite 1-D supramolecular chain in the crystal packing.

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Table 1 Selected bond lengths (Å) and angles (°) for PT1. Pt(1)-C(1) 1.966(16) C(1)-C(2) Pt(1)-C(10) 1.985(16) C(10)-C(11) S(2)-N(1) S(2)-N(2)* S(4)-N(3)

S(1)-C(6) S(3)-C(12)

1.669(17) 1.736(17)

S(4)-N(4) S(5)-C(22)

S(3)-C(15) C(1)-Pt(1)-C(10) C(1)-Pt(1)-P(1)

1.714(16) 177.6(6) 91.6(5)

S(5)-C(25) P(2)-Pt(1)-P(1) C(10)-Pt(1)-P(1)

C(1)-Pt(1)-P(2)

87.9(5)

C(10)-Pt(1)-P(2)

1.65(2) 1.59(2) 1.58(3)

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2.280(5) 2.279(5) 1.697(15)

1.63(4) 1.66(2)

1.64(2) 177.04(18) 90.7(5)

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Pt(1)-P(1) Pt(1)-P(2) S(1)-C(3)

1.23(2) 1.22(2)

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89.8(5)

2.3. Photophysical and electrochemical properties

The photophysical properties of the diethynyl ligands L1− −L6 and their corresponding platinum(II) compounds PT1−PT6 were investigated by UV/Vis and photoluminescence (PL) spectroscopy in

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CH2Cl2 at 293 K. The photophysical data for L1− −L6 and PT1−PT6 are presented in Tables 2 and 3, respectively. Figure 2 illustrates the UV/Vis absorption spectra of PT1−PT6. Generally, compounds L1−L6 and PT1−PT6 showed two or three broad absorption bands in the range of 300−700 nm. The

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absorption bands at the short wavelength below 420 nm are ascribed as π → π* transitions of the organic

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aryleneethynylene segment. The low-energy broad absorption bands centered at 499−636 nm are assigned to the ICT from the electron-donating group to the electron-withdrawing unit in such molecular architecture. There are significant shift in their absorption profile after the introduction of Pt(II) fragments. For example, an obvious red shift of ~128 nm from L5 to PT5 was observed due to the increased electronic conjugation length and enhanced ICT strength in the latter. The design of photovoltaic materials should take into consideration the fact that they not only lower the energy bandgap but also increase the absorption coefficients of the materials. As shown in Table 4, the

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absorption intensities are enhanced significantly by the introduction of Pt(II) fragment, due to the strong intramolecular D-A interactions as the π-conjugation is extended [33]. The molar absorptivities are in

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the range of 2.07–17.20 × 104 M–1 cm–1 for PT1−PT6. PT4 exhibits the longest absorption edge which gives the lowest optical bandgaps (Eg) of 1.85 V among all the complexes. It is mainly attributed to the concurrent π−π intermolecular interactions in the solid state of diketopyrrolopyrrole (DPP), rendering it

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to show the strongest ICT interaction among all the platinum(II) compounds. All the ligands and platinum(II) compounds are photoluminescent at room temperature. The trends of their

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photoluminescence (PL) spectra are similar to their UV/Vis absorption spectra (Figure 2). All the Pt(II) complexes display red emission peaks with the maxima within the range of 647−763 nm and their respective emission lifetimes of 10.12, 8.79, 9.26, 6.86, 7.52 and 5.98 ns for PT1−PT6, are indicative of their fluorescence origin. The charge-transfer nature in their PL was supported by the solvent dependent

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emission spectra of our compounds in solvents of different polarities (Table 4). For example, compound PT1 exhibited a marked positive solvatochromism with a red-shift of the emission maximum of ~ 33 nm from toluene (λem = 642 nm) to CH2Cl2 (λem = 675 nm), which suggests a less polar excited state (Figure

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4). Similar bathochromic shifts of 38, 30, 13, 40 and 42 nm were observed for PT2−PT6 upon changing

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the solvent from toluene to CH2Cl2, respectively.

Table 2 Photophysical data for compounds L1−L6 in CH2Cl2 at 293 K. λabs [nm] (ε [104 M–1 cm–1])

Emission λem [nm] [a]

L1

332 (2.40), 465 (1.69)

575

L2

0.93 (2.86), 413 (3.89)

500

L3

279 (3.81), 316 (2.39), 330 (4.38), 395 (1.37)

453

L4

316 (0.48), 377 (0.33), 399 (0.34), 545 (0.88), 588 (1.03)

609

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276 (0.65), 305 (0.34), 378 (1.21)

413, 440sh

L6

325 (1.89), 440 (1.66), 552 (1.37)

535

sh = shoulder peak.

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[a]

L5

Table 3 Photophysical data for compounds PT1−PT6 in CH2Cl2 at 293 K.

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Absorption Emission 4 –1 λabs [nm] (ε [10 M onset λabs λem [nm] τF [ns] ΦF [%][b] cm–1])[a] [nm] 370 (8.43), 533 (7.99) 622 675 1.28 10.12 PT1 354 (5.12), 499 (8.62) 591 650 1.19 8.79 PT2 376 (17.20), 408sh 589 647 1.50 9.26 PT3 (16.60), 505 (10.80) 669 666 3.68 6.86 PT4 359 (7.06), 585sh (9.92), 637 (13.70) 263 (2.38), 413 (3.77), 593 655 4.24 7.52 PT5 505 (2.07) 366 (3.23), 519 (2.51), 742 763 1.01 5.98 PT6 601sh (1.98) [a] sh = shoulder peak. [b] Quantum yields were measured with an excitation wavelength of 488 nm using

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Rhodamine 6G in water as the reference (ΦF = 0.95) [34].

Table 4 Solvatochromic effect of the PL data for PT1−PT6. THF

CHCl3

CH2Cl2

642

658

671

675

612

633

645

650

PT3

617

634

645

647

PT4

653

657

662

666

PT5

615

636

645

655

PT6

721

727

760

763

PT1

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PT2

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toluene

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PT1 PT2 PT3 PT4 PT5 PT6

1.0

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0.8 0.6 0.4

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0.2 0.0

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Normalized Absorbance (a.u.)

