Grignard Metathesis Polymerization and Properties of 1,1-Disubstituted-2,5-dibromo-3,4-diphenylsiloles

Abstract

Grignard metathesis polymerizations of 1,1-disubstituted-2,5-dibromo-3,4-diphenylsiloles such as 1,1-dimethyl-2,5-dibromo-3,4-diphenylsilole, 1,1-diethyl-2,5-dibromo-3,4-diphenylsilole, 1,1-diisopropyl-2,5-dibromo-3,4-diphenylsilole, and 1,1-dihexyl-2,5-dibromo-3,4-diphenylsilole were performed to yield poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s containing fluorescent aromatic chromophore groups such as phenyl and silole in the polymer main chain: poly(1,1-dimethyl-3,4-diphenyl-2,5-silole), poly(1,1-diethyl-3,4-diphenyl-2,5-silole), poly(1,1-diisopropyl-3,4-diphenyl-2,5-silole), and poly(1,1-dihexyl-3,4-diphenyl-2,5-silole), respectively. The obtained materials are highly soluble in common organic solvents such as chloroform and tetrahydrofuran. Fourier-transform infrared spectra of all the polymers have characteristic C=C stretching frequencies at $1620-1628cm^{-1}$. The prepared organosilicon polymers exhibit strong absorption maximum peaks at 273-293 nm in the tetrahydrofuran solution, showing a red-shift of 18-34 nm relative to those of the monomer, strong excitation maximum peaks at 276-303 nm, and strong fluorescence emission maximum bands at 350-440 nm. Thermogravimetric analysis shows that most of the polymers are stable up to $200^{\circ}C$ with a weight loss of 6-16% in nitrogen.

Introduction

π-Conjugated organosilicon polymeric materials have excited much interest because of their potentially useful applications.1,2 Organosilicon polymers bearing fluorescent groups are also of great interest for use in electrolumine-scence materials.3,4

Silacyclopenta-2,4-dienes, also called siloles, are a series of five-membered silacyclic dienes that contain unique π-electron systems.5 Silole derivatives are new π-electronic materials with novel electronic and optical properties.6-8 π-Conjugated polymers containing siloles have also received much attention for potential optoelectronic, photolumine-scence,9-11 and sensor applications.12,13 End-capped silole dendrimers on an ethenyl-phenyl-carbosilane skeleton show green to greenish-blue fluorescence and have potential applications as electroluminescent materials.14 However, few syntheses of poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s have been reported.15,16

Aryl- and heteroaryl-conjugated polymers are usually synthesized through metal-catalyzed polycondensation reac-tions, based on Yamamoto, Suzuki, or Stille coupling reac-tions,17,18 including the Grignard metathesis (GRIM) method.19 In GRIM, Ni(II) complexes are used to polymerize function-alized Grignard monomers at room temperature, which is an advantage over previous procedures. Recently, to expand the use of GRIM, “turbo-Grignard” reagents (LiCl plus a Grignard reagent) have been used for the synthesis of vari-ous aryl and heteroaryl conjugated polymers.20 The GRIM method can shorten polymerization times and lower reaction temperatures, facilitating the preparation of aryl and hetero-aryl conjugated polymers.21

The melt copolymerizations of 1,3-bis(diethylamino)tetra-methyldisiloxane with several fluorescent aryldiols have been reported to yield poly(arylcarbotetramethyl-disiloxane)s containing fluorescent aromatic chromophores in the main chains.22 The melt copolymerizations of several bis(diethyl-amino)silane derivatives with 2,7-dihydroxyfluoren-9-one were also examined, and were found to produce poly[oxy-(2,7-fluoren-9-onenylene)oxy(diorgnaosilylene)]s contain-ing fluoren-9-one as a fluorescent aromatic chromophore group in the main chains.23 Recently, the melt copolymeri-zations of 1,2-bis(diethylamino)tetramethyldisilane with various aryldiols were studied, and these afforded poly[oxy-(arylene)oxy(tetramethyldisilylene)]s containing fluorescent aromatic chromophore groups in the polymer main chains.24

With these results in mind, we focused on the preparation of fluorescent poly(carbosilane) materials containing aromatic chromophores from silole derivatives in the polymer main chain, using turbo-Grignard metathesis polymerization to produce poly(1,1-disubstituted-3,4-diphenylsilole)s and evaluated their photoelectronic properties.

