Synthesis and properties of fluorinated benzotriazole‐based donor‐acceptor‐type conjugated polymers via Pd‐catalyzed direct CH/CH coupling polymerization

Abstract

Fluorine substituted benzotriazole (BTz) units have shown great potential in improving various conjugated polymers (CPs)-based optoelectronic devices' performance. Thus, it is highly expected for the establishment of simple, efficient, and inexpensive accesses to such polymers. In this paper, Pd-catalyzed direct C H/ C H coupling polymerization is first employed for the synthesis of 5,6-difluorobenzotriazole containing π-CPs, which fully avoids prefunctionali zation of monomers. Under the optimized conditions, a series of donor-acceptortype π-CPs with excellent regio-regularity are facilely obtained via the direct C H/ C H coupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-BTz with different thiophene analogs. The chemical structure of the as-synthesized polymers are confirmed by NMR technique including 1 H NMR, 19 F NMR, and the edited heteronuclear singular quantum correlation and heteronuclear multiple bond correlation spectra as well as comparative study on the same polymers obtained via Stille coupling and direct (hetero)arylation polymerization. Further, their optical properties, electrochemical properties, and thermal stabilities are also carefully explored by UV-Vis absorption spectra, cyclic voltammograms as well as thermogravimetric analysis, respectively. On the basis of density functional theory (DFT) simulation, the effect of alkyl substituents attached to thiophene units on the reactivity and optical performance of the resultant polymers is explained. Our protocol exhibits remarkable advantages in synthetic simplicity, atom-economy, high efficiency, and excellent regioselectivity of cross-coupling, providing an alternative synthetic strategy for high-performance optoelectronic materials.

Synthesis of π-Conjugated Polymers Containing Benzotriazole Units via Palladium-Catalyzed Direct C-H Cross-Coupling Polycondensation for OLEDs Applications

“…The peak at 2.70 nm (c in Figure 1A) corresponds to -CH2 groups of thiophene side chains. It was noted that the signal of aromatic hydrogen of thiophene units (d in Figure 1A) significantly shifted to low field compared with the corresponding thiophene monomer, which was possibly caused by F⋯H noncovalent interaction between the fluorine atoms on benzotriazole unit and the hydrogen atoms on thiophene units as demonstrated by our recent work [29] and the literature [11]. Besides, 19 F NMR was also applied to confirm the polymers' chemical structure since it has many merits, including high sensitivity, little interference, a large range of chemical Besides, 19 F NMR was also applied to confirm the polymers' chemical structure since it has many merits, including high sensitivity, little interference, a large range of chemical shifts, and similar structures that are not easy to overlap, etc.…”

“…The peak at 2.70 nm (c in Figure 1A) corresponds to -CH 2 groups of thiophene side chains. It was noted that the signal of aromatic hydrogen of thiophene units (d in Figure 1A) significantly shifted to low field compared with the corresponding thiophene monomer, which was possibly caused by F• • • H noncovalent interaction between the fluorine atoms on benzotriazole unit and the hydrogen atoms on thiophene units as demonstrated by our recent work [29] and the literature [11].…”

“…The luminance of OLEDs was measured with a PhotoResearch SpectraScan PR-650 Colorimeter. [29], namely, Pd(OAc) 2 (10 mol%) as catalyst, Ag 2 CO 3 (3.0 equiv) as oxidant, K 2 CO 3 (3.0 equiv) as base, PivOH (2.0 equiv) as additive, and DMAc/xylene (v/v, 10/1) as solvents at 110 • C for 48 h. A branched side chain (2hexyldecyl) was attached to benzotriazole units, aiming to improve the solubility of com-pound 1 and the resultant copolymers in the common organic solvents, such as DMAc, DMF, CHCl 3 , etc. [11].…”

“…As depicted in Scheme 1, P1-P4 were prepared by Pd-catalyzed direct C-H crosscoupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-benzotriazole (1) with four different thiophene derivatives, including 3-octylthiophene, 2,2'-bithiophene, thieno [3,4-b][1,4]dioxine, and 4,4-dioctyl-4H-silolo-[3,2-b:4,5-b']dithiophene under the optimized conditions as reported in our recent work [29], namely, Pd(OAc)2 (10 mol%) as catalyst, Ag2CO3 (3.0 equiv) as oxidant, K2CO3 (3.0 equiv) as base, PivOH (2.0 equiv) as additive, and DMAc/xylene (v/v, 10/1) as solvents at 110 °C for 48 h. A branched side chain (2-hexyldecyl) was attached to benzotriazole units, aiming to improve the solubility of compound 1 and the resultant copolymers in the common organic solvents, such as DMAc, DMF, CHCl3, etc. [11].…”

Improving the efficiency and sustainability of catalysts for direct arylation polymerization (DArP)

“…Although recent advances of this protocol have demonstrated examples of Oxi-DArP without the assistance of any directing group, which significantly broaden the scope of this methodology, [204][205][206] the use of stoichiometric metal oxidants in most cases remains a major concern. Conversely, the inclusion of directing groups in the design of monomers has significantly promoted the efficiency of the catalysts toward highly regioselective polymerizations and enhanced the sustainability of the method by allowing the use of lower metal loadings and milder conditions.…”