Synthesis and Photovoltaic Properties of New Metalloporphyrin

ARTICLE pubs.acs.org/Macromolecules

Synthesis and Photovoltaic Properties of New Metalloporphyrin-Containing Polyplatinyne Polymers Hongmei Zhan,† Simon Lamare,‡ Annie Ng,§ Tommy Kenny,‡ Hannah Guernon,‡ Wai-Kin Chan,f Aleksandra B. Djuri
sic,*,§ Pierre D. Harvey,*,‡ and Wai-Yeung Wong*,† †

Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee, Hong Kong) and Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong, P.R. China ‡ Departement de Chimie, Universite de Sherbrooke, 2550 Boul. Universite, Sherbrooke, PQ, J1K 2R1 Canada § Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China f Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China

bS Supporting Information ABSTRACT: Three new solution-processable platinum(II) polyyne polymers containing zinc(II) porphyrinate chromophores P1, P2, and P3 and their corresponding dinuclear model complexes were synthesized via the CuI-catalyzed dehydrohalogenation reaction of the platinum(II) chloride precursor and each of the respective bis(ethynyl)-zinc(porphyrin) metalloligands. The thermal, photophysical (absorption, excitation and emission spectra), electrochemical, and photovoltaic properties of P1
P3 were investigated. These results are also correlated by time-dependent density functional theory (TDDFT) calculations. The computations corroborate the presence of moderate conjugation in the π-systems, somewhat more accentuated for P3 where more favorable dihedral angles between the porphyrin and thiophene rings are noted. Moreover, the computed excited states are predicted to be π
π* in nature with some charge transfer components from the trans-[
CtCPt(L)2CtC
]n unit to the porphyrin rings. The optical bandgaps range from 1.93 to 2.02 eV for P1
P3. Intense π
π*-localized fluorescence emissions typical of the Q-bands of the polymers were observed. The effect of thiophene ring along the polymer chain on the extent of π-conjugation, luminescent and photovoltaic properties of these metalated materials was also examined. Bulk heterojunction solar cells using these metallopolymers as an electron donor blended with a methanofullerene electron acceptor were studied. In one case, the metallopolymer P3 showed a power conversion efficiency of 1.04% with the open-circuit voltage of 0.77 V, short-circuit current density of 3.42 mA cm
2 and fill factor of 0.39 under illumination of an AM 1.5 solar cell simulator.

’ INTRODUCTION Organic solar cells have attracted much attention in recent years owing to their advantages of low-cost fabrication by solution processing and easy chemical tailoring, as well as potential applications in flexible, lightweight and large-area energy-harvesting devices. Bulk heterojunction devices fabricated by simply blending organic donor materials and methanofullerene acceptor materials, such as [6,6]-phenyl C61-butyric acid methyl ester (PCBM), in the same organic solvents has become one of the most successful device architectures developed in this field, which result in the efficient photoinduced electron transfer from donor materials to fullerene derivatives.1 Most of the efforts have been focused on developing novel donor materials with sufficient solubility, low optical band gap and high hole mobility, which would lead to efficient solar cells. Porphyrins contain an extensively conjugated two-dimensional π-system which renders them suitable for light-harvesting and efficient electron transfer because the uptake or release of r 2011 American Chemical Society

electrons results in minimal structural change.2 Porphyrin has rich and extensive optical absorption in the visible spectrum and high mobility.3
5 The typical absorption spectra of porphyrin units exhibit sharp and strong Soret bands (410
430 nm) and weak Q-bands (530
540 nm) without absorption features between them. In addition, efficient photoinduced electron separation and transfer between porphyrins and fullerene derivatives have also been reported.6
8 Therefore, organic solar cells using porphyrincontaining molecules,9
11 oligomers,12 and polymers13
15as photoactive layers have been extensively investigated in recent years. Unfortunately, only low power conversion efficiencies (PCEs) were obtained so far. For example, the PCEs of the devices based on porphyrin triad,9 liquid-crystalline porphyrin,4 porphyrin dendrimer,10 porphyrin-containing oligomers,12 and main-chain Received: March 17, 2011 Revised: May 22, 2011 Published: June 13, 2011 5155

