Polyalkylthiophene-containing electron donor and acceptor heteroaromatic bicycles: synthesis, photo-physical, and electroluminescent properties

Abstract

The synthesis and characterization of a series of polyalkylthiophenes-containing electron-rich thienothiophene (donor heteroaromatic bicycle) and electron-deficient benzothiadiazole (acceptor heteroaromatic bicycle) block have been reported. The polymers are synthesized by Stille cross-coupling reaction and are found to be having high molecular weight with number-average molecular weight in the range of 7.1 × 104–5.7 × 104. The photo-physical, electro-chemical, and electroluminescent (EL) properties of the polymers are investigated in detail. The optical band gap of the polymers is found to be in the range of 1.53–1.54 eV. These new polymers are luminescent in nature and showed red photoluminescence in chloroform solution (722–740 nm) as well as in thin film (781–786 nm). Ionization potential for these polymers is calculated and falling in the range of 5.23–5.33 eV. Polymer light emitting diodes with configuration ITO/PDOT:PSS/polymer/BCP/Alq3/LiF/Al have been fabricated, and a deep red emission is observed. The EL maxima of polymers are found to be in the range of 750–760 nm with threshold voltages around 4.0–5.5 V. The fabricated devices show luminescence around 40 cd/m2 at current density of 100 mA/cm2 with maximum value of 580–810 cd/m2 at 11 V.