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

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 x 10(4)-5.7 x 10(4). 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/Alq(3)/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/m(2) at current density of 100 mA/cm(2) with maximum value of 580-810 cd/m(2) at 11 V