dx.doi.org/10.1021/ma2006206 | Macromolecules 2011, 44, 5155–5167

Macromolecules porphyrin polymers14 are only 0.035%, 0.775%, 0.32%, 0.000081% and 0.3%, respectively. More recently, new advances have been realized using supramolecular and nanocomposite systems. Novel organic photovoltaic systems using supramolecular complexes of porphyrin-peptide oligomers with fullerene clusters assembled as three-dimensional arrays onto SnO2 films have been constructed with the PCE reaching 1.6%16 whereas photovoltaic cells using composite nanoclusters of porphyrins and fullerenes with gold nanoparticles were also developed to afford a PCE of 1.5%.3 On the other hand, platinum metallopolyyne polymers of the form trans-[
Pt(L)2CtCRCtC
]n (L is an auxiliary phosphine ligand, and R is an aromatic spacer unit) have attracted a great deal of research attention. The interest derives from the fact that incorporation of platinum into the conjugated polymers can result in good overlap between the d-orbital of Pt with the p-orbital of the alkyne unit, and so the two alkyne units can mutually interact through the Pt dxy and dyz orbitals, which lead to efficient electronic π-conjugation and delocalization along the polymer chain.17 Moreover, due to strong spin
orbit coupling resulting from the presence of platinum, intersystem crossing is enhanced which enables the spin-forbidden triplet emission to become partially allowed,18
24 and can extend the exciton diffusion length. These features enable platinum-containing metallopolyyne polymers more feasible to be used as the donor materials in photovoltaic cells, and encouraging progress has been made in recent years.25
28 In view of the considerations above, the use of metalloporphyrins as the building block in combination with linear conjugated systems of transition metal-alkyne polymers for the design of new p-type photovoltaic active materials serves as a good illustration of the recent trend toward solution-processable functional polymers. We present here the synthesis, characterization and theoretical modeling studies of several platinum polyyne polymers coupled with zinc(II) porphyrinate chromophores, and their photovoltaic properties have been investigated. The introduction of thiophene unit into the porphyrin-based polymer main chain is expected to extend the π-conjugation and cover the missing absorption region (430
530 nm) or enhance the absorption of the weaker Q-bands. Phenyl rings at positions 10 and 20 of the zinc porphyrin ring are used for enhancing the molecular ordering, hence improving the interpenetrating network with the fullerene derivative. This work represents the first example of porphyrin-containing polymetallaynes used for harvesting solar energy in solution-processed photovoltaic devices.

’ EXPERIMENTAL SECTION Materials. All reactions were carried out under a nitrogen atmosphere by using standard Schlenk techniques. Solvents were dried and distilled from appropriate drying agents under an inert atmosphere prior to use. Glassware was oven-dried at about 120 °C. All reagents and chemicals, unless otherwise stated, were purchased from commercial sources and used without further purification. 5-Bromothiophene-2carbaldehyde29 and meso-phenyldipyrromethane30 trans-[PtCl(Ph)(PEt3)2]31 and trans-[Pt(PBu3)2Cl2]32 were prepared according to the literature methods. All reactions were monitored by thin-layer chromatography (TLC) with Merck precoated glass plates. Flash column chromatography and preparative TLC were carried out using silica gel from Merck (230
400 mesh). Syntheses. The syntheses of all the ligand precursors are given in the Supporting Information.

