Direct Arylation Polycondensation of Bithiazole Derivatives with Various Acceptors

Abstract

Novel π-conjugated polymers with a bithiazole unit and various acceptor units were synthesized by polycondensation via Pd-catalyzed direct arylation. The results of polycondensation reactions depend on chalcogen elements in the monomers. The presence of a Se atom inhibited polymerization, presumably owing to the coordination of the Se moiety to the Pd center; the issue was resolved by increasing the reaction temperature (120 °C). The chalcogen elements also affected the interchain interactions of the obtained polymers. The strong interchain interactions led to low solubility, high crystallinity, and a large red-shift of absorption in the film state compared with that in the solution state. Absorption spectra and DFT calculations revealed that the bithiazole units served as weak donor units in case that the bithiazole units were directly connected to strong acceptor units. The combination of the bithiazole units with the strong acceptor units afforded deep HOMO−LUMO levels.

Pd-catalysed oxidative C–H/C–H coupling polymerization for polythiazole-based derivatives

“…Otherwise, the polythiazole with three thiophenes in absence of alkyl groups would precipitate from the polymerization system. In such a case, the polymerization would cease to obtain polythiazoles with smaller molecular weight than that with alkyl groups [13,14,20]. We began our investigation using M3 as the model substrate for screening and optimizing conditions for Pdcatalysed oxidative CeH/CeH coupling polymerization, considering its better solubility in common organic solvents compared to M1 and M2 due to the long chain alkyl groups attached to the thiophene ring.…”

“…Recently, polycondensation via direct CeH arylation, which is widely recognized as an atom-economic and environmentally friendly method for synthesis of p-conjugated polymers in comparison to the traditional cross-coupling reactions, has also been achieved for the synthesis of conjugated polythiazole derivatives [10e12]. For examples, Kanbara's group reported a protocol via direct arylation of 4,4 0 -dinonyl-2,2 0 -bithiazole with dibromoarylenes [13,14]. Although this protocol avoids the use of organometallic monomers, it still required multiple synthetic steps that sometimes are very challenging, and more importantly, end-capping procedures in most cases.…”

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics

“…On the other hand, direct C-H arylation polymerization has attracted much attention because it presents an economically and ecologically attractive alternative to the traditional cross-coupling reactions. [26][27][28][29]38,39,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61] Recently, the application of directly arylated polymers to the preparation of OPVs has been investigated. 45,54,55 In this study, we report the synthesis and characterization of double acceptor copolymers, -(CPDT-TPD-CPDT-BT) n -, comprising TPD, BT and two CPDT units in the polymer-repeating unit (Figure 1).…”

Significant Difference in Semiconducting Properties of Isomeric All‐Acceptor Polymers Synthesized via Direct Arylation Polycondensation

“…The NDI-Tz and TPD-Tz monomers were obtained by the Stille coupling reactions of 2-(tributylstannyl)thiazole with the brominated acceptor units,t hat is,N DI-Br or TPD-Br, respectively (Scheme 1). As aconsequence,wechanged the synthetic approach and adopted DArP to produce these all-acceptor copolymers.I nspired by Kanbara and co-workers' work involving the successful DArP of the bithiazole derivatives, [12] we initially tried to synthesize P1 by using the same conditions.H owever, unfortunately,t he low molecular weight (M n )o f4 .3 kg mol À1 and the polydispersity index (PDI) of 1.6, determined by polystyrenecalibrated gel permeation chromatography (GPC) using odichlorobenzene at 40 8 8C, were obtained ( Table 1, entry 1). Note that the synthesis of these polymers by Stille polycondensation was also attempted.…”