Synthesis of a Bithiophene-Isoindigo-Based π-Conjugated Polymer via Direct Arylation Polycondensation Using Palladium Immobilized on Thiol-modified Silica Gel (PITS)

Abstract

The direct arylation polycondensation of 3,3′-dihexyl-2,2′-bithiophene (BT6) with dibromoisoindigo (ID) was achieved by using PITS, palladium immobilized on thiol-modified silica gel. The polycondensation of BT6 with ID using PdCl₂ for 1 h gave PBT6ID (M_n = 6900) in 74% yield. On the other hand, the polycondensation for 2 h gave PBT6ID (M_n = 5600) in low (12%) yield along with insoluble polymer products. This is probably due to chain branching based on β-defects of the polymers. The polycondensation of BT6 with ID for 12 h was performed with PITS-Cl catalyst, furnishing PBT6ID (M_n = 9800) in 79% yield. The optical and electrochemical properties of PBT6ID are also described.