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General Synthetic Procedures of Porphyrin Compounds.14 5,15-Bis(1,4-trimethylsilylethynylbenzene)-10,20-bis(phenyl)porphyrin (L1H-TMS). A solution of 4-(2-(trimethylsilyl)ethynyl)benzaldehyde (119 mg, 0.59 mmol) and meso-phenyldipyrromethane (139 mg, 0.59 mmol) in CH2Cl2 (60 mL) was purged with nitrogen for 30 min, and then trifluoroacetic acid (TFA) (47 mg, 0.41 mmol) was added. The mixture was stirred for 3 h at room temperature, and then 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (267 mg, 1.2 mmol) was added. After the mixture was stirred at room temperature for an additional 30 min, the reaction was quenched by adding triethylamine (0.6 mL). The solvent was removed, and the residue was purified by flash column chromatography on silica gel using CH2Cl2/hexane (1:1, v/v) as the eluent. Recrystallization from CH2Cl2/methanol gave L1H-TMS as a purple solid (45 mg, 11%). ν(CtC) 2153 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 8.86 (d, J = 5.2 Hz, 4H, Ar), 8.81 (d, J = 5.0 Hz, 4H, Ar), 8.21
8.19 (m, 4H, Ar), 8.18
8.15 (m, 4H, Ar), 7.86 (d, J = 8.1 Hz, 4H, Ar), 7.78
7.74 (m, 6H, Ar), 0.38 (s, 18H, TMS),
2.82 (s, 2H, NH) ppm. FAB-MS: m/z 807.5 (Mþ). The same procedures were applied to prepare L2H-TMS and L3HTMS from their corresponding aromatic aldehyde derivatives and mesophenyldipyrromethane. 5,15-Bis(1,4-(2,5-trimethylsilylethynylthienyl)benzene)-10,20-bis(phenyl)porphyrin (L2H-TMS). Purple solid, yield: 10%. ν(CtC) 2141 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 8.91
8.89 (m, 4H, Ar), 8.87
8.85 (m, 4H, Ar), 8.21 (d, J = 7.8 Hz, 8H, Ar), 7.94 (d, J = 7.9 Hz, 4H, Ar), 7.77
7.74 (m, 6H, Ar), 7.45 (d, J = 3.7 Hz, 2H, Ar), 7.35 (d, J = 3.7 Hz, 2H, Ar), 0.31 (s, 18H, TMS),
2.76 (s, 2H, NH) ppm. FAB-MS: m/z 971.5 (Mþ). 5,15-Bis(2,5-trimethylsilylethynylthiophene)-10,20-bis(phenyl)porphyrin (L3H-TMS). Purple solid, yield: 14%. ν(CtC) 2144 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.06 (d, J = 4.7 Hz, 4H, Ar), 8.84 (d, J = 4.7 Hz, 4H, Ar), 8.20
8.19 (m, 4H, Ar), 7.81
7.77 (m, 6H, Ar), 7.75 (d, J = 3.6 Hz, 2H, Ar), 7.64 (d, J = 3.6 Hz, 2H, Ar), 0.35 (s, 18H, TMS),
2.76 (s, 2H, NH) ppm. FAB-MS: m/z 819.4 (Mþ).

General Synthetic Procedures of Zn
Porphyrin Complexes. Zinc(II) 5,15-Bis(1,4-trimethylsilylethynylbenzene)-10,20-bis(phenyl)porphyrin (L1-TMS). To a solution of L1H-TMS (41 mg, 0.05 mmol) in CH2Cl2 (16 mL) was added a solution of Zn(OAc)2 3 H2O (25 mg, 0.11 mmol) in methanol (1 mL). The reaction mixture was stirred at room temperature for 5 h. Evaporation of the solvent and purification by column chromatography using CH2Cl2/hexane (1:1, v/v) as the eluent afforded the product L1-TMS (44 mg, 98%) as a purple solid. ν(CtC) 2156 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 8.97 (d, J = 4.8 Hz, 4H, Ar), 8.91 (d, J = 4.8 Hz, 4H, Ar), 8.22
8.19 (m, 4H, Ar), 8.17
8.15 (m, 4H, Ar), 7.87 (d, J = 8.0 Hz, 4H, Ar), 7.77
7.75 (m, 6H, Ar), 0.38 (s, 18H, TMS) ppm. 13C NMR (CDCl3, 125 MHz, δ): 150.21, 149.81, 143.03, 142.56, 134.29, 134.19, 132.18, 131.67, 130.15, 128.82, 127.51, 126.51, 121.31, 120.27 (Ar), 105.02, 95.32 (CtC), 0.09 (TMS) ppm. FAB-MS: m/z 869.4 (Mþ). The same procedures were used to prepare L2-TMS and L3-TMS from their corresponding starting materials L2H-TMS and L3H-TMS. Zinc(II) 5,15-Bis(1,4-(2,5-trimethylsilylethynylthienyl)benzene)-10,20-bis(phenyl)porphyrin (L2-TMS). Purple solid, yield: 93%. ν(CtC) 2142 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.02 (m, 4H, Ar), 8.97
8.95 (m, 4H, Ar), 8.24
8.21 (m, 8H, Ar), 7.95 (d, J = 7.9 Hz, 4H, Ar), 7.79
7.73 (m, 6H, Ar), 7.45 (d, J = 3.8 Hz, 2H, Ar), 7.35 (d, J = 3.8 Hz, 2H, Ar), 0.32 (s, 18H, TMS) ppm. 13C NMR (CDCl3, 125 MHz, δ): 150.36, 150.12, 145.70, 142.76, 135.11, 134.49, 134.10, 132.96, 132.28, 131.87, 128.96, 127.61, 126.66, 124.10, 123.38, 122.77, 121.43, 120.47 (Ar), 99.99, 97.82 (CtC), 0.09 (TMS) ppm. FAB-MS: m/z 1033.4 (Mþ). Zinc(II) 5,15-Bis(2,5-trimethylsilylethynylthiophene)-10,20-bis(phenyl)porphyrin (L3-TMS). Purple solid, yield: 96%. ν(CtC) 2145 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.16 (d, J = 4.7 Hz, 4H, Ar), 8.94 (d, J = 4.7 Hz, 4H, Ar), 8.21
8.19 (m, 4H, Ar), 7.80
7.76 (m, 6H, Ar), 7.74 5156

