Hybridization of Thiol-Functionalized Poly ( phenylacetylene ) with Cadmium Sulfide Nanorods : Improved Miscibility and Enhanced Photoconductivity

Molecules of a thiol-functionalized phenylacetylene derivative were assembled on the CdS nanorod surface and copolymerized with phenylacetylene, affording an inorganic semiconductor-conjugated polymer hybrid with excellent solubility and high photoconductivity.

Molecular weights (M w and M n ) and polydispersity indexes (M w /M n ) of the polymers were estimated in THF by a Waters Associates gel permeation chromatography (GPC) system.A set of monodisperse polystyrene standards covering molecular weight range of 10 3 -10 7 was used for the molecular weight calibration.
Thermogravimetric analysis (TGA) was carried out on a Pyris 6 thermogravimetric analyzer (Perkin Elmer).A sample of ~3 mg was heated at the rate of 10 ℃/min under a constant flow of dry nitrogen.
Information about the shape and dispersion of the CdS nanorods and the hybrid were obtained from a JSM-5510 scanning electron microscopy (SEM), a JEM-200CX transmission electron microscope (TEM), and a Philips CM200 high-resolution TEM (HRTEM) coupled with an energy dispersive X-ray (EDX) analyzer.
Monomer Synthesis.The thiol-containing monomer (M1) was prepared according to the synthetic route shown in Scheme S1.Detailed experimental procedures are given below.Preparation of .Into a 500mL round-bottom flask equipped with a reflux condenser were added 11-bromoundecanoic acid (13.3 g, 50 mmol) and 200 mL of methanol.

Scheme S1
With gentle stirring, 5 mL of concentrated sulfuric acid was added dropwise into the flask.The reaction mixture was refluxed for 2 h.After cooling the content to room temperature, calcium carbonate was added gradually to neutralize the excess acid.The solvent was removed with a rotary evaporator.The residue in the flask was re-dissolved in 200 mL of chloroform and washed with deionized water.The organic layer was dried over 5 g of magnesium sulfate.After filtration of the solids and removal of the solvent, the crude product was purified on a silica gel chromatography column using chloroform as eluent.Evaporation of the solvent afforded 11.9 g of 5 as a colorless liquid (yield: 85.2%  and 5.7 g (34.3 mmol) of potassium iodide were dissolved in 100 mL of acetone/DMSO mixture (9:1 by volume) with gentle stirring.To the mixture was added 6.3 g (22.6 mmol) of 5, and the content was then refluxed for 24 h.The solids were removed by filtration, and the filtrate was evaporated under reduced pressure.The crude product was dissolved in 50 mL of DCM, and the resultant solution was washed with 50 mL of deionized water.The aqueous phase was extracted twice with 50 mL of DCM.
The combined organic layers were dried over 5 g of magnesium sulfate.The crude product was condensed and purified on a silica gel column using chloroform as eluent.Evaporation of the solvent gave 7.5 g of a pale yellow solid of 4 (yield: 79.3% under nitrogen.After all the catalysts were dissolved, 1.7 mL (12 mmol) of trimethylsilylacetylene was injected into the flask, and the mixture was stirred at room temperature for 12 h.The solids formed during the reaction were removed by filtration and washed with TEA.The filtrate was then evaporated with a rotary evaporator.The residue in the flask was redissolved in 100 mL of chloroform and washed with 50 mL of hydrochloric acid (1 M) and then 50 mL of deionized water.The crude product was condensed and purified on a silica gel column using chloroform as eluent.Removal of the solvent gave 3.6 g of a light yellow solid of 3 (yield: 92.7%).IR (KBr), ν (cm -1 ): 2158 (w, C≡C), 1733 (s, C=O). 1 H NMR (300 MHz, CDCl 3 ), δ (TMS, ppm): 7.4 (m, 2H, aromatic protons meso to -O-), 3.9 (m, 2H,
Cadmium chloride and sulfur powders were stoichiometrically added into a mixture of deionized water and diethylamine under stirring.The contents were then transferred to a Teflon-lined stainless steel autoclave, which was airproofed and put into an oven.The solution was neither shaken nor stirred during the period of heating process.The autoclave was gradually heated to 120-200℃ and maintained at the temperatures for 24 h and then cooled to room temperature.The product was collected by precipitation and washed with CS 2 , ethanol and deionized water.A yellow powdery product was obtained after drying in a vacuum oven and treated at a temperature of ∼650 ℃ for 1 h.Inset: a typical HRTEM image of a single nanorod capped with an assembly of M1 molecules.

