A new electroluminescence (EL) polymer utilizing a new backbone, poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[det]phenanthrene)) (PCPP), with stabilized blue emission is reported. PCPP was synthesized from 4H-cyclopenta[def]phenanthrene over five steps. The photoluminescence (PL) spectra of PCPP did not show any peak in the long wavelength region even after annealing for 18 h at 150 degrees C in air. The OLED with the configuration of ITO/PEDOT:PSS/PCPP/Al generates EL emission with a maximum peak at 400 nm, low turn-on voltage (6.0 V), and excellent CIE coordinates (x = 0.17, y = 0.12) for the blue color without any filtering. The maximum brightness of the OLEDs using PCPP was 1500 cd/m(2) at 14 V. The maximum luminescence efficiency of the polymer LEDs with PCPP was 0.70 cd/A at 180 mA/cm(2). In addition to this, PCPP displays stabilized blue EL emission without any low-energy emission band in the region of 500-600 nm even after annealing for 18 h at 150 degrees C or operation of the device for 40 min in air.