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300

400

500

600

700

800

Wavelength (nm)

PT1 PT2 PT3 PT4 PT5 PT6

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0.8

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1.0

0.6 0.4

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Normalized Intensity (a.u.)

Figure 2 Normalized absorption spectra of PT1−PT6 in CH2Cl2 at 293 K.

0.2

0.0 500

600

700

800

900

Wavelength (nm) Figure 3 Normalized photoluminescence spectra of PT1−PT6 in CH2Cl2 at 293 K.

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Toluene THF CHCl3

0.8

CH2Cl2 0.6 0.4 0.2 0.0 550

600

650

700

750

800

850

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0.6

0.2

550

600

650

700

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0.0 750

Wavelength (nm)

800

850

Normalized PL intensity (a.u.)

CH2Cl2

0.4

0.8 0.6 0.4 0.2

CH2Cl2

0.0

550

600

650

700

750

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0.8

Toluene THF CHCl3

800

850

1.0

(d)

Toluene THF CHCl3

0.8

CH2Cl2

0.6 0.4 0.2 0.0

550

600

650

700

750

800

850

Wavelength (nm)

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Normalized PL intensity (a.u.)

Toluene THF CHCl3

(c)

(b)

Wavelength (nm)

Wavelength (nm)

1.0

1.0

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(a)

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1.0

Normalized PL intensity (a.u.)

Normalized PL intensity (a.u.)

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0.8

CH2Cl2

0.6 0.4 0.2 0.0 550

600

650

700

750

800

850

1.0

Toluene THF CHCl3

(f)

0.8

CH2Cl2

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Toluene THF CHCl3

0.6 0.4 0.2

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(e)

Normalized PL intensity (a.u.)

1.0

0.0

550

600

650

700

750

800

850

Wavelength (nm)

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Wavelength (nm)

Figure 4 Positive solvatochromism of the PL spectra for (a) PT1, (b) PT2, (c) PT3, (d) PT4, (e) PT5 and (f) PT6. (note: the portion of the spectrum above 800 nm for P6 is not very accurate due to the PMT

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response)

2.4. Electrochemical Properties

To investigate the electrochemical properties of platinum(II) compounds PT1−PT6, cyclic

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voltammetry (CV) was performed [35]. They were measured in their thin films on glassy carbon electrode in 0.1 mol L−1 [Bu4N]PF6 acetonitrile solution with a Pt wire counter electrode and a Ag/AgCl reference electrode under N2 atmosphere at a scan rate of 50 mV s−1. The highest occupied molecular

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Normalized PL intensity (a.u.)

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orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels are calculated from the onset potentials of their oxidation and reduction. The formal potential of Fc/Fc+ was measured as 0.07 V against Ag/AgCl, which has an absolute energy level of –4.73 eV relative to the vacuum level for calibration. The results are shown in Table 5 and their voltammograms are shown in Figure 5. All the compounds PT1−PT6 have their LUMO level at around –3.5 eV which are higher than the PC70BM

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level (–4.3 eV), making the photoinduced ICT and charge separation possible at the interface between the donor and acceptor. As shown in Table 5, EHOMO for PT1−PT6 are between –5.11 eV and –5.25 eV,

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and ELUMO for PT1−PT6 are between –3.53 and –3.58 eV, which are desired for BHJ photovoltaic materials [36]. These platinum complexes have low energy bandgaps with good molar extinction

Table 5 Electrochemical data of PT1−PT6.

PT1

0.50

–5.23

PT2

0.46

–5.19

PT3

0.49

–5.22

PT4

0.38

–5.11

PT5

0.45

PT6

0.52

Ered [V][a]

LUMO [eV][c]

Eg, ec [eV] [d]

Eg, opt [eV] [e]

–1.17

–3.56

1.67

1.99

–1.16

–3.57

1.62

2.09

–1.20

–3.53

1.69

2.10

–1.15

–3.58

1.53

1.85

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HOMO [eV][b]

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[a]

Eox [V][a]

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coefficients which indicating that they are attractive materials for light-harvesting.

–5.18

–1.19

–3.54

1.64

2.09

–5.25

–1.16

–3.57

1.68

1.67

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Onset oxidation and reduction potentials (V) were measured in acetonitrile solution containing 0.1 M Bu4NPF6 with a scan rate of 50 mV s−1 [b] HOMO = –e(Eox + 4.73) (eV) [c] LUMO = –e(Ered + 4.73) (eV) [d] Electrochemical band gap was obtained from −(HOMO−LUMO) [e] Optical band gap was determined from onset of absorption in dichloromethane

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PT6

Current (mA)

PT5 PT4

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PT3

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PT2

PT1

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Potential (V vs Ag/Ag+)

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Figure 5 Cyclic voltammograms of the thin films for PT1−PT6 on glassy carbon electrode measured in 0.1 mol L−1 [Bu4N]PF6 acetonitrile solutions at a scan rate of 50 mV s−1.

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2.5. Performance of organic solar cells

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With the good solubility and efficient absorption range and intensity, BHJ devices based on

PT1–PT6 were fabricated using PC70BM as the acceptor with a conventional structure of glass/ITO/PEDOT:PSS/donor:PC70BM/LiF/Al. The active layers were prepared by spin-coating the solution of PT1–PT6 with PC70BM in a 1:3 (w/w) ratio in chlorobenzene. The photovoltaic data were collected under simulated AM 1.5G solar illumination. To better optimize the charge transport properties and the absorption of the irradiated light, active layers with different thickness were measured and the results are summarized in Table 6. From the results, it was shown that the active-layer thickness

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had an influence on the performance of the devices; the optimized active layer thickness was 55–60 nm for these Pt-containing photosensitizers. Thicker active layers resulted in lower PCEs, which is probably

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due to the fact that a very thick active layer slows down the charge transport in the active layer of the solar cells. The current density versus voltage (J–V) curves of the BHJ devices based on

PT1–PT6:PC70BM (1:3 w/w) blends with different active layer thicknesses are plotted in Figure 6. The

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devices based on PT6 with indolin-2-one functionalities as the central group showed a minimum PCE of 0.17% with the active layer thickness of 55 nm, resulting in a Voc of 0.59, Jsc of 1.06 mA cm–2 and a FF

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of 0.28. The low PCE values of PT6 based devices are mainly attributed to the low IPCE values over the whole absorption range as shown in Figure 7. The photovoltaic performance can be significantly improved by introducing a stronger donor group of 2,7-carbazole unit in PT5. The devices based on

PT5 showed a better performance with higher Jsc of 6.17 mA cm–2, higher FF of 0.33 and higher PCE of

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1.46% at the active layer thickness of 60 nm. The higher Jsc of the device based on PT5 may plausibly be caused by the stronger ICT interaction between the electron-donating carbazole unit and the electron-accepting benzothiadiazole unit in PT5 which is in agreement with the measured IPCE curve.