Assemblies of M1 on
The absorption spectrum of C1 is shown as Figure S3.The characteristic feature of CdS crystal can be observed at ~485 nm, confirming the existence of the CdS nanorods in the solution.The TEM images of C1 reveal that the CdS nanorods retain their original shapes (Figure S4).A typical HRTEM image of C1 given in the inset of Figure S3 shows that the surface of the assembly is not as smooth as those of the original nanorods.A rational explanation is that the clear surfaces of the original nanorods have been covered with M1 molecules.EDX analysis data are listed in Table S1, which clearly tell that C, N, Cd and S elements co-exist in the assemblies.a Recorded on a Hitachi H-900 TEM microscope, using an accelerating voltage of 300 kV.
Copolymerization of C1 with PA.The copolymerization reaction was carried out under nitrogen using the Schlenk technique in a vacuum-line system.Into a 20 mL Schlenk tube, 10 mg of purified C1 was added.The tube was evacuated under vacuum and then flushed with dry nitrogen three times, followed by injecting 50 mg of PA into the tube.DCM (1.5 mL) was then injected into the tube to dissolve the monomer.The catalyst was prepared in another tube by dissolving 2.5 mg of [Rh(cod)Cl] 2 in 0.5 mL of DCM with one drop of TEA, which was transferred to the monomer solution using a hypodermic syringe.After stirring at room temperature for 24 h, the polymerization mixture was diluted with 5 mL of DCM and added dropwise to 500 mL of methanol under stirring.The precipitate was collected by filtration.The solid product was washed with methanol and dried under vacuum at room temperature to a constant weight.
The copolymerization of C1 and PA gave rise to the expected PPA-CdS hybrid (H1).Because the inorganic nanorods cannot penetrate through the columns in the GPC instrument, we removed the CdS nanorods in H1 by extracting it with concentric hydrochloric acid.After removal of the CdS component and drying in a vacuum oven, the yield of the polymer was calculated to be ~71%.The M w and M w /M n values of the sample were estimated to be 72600 and 2.9, respectively.The 1 H NMR spectrum of H1 is shown in Figure S5.The appearance of the resonance peak for =C−H at δ ~ 5.8 and the upfield shift of the resonance peaks of the aromatic protons confirm the transformation of the acetylenic triple bonds to the vinyl double bonds by the acetylene polymerization process.The elemental analysis data for M1, PPA and H1 are summarized in Table S2.The nitrogen in H1 is entirely from M1, thus the relative content of M1 in H1 can be can be calculated by equation 1 to be 7.78 wt %: where W M1/H1 is the weight percentage of M1 in H1, and W N/H1 and W N/M1 stand for the weight percentages of nitrogen element in H1 and M1, respectively.The weight percentage derived from the elemental analysis data is given in Table S2.
Rationally, M1 component also contributes the same percentage to the total carbon content in H1.
Based on this analysis, the PA component contributes 92.22 wt % of carbon to H1, i.e., 78.28 wt % of the total 84.88 wt % in H1.Therefore, the relative content of PA in H1 can be calculated by equation 2 to be 83.21wt %: where W PA/H1 is the weight percentage of PA component in H1, and W C/H1 and W C/PA stand for the weight percentage of carbon element in H1 and PA, respectively.Finally, the relative content of CdS nanorods in H1 can be calculated to be 9.01 wt % by subtracting the weight percentages of M1 and PA components from 100%.was replaced by pure CdS nanorods.In another case, 10 mg of CdS nanorods and 80 mg of preformed PPA was dissolved in 4 mL of DCM.The mixture was stirred for 24 h and the solvent was evaporated with a rotary evaporator.Blend 2 or B2 was obtained after drying in vacuum oven at 40 ℃ overnight.Photoconductivity Measurement.Photoconductivity of the obtained double-layered photoreceptor was measured using a standard GDT-II photoinduced discharge instrument, which constitutes the basis of the xerographic process in the photoimaging system.The surface of the photoreceptor was first negatively corona charged to a surface potential V 0 .After a dark discharge for 3 s, its surface potential dropped to V i .The photoreceptor was then exposed to a light with an intensity of I (11 µW/mm 2 in this work).The light source was a halogen lamp (5 W, 24 V).The electron-hole pairs were immediately generated in the CGL upon the photon absorption and injected into the CTL.The photogenerated pairs migrated towards the negatively charged surface following the applied field through the CTL.The surface charges were thus neutralized with a low potential V r remained.From the discharge experiment we can obtain the parameter of half-discharge exposure energy E 1/2 , which equals to t 1/2 I, where t 1/2 is the time from initial potential V i to its half value under exposure to light.Photosensitivity S is defined as the reciprocal of E 1/2 , or S = 1/E 1/2 .
Figure S1. 1 H NMR spectrum of thiol-containing monomer M1 in chloroform-d.The solvent and water

FigureFigure S6 .
Figure S5. 1 H NMR spectra of H1 in chloroform-d.The solvent and water peaks are marked with