Here, we report the syntheses of poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s, namely poly(1,1-dimethyl-3,4-diphenyl-2,5-silole) (4a), poly(1,1-diethyl-3,4-diphenyl-2,5-silole) (4b), poly(1,1-diisopropyl-3,4-diphenyl-2,5-silole) (4c), and poly(1,1-dihexyl-3,4-diphenyl-2,5-silole) (4d) via GRIM polymerizations of 1,1-disubstituted-2,5-dibromo-3,4-diphenylsiloles, namely 1,1-dimethyl-2,5-dibromo-3,4-diphenylsilole (3a), 1,1-diethyl-2,5-dibromo-3,4-diphenyl-silole (3b), 1,1-diisopropyl-2,5-dibromo-3,4-diphenylsilole (3c), and 1,1-dihexyl-2,5-dibromo-3,4-diphenylsilole (3d), respectively, using a “turbo-Grignard” reagent.

The goal of these GRIM polymerizations was to synthe-size poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s with high molecular weights. The materials obtained were charac-terized using Fourier-transform infrared (FTIR) and 1H, 13C, and 29Si nuclear magnetic resonance (NMR) spectroscopies in the solution state. We focused on investigating the photo-electronic and thermal properties of the prepared polymers 4a-d using solution-state absorption, excitation, and fluore-scence emission spectrophoscopies and thermogravimetric analysis (TGA).

 

Results and Discussion

Monomer Synthesis. 2,5-Dibromo-3,4-diphenylsilole mono-mers 3a-d were prepared via a two-step reaction, as shown in Scheme 1. For example, in the first step, dichlorodi-methylsilane (1a) was reacted with phenylethynyllithium, which was prepared in situ by a reaction of phenylacetylene with n-butyllithium in tetrahydrofuran (THF) at −70 °C, to yield dimethylbis(phenylethynyl)silane (2a) quantitatively. In the second step, intramolecular reductive cyclization of 2a was performed by treatment with lithium naphthalenide (4 mol), followed by anhydrous ZnCl2 and N-bromosucci-nimide (NBS), to afford 2,5-dibromo-1,1-dimethyl-3,4-di-phenylsilole (3a).

2,5-Dibromosiloles 3b-d were similarly prepared by cycli-zation reactions of diethylbis(phenylethynyl)silane (2b), diisopropylbis(phenylethynyl)silane (2c), and dihexylbis-(phenylethynyl)silane (2d), respectively, which were pre-pared from dichlorodiethylsilane (1b), dichlorodiisopropyl-silane (1c), and dichlorodihexylsilane (1d), respectively.

The monomers 3a-d were characterized using various spectroscopic methods, such as 1H, 13C, and 29Si NMR spectroscopies in the solution state. The 1H NMR spectrum of 3a exhibits a clear singlet resonance at 0.47 ppm, ascribed to the methyl group bonded to the silole silicon.6,25 In the 13C NMR spectrum of 3a, one carbon peak from the methyl group bonded to the silicon is observed at −6.05 ppm.6,25 In the 29Si NMR spectrum of 3a, the silicon resonance is observed at 4.96 ppm. The monomers 3a-d were success-fully prepared via two-step reactions under the conditions described.