EP

These results suggest that these conjugated D-A framework with Pt(II) centers are potential materials for

AC C

BHJ solar cell applications.

Table 6 Device performance parameters for BHJ solar cells based on PT1−PT6. Donor

PT1

PT2

Film thickness

Voc

Jsc

FF

PCE (%)

(nm)

(V)

(mA cm–2)

60

0.68

3.41

0.29

0.68

80

0.66

2.60

0.27

0.47

60

0.69

4.14

0.29

0.82

17

ACCEPTED MANUSCRIPT

PT6

2

0.28

0.64

55

0.71

2.31

0.27

0.44

90

0.71

1.14

0.25

0.20

55

0.69

3.49

0.29

0.71

85

0.67

2.36

60

0.70

6.17

75

0.69

5.06

55

0.59

1.06

75

0.61

0.84

RI PT

PT5

3.24

0.30

0.48

0.33

1.46

0.31

1.08

0.28

0.17

SC

PT4

0.70

0.28

M AN U

PT3

80

0.14

2

(a)

-2

-2 80 nm 60 nm -4

0.4

1 0

-2 -3

AC C

-2

current density (mA cm )

(c)

-4 -0.4

55 nm 90 nm PT3:PC71BM=1:3

0.0

0.4 voltage (V)

0

-2

80 nm 60 nm PT2:PC71BM=1:3

-4

0.8

EP

voltage (V)

0.8

-0.4

0.0

0.4

0.8

voltage (V)

2

-2

0.0

TE D

PT1:PC71BM=1:3

-0.4

-1

current density (mA cm )

0

current density (mA cm )

-2

current density (mA cm )

(b)

(d)

0

-2 55 nm 85 nm PT4:PC71BM=1:3

-4 -0.4

0.0

0.4

0.8

voltage (V)

18

ACCEPTED MANUSCRIPT

0.4

0 -2 -4

75 nm 60 nm PT5:PC71BM=1:3

-6

0.0 -0.4 -0.8 -1.2 -0.4

0.0

0.4

0.8

75 nm 55 nm

PT6:PC71BM=1:3

0.0

0.4

0.8

voltage (V)

SC

-8 -0.4

(f)

RI PT

-2

current density (mA cm )

-2

current density (mA cm )

2

(e)

M AN U

voltage (V)

Figure 6 Current density-voltage (J-V) curves of OSCs based on (a) PT1, (b) PT2, (c) PT3, (d) PT4, (e) PT5 and (f) PT6, with different active layer thickness under illumination of AM 1.5G at 100 mW cm–2.

0.5

PT1 PT2 PT3 PT4 PT5 PT6

EP

IPCE

0.4

TE D

0.6

0.3

AC C

0.2 0.1 0.0

400

500

600

700

Wavelength (nm) Figure 7 Incident photon conversion efficiency (IPCE) spectra of PT1–PT6.

19

ACCEPTED MANUSCRIPT

3. Conclusions

RI PT

A new series of platinum(II) acetylide donor-acceptor triads PT1−PT6 which were end-capped by 4,7-di-2-thienyl-2,1,3-benzothiadiazole have been successfully designed and prepared by convenient synthetic processes with reasonably good yields. These platinum(II) containing complexes were

SC

characterized by photophysical and electrochemical methods. The absorption profile of these metal complexes is significantly broadened by the D−A motif, which lead to the enhancement of the overlap

M AN U

for the absorption of PT1−PT6 with the solar spectrum. In addition, using the platinum groups as exciton confinement centers, we can easily extend the absorption into the low energy range beyond 600 nm. The energy bandgaps of PT1−PT6 are within 1.53–1.69 eV. By introducing strong 2,7-carbazole donor in the molecule, the highest PCE of 1.46% was obtained among all the devices with high Voc of

TE D

0.70 V, Jsc of 6.17 mA cm–2 and FF of 0.33 at the optimized active layer thickness of 60 nm. These results indicate that these solution-processible platinum(II) acetylide complexes are attractive materials for photovoltaic cell applications, and further improvement in the device efficiency could be achieved by

AC C

film morphology.

EP

tuning the ICT absorption and HOMO/LUMO energy levels of this type of material as well as their thin

4. Experimental

4.1. Materials and reagents

All manipulations were performed by using Schlenk techniques under dry nitrogen atmosphere. Solvents were dried by the standard methods and distilled prior to use except for those of spectroscopic grade for photophysical and electrochemical measurements.

20

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4.2. Physical measurements

RI PT

NMR spectra were measured in deuterated solvents as the lock and reference on a Bruker AV 400 instrument. Chemical shifts are given relative to tetramethylsilane for 1H and

13

C NMR data and 85 %

H3PO4 (external standard) for 31P NMR data. Infrared spectra were recorded on the Nicolet Magna 550

SC

Series II FT-IR spectrometer using KBr pellets for solid state spectroscopy. Fast atom bombardment (FAB) mass spectra were recorded on a Finnigan MAT SSQ710 system. The matrix-assisted laser

M AN U

desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a Autoflex Bruker MALDI-TOF system. UV/Vis absorption spectra were obtained on an HP-8453 diode array spectrophotometer. The photoluminescence spectra were measured in dichloromethane with a PTI Fluorescence Master Series QM1 spectrophotometer. Cyclic voltammograms were measured on a CHI

TE D

model 600D electrochemistry station in 0.1 mol L–1 Bu4NPF6 acetonitrile solution with a glassy carbon working electrode, a Pt wire counter electrode and a Ag/AgCl reference electrode under a N2

EP

atmosphere at a scan rate of 50 mV s–1.

