Sterically hindered and highly thermal stable spirobifluorenyl-substituted poly(p-phenylenevinylene) for light-emitting diodes

The sterically hindered and highly thermal stable spirobifluorenyl-substituted poly(p-phenylenevinylene) derivative was synthesized by Gilch polymerization. The defect-free polymer structure was characterized by various spectroscopies. The polymer was completely soluble in common organic solvents, and it had high thermal stability with high T-g of 205 degreesC. The polymer film showed maximum emission at 515 nm with a shoulder peak at around 560 nm and showed photoluminescence efficiency of 26 +/- 5%. The study of thermal annealing of PL spectrum showed inhibited excimer formation. A cyclic voltammetry study revealed that the HOMO and LUMO energy level of the polymer are 3.08 and 5.46 eV, respectively. The EL spectrum from the device using polymer as emitting material showed a maximum peak of 515 nm, corresponding to the green region (x = 0.31, y = 0.61) in CIE (Commission Internationale de l'Eclairage) chromaticity coordinates. The LED based on polymer was shown to have a maximum brightness of 1155 cd/m(2) at 12.6 V and a maximum power efficiency of 0.118 lm/W (143 cd/m(2), 7.8 V, 1.67 mA).