We examined the absorption spectra of the monomers 3a-d in THF solution. The maximum absorption band for 3a is observed at 275 nm, with a molar absorptivity of 8.50 × 103 cm–1 M–1. The absorption spectra of 3b-d also show strong absorption peaks at 260, 253, and 243 nm, respectively. These strong absorption bands in the ultraviolet-visible (UV-vis) spectra of 3a-d may result from chromophores such as phenyl and diene groups in the 3,4-diphenylsiole monomers.3

Grignard Metathesis Polymerization. Poly(1,1-disub-stituted-3,4-diphenyl-2,5-silole)s were synthesized by GRIM polymerizations,20 using a “turbo-Grignard” reagent. Ni(II) complexes such as [1,3-bis(diphenylphosphine)propane]di-chloronickel(II) [Ni(dppp)Cl2] were used to polymerize the functionalized Grignard monomers at room temperature.26 The addition of LiCl to a Grignard reagent dissociates the polymeric aggregates formed in solution to produce a very reactive complex [i-PrMgCl2−Li+].20

A solution of dibromosilole 3a in THF was added to i-PrMgCl⋅LiCl and stirred for 17 h at room temperature, resulting in magnesium-halogen exchange, as shown in Scheme 2.20 Then Ni(dppp)Cl2 was added to the reaction mixture, and polymerization was allowed to proceed for 48 h.26 Poly(1,1-dimethyl-3,4-diphenyl-2,5-silole) (4a) was obtained as a yellowish viscous liquid. Poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s 4b-d were also prepared by GRIM polymerizations of 2,5-dibromo-1,1-diethyl-3,4-diphenyl-silole (3b), 2,5-dibromo-1,1-diisopropyl-3,4-diphenylsilole (3c), and 2,5-dibromo-1,1-dihexyl-3,4-diphenylsilole (3d), respectively, as shown in Scheme 2.

Scheme 1

Scheme 2

Table 1.aDetermined by GPC in THF relative to polystyrene standards. Mw/Mn = polydispersity index (PDI). bIn CDCl3. cIn KBr. dIn THF solution. eDetection wavelengths 380, 350, 440, and 393 nm in THF solution for 4a-d, respectively. fExcitation wavelengths 300, 297, 276, and 303 nm in THF solution for 4a-d, respectively. gFWHM = full width at half maximum. h% Percentage weight remaining at 300 °C in nitrogen.

The prepared poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s 4a-d are brownish or yellowish powders or viscous liquids, and are soluble in common organic solvents such as CHCl3 and THF. The observed weight-average molecular weights (Mw) of 4a-d are in the range 658-1450, with poly-dispersities of 1.08-1.37, as shown in Table 1, indicating that the obtained materials 4a-d are oligomeric. This phenomenon can be explained by the intrinsic-low reactivities of the func-tionalities at the 2,5-position of the silole monomers15 and severe steric congestion.27

We characterized polymers 4a-d using various spectro-scopic methods. Some selected spectral properties of polymers 4a-d are listed in Table 1. The FTIR spectra of 4a-d show characteristic C=C stretching frequencies at 1620, 1628, 1622, and 1628 cm−1, respectively, suggesting that conju-gated C=C alkene double-bond are formed during copoly-merizations.28,29 The 29Si NMR spectra of polymers 4a-d in CDCl3 solution show major singlet resonance peaks at 11.43, 8.58, 7.03, and 6.43 ppm, respectively, indicating that the silicon atoms in the polymer main chains have the structural environments of silole groups, suggesting structures con-sistent with the backbone shown in Scheme 2.30

Polymer Properties. We ex-amined the absorption, excitation, and fluorescence emission spectra of polymers 4a-d in THF solution. A typical absorption spectrum of polymer 4a in THF is shown in Figure 1 as a dashed line. The maximum absorption band for 4a is observed at 293 nm, and the band extends from 244 to 460 nm with a molar absorp-tivity of 5.95 × 103 cm–1 M–1. The absorption spectra of 4b-d reveal strong absorption peaks at l max values ranging from 273 to 283 nm. These strong absorption bands in the UV-vis spectra of 4a-d are attributed to chromophores such as phenyl and diene groups along the polymer backbone.3 A comparison of maximum the absorption bands of polymers 4a-d with those of the monomers 3a-d in THF solution shows a red shift of 18-34 nm, probably because of strong intermolecular interactions through the polymer backbone.

