Sterically Hindered and Highly Thermal Stable Spirobifluorenyl-Substituted Poly(p-phenylenevinylene) for Light-Emitting Diodes

Abstract

The sterically hindered and highly thermal stable spirobifluorenyl-substituted poly(pphenylenevinylene) 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 °C. 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).

Synthesis and characterization of stable blue light‐emitting poly(spirobifluorene) derivatives containing alkoxy group

“…This structure reduces the probability of interchain interactions and prevents the close packing of the polymer chains, resulting in good solubility of the polymer. In addition, the spiroannulated segment enhanced the rigidity of the polymer, leading to significant increase in both T g values and thermal stability 26–29…”

Poly(p‐phenylenevinylene) presenting pendent pentaphenylene dendron groups for light‐emitting diodes

“…On excitation of the PPV main chain at 444 nm, the PL displays an emission band at 503 nm combined with a shoulder at 532 nm. When the PL of PPV‐PP was compared with that of MEH‐PPV, the PL spectrum of PPV‐PP was relatively blue‐shifted 27. This was attributed to the presence of bulky pendent groups, which may disrupt the coplanarity of the main chain and cause a partial destruction of the π‐delocalization along the polymer backbone.…”

“…The major cause of the PPVs' low PL quantum efficiencies is mutual cofacial stacking of their conjugated backbones through favorable interchain π–π interactions, especially in the solid state, which leads to self‐quenching arising from the formation of excimers 12, 13. To overcome this problem, various bulky substituents, such as alkoxy, alkylsilyl, phenyl (aryl), and fluorenyl groups, have been attached to the PPV backbone to prevent its close packing and suppress the intermolecular interactions that lead to the formation of excimers 14–27…”

Synthesis and nonlinear optical properties of chromophores for photorefractive polymer materials

“…Compound 5 was prepared in a similar way starting from 2-ethylhexyl 4-bromo-2,5-dimethylphenyl ether. 17 Knoevenagel condensation of aldehydes 11, 16 and 17 with 2-dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran 18 afforded compounds 6 (Scheme 1), 7 and 8 (Scheme 3), respectively.…”