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Macromolecules (d, J = 3.6 Hz, 2H, Ar), 7.64 (d, J = 3.6 Hz, 2H, Ar), 0.35 (s, 18H, TMS) ppm. 13C NMR (CDCl3, 125 MHz, δ): 150.81, 150.61, 145.51, 142.43, 134.43, 133.27, 132.56, 131.90, 131.80, 127.74, 126.69, 125.18, 122.11, 111.47 (Ar), 99.92, 97.61 (CtC) ppm. FAB-MS: m/z 881.2 (Mþ). Synthesis of Zn(II) Porphyrinate Ligands. The ligands were synthesized by deprotection reaction of L1-TMS to L3-TMS using tetrabutylammonium fluoride (TBAF) as a base in THF. A typical example was given for L1. Zinc(II) 5,15-Bis(1,4-ethynylbenzene)-10,20-bis(phenyl)porphyrin (L1). TBAF (0.13 mL, 1 M in THF) was added to a stirred solution of L1TMS (54 mg, 0.06 mmol) in THF (8 mL). After stirring for 5 min, water (30 mL) was added to quench the reaction. The solution was extracted with chloroform, washed with water and dried over anhydrous MgSO4. After evaporation of the solvent, the residue was purified by column chromatography using CH2Cl2/hexane (1.2:1, v/v) as the eluent to give L1 (41 mg, 90%) as a purple solid. IR (KBr): ν(CtC) 2106 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 8.97
8.95 (m, 4H, Ar), 8.93 (m, 4H, Ar), 8.22
8.17 (m, 8H, Ar), 7.88 (d, J = 7.8 Hz, 4H, Ar), 7.77
7.74 (m, 6H, Ar), 3.31 (s, 2H, CtCH) ppm. 13C NMR (CDCl3, 125 MHz, δ): 150.29, 149.83, 143.44, 142.62, 134.40, 134.32, 132.29, 132.06, 131.63, 130.08, 127.59, 126.59, 121.41, 120.18 (Ar), 83.73, 78.16 (CtC) ppm. FABMS: m/z 725.0 (Mþ). Anal. Calcd for C48H28N4Zn: C, 79.39; H, 3.89; N, 7.72. Found: C, 79.21; H, 4.05; N, 7.57. Zinc(II) 5,15-Bis(1,4-(2,5-ethynylthienyl)benzene)-10,20-bis(phenyl)porphyrin (L2). Purple solid, yield: 85%. IR (KBr): ν(CtC) 2098 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.02
9.00 (m, 4H, Ar), 8.98
8.95 (m, 4H, Ar), 8.25
8.22 (m, 8H, Ar), 7.97 (d, J = 8.1 Hz, 4H, Ar), 7.77 (m, 6H, Ar), 7.48 (d, J = 3.8 Hz, 2H, Ar), 7.41 (d, J = 3.7 Hz, 2H, Ar), 3.49 (s, 2H, CtCH) ppm. 13C NMR (CDCl3, 125 MHz, δ): 145.56, 142.18, 142.12, 141.98, 135.27, 134.63, 134.11, 133.16, 127.86, 127.82, 126.80, 126.78, 124.22, 123.47, 122.85, 120.44, 120.32, 119.47 (Ar), 100.07, 97.78 (CtC) ppm. FAB-MS: m/z 889.4 (Mþ). Anal. Calcd for C56H32N4S2Zn: C, 75.54; H, 3.62; N, 6.29. Found: C, 75.34; H, 3.79; N, 6.42. Zinc(II) 5,15-Bis(2,5-ethynylthiophene)-10,20-bis(phenyl)porphyrin (L3). Purple solid, yield: 87%. ν(CtC) 2101 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.17 (d, J = 4.7 Hz, 4H, Ar), 8.96 (d, J = 4.7 Hz, 4H, Ar), 8.21
8.19 (m, 4H, Ar), 7.79
7.77 (m, 8H, Ar), 7.68 (d, J = 3.6 Hz, 2H, Ar), 3.57 (s, 2H, CtCH) ppm. 13C NMR (CDCl3, 125 MHz, δ): 150.75, 150.61, 145.75, 142.36, 134.38, 133.11, 132.58, 132.22, 131.74, 127.72, 126.66, 123.99, 122.13, 111.26 (Ar), 82.13, 77.10 (CtC) ppm. FAB-MS: m/z 737.2 (Mþ). Anal. Calcd for C44H24N4S2Zn: C, 71.59; H, 3.28; N, 7.59. Found: C, 71.68; H, 3.50; N, 7.45. Synthesis of Platinum Polyyne Polymers (P1
P3). The polymers were prepared by the dehydrohalogenative polycondensation between trans-[Pt(PBu3)2Cl2] and each of the ligands (L1
L3). A typical procedure was given for P1 starting from L1. Polymerization was carried out by mixing L1 (30 mg, 0.04 mmol), trans-[Pt(PBu3)2Cl2] (28 mg, 0.04 mmol) and CuI (3.00 mg) in Et3N/ CH2Cl2 (12 mL, 1:1, v/v). After stirring at room temperature for 24 h under nitrogen, the solution mixture was evaporated to dryness. The residue was redissolved in CH2Cl2 and filtered through a short alumina column using the same eluent to remove ionic impurties and catalyst residues. After removal of the solvent, the crude product was purified by precipitation in CH2Cl2 from MeOH twice to give the polymer P1 (15 mg, 27%) as a purple solid. IR (KBr): ν(CtC) 2099 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.05
8.95 (m, 8H, Ar), 8.24
8.09 (m, 8H, Ar), 7.78
7.71 (m, 10H, Ar), 2.42
2.38 (m, 12H, PBu3), 1.70
1.58 (m, 12H, PBu3), 1.51
1.42 (m, 12H, PBu3), 0.94 (t, 18H, PBu3) ppm. 31P NMR (CDCl3, 162 Hz, δ): 3.16 (1JP
Pt = 2352 Hz) ppm. Anal. Calcd for (C72H80N4P2PtZn)n: C, 65.32; H, 6.09; N, 4.23. Found: C, 65.45; H, 5.87; N, 4.10. GPC (THF): Mw = 22325, Mn = 9500, PDI = 2.35, DP = 7. P2. Purple solid, yield: 32%. IR (KBr): ν(CtC) 2086 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.05
9.03 (m, 4H, Ar), 8.98
8.95 (m, 4H, Ar), 8.22
8.20 (m, 8H, Ar), 7.95 (m, 4H, Ar), 7.78
7.76 (m, 6H, Ar),

