Synthesis of High-Quality Carboxyl End-Functionalized Poly(3-hexylthiophene)/CdSe Nanocomposites

Hindawi Journal of Nanomaterials Volume 2019, Article ID 1251598, 8 pages https://doi.org/10.1155/2019/1251598 Research Article Synthesis of High-Quality Carboxyl End-Functionalized Poly(3-hexylthiophene)/CdSe Nanocomposites He-Ping Shi,1 Da-Wei Lin ,2 and Rui-feng Wu 1 2 2 College of Science, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia 010018, China College of Chemical Engineering, Inner Mongolia University of Technology, Hohhot 010051, China Correspondence should be addressed to Rui-feng Wu; Received 26 September 2018; Accepted 18 August 2019; Published 15 September 2019 Guest Editor: Kakarla R. Reddy Copyright © 2019 He-Ping Shi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Carboxyl end-functionalized poly(3-hexylthiophene) (P3HT-COOH) was grafted chemically with CdSe nanocrystals (NCs) by a phosphine-free method. The particle quality of P3HT-COOH/CdSe nanocomposites was better than that of P3HT/CdSe nanocomposites, which were synthesized using the same method. Nanocrystals with controllable particle size exhibited a wurtzite crystalline structure and showed excellent nanocrystal dispersion in the P3HT-COOH matrix. Photoluminescence (PL) characterization performed on nanocomposites suggested the efficient charge transfer at the P3HT-COOH/CdSe interface. This approach based on the phosphine-free method is not only environmentally friendly but also highly efficient. 1. Introduction P3HT has been extensively utilized as conjugated polymers (CPs) for CP/CdSe nanocomposites due to its well-matched energy level with CdSe [1–5]. However, P3HT/CdSe was widely prepared by physically mixing P3HT and CdSe. Phase separation of P3HT and CdSe is inevitable, thereby limiting the direct electronic interaction between them [6–8]. Grafting P3HT with CdSe by a chemical method is an effect strategy to eliminate phase separation and to promote the electronic interaction between P3HT and CdSe [6, 8]. Previously, the ligand exchange process was used to graft CPs to NCs because the derivatization of the composite has a broad range of functional groups [9, 10]. In spite of the fact that the original ligands can be replaced by the desired ligands, NCs still tend to aggregate when mixed with CPs, which leads to phase separation [11–14]. A strategy to decrease or eliminate macrophase separation is to use end-functionalized P3HT as ligands [2, 8, 15–17]. End-functionalized P3HT equipped with alcohol, ethynyl, carboxylic acid, pyridines, thiols, amine, and phosphate groups has been developed [14, 17–19]. The research shows that it also generates chemically defined interfaces that improve elec- tronic communication between the CPs and NCs. Polythiophene with carboxylic acid functional groups has been used to prepare many nanocomposites because it increases the interactions at the interface with the NCs [20–22]. Photoinduced electron transfer from CPs to NCs was also improved by replacing the P3HT with P3HT-COOH [23]. Many works on the synthesis of CP/NC nanocomposites have been reported [9, 19, 24–31]. But some key chemicals, such as tri-n-octylphosphine oxide (TOPO) and trioctylphosphine (TOP), used in traditional routes are extremely toxic, expensive, explosive, and pyrophoric [7, 11, 12, 28, 31]. So phosphine-free synthesis schemes have extended to green and low-cost cadmium carboxylate precursors, fatty acid ligands, and noncoordination solvents (ODE, heat transfer fluids, and paraffin liquid) [32–34]. P3HT/CdSe has been successfully synthesized in ODE without using TOP and TOPO [4]. The result shows that it is a uniform dispersion of NCs without any indication of phase separation. However, this method is not desirable because dimethylcadmium is used, which is a pyrophoric and explosive reagent. CdSe NCs obtained from the phosphine-free solvent systems are generally imperfect. The size of CdSe NCs is not easily controlled [9, 32, 35], and their surface is not suitable for epitaxial 2 growth [36, 37]. An environmentally friendly, effective, and ligand exchange-free method should be developed to achieve chemically grafted CPs on the QD surface. In this paper, two kinds of P3HT-COOH/CdSe nanocomposites were prepared by an in situ synthesis method without using organophosphine as a ligand. The p-type/ntype hybrid nanocomposites have high quality and show fluorescence quenching, indicating an effective charge transfer at the interface between P3HT-COOH and CdSe. Journal of Nanomaterials zene (1 mL) and kept at 220°C under Ar until the liquid color was bright orange. The product is P3HT-COO-Cd solution (P3HT-Z-COO-Cd or P3HT-M-COOH-Cd). Subsequently, 10 mL Se precursor solution was rapidly injected into the P3HT-COOH-Cd solution. The reaction solution color immediately changed to brown from bright orange indicating the formation of CdSe nanoparticles. Nanoparticles were allowed to grow at 220°C for 1 h. The resulting P3HTCOOH/CdSe nanocomposites were cooled down and precipitated with methanol and redissolved in chloroform. 2. Experiment 2.1. General Procedures and Chemicals. All reactions were carried out under nitrogen gas flow using a standard Schlenk line. The glassware was predried before use at 120°C. All chemicals, including 1-octadecene (ODE), trichlorobenzene, selenium powder, ethynylmagnesium bromide (1 mol/L in THF), and P3HT (number average molecular weight was 30,000 g/mol), were purchased from J&K (China). Cadmium stearate was purchased from Aladdin (China). THF (Aladdin, 99%) was refluxed over sodium wire. 2.2. Synthesis of Ethynyl-Terminated P3HT. Ethynyl-terminated P3HT (i.e., P3HT-≡) was synthesized by the quasiliving Grignard metathesis (GRIM) method [38]. P3HT (0.09 g, 0.03 mmol) was dissolved in 20 mL THF, and Ni(dppp)Cl2 (0.0225 g, 0.041 mmol) was added. The resulting mixture was first stirred for 10 min at room temperature, followed by a reaction with ethynylmagnesium bromide (0.03 mL, 0.03 mmol) in THF for 30 min. The product, P3HT-≡, was obtained by precipitating the reaction mixture in methanol, filtering in an extraction thimble, and washing by Soxhlet extraction with methanol, hexanes, and chloroform sequentially. 2.3. Synthesis of P3HT-COOHs. P3HT-COOHs contain P3HT-Z-COOH, and P3HT-M-COOH is synthesized by click reaction [38] (Scheme 1). The 4-aminophenylacetic acid (i.e., Z) and sodium azide were mixed in water to substitute the amino group of 4-aminophenylacetic acid into azide (N3), yielding N3-functionalized-phenylacetic acid complexes (ZN3). The 4-(bromomethyl)benzoic acid (i.e., M) and sodium azide were mixed in DMF to substitute the bromide group of 4-(bromomethyl)benzoic acid into azide (N3), yielding N3-functionalized-methylbenzoic acid complexes (M-N3). Subsequently, the synthesized P3HT-≡ and Z-N3 or MN3 were mixed in THF and kept at 60°C under Ar for 3 days, yielding P3H (...truncated)