The excitation spectrum for 4a at a detection wavelength of 380 nm shows a strong excitation peak at λex,max = 300 nm (Table 1). A typical excitation spectrum of polymer 4a in THF solution is shown in Figure 1 as a dotted line. The excitation spectra of 4b-d at the detection wavelengths of 350, 440, and 393 nm, respectively, exhibit strong excitation peaks at λex,max values of 297, 276, and 303 nm, respectively (Table 1). These strong excitation bands in the excitation spectra of polymers 4a-d are attributed to the phenyl and diene groups along the polymer backbone.3

The fluorescence emission spectrum of 4a at an excitation wavelength of 300 nm in THF solution has a strong emission peak at λem,max = 380 nm (Table 1). A typical fluorescence spectrum of polymer 4a in THF solution is shown in Figure 1 as a solid line. The fluorescence spectra of 4b-d at ex-citation wavelengths of 297, 276, and 303 nm, respectively, show strong emission peaks at λem,max values of 350, 440, and 393 nm, respectively (Table 1). These strong emission bands in the fluorescence spectra of the polymers are ascribed to fluorophores such as phenyl and diene groups along the polymer backbone.3 As shown in Table 1, fluore-scence emission FWHM (full width at half maximum) values of 4a-d are observed at 105, 104, 94, and 106 nm, respectively. The excitation and fluorescence emission spectra of the polymers imply that poly(3,4-diphenyl-2,5-silole)s 4a-d have chromophores containing phenyl and diene groups along the polymer main chains.3 An ultrafast time-resolved kinetic study is needed for further study of the electronic conjugation properties of the prepared polymeric materials as well as the substituent’s effects in the 3,4-diphenylsilole derivatives.

Figure 1.Absorbance (dashed line, λmax = 293 nm), excitation (dotted line, λdet = 380 nm), and fluorescence emission (solid line, λex = 300 nm) spectra of polymer 4a in THF solution.

Figure 2.TGA thermograms of polymers 4a-d in nitrogen.

The thermal stabilities of poly(1,1-disubstituted-3,4-di-henyl-2,5-silole)s 4a-d in a nitrogen atmosphere were examined using TGA, with a heating rate of 10 °C/min; the results are shown in Figure 2. Polymers 4a-d were stable up to 200 °C, with only 6-16% loss of the initial weights in nitrogen. Polymers 4a-d rapidly lost weight on heating above 200 °C. Rapid weight losses of 53-70% of the initial weights occurred between 200 and 600 °C. Additionally, weight losses of 4-8% of the initial weights occurred bet-ween 600 and 900 °C. When 4a-d were heated to 900 °C, the polymers lost 64-88% of their initial weights, and char yields of about 12-36% were observed.

The prepared polymers 4a-d were stable up to 200 °C, with weight losses of only 6-16% of the initial weight in nitrogen, and about 19-42% of the initial polymer weights remained at 600 °C in nitrogen, as shown in Figure 2 and Table 1.

 

Conclusion

We successfully prepared poly(1,1-dimethyl-3,4-diphenyl-2,5-silole) (4a), poly(1,1-diethyl-3,4-diphenyl-2,5-silole) (4b), poly(1,1-diisopropyl-3,4-diphenyl-2,5-silole) (4c), and poly(1,1-dihexyl-3,4-diphenyl-2,5-silole) (4d) by GRIM polymerizations of 1,1-dimethyl-2,5-dibromo-3,4-diphenyl-silole (3a), 1,1-diethyl-2,5-dibromo-3,4-diphenylsilole (3b), 1,1-diisopropyl-2,5-dibromo-3,4-diphenylsilole (3c), and 1,1-dihexyl-2,5-dibromo-3,4-diphenylsilole (3d), respective-ly. The prepared materials are soluble in common organic solvents such as CHCl3 and THF. The polymers were charac-terized in solution, using various spectroscopic methods. The FTIR spectra of all the polymeric materials show characteristic C=C stretching frequencies at 1620-1628 cm–1. In THF solution, the materials have strong maximum ab-sorption bands at 273-293 nm, with red shifts of 18-34 nm relative to those of the monomers, strong maximum ex-citation peaks at 276-303 nm, and strong maximum fluore-scence emission bands at 350-440 nm. All the absorption, excitation, and emission spectra suggest that the obtained poly(1,1-disubstituted-3,4-diphenyl-2,5-silole)s contain chromophores such as phenyl and diene groups in the poly-mer main chains. TGA shows that most of these polymers are stable up to 200 °C with weight losses of 6-16% in nitrogen.

