Converging the Hole Mobility of Poly(2-N-carbazoylethyl acrylate) with Conjugated Polymers by Tuning Isotacticity

Nonconjugated electroactive polymers (also known as pendant or side-chain electroactive polymers) promise several potential advantages relative to conjugated polymers including enhanced mechanical durability, greater stability and synthesis via living polymerization techniques. However, most previous examples suffer from low charge carrier mobility. Here, using poly(2-N-carbazoylethyl acrylate) (PCzEA) as a model polymer, we investigate the ability of side-chain tacticity to influence hole mobility. Specifically, we investigated polymers with dyad isotacticity (m) ranging from ∼45 to ∼95% synthesized by several methods including free radical polymerization and anionic polymerization. We found that the hole mobility (μ_h) measured via the space charge limited current (SCLC) technique increased proportionally to the increasing isotacticity from 2.11 × 10^-6 cm² V^-1 s^-1 (m = 45.5%) to 4.68 × 10^-5 cm² V^-1 s^-1 (m = 94.7%) in unannealed samples and that mobilities could be boosted as high as 2.74 × 10^-4 cm² V^-1 s^-1 (m = 94.7%) with thermal annealing, which rivaled the well-known conjugated polymer poly(3-hexylthiophene) (P3HT) (μ_h = 5.8 × 10^-4 cm² V^-1 s^-1). As such, we report here clear experimental evidence that control of side chain tacticity can enhance charge carrier mobility in nonconjugated pendant electroactive polymers, converging with mobilities typically only observed in conjugated polymers.