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7.44 (m, 2H, Ar), 7.00 (m, 2H, Ar), 2.24
2.22 (m, 12H, PBu3), 1.71
1.67 (m, 12H, PBu3), 1.61
1.54 (m, 12H, PBu3), 1.01 (t, J = 7.2 Hz, 18H, PBu3) ppm. 31P NMR (CDCl3, 162 Hz, δ): 3.42 (1JP
Pt = 2328 Hz) ppm. Anal. Calcd for (C80H84N4P2S2PtZn)n: C, 64.57; H, 5.69; N, 3.76. Found: C, 64.76; H, 5.85; N, 3.68. GPC (THF): Mw = 50820, Mn = 13620, PDI = 3.73, DP = 9. P3. Green solid, yield: 35%. IR (KBr): ν(CtC) 2084 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.30
9.25 (m, 4H, Ar), 8.93
8.88 (m, 4H, Ar), 8.21
8.19 (m, 4H, Ar), 7.82
7.66 (m, 8H, Ar), 7.26 (m, 2H, Ar), 2.29
2.18 (m, 12H, PBu3), 1.73
1.70 (m, 12H, PBu3), 1.57
1.53 (m, 12H, PBu3), 1.03
0.88 (m, 18H, PBu3) ppm. 31P NMR (CDCl3, 162 Hz, δ): 3.30 (1JP
Pt = 2325 Hz) ppm. Anal. Calcd for (C68H76N4P2S2PtZn)n: C, 61.14; H, 5.73; N, 4.19. Found: C, 61.34; H, 5.56; N, 4.24. GPC (THF): Mw = 112250, Mn = 32470, PDI = 3.46, DP = 24. Synthesis of Platinum Model Complexes (M1
M3). All of them were synthesized following the dehydrohalogenating coupling between trans-[PtCl(Ph)(PEt3)2] and their corresponding diterminal alkynes. A typical procedure was given for M1 starting from L1. To a solution of L1 (6 mg, 0.008 mmol) and trans-[PtCl(Ph)(PEt3)2] (10 mg, 0.018 mmol) in Et3N (2 mL) and CH2Cl2 (2 mL) was added CuI (1.0 mg) under nitrogen. After stirring overnight at room temperature, all volatile components were removed under reduced pressure. The residue was dissolved in CH2Cl2 and purified by preparative silica TLC plates using CH2Cl2/hexane as the eluent. The product M1 was obtained as a purple solid (6 mg, 46%). ν(CtC) 2091 cm
1; 1H NMR (CDCl3, 400 MHz, δ): 9.04 (d, J = 4.6 Hz, 4H, Ar), 8.93 (d, J = 4.7 Hz, 4H, Ar), 8.24
8.22 (m, 4H, Ar), 8.05 (d, J = 8.1 Hz, 4H, Ar), 7.79
7.73 (m, 6H, Ar), 7.69
7.67 (m, 4H, Ar), 7.40 (d, J = 7.1 Hz, 4H, Ar), 7.02 (t, J = 7.4 Hz, 4H, Ar), 6.85 (t, J = 7.2 Hz, 2H, Ar), 1.92
1.87 (m, 24H, PEt3), 1.25
1.21 (m, 36H, PEt3) ppm; 31P NMR (CDCl3, 162 Hz, δ): 10.08 (1JP
