Donor-acceptor random regioregular π-conjugated copolymers based on poly(3-hexylthiophene) with unsymmetrical monothienoisoindigo units.

Kaoru Uegaki,Shin-Ichi Yamamoto,Kazuhiro Nakabayashi,Toshio Koizumi,Shotaro Hayashi

doi:10.1039/d0ra03557b

Abstract

Donor–acceptor π-conjugated random copolymers based on regioregular poly(3-hexylthiophene), rr-P3HT, with unsymmetrical monothienoisoindigo moieties were obtained by direct arylation polycondensation of 2-bromo-3-hexylthiophene with unsymmetrical monothienoisoindigo motifs under the optimized conditions [palladium-immobilized on thiol-modified silica gel with chloride counter anions, PITS-Cl (2.5 mol%), PivOH (1.0 equiv.), K2CO3 (3.0 equiv.), DMAc, 100 °C, 24 h]. Incorporation of unsymmetrical monothienoisoindigo electron-acceptor units into the polymers tuned their highest occupied and lowest unoccupied molecular orbital levels, which were close to those of the hole transport material (PEDOT) and electron transport material (PCBM), respectively, in thin-film organic solar cells. Alkyl chains of the unsymmetrical monothienoisoindigo units in the polymers tuned their macrostructural order, resulting in the observation of crystalline patterns and specific absorption peaks in thin films. An organic solar cell containing the most crystalline random copolymer showed an efficiency of 1.91%.

Highlights

There have been many reports on electron-donating p-conjugated polymers with thiophene units in the main chain.[1]
Regioregular electron-accepting p-conjugated polymers have been synthesized by direct arylation polycondensation using unsymmetrical monothienoisoindigo as a monomer.[5]
Rr-P3HT can be obtained by Grignard metathesis polymerization.3a,b In addition, Suzuki–Miyaura and Stille cross-coupling reactions are useful approaches to synthesize rr-P3HT.3c,d Recently, Ozawa's group achieved direct arylation polycondensation of 2-bromo-3-hexylthiophene to form rr-P3HT with high molecular weight.[9]

Summary

Introduction

There have been many reports on electron-donating p-conjugated polymers with thiophene units in the main chain.[1]. We report the direct arylation polycondensation of 2-bromo-3-hexylthiophene (3HT) with unsymmetrical monothienoisoindigo (uTII) units to synthesize donor– acceptor regioregular p-conjugated random copolymers (Scheme 1). N-Methylpyrrolidone (NMP) was used as the solvent instead of DMAc because it was thought that the results were affected by the solubility of the polymer, but no improvement was observed (Table 1, Entry 7).

Results

Conclusion