Syntheses and Characterization of Alkoxyphenyl-Substituted PCPP with Stabilized Blue Emission and Its Derivatives with Ketone Unit in the Main Chain

The syntheses and characterization of alkoxyphenyl-substituted PCPP, poly(2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4 H -cyclopenta[ def ]phenanthrene)) (BEHP-PCPP), with stabilized blue emission and its derivatives with ketone unit in the main chain, poly(2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4 H -cyclopenta[ def ]phenanthrene)- co -2,6-(cyclopenta[ def ]phenanthren-4-one)) (K-PCPPs), are presented. The device utilizing BEHP−PCPP provided stabilized blue emission and incorporation of small amount of the ketone unit in the backbone generated variable emission colors. The purity of the monomer is very important for the stable blue emission, and it was possible to purify the bis(alkoxyphenyl)-substituted monomer by recrystallization to remove monoarylated impurity completely. The PL spectra of BEHP-PCPP thin film did not show any peak in the region of 500−600 nm even after annealing for 9 h at 150 °C in air. The OLED with the configuration of ITO/PEDOT:PSS/BEHP-PCPP/Ca/Al generates EL emission with maximum peak at 430 nm, turn-on voltage of 5.0 V, maximum brightness of 1035 cd/m 2 at 9.0 V, efficiency of 0.11 cd/A at 75 mA/cm 2, and CIE coordinates of ( x = 0.20, y = 0.16), without any filtering, which are quite close to those of the standard blue ( x = 0.14, y = 0.08). Moreover, the OLED with BEHP-PCPP displays stabilized blue emission without showing any peak in the region of 500−600 nm even after annealing the device for 23 h at 150 °C or operation of the device for 50 min with 8 V. The device of K1-PCPP (BEHP-PCPP with 1% of ketone unit) show EL emission with maximum peak at 540 nm, CIE coordinates of ( x = 0.36, y = 0.57), turn-on voltage of 10.5 V, maximum brightness of 1143 cd/m 2, and luminescence efficiency of 0.11 cd/A. The device of K001-PCPP (BEHP-PCPP with 0.01% of ketone unit) shows EL emission with maximum peaks at 430 and 520 nm, CIE coordinates of ( x = 0.26, y = 0.38) which are close to those of standard white, turn-on voltage of 5.5 V, maximum brightness of 1143 cd/m 2, and luminescence efficiency of 0.53 cd/A.