 

Experimental Section

General Procedures. All chemicals were purchased from Aldrich Chemicals Inc. All glassware was assembled and then flame-dried while being swept with argon. All solvents were purified prior to use, using the standard literature methods; THF was distilled from sodium benzophenone ketyl before use.31 1H and 13C NMR spectra were obtained using a Varian Mercury Plus 300 or a Bruker DRX Avance 400 MHz FT-NMR spectrometers, with CDCl3 as the solvent. 29Si NMR spectroscopy was performed using a Varian Unity INOVA 500 MHz FT-NMR spectrometer at the Daegu Center of the Korea Basic Science Institute using CDCl3 as the solvent. Chemical shifts were measured using tetramethylsilane as an internal standard or the residual proton signal of the solvent as the standard. IR spectra were recorded using a Shimadzu IR 430 or Bruker IFS-48 FT-IR spectrometer. Gel permeation chromatography (GPC) was performed at 40 °C, using a Waters 1525 pump and Breeze software system, with a Waters Styragel HR 3 column and refractive index detector. The eluent was THF at a flow rate of 1.0 mL/min. Calibration was performed using a series of monodispersed polystyrene standards: Mp 580, 3250, 10100, and 28500 whose Mw/Mn were less than 1.2. UV-vis absorp-tion spectra were obtained using a Hewlett Packard 8453 spectrophotometer. Excitation and fluorescence emission spectra were obtained using a Spex Fluorolog-3-11 fluore-scence spectrophotometer. TGA of polymer samples was performed using a TGA-50 Shimadzu thermal analysis system. The temperature was increased at a heating rate of 10 °C/min from room temperature to 900 °C, with a nitrogen flow rate of 20 mL/min.

Dimethylbis(phenylethynyl)silane (2a)6. A three-necked flask equipped with a thermometer, rubber septa, and mag-netic stirring bar was charged with phenylacetylene (25.5 mL, 232 mmol) and THF (180 mL). The solution was cool-ed to −70 °C in a dry ice/acetone bath. n-Butyllithium (2.5 M, 78.6 mL, 197 mmol) was added to the stirred solution, using a syringe, under a stream of argon. The acetone/dry ice bath was replaced with an ice/water bath. When the reaction temperature reached approximately −5 °C, dichlorodimeth-ylsilane (1a; 11.2 mL, 92.8 mmol) was added dropwise using a syringe. The solution was allowed to warm to room temperature, with stirring. The reaction mixture was poured into aqueous ammonium chloride solution (200 mL). The organic phase was separated using a separating funnel and the aqueous layer was extracted with diethyl ether. The combined organic layer was washed with water and brine, dried over anhydrous magnesium sulfate, filtered, and con-centrated by rotary evaporation under vacuum. The yellow-white solid was dissolved in boiling hexane, and then cooled in a freezer. White needles of product 2a (21.4 g, 89%) were obtained by vacuum filtration. 1H NMR (300 MHz, CDCl3) δ 0.51 (s, 6H), 7.31-7.35 (m, 6H), 7.52-7.55 (m, 4H). 13C NMR (75 MHz, CDCl3) δ 0.71, 90.85, 106.14, 122.90, 128.43, 129.07, 132.35. 29Si NMR (99.36 MHz, CDCl3) δ −39.80.