4.3. X-ray crystallography

AC C

Single crystals of PT1 suitable for X-ray crystallographic analysis were grown by slow evaporation of its solution in dichloromethane at room temperature. The crystal was chosen and mounted on a glass fiber using epoxy resin. The diffraction experiment was carried out at 100 K on a Bruker APEX DUO CCD area-detector diffractometer equipped with a IµS CuKα copper microfocus tube (λ = 1.54184 Å). The collected frames were processed using the software SAINT
[37] and an absorption correction was applied (SADABS) [38] to the collected reflections. The structure was solved by direct methods

21

ACCEPTED MANUSCRIPT

(SHELXTL) [39] in conjunction with standard difference Fourier techniques and subsequently refined by full-matrix least-squares analyses on F2. The di(thienyl)benzothiadiazole groups are disordered by

RI PT

flipping of the central benzothiadiazole group, meanwhile the terminal thiophene groups are also disordered by flipping. Some restraints were applied. Since the single crystal diffracted relatively weakly, there was not enough reflections collected. Therefore, only Pt, P and S atoms were refined

SC

anisotropically and other non-hydrogen atoms were refined isotropically. Hydrogen atoms were generated in their idealized positions. The cif file was deposited in the CCDC with the number

M AN U

CCDC-1039410 (PT1) which is included in the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Crystal data for PT1: C98H128N6P4S9Pt2 Mw = 2192.66, triclinic, space group P-1, a = 9.4468(10), b = 10.6766(10), c = 25.484(3) Å, α = 80.46(2), β = 86.97(2), γ =

TE D

81.32(2), V = 2504.7(5) Å3, Z = 1, ρcalcd = 1.454 Mg m-3, µ(CuKα) = 7.864 mm−1, F(000) = 1118, T = 100 K. 18001 reflections measured, of which 5332 were unique (Rint = 0.0351). Final R1 = 0.0828 and wR2 =

EP

0.2214 for 5332 observed reflections with I > 2σ(I).

4.4. Fabrication and characterization of bulk heterojunction solar cells

AC C

All the BHJ devices were fabricated with structure ITO/PEDOT:PSS/active layer/LiF/Al, in which the active layer consisted of a blend film of platinum(II) compounds as the electron donor and PC70BM as the electron acceptor in a weight ratio of 1:3. ITO glass substrates (10 Ω per square) were cleaned by sonication in toluene, acetone, ethanol and deionized water in sequence, dried in oven and then cleaned with UV ozone for 300 s. PEDOT:PSS (Baytron P AI 4083) was spin-coated onto the pre-cleaned ITO substrate to form a 40 nm thick layer, followed by drying at 120 oC for 30 min in air. Then, the

22

ACCEPTED MANUSCRIPT

substrates were transferred to a glove box filled with nitrogen. The prepared solution containing a mixture of PT1−PT6:PC70BM (1:3, w/w) in chlorobenzene was spin-coated on the top of PEDOT:PSS

RI PT

layer. Finally, the samples were transferred into an evaporator where 1 nm of LiF and 80 nm of Al were thermally deposited under vacuum at 10–6 Torr. The devices were encapsulated in the glove box and measured in air. Current-voltage characteristics were measured using a computer controlled Keithley

SC

236 source meter. The photocurrent was measured under AM 1.5G illumination at 100 mW cm–2 from a solar simulator (Oriel, 91160 A-1000). The EQE spectrum was measured at a chopping frequency of

M AN U

275 Hz with a lock-in amplifier (Stanford, SR830) during illumination with the monochromatic light from a xenon lamp. The AFM measurements were performed on a SPA300HV instrument with an SPI3800 controller (Seiko Instruments). The images were taken with the tapping mode.

TE D

4.5. Synthesis

The compounds L1-2Br−L6-2Br and triisopropyl((5-(tributylstannyl)thiophen-2-yl)ethynyl)silane were prepared according to the procedures reported in the literature [26−31]. Trans-[PtCl2(PBu3)2] was

EP

synthesized as described previously [32] and other chemicals were commercially available and used as

AC C

received unless otherwise stated.

4.5.1. General procedures for the synthesis of L1-2TMS−L4-2TMS Compounds L1-2TMS−L4-2TMS were prepared by the Pd-catalyzed Sonogashira coupling reaction from the corresponding dibrominated compounds L1-2Br−L6-2Br. A typical procedure is illustrated as follows for the compound L1-2TMS. To an ice-cooled mixture of L1-2Br (458.2 mg, 1 mmol) in CH2Cl2/NEt3 (v/v, 1:1) solution mixture

23

ACCEPTED MANUSCRIPT

was added CuI (9.5 mg, 0.05 mmol), Pd(OAc)2 (6.8 mg, 0.03 mmol, 3 mol%) and PPh3 (24 mg, 0.09 mmol, 9 mol%). After the solution was stirred for 30 min at 0 °C, trimethylsilylacetylene (0.30 mL, 2.13

RI PT

mmol) was then added and the suspension was stirred for 30 min in an ice-water bath before being warmed to room temperature. After reacting for 30 min at room temperature, the mixture was heated up to 55 °C overnight. Then the solution was cooled to room temperature and the solvent mixture was

SC

evaporated in vacuo. The crude product was purified by column chromatography on silica gel with a solvent combination of n-hexane/CH2Cl2 (4:1, v/v) as eluent to provide L1-2TMS as a red solid (418.8

M AN U

mg, 85 %). 1H NMR (400 MHz, CDCl3, δ/ppm): 7.96–7.95 (d, J = 3.9 Hz, 2H, Ar), 7.84 (s, 2H, Ar), 7.31–7.30 (d, J = 3.9 Hz, 2H, Ar), 0.28 (s, 18H, TMS);

13

C NMR (100 MHz, CDCl3, δ/ppm): 152.56,

140.51, 133.55, 127.28, 128.81, 125.77, 124.85 (Ar), 101.26, 97.71 (C≡C), 0.0034 (TMS); FAB-MS (m/z): 492.3 [M]+.