Pt = 2639 Hz) ppm; FAB-MS: m/z 1739.7 (Mþ). Anal. Calcd for C84H96N4P4Pt2Zn: C, 57.95; H, 5.56; N, 3.22. Found: C, 58.12; H, 5.43; N, 3.45. M2. Purple solid, yield: 38%. ν(CtC) 2079 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.05
9.03 (m, 4H, Ar), 8.96
8.94 (m, 4H, Ar), 8.22 (d, J = 6.5 Hz, 4H, Ar), 8.18 (d, J = 7.7 Hz, 4H, Ar), 7.93 (d, J = 8.1 Hz, 4H, Ar), 7.79
7.75 (m, 6H, Ar), 7.41 (d, J = 3.7 Hz, 2H, Ar), 7.35 (d, J = 7.0 Hz, 4H, Ar), 7.01
6.97 (m, 6H, Ar), 6.83 (t, J = 7.2 Hz, 2H, Ar), 1.84
1.74 (m, 24H, PEt3), 1.25
1.19 (m, 36H, PEt3) ppm. 31P NMR (CDCl3, 162 Hz, δ): 10.01 (1JP
Pt = 2627 Hz) ppm. MALDI
TOF: m/z 1905.4798 [M þ H]þ, calculated: 1904.4922. Anal. Calcd for C92H100N4P4S2Pt2Zn: C, 57.99; H, 5.29; N, 2.94. Found: C, 57.76; H, 5.34; N, 3.20. M3. Purple solid, yield: 48%. ν(CtC) 2081 cm
1. 1H NMR (CDCl3, 400 MHz, δ): 9.30 (d, J = 4.7 Hz, 4H, Ar), 8.92 (d, J = 4.7 Hz, 4H, Ar), 8.22
8.19 (m, 4H, Ar), 7.79
7.73 (m, 6H, Ar), 7.64 (d, J = 3.5 Hz, 2H, Ar), 7.36 (d, J = 7.0 Hz, 4H, Ar), 7.27 (d, J = 3.5 Hz, 2H, Ar), 6.99 (t, J = 7.4 Hz, 4H, Ar), 6.83 (t, J = 7.2 Hz, 2H, Ar), 1.87
1.80 (m, 24H, PEt3), 1.18
1.12 (m, 36H, PEt3) ppm. 31P NMR (CDCl3, 162 Hz, δ): 10.03 (1JP
Pt = 2630 Hz) ppm. FAB-MS: m/z 1751.7 (Mþ). Anal. Calcd for C80H92N4P4S2Pt2Zn: C, 54.81; H, 5.29; N, 3.20. Found: C, 54.98; H, 5.10; N, 3.12. Physical Measurements. Fast atom bombardment (FAB) mass spectra were recorded on a Finnigan MAT SSQ710 system. NMR spectra were measured in CDCl3 on a Bruker AVANCE 400 MHz FTNMR spectrometer using tetramethylsilane as an internal standard for 1 H and 13C nuclei or 85% H3PO4 as an external standard for 31P nucleus. UV
visible spectra were obtained on an HP-8453 diode array spectrophotometer. The solution emission spectra of the compounds were measured on a Photon Technology International (PTI) Fluorescence QuantaMaster Series QM1 spectrophotometer. Thermogravimetric analysis (TGA) measurements were performed on thermal gravimetric analyzer (model Perkin-Elmer TGA-6) under a nitrogen flow at a 5157