Diethylbis(phenylethynyl)silane (2b) was prepared, using the same procedure as for 2a from dichlorodiethyl-silane (1b). The solvent and unreacted materials were removed by rotary evaporation under vacuum. A yellow liquid 2b was obtained quantitatively. 1H NMR (300 MHz, CDCl3) δ 0.91 (q, J = 8 Hz, 18 Hz, 4H), 1.21 (t, J = 8 Hz, 6H), 7.31-7.36 (m, 6H), 7.53-7.57 (m, 4H). 13C NMR (75 MHz, CDCl3) δ 6.78, 7.52, 89.03, 106.89, 122.95, 128.37, 128.97, 132.33. 29Si NMR (99.36 MHz, CDCl3) δ −30.70.

Diisoproylbis(phenylethynyl)silane (2c) was prepared, using the same procedure as for 2a from dichlorodiisoprop-ylsilane (1c). A reddish-yellow liquid 2c was obtained quantitatively. 1H NMR (300 MHz, CDCl3) δ 1.22-1.25 (m, 14H), 7.33-7.36 (m, 6H), 7.53-7.57 (m, 4H). 13C NMR (75 MHz, CDCl3) δ 12.75, 17.95, 87.83, 107.35, 123.08, 128.39, 128.95, 132.39. 29Si NMR (99.36 MHz, CDCl3) δ −23.13.

Dihexylbis(phenylethynyl)silane (2d) was prepared, using the same procedure as for 2a from dichlorodihexyl-silane (1d). A scarlet liquid 2d was obtained quantitatively. 1H NMR (300 MHz, CDCl3) δ 0.84-1.62 (m, 26H), 7.28-7.33 (m, 6H), 7.48-7.52 (m, 4H). 13C NMR (75 MHz, CDCl3) δ 14.34, 15.06, 22.81, 23.90, 31.73, 32.92, 89.71, 106.81, 123.10, 128.37, 128.47, 132.33. 29Si NMR (99.36 MHz, CDCl3) δ −34.69.

2,5-Dibromo-1,1-dimethyl-3,4-diphenylsilole (3a)6. A three-necked flask equipped with a thermometer, rubber septa, and magnetic stirring bar was charged with lithium (0.53 g, 75.6 mmol), naphthalene (10.12 g, 79.0 mmol) and THF (50 mL) under a stream of argon. The reaction mixture was stirred at room temperature for 3 h to dissolve the lithium. A solution of 2a (4.37 g, 16.8 mmol) in THF (120 mL) was added dropwise, through a cannula, to the lithium naphthalenide over 20 min. Once the addition was complete, the solution was cooled to −10 °C using an acetone bath with a small amount of dry ice. A solution of anhydrous ZnCl2 (11.45 g, 84.0 mmol) in THF (70 mL) was added to the naphthalenide/silane mixture, through a cannula, over 20 min. The acetone/dry ice bath was removed and the resulting solution was allowed to warm to room temperature. A three-necked, foil-wrapped, round-bottomed flask equipped with a thermometer, stirring bar, and rubber septa was charged with NBS (7.45 g, 41.9 mmol) and THF under an argon atmos-phere. The resulting solution was cooled to −70 °C using a dry ice/acetone bath. The room-temperature silane solution was added to the cold NBS solution through a cannula, ensuring that the internal temperature did not exceed −50 °C. After the addition was complete, the resulting mixture was stirred for a further 30 min at −70 °C. The reaction mixture was poured into aqueous ammonium chloride solution (200 mL). The organic phase was separated using a separating funnel and the aqueous layer was extracted with diethyl ether. The combined organic layer was washed with aqueous sodium thiosulafate solution, water, and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated by rotary evaporation. The crude naphthalene-silole mixture was sublimed under vacuum at 35 °C. The residual material from the sublimation was dissolved in hot hexane, followed by cooling in a freezer. Colorless needles of 3a (3.2 g, 44%) were obtained by vacuum filtration. 1H NMR (300 MHz, CDCl3) δ 0.47 (s, 6H), 6.94-6.99 (m, 4H), 7.14-7.18 (m, 6H). 13C NMR (75 MHz, CDCl3) δ −6.05, 122.98, 127.66, 127.74, 129.24, 137.17, 156.21. 29Si NMR (99.36 MHz, CDCl3) δ 4.96. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 275 (8.50 × 103).