TE D

The same procedures were applied to prepare other TMS-intermediates. Synthesis of compound L2-2TMS: Red solid, yield: 87%. 1H NMR (400 MHz, CDCl3, δ/ppm): 7.93 (d, J = 3.9 Hz, 2H, Ar), 7.59 (s, 2H, Ar), 7.29 (d, J = 3.9 Hz, 2H, Ar), 4.82–4.74 (m, 2H, alkyl),

EP

1.43–1.26 (m, 8H, alkyl), 0.91–0.88 (t, J = 6.9 Hz, 3H, Me), 0.28 (s, 18H, TMS); 13C NMR (100 MHz, CDCl3, δ/ppm): 144.46, 136.01, 133.17, 132.50, 130.65, 128.48, 125.32 (Ar), 100.94, 97.29 (C≡C),

AC C

0.0034 (TMS); FAB-MS (m/z): 559.7 [M]+.

Synthesis of compound L3-2TMS: Yellow solid, yield: 78%.1H NMR (400 MHz, CDCl3, δ/ppm): 7.55 (s, 2H, Ar), 4.12–4.10 (m, 4H, alkyl), 1.79–1.76 (m, 2H, alkyl), 1.56–1.64 (m, 8H, alkyl), 1.39–1.35 (m, 10H, alkyl), 1.01–0.92 (m, 12H, alkyl), 0.28 (s, 18H, TMS); 13C NMR (100 MHz, CDCl3, δ/ppm): 144.21, 131.80, 130.12, 126.17, 122,98 (Ar), 101.81, 98.02 (C≡C), 40.82, 30.52, 29.36, 23.96,

24

ACCEPTED MANUSCRIPT

29.56, 22.32, 14.36, 11.51, 0.0034 (TMS); FAB-MS (m/z): 653.0 [M]+.

RI PT

Synthesis of compound L4-2TMS: Purple solid, yield: 85%. 8.87–8.86 (d, J = 4.1 Hz, 2H, Ar), 7.34–7.33 (d, J = 4.2 Hz, 2H, Ar), 4.06–4.02 (t, J = 7.8 Hz, 4H, alkyl), 1.74–1.71 (m, 4H, alkyl), 1.43–1.31 (m, 12H, alkyl), 0.90–0.87 (m, 6H, alkyl), 0.28 (s, 18H, TMS); 13C NMR (100 MHz, CDCl3,

SC

δ/ppm): 161.40 (C=O), 139.45, 135.58, 134.04, 130.61, 128.71, 108.96, 104.62 (Ar), 96.91, 77.62

M AN U

(C≡C), 42.61, 32.05, 29.45, 27.12, 22.91, 14.40 (alkyl), 0.0034 (TMS); FAB-MS (m/z): 662.1 [M]+.

4,5,2, General procedures for the synthesis of diacetylide ligands L1−L4 Ligands L1−L4 were prepared by deprotection of trimethylsilyl group reaction from compounds

L1-2TMS−L4-2TMS. A typical procedure is illustrated as follows for the compound L1.

TE D

To a solution of L1-2TMS (257.1 mg, 0.52 mmol) in a MeOH/CH2Cl2 mixture (v/v = 1:1) was added K2CO3 (145 mg, 1.05 mmol). The reaction mixture was stirred at room temperature overnight under N2 atmosphere. After removal of the solvent, the crude product was purified by column

EP

chromatography on silica gel using n-hexane/ CH2Cl2 (3:1, v/v) as eluent to afford the desired diethynyl ligand L1 (167.2 mg, 92%) as a red solid. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.13–8.11 (m, 1H, Ar),

13

AC C

7.98 (d, J = 4.0 Hz, 2H, Ar), 7.87 (s, 2H, Ar), 7.36–7.35 (d, J = 3.9 Hz, 2H, Ar), 3.49 (s, 2H, C≡CH); C NMR (100 MHz, CDCl3, δ/ppm): 152.48, 138.32, 129,56, 128.01, 122.91, 122.13 (Ar), 81.11, 79.30

(C≡C); IR (KBr) (cm−1): v = 3286 (w, v(C≡C−H)), 2093 (w, v(C≡C)); FAB-MS (m/z): 349.2 [M]+. Similar procedures were applied to the preparation of other ligands. Synthesis of L2: Yellow solid, yield: 89%. 1H NMR (400 MHz, CDCl3, δ/ppm): 7.95-7.95 (d, J = 3.9 Hz, 2H, Ar), 7.60 (s, 2H, Ar), 7.34−7.33 (d, J = 3.8 Hz, 2H, Ar), 4.83−4.79 (m, 2H, alkyl), 3.46 (s, 2H,

25

ACCEPTED MANUSCRIPT

C≡CH), 2.19-2.17 (m, 2H, alkyl), 1.42-1.26 (m, 6H, alkyl), 0.91-0.86 (m, 4H, alkyl);

13

C NMR (100

MHz, CDCl3, δ/ppm): 142.44, 141.94, 134.68, 127.23, 123.84, 123.37, 122.57 (Ar), 83.12, 85.67 (C≡C),

RI PT

57.50, 32.13, 30.57, 30.24, 23.19, 14.65 (alkyl); IR (KBr) (cm−1): v = 3294 (w, v(C≡C−H)), 2090 (w, v(C≡C)); FAB-MS (m/z): 415.8 [M]+.

SC

Synthesis of L3: Yellow crystal, yield: 85%. 1H NMR (400 MHz, CDCl3, δ/ppm): 7.61 (s, 2H, Ar), 3.48 (s, 2H, C≡CH), 4.13–4.12 (m, 4H, alkyl), 1.80–1.74 (m, 2H, alkyl), 1.65–1.53 (m, 8H, alkyl), 13

C NMR (100 MHz, CDCl3, δ/ppm): 144.12,

M AN U

1.38–1.36 (m, 10H, alkyl), 1.09–0.92 (m, 12H, alkyl);

131.54, 129.96, 126.56, 121.84 (Ar), 83.45, 81.26 (C≡C), 40.61, 30.36, 29.17,23.78, 23.10, 22.51, 14.15, 11.31 (alkyl) ; IR (KBr) (cm−1): v = 3280 (w, v(C≡C−H)), 2094 (w, v(C≡C)); FAB-MS (m/z): 509.7

TE D

[M]+.

