New classes of liquid-crystalline semiconductor polymers based on perylene diester benzimidazole and perylene diester imide mesogens are reported. Two highly soluble side-chain polymers, poly(perylene diester benzimidazole acrylate) (PPDB) and poly(perylene diester imide acrylate) (PPDI) are synthesized by nitroxide-mediated radical polymerization (NMRP). PPDB shows n-type semiconductor performance with electron mobilities of 3.2 × 10−4 cm2 V−1 s−1 obtained in a diode configuration by fitting the space-charge-limited currents (SCLC) according to the Mott–Gurney equation. Interestingly, PPDI performs preferentially as a p-type material with a hole mobility of 1.5 × 10−4 cm2 V−1 s−1, which is attributed to the less electron-deficient perylene core of PPDI compared to PPDB. Optical properties are investigated by UV-vis and fluorescence spectroscopy. The extended π-conjugation system due to the benzimidazole unit of PPDB leads to a considerably broader absorption in the visible region compared to PPDI. HOMO and LUMO levels of the polymers are also determined by cyclic voltammetry; the resulting energy band-gaps are 1.86 eV for PPDB and 2.16 eV for PPDI. Thermal behavior and liquid crystallinity are studied by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction measurements. The results indicate liquid-crystalline order of the polymers over a broad temperature range. These thermal, electrical, and optical properties make the perylene side-chain polymers attractive materials for organic photovoltaics.
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