2,5-Dibromo-1,1-diethyl-3,4-diphenylsilole (3b) was prepared, using the same procedure as for 3a, from 2b. A pale yellowish crystalline product 3b (4.2 g, 55%) was obtained. 1H NMR (300 MHz, CDCl3) δ 1.03 (q, J = 7.5 Hz, 10.8 Hz, 4H), 1.15 (t, J = 6.9 Hz, 6H), 6.94-6.98 (m, 4H), 7.14-7.18 (m, 6H). 13C NMR (75 MHz, CDCl3) δ 1.74, 6.75, 121.06, 127.62, 127.76, 129.22, 137.36, 157.54. 29Si NMR (99.36 MHz, CDCl3) δ 8.54. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 260 (1.19 × 104).

2,5-Dibromo-1,1-diisopropyl-3,4-diphenylsilole (3c) was prepared, using the same procedure as for 3a, from 2c. A pale brownish crystalline product 3c (2.4 g, 30%) was obtained. 1H NMR (300 MHz, CDCl3) δ 1.27 (d, J = 6.9 Hz, 12H), 1.46-1.58 (m, 2H), 6.92-6.96 (m, 4H), 7.14-7.27 (m, 6H). 13C NMR (75 MHz, CDCl3) δ 10.05, 17.41, 120.03, 127.57, 127.78, 129.19, 137.55, 158.14. 29Si NMR (99.36 MHz, CDCl3) δ 7.46. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 253 (1.21 × 104).

2,5-Dibromo-1,1-dihexyl-3,4-diphenylsilole (3d) was prepared, using the same procedure as for 3a, from 2d. A pale brownish powder product 3d (4.0 g, 43%) was obtain-ed. 1H NMR (300 MHz, CDCl3) δ 0.89-1.54 (m, 26H), 6.93-6.97 (m, 4H), 7.14-7.18 (m, 6H). 13C NMR (75 MHz, CDCl3) δ 9.96, 14.36, 22.81, 23.11, 31.66, 32.91, 122.11, 127.59, 127.76, 129.19, 137.46, 157.08. 29Si NMR (99.36 MHz, CDCl3) δ 6.18. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 243 (1.28 × 104).

Poly(1,1-dimethyl-3,4-diphenyl-2,5-silole) (4a) Prepara-tion Using i-PrMgCl⋅LiCl.

Preparation of i-PrMgCl⋅LiCl.20 A three-necked flask was charged with i-PrMgCl in THF (2 M, 1.8 mL, 3.6 mmol) and anhydrous THF (5 mL). LiCl (0.15 g, 3.6 mmol) was added to the flask under nitrogen. The reaction mixture was stirred for 8 h at room temperature.

Poly(1,1-dimethyl-3,4-diphenyl-2,5-silole) (4a). A solu-tion of 3a (1.50 g, 3.59 mmol) in anhydrous THF (5 mL) was added under nitrogen to the previously prepared solu-tion of i-PrMgCl⋅LiCl (3.59 mmol). The reaction mixture was stirred at room temperature for 17 h. Ni(dppp)Cl2 (0.020 g, 0.036 mmol) dissolved in anhydrous THF (10 mL) was added to the reaction mixture. The polymerization was allowed to proceed for 48 h at room temperature, followed by quenching of the reaction mixture with methanol. The precipitated polymer was separated and dried under reduced pressure. A viscous yellowish liquid, 4a (0.79 g, 85%), was obtained. 1H NMR (300 MHz, CDCl3) δ 0.11-0.47 (br s, 6 H), 7.08-7.54 (br m, 10 H). 13C NMR (75 MHz, CDCl3) δ −1.49 (br s), 120.87, 126.02-131.20 (br m), 139.04, 151.65. 29Si NMR (99.36 MHz, CDCl3) δ 11.43. IR (KBr disk) ṽmax 3068, 3025, 2956 (νC-H), 1755, 1689, 1620 (νC=C), 1593, 1446, 1256 (νSi-C), 1072, 1029, 810, 761, 698 cm−1. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 293 (5.95 × 103). GPC (THF) Mw = 784, Mn = 573, polydispersity index (PDI) = 1.37.