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Macromolecules

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Scheme 1. Synthetic Routes to Ligand Precursors

heating rate of 15 °C min
1. The gel permeation chromatography (GPC) measurements were performed on the Agilent 1050 HPLC system with VWD, using THF as eluent and polystyrene standards as calibrants. Electrochemical measurements were carried out on a deoxygenated solution of [nBu4N]PF6 (0.1 M) in acetonitrile using a computer-controlled electrochemical workstation, a eDAQ EA161 potentiostat electrochemical interface equipped with a thin film coated indium tin oxide (ITO) covered glass working electrode, a Pt wire as the counter electrode, and a Ag/AgCl (in 3 M KCl) as the reference electrode (at the scan rate of 100 mV s
1). Polymer film was prepared by dipping a glass plate in the polymer solution of chlorobenzene and then dried under vacuum, and one side of the glass plate had been casted ITO film beforehand. The onset oxidation and reduction potentials were used to determine the HOMO and LUMO energy levels using the equations EHOMO = [
(Eonset, ox (vs Ag/AgCl)
Eonset (NHE vs Ag/AgCl))]
4.50 eV and ELUMO = [
(Eonset, red (vs Ag/AgCl)
Eonset (NHE vs Ag/AgCl))]
4.50 eV, where the potentials for NHE versus vacuum and NHE versus Ag/AgCl are 4.50 and
0.22 V, respectively.33 Computational Details. Calculations were performed with the Gaussian 0934 program at the Universite de Sherbrooke with Mammouth super computer supported by le Reseau Quebecois de Calculs de Haute Performances. The DFT35
38 and TDDFT39
41 were calculated with the B3LYP42
44 method. 3-21G*45
50 basis sets were used for C, H, S, N and Zn. Polarized VDZ (valence double ζ)51with SBKJC effective core potentials52
55 were applied for Pt as well. The predicted phosphorescence wavelengths were obtained by energy differences between the total energy of the triplet and singlet optimized states.56 The calculated absorption spectra and related molecular orbital (MO) contributions were obtained from the TDDFT/singlets output file and Gausssum 2.1.57

Fabrication and Characterization of Bulk Heterojunction Solar Cells. The device structure was ITO/poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer:PCBM blend/Al. Indium tin oxide (ITO) coated glass substrates (10 Ω per square) were cleaned by sonication in toluene, acetone, ethanol, and deionized water, dried in an oven, and then cleaned with UV ozone for 300 s. As-received PEDOT:PSS solution was passed through the 0.45 μm filter and spin-coated on patterned ITO substrates at 5000 rpm for 2 min, followed by baking in N2 at 120 °C for 20 min. P1
P3:PCBM (1:4 by weight) active layer was prepared by spincoating the chlorobenzene solution (4 mg mL
1 of polymer, 16 mg mL
1 of PCBM) at 1000 rpm for 2 min. The substrates were dried at room temperature under high vacuum (10
5 to 10
6 Torr) for 2 h and then stored in a glovebox under Ar atmosphere overnight. An Al electrode (100 nm) was evaporated through a shadow mask to define the

active area of the devices (2 mm diameter circle). All the fabrication procedures (except drying, PEDOT:PSS annealing, and Al deposition) and cell characterization were performed in air. PCE was determined from J
V curve measurement (using a Keithley 2400 sourcemeter) under white light illumination (at 100 mW cm
1). For white light efficiency measurements, an Oriel 66002 solar light simulator with an AM1.5 filter was used. The light intensity was measured by a Molectron Power Max 500D laser power meter.