Synthesis of L4: Purple solid, yield: 86 %. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.87 (d, J = 4.1 Hz, 2H, Ar), 7.40 (d, J = 4.1 Hz, 2H, Ar), 4.05–4.02 (t, J = 7.9 Hz, 4H, alkyl), 3.61 (s, 2H, C≡CH),

EP

1.75-1.69 (m, 4H, alkyl), 1.44–1.31 (m, 12H, alkyl), 0.90–0.87 (t, J = 7.1 Hz, 6H, alkyl); 13C NMR (100 MHz, CDCl3, δ/ppm): 161.20 (C=O), 139.25, 135.19, 134.20, 130.82, 127.21, 108.82 (Ar), 85.61, 77.24

AC C

(C≡C), 42.36, 31.12, 29.16, 26.83, 22.63, 14.10 (alkyl); IR (KBr) (cm−1): v = 3288 (w, v(C≡C−H)), 2092 (w, v(C≡C)), 1656 (w, v(C=O)); FAB-MS (m/z): 516.1 [M]+.

4.5.3. Synthesis of compound L5-SiPr3 To

a

solution

of

L5-2Br

(300

mg,

0.90

mmol)

and

triisopropyl((5-(tributylstannyl)thiophen-2-yl)ethynyl)silane (1.24 g, 2.25 mmol) in dry toluene (30 mL),

26

ACCEPTED MANUSCRIPT

Pd(PPh3)4 (0.53 g, 0.045 mmol, 5 mol%) was added as the catalyst. The mixture was heated up to 110 o

C overnight. Then the reaction mixture was cooled to room temperature and the solvent was removed

RI PT

by evaporation under reduced pressure. The resulting residue was purified by column chromatography on silica gel to get L5-SiPr3 as a fluorescent yellow solid (447.8 mg, yield: 71%). 1H NMR (CDCl3, 400 MHz, δ/ppm): 8.04–8.02 (m, 2H, Ar), 7.54 (s, 2H, Ar), 7.48–7.46 (m, 2H, Ar), 7.27–7.23 (m, 4H, Ar),

SC

4.35–4.32 (m, 2H, alkyl), 1.91–1.87 (m, 2H, alkyl), 1.47–1.41 (m, 2H, alkyl), 1.15 (m, 12H, alkyl), 0.99–0.96 (m, 3H, alkyl); 13C NMR (100 MHz, CDCl3, δ/ppm): 146.23, 138.76, 132.80, 128.09, 122.94,

(alkyl). FAB-MS (m/z): 747.8 [M]+.

M AN U

122.34, 119.44, 115.53, 112.65, 109.22 (Ar), 91.29, 75.32 (C≡C), 58.49, 32.66, 19.99, 18.76, 14.03

Similar procedures were applied to prepare L6-SiiPr3.

Synthesis of compound L6-SiPr3: Brown solid, yield: 68%. 1H NMR (CDCl3, 400 MHz, δ/ppm):

TE D

9.15–9.13 (m, 2H, Ar), 7.22–6.99 (m, 4H,Ar), 6.94–6.93 (m, 2H, Ar), 1.30–1.26 (m, 36H, alkyl), 1.14–1.13 (m, 16H, alkyl), 0.97–0.83 (m, 24H, alkyl);

13

C NMR (100 MHz, CDCl3, δ/ppm): 169.43

(C=O), 147.56, 145.24, 134.88, 133.78, 128.45, 123.32, 123.02, 120.98, 119.80, 118.98, 106.21 (Ar),

AC C

1010.5 [M]+.

EP

90.76, 76.33 (C≡C), 45.95, 37.20, 31.90, 26.82, 24.88, 22.04, 17.88, 18.90, 14.11 (alkyl). FAB-MS (m/z):

4.5.4. General procedures for the synthesis of L5−L6 Synthesis of compound L5

L5-SiPr3 (300 mg, 0.40 mmol) was dissolved in 15 mL of dichloromethane and the mixture was stirred at room temperature under N2 atmosphere with pre-coated aluminium foil sheets, then some drops of tetra-n-butylammonium fluoride (TBAF) was added. The reaction was monitored by thin-layer

27

ACCEPTED MANUSCRIPT

chromatography (TLC). About 2 hours later, the reaction ended. Then the solvent was removed by evaporation under reduced pressure, and the residue was filtered over a short silica gel column with

RI PT

dichloromethane as eluent. L5 was obtained as a pale yellow solid (148.5 mg, 85%). 1H NMR (400 MHz, CDCl3, δ/ppm): 8.04–8.02 (m, 2H, Ar), 7.54 (s,2H, Ar), 7.47–7.45 (m, 2H, Ar), 7.29–7.26 (m, 4H, Ar), 4.35–4.31 (m, 2H, alkyl), 3.43 (s, 2H, C≡CH), 1.90–1.87 (m, 2H, alkyl), 1.46–1.41 (m, 2H, alkyl),

SC

0.99–0.96 (m, 3H, alkyl). 13C NMR (100 MHz, CDCl3, δ/ppm): 146.91, 142.35, 138.76, 132.56, 128.98, 122.34, 120.20, 116.78, 115.40, 110.22 (Ar), 83.50, 75.32 (C≡C), 58.52, 32.01, 19.82, 14.12 (alkyl); IR

M AN U

(KBr) (cm−1): v = 3294 (w, v(C≡C−H)), 2092 (w, v(C≡C)); FAB-MS (m/z): 434.7 [M]+. The same procedures were applied to prepare L6.

