Synthesis and characterization of new 3-alkylthiophene copolymer that exhibit orange-red photoluminescence and electroluminescence

Using copolymerization functionalization, a Novel solution-processable pi-conjugated 3-alkylthiophene copolymer (molar ratio of monomer 3-octylthiophene (3OT) and 3-(2-ethyl-1-hexyl) thiophene (3EHT) was 1:1) combining electrochemical properties of poly (3-octylthiophene) (P3OT) and poly (3-isooctylthiophene) (P3EHT) was synthesized by FeCl3-oxidative approach. Characterization of the polymers included FT-IR, NMR, gel permeation chromatography (GPC), thermo-gravimetric analysis (TGA), UV-Vis spectroscopy photoluminescence (PL) and electroluminescence (EL). P3OTEHT depicted excellent solubility in common organic solvents. The optical properties investigations showed that the band-gap energy of P3OTEHT was similar to P3OT (2.43 eV) at 2.45 eV and 6% lower than that of P3EHT in CHCl3 solution. The emission maxima of P3OTEHT was 50 nm blue-shifted with respect to that of P3OT. However, the PL intensity of P3OTEHT was seven times higher than that of P3OT in film. The turn-on voltage of LED (ITO/P3OTEHT/Ag) devices was approaching to P3OT (5.5 V) at 5.6 V and 1.9 V lower than that of P3EHT. The EL color of P3OTEHT was bright pure orange-red (emission lambda(EL)(max) of 600 nm), meanwhile, the half-wave bandwidth was 70 urn. TGA studies showed that P3OTEHT exhibited very good thermal stabilities, losing 5% of its weight on heating to 300 degrees C. The results indicate that the P3OTEHT with low band-gap energy, low turn-on voltage, high photoluminescence quantum yield pure EL color and processability, and might be promising polymer materials for applications in polymer light-emitting diodes, light-emitting electrochemical cells and polymer solar cells, etc.