’ RESULTS AND DISCUSSION Synthesis and Characterization. The three aromatic aldehyde derivatives were prepared from 4-bromobenzaldehyde and thiophene-2-carbaldehyde according to the pathways depicted in Scheme 1. Following appropriate chemical modifications of the published synthetic procedures, the key trans-substituted porphyrins L1H-TMS, L2H-TMS and L3H-TMS were synthesized by the acid-catalyzed condensation of meso-phenyldipyrromethane with the aromatic aldehyde derivatives, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) at room temperature.14 The free base porphyrins were then coordinated with zinc(II) ion from zinc acetate in the solvent mixture of CH2Cl2 and MeOH to form the trimethylsilylethynyl-containing zinc(II) porphyrins L1-TMS to L3-TMS in high yields. The diethynyl ligands L1, L2 and L3 were then prepared by removing the protecting groups with tetrabutylammonium fluoride (TBAF) as shown in Scheme 2. Scheme 3 shows the synthetic routes toward Pt(II)-containing Zn(II)-porphyrinate polymers and their corresponding model complexes. By CuI-catalyzed dehydrohalogenation method, model compounds M1
M3 were prepared from ligands L1
L3 and trans-[PtCl(Ph)(PEt3)2] (in a 1:2.2 stoichiometry) in CH2Cl2 and Et3N (1:1, v/v) in moderate yields. Using the same approach, the reaction of metalloligands with trans-[Pt(nBu3P)2Cl2] in a 1:1 ratio gave the respective polymers P1, P2, and P3 in 27
35% yields. All of the metal alkynyl complexes and polymers are stable and generally exhibit good solubility in chlorocarbons CH2Cl2 and CHCl3. For P3, it is more soluble in THF and chlorobenzene than in chloroalkanes. FTIR spectra show that the ν(CtC) stretching frequencies for the platinum polymers at about 2086 cm
1 and model compounds at about 2081 cm
1 are lower than those for the free diethynyl ligands near 2101 cm
1, which reveal a higher 5158

dx.doi.org/10.1021/ma2006206 |Macromolecules 2011, 44, 5155–5167

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ARTICLE

Scheme 2. Synthetic Pathways to Diethynyl Ligands L1
L3

Scheme 3. Synthetic Pathways to Pt(II) Polyynes P1
P3 and Diynes M1
M3

degree of conjugation in the former. Moreover, the absence of the stretching vibrations for the terminal acetylenic C
H bonds at around 3286 cm
1 further confirms the successful formation

of platinum
carbon bond. 31P NMR spectra of the platinumcontaining complexes and polymers exhibit a strong 31P singlet signal flanked with two satellites, consistent with a trans-geometry 5159

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Figure 1. Absorption (black), excitation (red) and fluorescence (blue) spectra of P1 (up), P3 (middle), and P2 (bottom) in 2-MeTHF at 298 (left) and 77 K (right).

of the square-planar Pt unit, and their 1JP
Pt values between 2627 to 2639 Hz for the PEt3 moieties and 2325 and 2352 Hz for the PBu3 moieties are typical of those for related trans-PtP2 systems.58 The Pt model complexes were also successfully characterized by mass spectrometry in which the respective molecular ion was observed in each case. Molecular weights of these polymers were determined by GPC in THF solution using polystyrene standards for the method calibration. P2 has a relatively higher degree of polymerization than that of P1. This is probably ascribed to the more reactive terminal acetylenic C
H bond at the R-position of thiophene ring than that of benzene ring in the dehydrohalogenative polymerization reaction. This is also corroborated with the data of P3, which has a Mn of 32470 with a higher degree of polymerization of 24. The thermal properties of the polymers were determined by thermogravimetric analysis (TGA). The polymers P1, P2, and P3 have relatively good thermal stability with onset decomposition temperatures of 305, 348, and 366 °C, respectively. Absorption and Photoluminescence Spectra. The absorption and emission data for the three polymers are presented in Figure 1 and Table 1. All the polymers show a sharp and strong Soret band at about 430 nm (π f π* transition, S0 f S2) and a set of weak Q-bands between 540 and 635 nm (π f π* transition, S0 f S1), which is a typical absorption profile for

Table 1. Spectral (Absorption, Top; Fluorescence, Bottom) and Photophysical Parameters polymer in 2-MeTHF polymer

temp (K)

P1

298 77 298

P3 P2

Soret, λ (nm)

Q-region, λ (nm)

342

398 sh, 430 406 sh, 432, 442

508 sh, 550, 593 522 sh, 558, 598 555, 607

297, 348

434, 456 sh

77

364

438, 460

522, 562, 612

298

377

401, 426

552, 610

77

382

410, 432, 448

556, 600

298 K polymer

λF (nm)

P1

608, 655

P3 P2

639 609, 655

ΦF

77 K τF (ns)

λF (nm)

τF (ns)

0.081

0.28

612, 642 663, 699

0.87

0.029 0.085