Synthesis of compound L6: Pale brown solid, yield: 87%. 1H NMR (400 MHz, CDCl3, δ/ppm): 9.17–9.15 (m, 2H, Ar), 7.28–7.26 (m, 6H, Ar), 6.95–6.94 (m, 2H, Ar), 3.74–3.69 (m, 4H, alkyl), 3.46 (s, 13

C NMR

TE D

2H, C≡CH), 1.89–1.87 (m, 2H, alkyl), 1.43–1.25 (m, 20H, alkyl), 1.05–0.89 (m, 8H, alkyl);

(100 MHz, CDCl3, δ/ppm): 168.48 (C=O), 145.80, 145.59, 136.88, 134.31, 132.15, 130.35, 123.94, 122.38, 121.56, 119.41, 105.04 (Ar), 82.82, 76.34 (C≡C), 44.16, 37.76, 30.11, 28.87, 24.20, 22.96,

EP

17.87, 14.09 (alkyl); IR (KBr) (cm−1): v = 3292 (w, v(C≡C−H)), 2086 (w, v(C≡C)), 1632 (w, v(C=O));

AC C

FAB-MS (m/z): 699.5 [M]+.

4.5.5. Synthesis of Pt(II) precursor 1 Under a N2 atmosphere, L-TMS (90 mg, 0.11 mmol) and trans-[PtCl2(PBu3)2] (306 mg, 0.44 mmol) were added to a mixture of NEt3 and THF (1:1, v/v) in the presence of a catalytic amount of CuI (2.1 mg, 0.011 mmol, 10 mol%) and KF (2 mg) . The reaction mixture was stirred at room temperature overnight. The solvent was then removed under reduced pressure and the residue was purified by chromatography

28

ACCEPTED MANUSCRIPT

over a silica column using n-hexane/CH2Cl2 (1:1, v/v) as eluent. Then compound 1 was obtained as a red solid (126 mg, 58%). 1H NMR (400 MHz, CDCl3, δ/ppm): 8.10 (m, 1H, Ar), 7.85–7.83 (d, J = 7.6 Hz,

RI PT

1H, Ar ), 7.77–7.75 (d, J = 7.6 Hz, 1H, Ar ), 7.49–7.44 (m, 1H, Ar), 7.21–7.19 (m, 1H, Ar), 6.92–6.91 (m, 1H, Ar), 2.04–2.01 (m, 12H, PBu3), 1.59–1.57 (m, 12H, PBu3), 1.49–1.46 (m, 12H, PBu3), 0.95 (m, 18H, PBu3); 13C NMR (100 MHz, CDCl3, δ/ppm): 152.75, 152.60, 139.59, 136.04, 131.56, 128.58,

22.07, 13.85 (PBu3);

31

SC

128.00,127.72, 127.23, 126.55, 126.20, 125.99, 125.22, 124.75 (Ar), 93.99, 93.53 (C≡C), 26.13, 24.34, P NMR (CDCl3, 162 Hz, δ/ppm): 7.17 (1JP−Pt = 2323 Hz); MALDI-TOF-MS

M AN U

(m/z): 959.3 [M]+.

4.5.6. General procedures for the synthesis of platinum(II) compounds (PT1−PT6) The platinum(II) compounds (PT1−PT6) were prepared by the CuI-catalyzed dehydrohalogenation

TE D

reaction between the corresponding diethynyl ligands (L1−L6) and compound 1. A typical procedure is illustrated as follows for the compound PT1.

Under a N2 atmosphere, L1 (30 mg, 0.086 mmol) and compound 1 (173.3 mg, 0.18 mmol) were

EP

added to CH2Cl2 /Et3N (1:1, v/v) in the presence of a catalytic amount of CuI (2.0 mg, 10 mol%). The reaction mixture was stirred at room temperature overnight. Afterwards, the solvent was then removed

AC C

under reduced pressure and purified by chromatography over a silica column using n-hexane/CH2Cl2 (1:1.5, v/v) as eluent. Pure sample of PT1 was obtained as a deep red solid (122.7 mg, yield: 62%). 1H NMR (400 MHz, CDCl3, δ/ppm): 8.11–8.09 (dd, J1 = 3.7 Hz, J2 = 1.1 Hz, 2H, Ar), 8.01–7.98 (m, 4H, Ar), 7.86–7.84 (d, J = 7.7 Hz, 2H, Ar), 7.78–7.76 (d, J = 7.6 Hz, 2H, Ar), 7.73 (s, 2H, Ar), 7.45–7.44 (m, 2H, Ar), 7.22–7.20 (m, 2H, Ar), 6.94–6.93 (d, J = 3.5 Hz, 4H, Ar), 2.20–2.14 (m, 24H, PBu3), 1.65–1.62 (m, 26H, PBu3), 1.55–1.49 (m, 22H, PBu3), 0.99–0.96 (m, 36H, PBu3).

31

P NMR (CDCl3, 162 Hz,

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δ/ppm): 3.46 (1JP−Pt = 2323 Hz); IR (KBr) (cm−1): v = 2075 (w, v(C≡C)); MALDI-TOF-MS (m/z): 2193 [M]+.

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Similar procedures were applied to prepare other Pt(II) complexes. Synthesis of PT2: Red solid, yield: 65%. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.10–8.09 (dd, J1 = 4.0 Hz, J2 = 1.1 Hz, 2H, Ar), 8.02–8.01 (d, J = 3.8 Hz, 2H, Ar), 7.94–7.93 (d, J = 3.8 Hz, 2H, Ar),

SC

7.86–7.84 (d, J = 7.6 Hz, 2H, Ar), 7.78–7.76 (d, J = 7.6 Hz, 2H, Ar), 7.48 (s, 2H, Ar), 7.45–7.44 (m, 2H, Ar), 7.22–7.20 (m, 2H, Ar), 6.94–6.91 (m, 4H, Ar), 2.18–2.14 (m, 26H, alkyl), 1.65–1.62 (m, 26H,

5H, alkyl);

31

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alkyl), 1.54–1.48 (m, 22H, alkyl), 1.42–1.38 (m, 4H, alkyl), 0.99–0.96 (m, 36H, alkyl), 0.92–0.84 (m, P NMR (CDCl3, 162 Hz, δ/ppm): 3.44 (1JP−Pt = 2320 Hz); IR (KBr) (cm−1): v = 2084 (w,

v(C≡C)); MALDI-TOF-MS (m/z): 2258.7 [M]+.