Poly(1,1-diethyl-3,4-diphenyl-2,5-silole) (4b) was pre-pared, using the same procedure as for 4a, from 3b (2.00 g, 4.20 mmol) and Ni(dppp)Cl2 (0.018 g, 0.034 mmol) for 4 d. A reddish-yellow powder 4b (0.59 g, 46%) was obtained. 1H NMR (300 MHz, CDCl3) δ 0.74-1.06 (br m, 10 H), 6.92-7.24 (br m, 10 H). 13C NMR (75 MHz, CDCl3) δ 0.80, 5.63, 120.88, 124.38-129.75 (br m), 143.75, 158.50. 29Si NMR (99.36 MHz, CDCl3) δ 8.58. IR (KBr disk) ṽmax : 3054, 2956, 2927, 2870 (νC-H), 1628 (νC=C), 1459, 1439, 1072, 1022, 768, 698, 549 cm−1. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 283 (4.10 × 103). GPC (THF) Mw = 1450, Mn = 1064, PDI = 1.36.

Poly(1,1-diisopropyl-3,4-diphenyl-2,5-silole) (4c) was prepared, using the same procedure as for 4a, from 3c (2.00 g, 4.20 mmol) and Ni(dppp)Cl2 (0.018 g, 0.034 mmol) for 5 d. A pale yellow powder 4c (0.54g, 41%) was obtained. 1H NMR (300 MHz, CDCl3) δ 1.12-1.53 (m, 14 H), 6.07 (s, 0.6H), 6.92-7.27 (m, 10H). 13C NMR (75 MHz, CDCl3) δ 10.07, 10.56, 17.41, 18.01, 18.30, 120.04, 124.63-129.36 (m), 137.56-140.98 (m), 156.87-163.11 (m). 29Si NMR (99.36 MHz, CDCl3) δ 7.03. IR (KBr disk) ṽmax : 3068, 2941, 2863 (νC-H), 1622 (νC=C), 1459, 1079, 698, 578 cm−1. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 273 (3.08 × 103). GPC (THF) Mw = 658, Mn = 610, PDI = 1.08.

Poly(1,1-dihexyl-3,4-diphenyl-2,5-silole) (4d) was pre-pared, using the same procedure as for 4a, from 3d (2.00 g, 4.46 mmol) and Ni(dppp)Cl2 (0.020 g, 0.036 mmol) for 5 d. A viscous brownish liquid 4d (0.84 g, 59%) was obtained. 1H NMR (300 MHz, CDCl3) δ 0.72-1.54 (br m, 26 H), 6.83-7.51 (br m, 10H). 13C NMR (75 MHz, CDCl3) δ 9.96. 14.36. 15.59, 22.91-23.59 (m), 31.59-31.75 (m), 32.92-33.44 (m), 122.10, 127.25-129.21 (m), 137.48, 157.08. 29Si NMR (99.36 MHz, CDCl3) δ 6.43. IR (KBr disk) ṽmax : 3062, 2956, 2927, 2856 (νC-H), 1628 (νC=C), 1446, 1199, 1092, 768, 691 cm−1. UV-vis (THF) λmax, nm (ε, cm–1 M–1): 277 (6.44 × 103). GPC (THF) Mw = 993, Mn = 922, PDI = 1.09.

The excitation and fluorescence emission spectra in THF solution and TGA thermograms for polymers 4a-d are described in the Results and Discussion.