Short conjugated phenylene (P)−thiophene (T) oligomers with varying α and ω alkyl and alkoxy
substitutions were synthesized using Stille and Suzuki coupling reactions to investigate the correlation
between end-group structure and electronic properties on P2TP and P3TP conjugated cores. Several soluble
oligomers were synthesized with 5,5‘-bis(4-n-octylphenyl)-2,2‘-bithiophene (do-PTTP) showing the highest
mobility (μ = 0.18 cm2 V-1 s-1) and on/off ratio of 107 at a substrate temperature of 50 °C. Thin film
morphologies analyzed using atomic force microscopy revealed higher nucleation densities for branched
alkoxy side-chain molecules compared to those of their straight alkyl side-chain counterparts. Field-effect mobility showed an inverse correlation to side-group bulkiness, indicating a strong morphological
component to charge transport in the P2TP and P3TP series.
A series of phenylene–fluorene derivatives (see figure) are synthesized and evaluated for use in organic field‐effect transistors. Average field‐effect mobilities as high as 0.32 cm2 V–1 s–1 are achieved by vacuum deposition at low substrate temperatures. The high ionization potentials in the derivatives lead to improved chemical and photostability. Transistor devices show no loss in performance when tested over a period of three months.
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