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Synthesis of PT3: Red solid, yield: 68%. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.11–8.10 (dd, J1 = 3.6 Hz, J2 = 1.1 Hz, 2H, Ar), 8.01−8.00 (d, J = 3.8 Hz, 2H, Ar), 7.87–7.84 (d, J = 7.6 Hz, 2H, Ar), 7.78–7.76 (d, J = 7.6 Hz, 2H, Ar), 7.45–7.43 (m, 2H, Ar), 7.22–7.20 (m, 2H, Ar), 7.12 (s, 2H, Ar),

EP

6.94–6.93 (d, J = 3.8 Hz, 2H, Ar), 4.08–4.06 (m, 4H, alkyl), 2.16–2.14 (m, 16H, alkyl), 1.17–1.61 (m, 30H, alkyl), 1.56–1.48 (m, 32H, alkyl), 1.37–1.35 (m, 8H, alkyl), 0.99–0.93 (m, 48H, alkyl); 31P NMR

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(CDCl3, 162 Hz, δ/ppm): 3.43 (1JP−Pt = 2324 Hz); IR (KBr) (cm−1): v = 2085 (w, v(C≡C)); MALDI-TOF-MS (m/z): 2338.8 [M]+.

Synthesis of PT4: Deep purple solid, yield: 61%. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.10–8.09 (dd, J1 = 3.6 Hz, J2 = 1.1 Hz, 2H, Ar), 8.02–8.01 (m, 2H, Ar), 7.94–7.93 (m, 2H, Ar), 7.86–7.84 (d, J = 7.6 Hz, 2H, Ar), 7.77–7.76 (d, J = 7.6 Hz, 2H, Ar), 7.48 (s, 2H, Ar), 7.45–7.44 (m, 2H, Ar), 7.22–7.20 (m,

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2H, Ar), 6.94–6.91 (m, 4H, Ar), 4.79–4.76 (m, 2H, alkyl), 2.18–2.14 (m, 26H, alkyl), 1.65–1.61 (m, 26H, alkyl), 1.54–1.49 (m, 22H, alkyl), 1.33–1.31 (m, 4H, alkyl), 0.99–0.96 (m, 36H, alkyl), 0.89–0.88 (m, 31

P NMR (CDCl3, 162 Hz, δ/ppm): 3.62 (1JP−Pt = 2316 Hz); IR (KBr) (cm−1): v = 2079 (w,

v(C≡C)), 1661 (w, v(C=O)); MALDI-TOF-MS (m/z): 2360.8 [M]+.

RI PT

5H, alkyl);

SC

Synthesis of PT5: Red solid, yield: 70%. 1H NMR (400 MHz, CDCl3, δ/ppm): 8.11–8.10 (dd, J1 = 3.6 Hz, J2 = 1.1 Hz, 2H, Ar), 8.02–7.99 (m, 4H, Ar), 7.86–7.84 (d, J = 7.6 Hz, 2H, Ar), 7.78–7.76 (d, J =

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7.6 Hz, 2H, Ar), 7.50 (s, 2H, Ar), 7.45-7.42 (m, 4H, Ar), 7.22–7.20 (m, 4H, Ar), 6.94–6.93 (m, 2H, Ar), 6.87–6.86 (m, 2H, Ar), 4.36–4.31 (m, 2H, alkyl), 2.19–2.14 (m, 24H, alkyl), 1.92–1.86 (m, 2H, alkyl), 1.65–1.62 (m, 26H, alkyl), 1.54–1.49 (m, 24H, alkyl), 1.00–0.96 (m, 36H, alkyl), 0.88–0.86 (m, 3H, alkyl);

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P NMR (CDCl3, 162 Hz, δ/ppm): 3.38 (1JP−Pt = 2329 Hz); IR (KBr) (cm−1): v = 2085 (w,

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v(C≡C)); MALDI-TOF-MS (m/z): 2280.1 [M]+.

Synthesis of PT6: Deep blue solid, yield: 65%. 1H NMR (400 MHz, CDCl3, δ/ppm): 9.11–9.09 (d, J

EP

= 8.4 Hz, 2H, Ar), 8.11–8.09 (dd, J1 = 3.6 Hz, J2 = 1.0 Hz, 2H, Ar), 8.01–7.80 (d, J = 3.8 Hz, 2H, Ar), 7.84–7.82 (d, J = 7.6 Hz, 2H, Ar), 7.76–7.74 (d, J = 7.6 Hz, 2H, Ar), 7.44–7.42 (m, 2H, Ar), 7.24–7.19

AC C

(m, 6H, Ar), 6.94–6.93 (m, 2H, Ar), 6.91 (s, 2H, Ar), 6.86–6.85 (m, 2H, Ar), 3.74–3.69 (m, 4H, alkyl), 2.17–2.14 (m, 24H, alkyl), 1.87–1.85 (m, 2H, alkyl), 1.64–1.63 (m, 28H, alkyl), 1.54–1.49 (m, 22H, alkyl), 1.40–1.32 (m, 8H, alkyl), 0.99–0.91 (m, 36H, alkyl), 0.90–0.88 (m, 12H, alkyl),

31

P NMR

(CDCl3, 162 Hz, δ/ppm): 3.48 (1JP−Pt = 2326 Hz); IR (KBr) (cm−1): v = 2084 (w, v(C≡C)), 1610 (w, v(C=O)); MALDI-TOF-MS (m/z): 2543.8 [M]+.

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Acknowledgements We thank the National Natural Science Foundation of China (project number 51373145), Areas of

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Excellence Scheme, University Grants Committee of HKSAR (project No. AoE/P-03/08), Hong Kong Baptist University (FRG2/12-13/083), Hong Kong Research Grants Council (HKBU203312) and the Science, Technology and Innovation Committee of Shenzhen Municipality (JCYJ20140419130507116)

SC

for financial support. The work was also supported by Partner State Key Laboratory of Environmental and Biological Analysis (SKLP-14-15-P011) and Strategic Development Fund of HKBU. The project

M AN U

was also supported by the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences.

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Highlights: • New platinum(II) acetylide donor-acceptor (D-A) triads were prepared

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• Spectroscopic, redox and structural characterization were carried out

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• Bulk heterojunction solar cells using these platinum complexes were fabricated