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(4-tetradecyloctadecyl)-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.

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