C–H/C–H Oxidative Direct Arylation Polycondensation to Isoindigo-Based n-Type Conjugated Polymers

Abstract

Two high molecular weight conjugated polymers (CPs), i.e., poly[N,N′-bis(4-tetradecyloctadecyl)-7,7′-difluoroisoindigo-alt-2,2′-bithiazole] (P2FI2Tz) and poly[N,N′-bis(4tetradecyloctadecyl)-5,5′,7,7′-tetrafluoroisoindigo-alt-2,2′-bithiazole] (P4FI2Tz), were synthesized via C−H/C−H oxidative direct arylation polycondensation (Oxi-DArP) using PdCl 2 /CuCl/Cu-(OAc) 2 as catalytic system and chlorobenzene as solvent. Both polymers are unipolar n-type semiconductors with electron mobility (μ e ) > 0.2 cm 2 V −1 s −1 , attributed to their low-lying highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbital (LUMOs), which are −6.01/−3.69 and −6.24/−3.82 eV for P2FI2Tz and P4FI2Tz, respectively. P2FI2Tz was also synthesized via C−Br/C−H direct arylation polycondensation (DArP) and Stille polycondensation. The resultant polymers P2FI2Tz-D and P2FI2Tz-S showed slightly lower μ e compared to Oxi-DArP-made polymer (P2FI2Tz-O1) with a similar molecular weight. Notably, Oxi-DArP is much faster and more efficient than DArP and Stille polycondensation. P2FI2Tz with a number-average molecular weight (M n ) above 40 kDa, was obtained in 9 h of Oxi-DArP, significantly shorter than 24 h with DArP and Stille polycondensation. P2FI2Tz with a M n as high as 191 kDa could be synthesized via Oxi-DArP by extending the polymerization time to 16 h. Our results prove Oxi-DArP to be an efficient protocol to synthesize polymer semiconductors. This is also the first comparative study on three methods, i.e., Oxi-DArP, DArP, and Stille polycondensation.